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(Circulation. 1995;91:580.)
© 1995 American Heart Association, Inc.

Articles

Exercise Standards

A Statement for Healthcare Professionals From the American Heart Association

Gerald F. Fletcher, MD, Chair; Gary Balady, MD; Victor F. Froelicher, MD; L. Howard Hartley, MD; William L. Haskell, PhD; Michael L. Pollock, PhD

The purpose of this report is to provide revised standards and guidelines for the exercise testing and training of individuals free from clinical manifestations of cardiovascular disease as well as those with known cardiovascular disease. These guidelines are intended for physicians, nurses, exercise physiologists, specialists, technologists, and other healthcare professionals involved in the regular exercise testing and training of these populations. This report is in accord with the "Statement on Exercise" published by the American Heart Association in Circulation (1992;86:340-344).

These guidelines are a revision of the 1990 standards¹ of the AHA that addressed the issues of exercise testing and training. An update of background, scientific rationale, and selected references are provided, and current issues of practical importance in the clinical use of these standards are considered.

Exercise Testing

The Cardiovascular Response to Exercise
Exercise, a common physiological stress, can elicit cardiovascular abnormalities not present at rest and can be used to determine the adequacy of cardiac function. Because exercise is only one of many stresses to which humans can be exposed, it is more appropriate to call an exercise test exactly that and not a "stress test." This is particularly relevant considering the increased use of nonexercise stress tests.

Types of Exercise
Three types of muscular contraction or exercise can be applied as a stress to the cardiovascular system: isometric (static), isotonic (dynamic or locomotory), and resistive (a combination of isometric and isotonic).^{2 3} Isometric exercise, defined as a muscular contraction without movement (eg, handgrip), imposes greater pressure than volume load on the left ventricle in relation to the body’s ability to supply oxygen. The cardiovascular response to isometric exercise is difficult to grade. In addition, cardiac output is not increased as much as in isotonic exercise because increased resistance in active muscle groups limits blood flow. Isotonic exercise, defined as muscular contraction resulting in movement, primarily provides a volume load to the left ventricle, and the cardiovascular response is proportional to the size of the muscle mass and the intensity of the exercise. Resistive exercise combines both isometric and isotonic exercise by using muscular contraction with movement, as in free weight lifting. Key Point: Dynamic exercise is preferred for testing because it puts a volume stress rather than a pressure load on the heart and because it can be graduated. However, most activities (especially employment and leisure time activities, such as sports) usually combine all three types of exercise in varying degrees.

Maximum Oxygen Uptake
When dynamic exercise is begun or increased, oxygen uptake by the lungs quickly increases. After the second minute, oxygen uptake usually remains relatively stable (steady state) at each intensity of exercise. During steady state, heart rate, cardiac output, blood pressure, and pulmonary ventilation are maintained at reasonably constant levels.²

O_2max is the greatest amount of oxygen a person can use while performing dynamic exercise involving a large part of total muscle mass.⁴ O_2max represents the amount of oxygen transported and used in cellular metabolism. It is convenient to express oxygen uptake in multiples of sitting, resting requirements. The metabolic equivalent (MET) is a unit of sitting, resting oxygen uptake (3.5 mL O₂ per kilogram body weight per minute [mL · kg^-1 · min^-1]). Rather than determining each person’s true resting oxygen uptake, a MET is taken as this average.

O_2max is significantly related to age, gender, exercise habits, heredity, and cardiovascular clinical status.

Age: Maximum values of O_2max occur between the ages of 15 and 30 years, decreasing progressively with age. At age 60, mean O_2max in men is approximately three fourths that at age 20. With a sedentary lifestyle, there is a 9% reduction per decade versus less than 5% per decade for an active lifestyle.

Gender: Through age 12 to 16 years, there is no significant difference in O_2max among children, but a decrease is observed in girls between 12 and 14 years of age. Reduced O_2max in women is attributed to smaller muscle mass, lower hemoglobin and blood volume, and smaller stroke volume as compared with men.

Exercise habits: Physical activity has an important influence on O_2max. After 3 weeks of bed rest, there is a 25% decrease in O_2max in healthy men. In moderately active young men, O_2max is about 12 METs, whereas individuals performing aerobic training such as distance running can have a O_2max as high as 18 to 24 METs (60 to 85 mL · kg^-1 · min^-1).

Heredity: There is a natural variation in O_2max related to genetic factors.

Cardiovascular clinical status: O_2max is affected by the degree of impairment caused by disease.

It is difficult to accurately predict O_2max from its relation to exercise habits and age because of considerable scatter and correlations that are generally low. Table 1 lists key values of METs that are clinically relevant, and Table 2 depicts normal values for age. The nomogram shown in Fig 1 expresses the concept of METs by reflecting it in terms of that expected for age, with 100% being normal.⁵

View this table: [in this window] [in a new window]   Table 1. Clinically Significant Key Metabolic Equivalents for Maximum Exercise

View this table: [in this window] [in a new window]   Table 2. Normal Values of Maximal Oxygen Uptake at Different Ages

View larger version (18K): [in this window] [in a new window]   Figure 1. Nomogram based on age, metabolic equivalents (METs), and activity status that provides a percent of age-expected exercise capacity.5

Maximum O₂ is equal to maximum cardiac output times maximum arteriovenous oxygen (aO₂) difference. Since cardiac output is equal to the product of stroke volume and heart rate, O₂ is directly related to heart rate. The maximum aO₂ difference during exercise has a physiological limit of 15 to 17 vol% hence, if maximum effort is achieved, O_2max can be used to estimate maximum cardiac output.

Myocardial Oxygen Uptake
Myocardial oxygen uptake (MO₂) is determined by intramyocardial wall tension ([left ventricular (LV) systolic pressure times end-diastolic volume] divided by LV wall thickness), contractility, and heart rate. Other less important factors include external work performed by the heart, the energy necessary for activation, and the basal metabolism of the myocardium (Table 3).

View this table: [in this window] [in a new window]   Table 3. Determinants and Methods of Measuring Ventilatory and Myocardial Oxygen Consumption

Accurate measurement of MO₂ requires cardiac catheterization. MO₂ can be estimated during clinical exercise testing by the product of heart rate and systolic blood pressure, which is called the double product or rate-pressure product. There is a linear relation between MO₂ and coronary blood flow. During exercise coronary blood flow increases as much as fivefold above the resting value. A subject with obstructive coronary disease often cannot maintain adequate coronary blood flow to supply the metabolic demands of the myocardium during exercise and, as a consequence, myocardial ischemia occurs. Angina pectoris usually occurs at the same double product rather than at the same external workload. Key Point: An important basic principle of exercise physiology is that O₂ and MO₂ have distinct determinants and methods of measurement or estimation (Table 3). Although they are directly related, this relation can be altered by training and cardioactive medications such as ß-blockers.

Response to Dynamic Exercise
The body’s response to dynamic exercise consists of a complex series of cardiovascular adjustments to provide active muscles with the blood supply appropriate for their metabolic needs, to dissipate the heat generated by active muscles, and to maintain the blood supply to the brain and the heart.

As cardiac output increases with dynamic exercise, peripheral resistance increases in organ systems and tissues that do not function during exercise and decreases in active muscles.⁶ Arterial blood pressure increases only mildly; thus, flow can increase as much as fivefold. Since the denominator (flow) increases much more than the numerator (pressure) in the formula for resistance, the result is a decrease in systemic vascular resistance.

Heart Rate Response
An increase in heart rate due to a decrease in vagal outflow is an immediate response of the cardiovascular system to exercise; this increase is followed by an increase in sympathetic outflow to the heart and systemic blood vessels. During dynamic exercise, heart rate increases linearly with workload and O₂. During low levels of exercise and at a constant work rate, heart rate will reach steady state within several minutes. As workload increases, the time necessary for the heart rate to stabilize will progressively lengthen.

Heart rate response is influenced by several factors, including age. There is a decline in mean maximum heart rate with age⁷ that appears to be related to neural influences. Dynamic exercise increases heart rate more than isometric or resistive exercise. An accentuated heart rate response is observed after bed rest. Other factors that influence heart rate include body position, certain physical conditions, state of health, blood volume, and environment.

Key Point: Heart rate response to maximum dynamic exercise depends on numerous factors, particularly age and health. It appears that the reduction in heart rate averages 5 to 7 beats per minute per decade.

Arterial Blood Pressure Response
Systolic blood pressure rises with increasing dynamic work as a result of increasing cardiac output, whereas diastolic pressure usually remains about the same or may be heard to zero in some normal subjects. Normal values of maximum systolic blood pressure for men have been defined and are directly related to age.

An inadequate rise in systolic blood pressure (less than 20 to 30 mm Hg) can result from aortic outflow obstruction, LV dysfunction, or myocardial ischemia. Changes of blood pressure reflect more than the contractile function of the LV since they also depend on peripheral resistance. Subjects who develop hypotension during exercise frequently have severe heart disease; subjects with valvular or myocardial disease can also exhibit a drop in systolic blood pressure. A drop in systolic pressure below standing rest is of great concern during the actual test or during follow-up.

After maximum exercise there is usually a decline in systolic blood pressure, which normally reaches resting levels in 6 minutes, then often remains lower than preexercise levels for several hours. In some subjects with coronary artery disease (CAD), higher levels of systolic blood pressure exceeding peak exercise values have been observed during the recovery phase. When exercise is terminated abruptly, some healthy persons have precipitous drops in systolic blood pressure due to venous pooling. Fig 2 shows the physiological response to submaximum and maximum treadmill exercise based on tests of more than 700 apparently healthy men aged 25 to 54 years. Maximum double product (heart rate times systolic blood pressure) ranges from a tenth percentile value of 25 000 to a 90th percentile value of 40 000.

View larger version (66K): [in this window] [in a new window]   Figure 2. Normal response to progressive treadmill protocol in healthy subjects. bpm Indicates beats per minute. From Froelicher VF. Exercise and the Heart: Clinical Concepts. Chicago, Ill: Yearbook Medical Publishers, Inc; 1987:102.

Testing Procedures
The Physician’s Role
Exercise testing should be conducted only by well-trained personnel with a basic knowledge of exercise physiology. Only technicians and physicians familiar with normal and abnormal responses during exercise can recognize or prevent untoward events. Equipment, medications, and personnel trained to provide cardiopulmonary resuscitation (CPR) must be readily available.

Although exercise testing is considered a safe procedure, there are reports of acute myocardial infarctions (MIs) and deaths. Multiple surveys confirm that up to 10 MIs or deaths or both can be expected per 10 000 tests.⁸ However, the relative risk of an adverse event during an exercise test versus during usual activity of subjects with CAD is estimated to be 60- to 100-fold. Risk is greater in the post-MI subject and in those being evaluated for malignant ventricular arrhythmias. A recent review summarizing eight studies of estimates of sudden cardiac death during exercise testing revealed rates from 0.0 (four studies) to 5 per 100 000 tests.⁸ Table 4 lists three classes of complications secondary to exercise tests.

View this table: [in this window] [in a new window]   Table 4. Complications Secondary to Exercise Tests

Good clinical judgment should be foremost in deciding indications and contraindications for exercise testing.⁹ Whereas absolute contraindications are definitive, in selected cases with relative contraindications even submaximum testing can provide valuable information. Table 5 lists absolute and relative contraindications to exercise testing.

View this table: [in this window] [in a new window]   Table 5. Absolute and Relative Contraindications to Exercise Testing

In any procedure with a risk of complications, the physician should be certain that the subject understands the situation and acknowledges the risks. Some physicians believe that informing subjects of possible risks may cause them to become anxious or discourage them from undergoing a test. This possibility and the fact that a signed consent form does not protect a physician from legal action have recently led to less insistence on obtaining written consent. However, if consent is not initially obtained, a physician may be held responsible for a major adverse event, even if the test is carefully performed. The argument can be made that the subject would not have undergone the procedure if he or she had been aware of the risks associated with the test. Good physician-subject communication about testing is mandatory.

Exercise testing should be performed under the supervision of a physician who is appropriately trained to conduct exercise tests. The physician should be responsible for ensuring that the exercise laboratory is properly equipped and that exercise testing personnel are appropriately trained. The degree of subject supervision needed during a test can be determined by the clinical status of the subject being tested. This determination is made by the physician or physician’s designated staff member, who asks pertinent questions about the subject’s medical history, performs a brief physical examination, and reviews the standard 12-lead ECG performed immediately before testing. The physician should interpret data derived from testing, suggest further evaluation or therapy, and help deliver effective and timely advanced CPR when necessary. The physician or senior medical professional conducting the test must be trained in advanced CPR. A defibrillator and appropriate medications should also be immediately available.

The degree of supervision can range from assigning direct monitoring of the test to a properly trained nonphysician (ie, a nurse or exercise physiologist or specialist) for testing apparently healthy younger persons (less than 40 years old) and those with stable chest pain syndromes to the physician who directly monitors the subject’s blood pressure and status throughout exercise and recovery. The latter is the ideal for testing subjects for diagnostic or prognostic purposes and is certainly a requirement for testing all subjects at increased risk for exercise-induced complications. A physician should be immediately available during all exercise tests.

Subject Preparation
Preparations for exercise testing include the following:

• The subject should be instructed not to eat or smoke for 3 hours before the test and to dress appropriately for exercise, especially with regard to footwear. No unusual physical efforts should be performed for at least 12 hours before testing.

• A brief history and physical examination should be performed to rule out contraindications to testing or to detect important clinical signs such as a cardiac murmur, gallop sounds, pulmonary bronchospasm, or rales. Subjects with a history of increasing or unstable angina or heart failure should not undergo exercise testing until their condition stabilizes. A cardiac physical examination should indicate which subjects have valvular or congenital heart disease. Because hemodynamic responses to exercise may be abnormal in such subjects, they always warrant careful monitoring, and at times they may be excluded from testing.

• When exercise testing is performed for diagnostic purposes, withdrawal of medications may be considered since some drugs interfere with exercise responses and complicate the test interpretation. There are no formal guidelines for tapering medications, but rebound phenomena may occur with discontinuance of ß-blockers. Therefore, most subjects are tested while taking their usual medications. Specific questioning is important to determine which drugs have been taken so that the physician can be aware of possible electrolyte abnormalities and other effects.

• If the reason for the exercise test is not clear, the subject should be questioned and the referring physician contacted.

• A resting 12-lead ECG should be obtained since it may differ from the resting preexercise ECG. This is essential, particularly in subjects with known heart disease, since an abnormality or a change may contraindicate testing. Recording the ECG before starting the exercise test and after hyperventilation at another time may be helpful in confirming a false-positive (or indeterminate) ECG change.

• Standing ECG and blood pressure should be recorded to determine vasoregulatory abnormalities, particularly ST depression.

• A detailed explanation of the testing procedure should be given that outlines risks and possible complications. The subject should be told how to perform the exercise test, and the testing procedure should be demonstrated.

Electrocardiographic Recording
Skin preparation. The most critical point of the electrode-amplifier-recording system is the interface between electrode and skin. Removal of the superficial layer of skin significantly lowers its resistance, thus decreasing the signal-to-noise ratio. The areas for electrode application are first shaved and then rubbed with alcohol-saturated gauze. After the skin dries, it is marked with a felt-tipped pen and rubbed with a fine sandpaper or rough material. With these procedures, skin resistance should be reduced to 5000 or less.

Electrodes and cables. Many electrodes are available for performing exercise testing. Silver plate or silver chloride crystal pellets are preferred because they have the lowest offset voltage. The electrodes should be constructed with a metal interface that is sunken, creating a column to be filled with either an electrolyte solution or a saturated sponge. When using fluid column electrodes, direct metal-to-skin contact should be avoided in order to decrease motion artifact.

Connecting cables between the electrodes and recorder should be light, flexible, and properly shielded. Most available commercial exercise cables are constructed to lessen motion artifact. Cables generally have a life span of a year or so, depending on use. They eventually become a source of both electrical interference and discontinuity and must be replaced.

Lead systems. Bipolar leads. Bipolar lead systems were the first to be used to detect ECG changes during exercise. The relatively short placement time, freedom from motion artifacts, and the ease with which noise problems can be located are factors that favor their use. The usual positive reference is an electrode placed in the same position as the positive reference for V5 (the fifth intercostal space at the midclavicular line). The negative reference for V5 is Wilson’s central terminal. Fig 3 illustrates negative electrode placement for most bipolar lead systems. CM₅ is the most sensitive for ST segment changes. CC₅ excludes the vertical component included in CM₅ and decreases the influence of atrial repolarization (Ta), thus reducing false-positive responses.¹⁰ Key Point: Electrode placement affects ST segment slope and amplitude. The various placements do not result in comparable waveforms for analysis. For comparison of the resting 12-lead recording, arm and leg electrodes should be moved to the wrists and ankles, with the subject in the supine position.

View larger version (71K): [in this window] [in a new window]   Figure 3. Negative electrode placement for most bipolar lead systems. B indicates back, subscapular; M, top of manubrium; X, midaxillary line, fifth intercostal level; C, anterior axillary line, fifth intercostal level; H, above shoulders (neck or above); S, right clavicular edge; R, right arm; and +, positive electrode placement for C5 bipolar electrodes. From Froelicher VF. Exercise and the Heart: Clinical Concepts. Chicago, Ill: Yearbook Medical Publishers, Inc; 1987:18.

Multiple leads. Since a standard 12-lead ECG with electrodes placed on the limbs cannot be obtained during exercise, other electrode placements have been used. Differences can be minimized by placing the arm electrodes as close to the shoulders as possible and the leg electrodes below the umbilicus and by recording the resting ECG with the subject supine. Any modification of lead placement should be recorded on the tracing.

Relative sensitivity of leads. The lateral precordial leads (V₄ through V₆) are capable of detecting 90% of all ST depression observed in multiple lead systems. Other reports indicate that using other leads in addition to V5 will increase the yield of abnormal responses by about 10%. However, the specificity of an abnormal response in other leads is lower. Key Point: Complete 12-lead tracings during exercise are not needed in many individuals with normal resting ECGs. However, they are necessary in subjects with arrhythmias, Q waves consistent with myocardial damage, or symptoms suggestive of coronary spasm and when evaluating severity of disease in subjects with known CAD.

Recorders. There are many good recorders designed to capture high-quality ECG data during exercise. Many use microprocessors to generate average waveforms and make ECG measurements. The physician must compare the raw analog data with computer-generated output to validate its accuracy. Computer processing is not completely reliable because of software limitations in handling noise and inadequacy of the available algorithms.

Equipment and Protocols
Fig 4 illustrates the relation of METs to stages in the common testing protocols. Numerous devices have been used in the past to provide dynamic exercise for testing, including steps, escalators, and ladder mills. However, the treadmill and cycle ergometer are now the most commonly used dynamic exercise testing devices.

View larger version (41K): [in this window] [in a new window]   Figure 4. Treadmill protocols with approximate oxygen uptakes. METS indicates metabolic equivalents; USAFSAM, United States Air Force School of Aerospace Medicine; ACIP, Asymptomatic Cardiac Ischemia Pilot; CHF, Congestive Heart Failure (Modified Naughton); Kpm/min, kilopond meters per minute; and %GR, percent grade. From Froelicher VF. Exercise and the Heart: Clinical Concepts. Chicago, Ill: Yearbook Medical Publishers, Inc; 1987:15.

Cycle. Mechanical or electrically braked cycles vary the force to the pedaling speed (rate-independent ergometers), permitting better power output control since it is common for uncooperative or fatigued subjects to decrease their pedaling speed. The highest values of O₂ and heart rate are obtained with pedaling speeds of 50 to 80 rpm. Cycles are calibrated in kiloponds (kp) or watts; 1 W is equivalent to approximately 6 kilopond-meters per minute (kpm/min). Since exercise on a cycle ergometer is non–weight bearing, kiloponds or watts can be converted to oxygen uptake in milliliters per minute. METs are obtained by dividing O₂ in milliliters per minute by the product of body weightx3.5.

The cycle ergometer is usually less expensive, occupies less space, and makes less noise than a treadmill. Upper body motion is usually reduced, making it easier to obtain blood pressure measurements and to record the ECG. Care must be taken to prevent isometric or resistive exercise of the arms.

There is a marked difference between the body’s response to acute exercise in the supine and upright positions. In healthy persons, stroke volume and end-diastolic volume change little during supine cycle exercise from volumes obtained at rest, whereas in the upright position, these values increase and then plateau during mild work. In subjects with cardiac abnormalities, LV filling pressure is more likely to increase during exercise in the supine position than in the upright position. When subjects with angina perform identical submaximum cycle work in the supine and upright positions, heart rate is higher in the supine position, maximum work performed is lower, and angina develops at a lower double product. ST segment depression is usually greater in the supine position because of the greater LV volume. A major limitation to cycle ergometer testing is the discomfort and fatigue of the quadriceps muscles. Usually leg fatigue of an inexperienced "cyclist" causes subjects to stop before reaching a true O_2max. Thus, O_2max is 10% to 15% lower in cycle versus treadmill testing in those not accustomed to cycling.

Treadmill. The treadmill should have front and/or side rails for subjects to steady themselves; some subjects may also require the assistance of the person administering the test. Subjects should not tightly grasp the front or side rails since this decreases O₂ and increases exercise time and muscle artifact. Most subjects can walk without the aid of hand rails, but older subjects may need such support. It is helpful if subjects take their hands off the rails, close their fists, and place one finger on the rails to maintain balance after they are accustomed to walking on the treadmill. The treadmill should have both variable speed and grade capability and must be accurately calibrated.

Protocols. Protocols for clinical exercise testing include an initial warm-up (low load), progressive uninterrupted exercise with increasing loads and an adequate duration in each level, and a recovery period. For cycle ergometry, the initial power output is usually 10 or 25 W (150 kpm/min), usually followed by increases of 25 W every 2 or 3 minutes until end points are reached. If arm ergometry is substituted for cycle ergometry, a similar protocol may be used, except that initial power output and incremental increases are lower. Two-minute stages are most popular with arm ergometry.^{11 12}

Several different treadmill protocols are in use. The advantages of the Bruce protocol include a seventh or final stage that cannot be completed by most individuals as well as its use in many published studies. Its disadvantages include large increments in work that make estimation of O_2max less accurate. The fourth stage can be either run or walked, resulting in different oxygen costs. Some subjects are forced to stop exercising prematurely because of musculoskeletal discomfort or an inability to tolerate the high workload increments. An initial zero and one-half stages (1.7 mph at 0% and 5% grades) can be used for subjects with compromised exercise capacities. Many exercise testing laboratories currently use Balke-type protocols (Stanford, McHenry, and the frequently used Naughton) with even MET level increments for stage advances. The optimum protocol should last 6 to 12 minutes and should be adjusted to the subject.

Exercise protocols should be individualized according to the type of subject being tested. Three-minute stages are not necessary to achieve steady state at a low workload. Performance can be estimated with the oxygen cost of maximum workload or power output achieved rather than by total treadmill time if subjects do not use hand rails, allowing comparison of performance in different protocols. A 9-minute targeted Ramp protocol that increases in small steps has many advantages, including more accurate estimates of MET level. Key Point:It is important to adjust or select the treadmill or cycle ergometer protocol to the subject being tested. The optimum protocol is 6 to 12 minutes. Exercise capacity should be reported in METs rather than minutes.

Submaximum Versus Maximum Exercise Testing
In some cases, testing is terminated when subjects reach 85% to 90% of predicted maximum heart rate for their age and level of training. Unfortunately, there is a wide spread of maximum heart rate around the regression line, declining with age (SD, 12 beats per minute). Thus, the target heart rate is maximal for some subjects, beyond the limit of others, and submaximal for still others. A test is considered maximal when the subject appears to give a true maximum effort (point of bodily exhaustion) or when other clinical end points are reached. Paradoxically, when using an age-predicted heart rate–targeted submaximum test, the most vulnerable subjects are stressed to a relatively greater extent, whereas the less impaired are limited by the submaximum target heart rate.

Perceived exertion. The subjective rating of the intensity of exertion perceived by the person exercising is generally a sound indicator of relative fatigue. Rather than using heart rate alone to clinically determine intensity of exercise, the 6 to 20 Borg scale of perceived exertion¹³ is useful (Table 6). Special verbal and written explanations about the rating of perceived exertion are available for subjects. Although there is some variation among subjects in their actual rating of fatigue, they seem to rate consistently from test to test. Thus, the Borg scale can assist the clinician in judging degree of fatigue reached from one test to another or to correlate the level of fatigue during testing with that experienced during daily activities.

View this table: [in this window] [in a new window]   Table 6. Borg Scale for Rating Perceived Exertion

Indications for terminating exercise testing. Indications for interruption of an exercise test have been derived from clinical experience.

Absolute indications

• Drop in systolic blood pressure (persistently below baseline) despite an increase in workload

• Increasing anginal pain

• Central nervous system symptoms (eg, ataxia, dizziness, or near syncope)

• Signs of poor perfusion (cyanosis or pallor)

• Serious arrhythmias (ie, high-grade ventricular arrhythmias such as multiform complexes, triplets, and runs)

• Technical difficulties monitoring the ECG or systolic blood pressure

• Subject’s request to stop

Relative indications

• ST or QRS changes such as excessive ST displacement, extreme junctional depression, or marked axis shift

• Fatigue, shortness of breath, wheezing, leg cramps, or claudication

• General appearance (see below)

• Less serious arrhythmias, including supraventricular tachycardias

• Development of bundle branch block that cannot be distinguished from ventricular tachycardia

Postexercise Period
Some abnormal responses occur only in recovery after exercise. If maximum sensitivity is to be achieved with an exercise test, subjects should be supine in the postexercise period; however, for subject comfort, many physicians prefer the sitting position. A cooldown walk after the test can delay or eliminate the appearance of ST segment depression; however, the cooldown may be indicated in some subjects. Monitoring should continue for 6 to 8 minutes after exercise or until changes stabilize, and heart rate and ECG are close to baseline. In the supine position, 4 to 5 minutes into recovery, approximately 85% of subjects with abnormal responses are abnormal at this time only or in addition to any other time. An abnormal ECG response occurring only in the recovery period is not unusual, nor is it more likely to be false-positive. Mechanical dysfunction and electrophysiological abnormalities in the ischemic ventricle after exercise can persist from minutes to hours. Monitoring of blood pressure should continue during recovery, as abnormal responses may occur.

Interpretation
Clinical Responses
Symptoms. Ischemic chest pain induced by the exercise test is strongly predictive of CAD and is even more predictive with ST depression. It is important to obtain a careful description of the pain from the subject to ascertain that it is typical angina rather than nonischemic chest pain.

Subject’s appearance. The subject’s general appearance is helpful in clinical assessment. A drop in skin temperature, cool and light perspiration, and peripheral cyanosis during exercise can indicate poor tissue perfusion due to inadequate cardiac output with secondary vasoconstriction. Such subjects should not be encouraged to attempt higher workloads. Neurological manifestations such as light-headedness or vertigo can also indicate inadequate cardiac output.

Physical examination. Cardiac auscultation immediately after exercise can provide information about ischemia-induced LV dysfunction. Gallop sounds or a precordial bulge can result from LV dysfunction. A new mitral regurgitant murmur suggests papillary muscle dysfunction, which may be related to transitory ischemia. It is preferable to have subjects lie supine after exercise testing and allow those who develop orthopnea to sit up. In addition, severe angina or ominous arrhythmias after exercise may be lessened by allowing the subject to sit up, since ischemia may be decreased. Key Point: Symptoms and signs of ischemia induced by exercise testing are clinically important, and their combinations influence interpretation.

Exercise or Functional Capacity
O_2max is a measure of the functional limit of the cardiovascular system and the best index of exercise capacity. As previously discussed, O_2max depends on many factors (training, age, and gender) and is an indirect estimate of maximum cardiac output. A decline in maximum cardiac output, which is the major hemodynamic consequence of symptomatic CAD, usually causes a decrease in exercise capacity. Although many subjects may stop exercising because of anginal pain, acute reduction in LV performance resulting in decreased stroke volume and heart rate and increasing pulmonary artery pressure appear to be the mechanisms limiting cardiac output. In normal women as opposed to normal men, LV ejection fraction (LVEF) "plateaus" and may decrease with maximal exercise.¹⁴

A mean exercise capacity of 10 METs has been observed in nonathletic middle-aged healthy men. If subjects with CAD reach 13 METs, their prognosis is good, regardless of other exercise test responses that may occur and medical or surgical treatment. Mortality is higher in subjects with an exercise capacity of 5 METs or less compared with subjects whose exercise capacities are higher.

A normal exercise capacity does not exclude severe cardiac impairment. Mechanisms proposed to explain a normal work performance in these subjects include increased peripheral oxygen extraction, preservation of systolic volume and chronotropic reserve, ability to tolerate elevated pulmonary wedge pressures without dyspnea, ventricular dilation, and increased levels of plasma norepinephrine at rest and during exercise. Many subjects with decreased ejection fractions at rest can perform relatively normal levels of exercise, some without side effects, whereas others report increased fatigue for some time after the test. Key Point: An exercise capacity of 5 METs or less is associated with a poor prognosis in subjects less than 65 years old. An exercise capacity of 13 METs indicates a good prognosis despite abnormal exercise test responses. Resting LVEF does not correlate well with exercise capacity.

Hemodynamic Responses
Blood Pressure During Exercise
Blood pressure is dependent on cardiac output and peripheral resistance. Systolic blood pressure at maximum exertion or at immediate cessation of exertion is considered a clinically useful first approximation of the heart’s inotropic capacity. An inadequate rise or a fall in systolic blood pressure during exercise can occur. Although some normal subjects have a transient drop in systolic blood pressure at maximum exercise, this finding is frequently associated with severe CAD and ischemic dysfunction of the myocardium. Exercise-induced hypotension also identifies subjects at increased risk for ventricular fibrillation in the exercise laboratory. Key Point: A drop in systolic blood pressure below standing rest during exercise is associated with increased risk in subjects with a prior MI or myocardial ischemia.

Heart Rate During Exercise
Relatively rapid heart rate during submaximum exercise or recovery could be due to deconditioning, a condition that decreases vascular volume or peripheral resistance, prolonged bed rest, anemia, or metabolic disorders. This finding is relatively frequent soon after MI and coronary artery surgery. Relatively low heart rate at any point during submaximum exercise could be due to exercise training, enhanced stroke volume, or drugs. The common use of ß-blockers, which lower heart rate, has complicated interpretation of the heart rate response to exercise. Conditions that affect the sinus node can attenuate the normal response of heart rate during exercise testing. Key Point: Abnormalities of exercise capacity, systolic blood pressure, and heart rate response to exercise can be due to either LV dysfunction, ischemia, cardioactive drugs, or autonomic dysfunction.

Responses in Subjects With Normal Resting ECGs
Normal responses. P wave. During exercise, P vectors become more vertical, and P wave magnitude increases significantly in inferior leads. There are no significant changes in P wave duration.

PR segment. The PR segment shortens and slopes downward in the inferior leads during exercise. The decreasing slope has been attributed to atrial repolarization (the Ta wave) and can cause false-positive ST depression in the inferior leads.

QRS complex. The Q wave shows very small changes from the resting values; however, it does become slightly more negative at maximum exercise. Changes in median R wave amplitude are noted near maximum effort. A sharp decrease in the R wave is observed in the lateral leads (V₅) at maximum exercise and into the first minute of recovery. In the lateral and vertical leads (V₅ and aVF), the S wave becomes greater in depth (more negative), showing a greater deflection at maximum exercise, and then gradually returns to resting values in recovery. As the R wave decreases in amplitude, the S wave increases in depth.

J-junction depression. The J-junction is depressed in lateral leads to a maximum depression at maximum exercise, then gradually returns toward preexercise values in recovery. A dramatic increase in J-junctional depression is observed in all leads and is greatest at 1 minute into recovery. Subjects with resting J-junction elevation may develop an isoelectric J-junction with exercise; this is a normal finding. These changes return toward pretest values later in recovery. The normal ST segment vector response both to tachycardia and exercise is a shift rightward and upward. There appears to be considerable biological variation in the degree of this shift.

T wave. A gradual decrease in T wave amplitude is observed in all leads during early exercise. At maximum exercise the T wave begins to increase, and at 1 minute into recovery the amplitude is equivalent to resting values in the lateral leads.

U wave. No significant changes are noted with exercise; however, U waves may be difficult to identify because of the close approximation of the T and P waves with the increased heart rate of exercise.

Abnormal responses. ST segment changes. The ST level is measured relative to the PR segment since the UP segment disappears during exercise. ST elevation is measured as the deviation from the baseline ST level. ST depression is measured from the isoelectric PR level since the normal response is a downward shift from early repolarization. If the baseline ST segment is depressed, the deviation from that level to the level during exercise or recovery is considered. The point for measuring the ST level is the J-junction. Points beyond this (60 or 80 milliseconds) should only be used if the ST segment slope is horizontal or downsloping. Considering ST depression that is rapidly upsloping to be abnormal increases sensitivity but decreases specificity. Many ST scores to quantify ischemia have been recommended, but none have been validated as superior to standard measurements. Exercise-induced myocardial ischemia can result in one of three ST segment manifestations on the surface ECG: depression, elevation, and normalization.

ST segment depression. ST segment depression is the most common manifestation of exercise-induced myocardial ischemia. It represents subendocardial ischemia, with direction determined largely by the placement of the heart in the chest. The standard criterion for this abnormal response is horizontal or downsloping ST segment depression of 0.10 mV or more for 80 milliseconds. However, as shown in Fig 5, other criteria have been considered. Downsloping ST segment depression is a more significant change than horizontal depression. In the presence of baseline abnormalities, exercise-induced ST segment depression is less specific for ischemia. Other factors related to the probability and severity of CAD include the amount, time of appearance, duration, and number of leads with ST segment depression.

View larger version (14K): [in this window] [in a new window]   Figure 5. Abnormal ST responses. From Froelicher VF. Exercise and the Heart: Clinical Concepts. Chicago, Ill: Yearbook Medical Publishers, Inc; 1987:46.

Severity of CAD is also related to the time of appearance of ischemic shifts. The lower the workload and double product at which it occurs, the worse the prognosis and the more likely the presence of multivessel disease. The persistence of ST depression in the recovery phase is also related to the severity of CAD. Key Point: The probability and severity of CAD are directly related to the amount of J-junction depression and are inversely related to the slope of ST segment (ie, the greater the depression and the downslope, the more likely and more severe the CAD).

ST segment elevation. ST elevation must be classified by whether it occurs over Q waves of an MI or in an ECG area without Q waves. The mechanisms and implications are markedly different. ST segment elevation has been more frequently observed in anterior leads (V₁ and V₂) with Q waves.¹⁵

ST segment elevation over Q waves of prior MI. Prior MI is the most frequent cause of ST segment elevation during exercise and appears to be related to the presence of dyskinetic areas or ventricular aneurysms. Approximately 50% of subjects with anterior MI and 15% of subjects with inferior MI exhibit this finding during exercise. Subjects with elevation usually have a lower ejection fraction than those without elevation over Q waves. These changes can result in reciprocal ST depression that simulates ischemia in other leads. ST segment elevation and depression during the same test may indicate multivessel CAD. The underlying extent of Q waves or myocardial damage actually determines the amount of ST elevation rather than independently reflecting the amount of dysfunction.

ST segment elevation without Q waves. In subjects without previous MI (absence of Q waves on the resting ECG), ST segment elevation during exercise frequently pinpoints the site of severe transient ischemia resulting from significant proximal disease or spasm. Key Point: Severe transmural ischemia is the mechanism for ST segment elevation during exercise in subjects without prior MI or diagnostic Q waves on the resting ECG. It locates the site of ischemia, in contrast to ST depression, which does not.¹⁶

In subjects with variant angina, ST segment elevation occurs during spontaneous anginal episodes, frequently at rest. During exercise, ST segment elevation has been reported in about 30% of these subjects. A reversible thallium-201 perfusion defect usually corresponds to the site of ST elevation. Many subjects with ST elevation have coexistent ST segment depression in other leads. Ventricular arrhythmias also appear to be more frequent in subjects with ST elevation.

ST segment normalization or absence of change. Another manifestation of ischemia may be normalization of or no change in the ST segment related to cancellation effects, but this is nonspecific. ECG abnormalities at rest, including T wave inversion and ST segment depression, reportedly return to normal during attacks of angina and during exercise in some subjects with ischemic heart disease, but they can also be observed in subjects with a persistent juvenile pattern on the resting ECG. This cancellation effect is rare but should be considered.

Diagnostic value of R wave changes. Many within-subject estimates of the variability of R wave amplitude changes during exercise in normal subjects have been reported. However, the average response in normal subjects is an increase in R wave amplitude during submaximum exercise, with a drop at maximum exercise. Exercise-induced changes in R wave amplitude have not improved diagnostic accuracy despite use of several lead systems, clinical subsets of subjects, and different criteria for an abnormal response. Key Point: A multitude of factors affect the R wave amplitude response to exercise, and the response does not have diagnostic significance.

T wave changes. In normal subjects, a gradual decrease in T wave amplitude is observed in all leads during early exercise. At maximum exercise the T wave begins to increase, and 1 minute into recovery amplitude is equivalent to resting values in lateral leads.

U wave changes. U wave inversion is associated with LV hypertrophy, CAD, and aortic and mitral regurgitation. These conditions are associated with abnormal LV distensibility. Exercise-induced U wave inversion in subjects with a normal resting ECG appears to be a marker of myocardial ischemia and suggests left anterior descending CAD.

ST/HR index and slope. Although research and clinical data are available on this methodology in exercise testing, the ST/HR index is not recommended because of problems with validation. A meta-analysis revealed that positive results with this method were obtained only by centers that were also responsible for over half the published reports.¹⁷

Other Studies
Exercise tests can be performed with radionuclear techniques to further evaluate myocardial perfusion and function. As an example, thallium, an isotope that behaves like potassium, is taken up by perfused, viable myocardium when injected at maximum exercise. Imaging performed immediately after exercise can reveal defects. If defective areas fill in during resting scans, they are usually due to ischemia; if such areas do not fill in, the defects can be due to scarring or severe ischemia. Technetium can be tagged to red blood cells and can provide an image of the LV cavity blood volume during exercise. Changes in ejection fraction, wall motion, and ventricular volume can be assessed.

Echocardiographic images and Doppler flow measurements can be made during and after exercise. Ejection fraction, wall motion, and valvular function can be assessed with this technique.

More recently, thallium single-photon emission computerized tomography has been used in exercise evaluation. Such evaluation should be delayed 10 to 15 minutes after exercise to avoid artifacts secondary to heart position and respiratory rate immediately after exercise.¹⁸ As further sophistication of imaging evolves, positron emission tomography will likely become a clinically applicable tool in exercise evaluation. This technique offers the opportunity to quantify regional function in the heart spanning blood flow, biochemical reaction rates, substrate fluxes, and receptors.¹⁹ Pharmacologic stress is available for subjects who are unable to exercise. Dipyridamole infusion as a coronary vasodilator causes an increase in myocardial blood flow that is altered in the presence of diseased coronary arteries.¹⁸ Adenosine infusion, which also causes vasodilation, can be used similarly to dipyridamole in pharmacological testing,¹⁸ and dobutamine, with its chronotropic and inotropic effects, can be used with thallium scintigraphy or echocardiography to delineate regional ischemia and wall motion abnormalities.¹⁸

Magnetic resonance imaging is a relatively new technology that may serve as an excellent tool for studying the effects of exercise in both the normal and failing heart. These methods are well-suited to study the myocardial effects of chronic exercise.²⁰

Diagnostic Value of the Exercise Test
Sensitivity and Specificity
Sensitivity and specificity define how effectively a test separates subjects with disease from healthy individuals, ie, how well a test diagnoses disease. Sensitivity is the percentage of those individuals with a disease who will have abnormal tests. Specificity is the percentage of those without the disease who will have normal test results; specificity may be affected by drugs such as digoxin, baseline ECG patterns, LV hypertrophy, and gender.

Sensitivity and specificity are inversely related; when sensitivity is the highest, specificity is lowest and vice versa. All tests have a range of inversely related sensitivities and specificities that can be selected by specifying a discriminate or diagnostic cut point.

The choice of a discriminate value is further complicated by the fact that some exercise test responses do not have established values that separate normal subjects from those with disease. Once a discriminate value that determines a test’s specificity and sensitivity is chosen, the population tested must be considered. If the population is skewed toward individuals with a greater severity of disease, the test will have a higher sensitivity. For instance, the exercise test has a higher sensitivity in individuals with triple-vessel disease than in those with single-vessel disease. A test can also have a lower specificity if it is used in individuals who are more likely to give false-positive results. For instance, the exercise test has a lower specificity in women and in individuals with mitral valve prolapse.

Sensitivity and specificity of exercise-induced ST segment depression can be demonstrated by comparing the results of exercise testing and coronary angiography.²¹ From these studies, it can be seen that the exercise test cut point of 0.1 mV horizontal or downsloping ST segment depression has approximately 84% specificity for angiographically significant CAD; ie, 84% of those without significant angiographic disease had a normal exercise test. These studies had a mean 66% sensitivity of exercise testing for significant angiographic CAD, with a range of 40% for one-vessel disease to 90% for three-vessel disease. Key Point: Sensitivity and specificity are inversely related, affected by the population tested, and determined by the choice of a cut point or discriminate value.

Relative Risk and Predictive Value
Relative risk and predictive value help define the diagnostic value of a test. Table 7 shows how sensitivity, specificity, relative risk, and predictive value are calculated.

View this table: [in this window] [in a new window]   Table 7. Calculation of Sensitivity, Specificity, Relative Risk, and Predictive Value and Definition of Terms

Prognostic Use of the Exercise Test
Rationale
There are two principal reasons for estimating prognosis. The first is to provide accurate answers to a subject’s questions about the probable outcome of his or her illness. Although discussion of prognosis is inherently delicate and probability statements can be misunderstood, most subjects find this information useful in planning their work, recreational activities, personal estates, and finances. The second reason for determining prognosis is to identify subjects in whom cardiovascular interventions might improve outcome.

Pathophysiology of CAD
The basic pathophysiological features of CAD include arrhythmic risk, myocardial damage (reflected by LV function), and the degree of myocardium in jeopardy. Arrhythmic risk does not appear to be independently predicted by exercise testing since the prognosis of arrhythmias is closely related to LV abnormalities. (Twenty-four hour ambulatory ECG recording provides more information about arrhythmias except for those that are clearly related to exercise.) Exercise test responses due to myocardial ischemia include angina, ST segment depression, and ST segment elevation over ECG areas without Q waves. Predicting the amount of ischemia (ie, the amount of myocardium in jeopardy) is difficult. It is inversely related to the double product at the onset of signs or symptoms of ischemia. Responses related to ischemia or LV dysfunction include chronotropic incompetence, drops in systolic blood pressure, and poor exercise capacity.

Exercise capacity correlates poorly with LV function in subjects without signs or symptoms of heart failure, nor is exercise testing helpful in identifying subjects with moderate LV dysfunction. LV dysfunction is better recognized by a history of heart failure, physical examination, resting ECG, echocardiogram, or radionuclide ventriculogram. Several subject groups have been studied to determine prognosis with exercise testing, including post-MI subjects, subjects with stable CAD (including silent ischemia), subjects after coronary artery bypass surgery (CABS), subjects after percutaneous transluminal coronary angioplasty (PTCA), and asymptomatic individuals.

Post-MI Subjects. Purpose. Table 8 lists reasons for performing an exercise test in post-MI subjects. Exercise testing may expedite and optimize discharge from the hospital of subjects recovering from an MI. Ventricular arrhythmias not present at rest can be provoked during exercise. The subject’s reaction to exercise, work capacity, and limiting factors at the time of discharge from the hospital can be assessed. An exercise test before discharge is important for providing guidelines for exercise at home, reassurance of physical status, and determination of risk of complications. It also provides a safe basis for advising the subject to resume or increase his or her activity level and return to work. The test can demonstrate to the subject, family, and employer the effect of MI on capacity for physical performance. Psychologically, it may improve self-confidence by decreasing the subject’s anxiety about daily physical activities. The test also reassures spouses of subjects’ physical capabilities. The response to exercise testing reassures and encourages many subjects to increase their activities.

View this table: [in this window] [in a new window]   Table 8. Purposes of Exercise Testing After Myocardial Infarction

Some investigators use symptoms or sign-limited end points 2 or 3 weeks after MI. However, a submaximum limited test using predetermined end points seems more clinically appropriate. A heart rate limit of 140 beats per minute and a MET level of 7 is arbitrarily used for subjects under the age of 40 years; a heart rate limit of 130 beats per minute and a MET level of 5 is used for subjects over 40. A Borg perceived exertion level in the range of 13 to 15 can be used as a test end point, particularly for subjects receiving ß-blockers. A symptom-limited maximum test is probably most appropriate more than 3 weeks after MI, when the subject is ready to resume full activities.

Safety. A review of numerous subjects with predischarge and post-MI exercise tests reports few serious complications: two cases of recurrent MI and two cases of ventricular fibrillation, one fatal. These findings represent 0.05% morbidity and 0.02% mortality.²²

Meta-analysis reveals that only an abnormal systolic blood pressure response or a low exercise capacity is significantly associated with poor outcome in post-MI subjects. Submaximum testing resulted in the highest proportion of positive associations and the highest risk ratios. Abnormal responses at higher workloads are not as predictive as those at lower workloads.²² Key Point: In post-MI subjects, clinical judgment identifies subjects at highest risk, and exercise-induced ST displacement is not as predictive as an abnormal systolic blood pressure response (drop of 20 mm Hg or more or flat response for duration of the test) or poor exercise capacity. However, exercise-induced ST segment depression appears to be associated with increased risk in subjects without diagnostic Q waves (ie, subendocardial MI).²³

Subjects with stable CAD. Studies using exercise testing of subjects with stable CAD have attempted to predict angiographic findings, cardiac events in subjects with silent ischemia, or improved survival with CABS.

Angiographic findings. Numerous studies have been devised to predict left main or triple-vessel disease or both.²⁴ Different criteria have been used with varying results. Predictive value refers to the percentage of those with abnormal criteria who actually have left main or triple-vessel disease.

Exertional hypotension. In most studies, exercise-induced hypotension predicts a poor prognosis, with a positive predictive value of 50% for left main or triple-vessel disease.²⁵ Exercise-induced hypotension is also associated with cardiac complications during exercise testing, appears to be alleviated by CABS, and can occur in subjects with CAD, valvular heart disease, or cardiomyopathy. Occasionally, subjects without clinically significant heart disease will exhibit exercise-induced hypotension during exercise related to dehydration, antihypertensive therapy, or prolonged strenuous exercise. Key Point: The definition of exercise-induced hypotension is of crucial importance in evaluating the exercise test response. A drop in systolic blood pressure below preexercise values is the most ominous criterion; a drop of 20 mm Hg or more after a rise is reason to stop a test if accompanied by serious ventricular arrhythmias or ischemia.

Cardiac events in subjects with silent ischemia. In the presence of unstable angina, asymptomatic (silent) ischemia detected by ambulatory ECG (Holter) recording appears to confer an adverse prognosis. The prognostic implication of asymptomatic ischemia detected during exercise testing is controversial. Subjects with silent ischemia may be at greater risk for cardiac death because they do not have an intact "warning system." However, in three large population studies of subjects with a high prevalence of CAD who underwent exercise testing, those with ST segment depression with or without angina during testing had similar prognoses.²⁶ Ischemia is silent in approximately 60% of subjects with ischemic ST segment depression. Silent ischemia occurring with treadmill testing does not confer an increased risk for death relative to subjects experiencing angina. Thus, therapy should not be more intense for silent ischemia than for subjects with angina and ST depression.

Exercise-induced ventricular arrhythmias. In subjects with CAD, exercise-induced ventricular arrhythmias do not usually represent an independent risk factor for subsequent mortality or coronary events. However, recent data suggest that these arrhythmias add independent prognostic information to thallium-201, ST segment, and heart rate changes,^{27 28} and they are associated with severe CAD and wall motion abnormalities. Exercise testing may be of considerable value in the evaluation of drug therapy for ventricular arrhythmias, particularly in subjects with CAD.

Prognostic scores. Scores based on the coefficients from Cox Hazzard Survival models appear to be the optimal way of estimating cardiovascular mortality. The Duke score represented in Fig 6 as a nomogram is the best validated and has been shown to function in a wide range of populations, including women.

View larger version (19K): [in this window] [in a new window]   Figure 6. The Duke nomogram uses five steps to estimate prognosis for a given individual from the parameters of the Duke score. First, the observed amount of ST depression is marked on the ST segment deviation line. Second, the observed degree of angina is marked on the line for angina, and these two points are connected. Third, the point where this line intersects the ischemia reading line is noted. Fourth, the observed exercise tolerance is marked on the line for duration of exercise. Finally, the mark on the ischemia reading line is connected to the mark on the exercise duration line, and the estimated 5-year survival or average annual mortality rate is read from the point at which this line intersects the prognosis scale. METs indicates metabolic equivalents.

Improved survival after CABS. One study suggests that subjects with cardiomegaly, exercise capacity of less than 5 METs, or a maximum systolic blood pressure of less than 130 mm Hg would have a better outcome if treated with surgery.²⁹ In one surgery trial, subjects who had an exercise test response of 1.5 mm of ST segment depression showed enhanced survival with surgery. Improved survival also extended to those with baseline ST segment depression and those with claudication.³⁰ In another trial³¹ the surgical benefit to mortality was greatest in subjects with 1 mm ST segment depression at less than 5 METs. There was no difference in mortality in subjects who exceeded exercise capacity of 10 METs, and in this group, the prognosis is generally quite good. Key Point: In subjects with stable CAD, studies comparing angiographic findings, cardiac events, and the differential outcome of CABS compared with medical therapy have shown the exercise test to have prognostic power. These studies indicate that subjects with marked degrees of ST segment depression (ie, greater than 2 mm, in multiple leads, and prolonged into recovery) accompanied by poor exercise capacity, exertional hypotension, ectopic ventricular contractions, angina, or all of the above are at increased risk of having triple-vessel or left main disease and a poor prognosis.

Subjects who become symptomatic after CABS. Because more than 300 000 Americans undergo CABS each year, predicting prognosis of subjects who become symptomatic after this procedure is an important issue. Several studies have evaluated graft occlusion and recurrence of symptoms; however, exercise-induced ST depression does not predict prognosis after CABS. An exercise capacity of 9 METs or more indicates a good prognosis, regardless of other responses.³²

Subjects who have undergone PTCA. More than 250 000 PTCAs are performed annually,³³ with an expected angiographic restenosis rate of 30% to 40%³⁴ within the subsequent first 6 months. Several studies have assessed the value of exercise testing in the detection of restenosis and/or in the prediction of adverse cardiac events after PTCA.^{34 35 36 37 38 39 40 41} Interpretation of these studies is limited because of their variability in subject populations and study design, with regard to the number of vessels diseased, the adequacy of revascularization after PTCA, the timing of the exercise test, and the definition of restenosis. Several general conclusions, however, can be drawn from these studies. Exercise electrocardiography early after PTCA is more often positive for an ischemic response among subjects with multivessel coronary disease and those who have incomplete revascularization.^{35 36 37} The sensitivity of exercise electrocardiography in the detection of angiographic restenosis has been reported to range widely, from 24% to 60%.^{38 39 40} Moreover, among asymptomatic subjects with single vessel CAD, the detection of restenosis and the utility of the exercise test to predict subsequent cardiac events is particularly low.^{36 38 39}

In summary, the sensitivity, specificity, and predictive value of exercise testing after PTCA is sufficiently low to preclude its routine use as a screening test for restenosis and the assessment of subsequent prognosis, particularly in asymptomatic subjects. Such testing appears to have the highest yield among symptomatic subjects with multivessel coronary disease and in those with incomplete revascularization. As such, exercise testing after PTCA, if done, should be performed and interpreted with regard to the timing of the test after PTCA, assessment of clinical symptoms, and assessment of coronary anatomy at the time of PTCA.

High risk coronary profile. Exercise testing in subjects with coronary risk factors such as hypercholesterolemia and high blood pressure may be beneficial, particularly if there are symptoms suggesting CAD. The detection of myocardial ischemia or other abnormal end points can lead to further diagnostic studies and appropriate management strategies.

Apparently healthy individuals. Silent ischemia induced by exercise testing in apparently healthy men is not as predictive of a poor outcome as once thought. Use of the exercise test for screening is even more misleading than previously appreciated because of the higher false-positive rate. Approximately 19 of 20 abnormal ST responses will be false-positives. Earlier superior results can be explained by inclusion of angina pectoris as an end point, which could be caused by cardiac concerns resulting from an abnormal exercise test.^{42 43} Key Point: The nonselective use of exercise testing for screening apparently healthy individuals should be discouraged because of the poor predictive value of minimum (1 mm) ST segment depression. Unfortunately, this abnormal response may lead to psychological and vocational disability as well as unnecessary medical expense and risk. In these individuals, the test is helpful for motivational purposes and for designating exercise prescriptions. Only combinations of other abnormal responses and at least 2 mm or more ST depression should be considered predictors of increased risk of cardiovascular events in asymptomatic men.

There is substantial evidence to support the use of exercise testing as the first noninvasive step after the history, physical examination, and resting ECG in prognostic evaluation of subjects with CAD. Exercise testing accomplishes both purposes of prognostic testing: it provides information about the subject’s status and is helpful when making recommendations for optimum management. Some studies show that the value of exercise testing for risk stratification is enhanced by the addition of radionuclide imaging, particularly with submaximum testing after an uncomplicated MI. Exercise test results enhance selection of subjects who should undergo further evaluation such as coronary angiography. Since the exercise test can be performed in the physician’s office and provides valuable information about activity levels, response to therapy, and disability, it is the reasonable first choice for prognostic assessment. Because of its widespread use, the exercise test can have an enormous impact on the cost-effective delivery of cardiovascular care.

Other Uses of the Exercise Test
Assessment of Valvular Heart Disease
Exercise testing has been used in subjects with valvular heart disease to quantify disability, to reproduce exercise-induced symptoms, and to evaluate responses to medical and surgical interventions.⁴⁴ The exercise test has also been used to identify concurrent CAD, but there is a high prevalence of false-positive responses (ST depression not due to ischemia) because of frequent baseline ECG abnormalities and LV hypertrophy. Some physicians use exercise testing to determine when surgery is indicated. Exercise testing has been used most frequently in subjects with aortic stenosis.

Aortic stenosis. Effort syncope in subjects with aortic stenosis^{45 46} is an important and well-appreciated symptom. Most guidelines for exercise testing list moderate to severe aortic stenosis as a relative contraindication for testing because of concern about syncope and cardiac arrest. Four proposed mechanisms for exercise-induced syncope in subjects with aortic stenosis include carotid hyperactivity, LV failure, arrhythmia, and LV baroreceptor stimulation. Exercise testing is relatively safe in both the pediatric and adult subject when performed appropriately. Attention should focus on the subject’s symptoms, minute-by-minute response of blood pressure, slowing heart rate, and ventricular and atrial arrhythmias. In the presence of an abnormal blood pressure response, the subject with aortic stenosis should take at least a 2-minute cooldown walk at a lower stage of exertion to avoid acute LV volume overload, which may occur when the subject lies down.

Exercise plays an important role in the objective assessment of symptoms, hemodynamic response, and functional capacity. Whether ST segment depression indicates significant CAD remains unclear. The benefits of surgery and baseline impairment can be quantified by performing an exercise test before and after the operation. Exercise testing offers the opportunity to objectively evaluate disparities between history and clinical findings, eg, in the elderly asymptomatic subject with physical and/or Doppler findings of severe aortic stenosis. Echocardiographic studies are often inadequate in such subjects, particularly in smokers. When Doppler echocardiography reveals a significant gradient in the asymptomatic subject with normal exercise capacity, progress should be monitored until symptoms develop. Surgery appears to be indicated in subjects with an inadequate systolic blood pressure response to exercise or a fall in systolic blood pressure from the resting value when symptoms occur.

Aortic regurgitation. Subjects with aortic regurgitation⁴⁷ usually maintain a normal exercise capacity for a longer time than those with aortic stenosis. Volume workload of the myocardium requires less oxygen than pressure work. During exercise, the decreases in diastolic duration and regurgitation volume favor forward output. As the myocardium fails, heart rate tends to slow, and ejection fraction and stroke volume decrease. There is an increase in ventricular diameter and metabolic requirements. Exercise testing is useful for monitoring subjects with aortic regurgitation, using onset of ST segment depression, a reduction of heart rate response to each workload, and decrease in peak O₂ as markers for worsening LV function.

Mitral stenosis. Subjects with mitral stenosis⁴⁸ may show either a normal or excessive increase in heart rate during exercise. Since stroke volume cannot be increased, the normal rise of cardiac output is attenuated and may eventually fall during exercise, frequently accompanied by exercise-induced hypotension. A rise in pulmonary resistance results in increases in myocardial oxygen demands. In subjects with mitral stenosis, chest pain and ST segment depression during exercise may occur as a consequence of reduction in coronary perfusion or because of pulmonary hypertension. ST depression is attributed to a decrease in coronary perfusion as a consequence of a fall in cardiac output and increased myocardial oxygen demand secondary to right ventricular overload. Shortening of diastole associated with tachycardia and increased pulmonary blood flow during exercise increases effects of preexistent mitral stenosis and may cause pulmonary congestion.

Mitral regurgitation. Subjects with mild to moderate mitral regurgitation⁴⁹ maintain normal cardiac output during exercise. Blood pressure, heart rate, and ECG responses are usually normal. When mitral regurgitation occurs suddenly during exercise as a result of ischemic papillary muscle dysfunction, a flat response in systolic blood pressure can occur. Subjects with severe mitral regurgitation usually show a decreased cardiac output and limited exercise capacity. ST segment depression is infrequent in these subjects since there is no significant increase in myocardial oxygen consumption with mitral regurgitation. However, a hypotensive response can develop, and arrhythmias frequently occur.

Mitral valve prolapse. Several mechanisms have been suggested to explain ST depression in subjects with mitral valve prolapse,⁵⁰ including regional ischemia of the papillary muscle, abnormalities of the coronary arteries, compression of the anterior descending artery, coronary spasm, and primary cardiomyopathy. Angiography and scintigraphy studies in these subjects have been normal. ECG changes can be normalized by propranolol or other nonselective ß-blockers, which will improve the specificity of the exercise test.

Evaluation of an Exercise Program
An exercise test is often used to evaluate the safety of an exercise training program and is useful in formulating an exercise prescription. In general, a sedentary individual who at the age of 40 years decides to enter an exercise program of a higher intensity than walking at 50% to 60% of maximum heart rate reserve should undergo an exercise test. Testing should also be recommended for younger individuals with coronary risk factors or a strong family history of CAD. Because of the wide scatter of maximum heart rate when plotted against age, determining an individual’s maximum heart rate during exercise in order to assign a target for training is preferable to giving a predicted value. It is advantageous in certain individuals to objectively evaluate the response to exercise in a monitored setting before an exercise program is begun. An exercise test can be used in adult exercise or cardiac rehabilitation programs to safely advance an individual to a higher intensity of effort. Test-demonstrated improvement in exercise capacity can also be an effective incentive to continue the program and encourage risk factor modification. (Further information may be found in the section titled "Exercise Training.")

Functional Classification of Disability
Exercise testing is used to determine the degree of disability of subjects with various forms of heart disease. Subjects who exaggerate their symptoms or who have a psychological impairment can often be identified. Exercise testing is a more accurate measure of the degree of cardiac impairment than a physician’s assessment of exercise capacity. O_2max is the best noninvasive measurement of the exercise capacity of the cardiovascular system. Inability to reach 5 METs (below 18 mL · kg^-1 · min^-1) without signs or symptoms is a criterion of disability used by the Social Security Administration. Determination of a subject’s exercise capacity affords an objective measurement of the degree of cardiac impairment and can be useful in treatment.⁵¹

Evaluation of Risk for Surgery
Results of exercise testing do not appear to substantially add to the risk stratification provided by the resting ECG in subjects without known CAD who are candidates for major elective noncardiac surgery.⁵² Therefore, exercise testing is not recommended as a routine procedure before major elective noncardiac surgery under general anesthesia. Exercise testing has been used in subjects with intermittent claudication to evaluate results of iliofemoral bypass.

Assessment of Special Populations
Subjects before and after revascularization. The efficacy of a revascularization intervention can be noninvasively assessed by exercise testing since signs and symptoms of ischemia can be demonstrated and exercise capacity can be measured.⁵³

The elderly. Exercise testing can be effectively performed in older individuals. Attention must focus on musculoskeletal stability, and often testing protocols must be modified. The expected lesser heart rate response (even in the absence of medications) and higher systolic pressure response must be interpreted appropriately for higher age ranges.

Subjects with heart failure. Testing protocols are usually modified in degree of graded work for those subjects with heart failure. Closer medical supervision is indicated, and care must be taken in assessing blood pressure response and ventricular arrhythmias. Auscultation after exercise may detect cardiac "gallop" rhythm, pulmonary rales, and bronchospasm.

The physically disabled. Special protocols are available for testing⁵⁴ musculoskeletally disabled subjects, especially those with hemiplegia or paresis after stroke or those with lower limb amputation or spinal cord injury. Many testing protocols use arm cycle ergometry with the subject sitting to optimize the exercise load, but some protocols consist of arm-leg or leg cycle ergometry. Effective testing can be performed by most of these subjects.

Cardiac transplantation recipients. These subjects often have exercise testing for prescription formulation for "reconditioning" in a supervised exercise program. Heart rate and blood pressure responses in these individuals are often quite modest, and other end points such as perceived exertion are best used as end points in exercise training. Exercise test protocols should be selected to provide slow increases in intensity of workload to allow time for the denervated heart to respond to circulating catecholamines.

Drugs and Exercise Testing
ß-Blockers
Subjects with angina who receive ß-blockers may achieve a higher exercise capacity with less ST segment depression and less angina if the drugs prevent their reaching the ischemic double product. Maximum heart rate and systolic blood pressure product may be profoundly reduced. The time of ingesting medications before testing should be recorded.

Vasodilators
These agents can increase exercise capacity in subjects with angina or heart failure or both.⁵⁵ There has been no scientific validation that long-acting nitrates increase exercise capacity in subjects with angina when they are tested after chronic administration. Hydralazine decreases peripheral resistance and arterial blood pressure. There is often an increase in heart rate (reflex tachycardia) that tends to increase cardiac output. This agent is useful in treatment of heart failure by decreasing afterload and increasing exercise capacity.

Angiotensin-Converting Enzyme Inhibitors
These agents decrease blood pressure at rest and during exercise through decreases in plasma levels of angiotensin II and aldosterone. They increase exercise capacity in subjects with chronic heart failure and enhance their survival rates.

Calcium Antagonists
Calcium antagonists (slow channel-blocking agents) have multiple hemodynamic effects. They can delay time to ischemia and improve exercise capacity. ST segment depression is usually delayed until higher workloads. Heart rate and systolic blood pressure are decreased for a given level of exercise.

Digitalis
ST segment depression can be induced or accentuated during exercise in individuals who are taking digitalis, including both normal subjects and subjects with CAD.⁵⁶ Profound ST segment depression (more than 2 mm above baseline) almost always indicates ischemia, even in subjects who are taking digitalis. A normal QT interval is associated with digitalis-induced ST changes, whereas prolonged QT intervals occur with ischemia, other drugs, electrolyte imbalance, and other medical problems. Exercise-induced ST segment depression is said to persist for 2 weeks after digitalis is discontinued.

Antiarrhythmic Agents
Quinidine can cause prolongation of phase 2 of the ventricular action potential, decreasing the repolarization gradient during the ST segment and thus diminishing the magnitude of ST depression. However, quinidine does not change the ST segment, heart rate, or O_2max in normal subjects or subjects with CAD.

A decrease of 20 beats per minute in maximum exercise heart rate has been reported in subjects taking amiodarone. Amiodarone also increases duration of the QRS complex during exercise.

Diuretics
Most diuretics have little influence on heart rate and cardiac performance but do decrease plasma volume, peripheral resistance, and blood pressure. Diuretics can cause hypokalemia, which results in muscle fatigue, ventricular ectopy, and, rarely, ST segment depression.

Special Cases of Exercise Testing Interpretation
Exercise Testing in Women
The difference in the predictive accuracy of exercise testing between men and women can be explained in part by the difference in prevalence of CAD.⁵⁷ However, because specificity is also intrinsically lower in women, two factors merit attention. First, careful characterization of chest pain is especially important; second, ST segment depression in the presence of typical angina is highly predictive of disease compared with atypical or no pain. Several mechanisms have been suggested to explain the high false-positive rate of ST depression in women, including medications (digitalis) and resting ST-T abnormalities. Because estrogens have a similar chemical structure to digitalis, they may be partially responsible for the high prevalence of false-positive exercise test results in women.

Hypertension
Exercise testing has been proposed as a means of detecting labile hypertensive subjects or individuals who will eventually become hypertensive, but there is a lack of support for this theory.^{58 59} In addition, subjects whose hypertension is poorly controlled (ie, those on therapy) may be identified by abnormally high pressure responses with exercise. Hypertensive subjects frequently have ECG abnormalities (LV hypertrophy with strain) and myocardial hypertrophy, both of which make false-positive ST responses more likely.

Cardiomyopathies
Exercise testing has been used in subjects with dilated cardiomyopathy to determine exercise capacity, assess pulmonary response to LV dysfunction, determine the grade of ventricular ectopy, and evaluate the effectiveness of treatment.⁶⁰ Subjects with LV dysfunction may have reduced exercise capacity and develop signs and symptoms of pulmonary and right ventricular involvement. There is an inadequate increase in cardiac output during exercise, which limits O_2max and exercise tolerance. Subjects with severe LV dysfunction can often double cardiac output only with upright exercise. Stroke volume may increase normally during upright exercise despite a decrease in LVEF. Ventricular dilation facilitates use of the Starling mechanism but may reduce chronotropic reserve. With increasing exercise, stroke volume and cardiac output cannot continue to meet the increased demands, and exertional hypotension is often observed.

Certain subjects may have normal exercise tolerance despite severe LV dysfunction. Several compensatory mechanisms have been proposed to explain the poor correlation between LV function and exercise capacity. This is especially so for those with a resistance to right-sided impairment (ie, pulmonary congestion). Exercise may increase the frequency of ventricular ectopy or induce other more serious arrhythmias. Even supraventricular arrhythmias can lead to ventricular tachycardia.

Hypertrophic Obstructive Cardiomyopathy
Exercise can be related to sudden death due to arrhythmias in this condition.^{61 62} Chest pain, an abnormal resting ECG, and exercise-induced ST segment depression are frequent. Exercise testing under careful supervision may be especially helpful to demonstrate the level at which significant events occur, such as the presence or severity of arrhythmias, myocardial ischemia, murmurs indicating obstruction in LV outflow, and presyncopal manifestations. Ventricular arrhythmias are often observed during exercise.

Intracardiac Conduction Blocks
Intraventricular blocks. Intracardiac conduction blocks can exist before exercise or develop or disappear during exercise. Rate-dependent intraventricular blocks that develop during exercise often precede the appearance of chronic blocks that are present at rest.^{63 64 65} Diagnosis of ischemia from the exercise ECG is impossible when left bundle branch block is present. There can be a marked degree of exercise ST segment depression in addition to that found at rest in normal subjects with left bundle branch block. There is no difference in ST segment response to exercise between those with and those without ischemia. Left bundle branch block that occurs with a heart rate below 125 beats per minute in subjects with typical angina is frequently associated with CAD, whereas left bundle branch block occurring at a heart rate above 125 beats per minute occurs more frequently in subjects with normal coronary arteries. The presence of intraventricular blocks and their disappearance during exercise are rare. Subjects with left bundle branch block who develop a normal QRS pattern during exercise have been reported.

Right bundle branch block. Preexisting right bundle branch block^{66 67 68 69 70} does not influence interpretation of the exercise test except in the anterior precordial leads (V₁, V₂), where ST depression is frequent. However, overall sensitivity of exercise testing in these subjects is uncertain.

Intraventricular blocks during exercise. In addition to left or right bundle branch block, left anterior or posterior hemiblock and bifascicular block (a combination of right bundle branch block and left anterior or posterior hemiblock) may be induced with exercise. The presence of such blocks is primarily a rate-related phenomenon that occurs during exercise as the sinus rate increases beyond a critical point. Intraventricular blocks are difficult to distinguish from ventricular tachycardia.

Conduction abnormalities. Atrioventricular (AV) conduction disturbance. Shortening of the PR interval (as much as 0.10 or 0.11 second) during exercise as the sinus rate increases is common, probably because of increased sympathetic tone, such as usually occurs in young, healthy individuals.

First-degree AV block. First-degree AV block occurs occasionally at the end of exercise or during the recovery phase. Medications or conditions that may produce prolonged AV conduction time (eg, digitalis, propranolol, myocarditis) predispose the individual to lengthening of the PR interval.

Second-degree AV block. The occurrence of Wenckebach Mobitz type I AV block during exercise is rare. The clinical significance of exercise-induced Mobitz type II AV block is not known, but the type II block may also be a rate-related phenomenon that appears as the sinus rate is accelerated beyond a critical level. It may, however, reflect more critical underlying conduction system disease, and if second-degree AV block develops with testing, the test should be terminated.

Complete AV block. Acquired complete AV block at rest is a relative contraindication to exercise testing. Exercise testing can be conducted in subjects with congenital complete AV block if there are no coexisting significant congenital anomalies.

Sinus arrest. Rarely, subjects develop long periods of sinus arrest immediately after exercise. Sinus arrest usually occurs in subjects with severe ischemic heart disease.

Preexitation syndromes. Exercise may provoke, abolish, or not interfere with anomalous AV conduction in individuals with known Wolff-Parkinson-White (WPW) syndrome.⁷¹ Exercise usually does not abolish anomalous AV conduction, but when it does, these individuals are thought to be in less danger of exercise-induced ventricular tachycardia. When exercise does not interfere with preexisting anomalous AV conduction, significant ST depression can be observed during exercise testing. In the presence of WPW syndrome, the ST depression may not be due to ischemia but may instead be a false-positive (indeterminate) occurrence. Although exercise has been considered a predisposing factor to initiate tachyarrhythmia in WPW syndrome, there is a low prevalence of tachyarrhythmias during or after exercise in WPW subjects. Approximately half of WPW subjects develop normal conduction during the test.

Cardiac Arrhythmias
Exercise may induce cardiac arrhythmias under several conditions, including diuretic and digitalis therapy,^{72 73 74} and recent ingestion of alcohol or caffeine may exacerbate arrhythmias. Since exercise increases myocardial oxygen demand, in the presence of CAD, myocardial ischemia could predispose the subject to ectopic activity during exercise. It appears that subendocardial ischemia (ST depression) is not as arrhythmogenic as transmural ischemia (ST elevation). Exercise-induced arrhythmias are generated by enhanced sympathetic tone, increased myocardial oxygen demand, or both. The immediate postexercise period is particularly dangerous because of the high catecholamine levels that are associated with a generalized vasodilation. Peripheral arteriolar dilation induced by exercise and reduced cardiac output resulting from diminished venous return secondary to sudden termination of muscular activity may lead to a reduction in coronary perfusion while the heart rate is still elevated. The increased sympathetic tone in the myocardium may stimulate ectopic Purkinje pacemaker activity by accelerating phase 4 of the action potential, which provokes spontaneous discharge and leads to increased automaticity.

Exercise can suppress cardiac arrhythmias present at rest. This phenomenon has been attributed to the overdrive suppression of the ectopic impulse formation by sinus tachycardia that is caused by exercise-induced vagal withdrawal and increased sympathetic stimulation. Exercise-induced sinus tachycardia may inhibit automaticity of an ectopic focus because it reduces automaticity of the Purkinje tissue.

Ectopic ventricular contractions are the most frequent cardiac arrhythmia during exercise, followed by supraventricular arrhythmias and fusion beats. Their prevalence is directly related to age and cardiac abnormalities. In general, ectopic ventricular contractions are of concern in subjects with a family history of sudden death or a personal history of cardiomyopathy, valvular heart disease, or severe ischemia.

Sinus arrhythmias with periods of sinus bradycardia and wandering atrial pacemaker are relatively common during exercise and the immediate recovery phase. Atrial ectopic contractions and atrial "group" beats can occur in either normal or diseased hearts. Exercise-induced transient atrial fibrillation and flutter occur in less than 1% of individuals who undergo exercise testing.⁷⁵ These arrhythmias may be induced by exercise in healthy individuals or subjects with rheumatic heart disease, hyperthyroidism, WPW syndrome, or cardiomyopathy. Paroxysmal AV junctional tachycardia is observed during exercise only rarely. Exercise-induced supraventricular arrhythmias alone are not related to CAD but are more often related to pulmonary disease, recent alcohol ingestion, or excessive caffeine intake.

Obtaining Informed Consent for Exercise Testing

Although obtaining written consent from a subject does not protect a physician from legal action, a signed consent form is nonetheless desirable because a physician may be held responsible for a major adverse event, even if the test is carefully administered and monitored.

Informed Consent for Exercise Testing

To determine my cardiovascular response to exercise, I voluntarily agree to engage in an exercise test. The information obtained about my heart and circulation will be used to help my doctor advise me about activities in which I may engage.

I have been told that before I undergo the test, I will be interviewed and examined by a physician in an attempt to determine if I have a condition indicating that I should not engage in this test.

I am told that the test I will undergo will be performed on a

(description), with gradually increasing effort until symptoms such as fatigue, shortness of breath, or chest discomfort may appear, indicating to me that I should stop. I have been told certain changes may occur during the test, including abnormal blood pressure, fainting, abnormal ECG showing heart "strain," disorders of heart beat (too rapid, too low, or ineffective), and, possibly, heart attack and death.

I agree that the information obtained may be used and published for statistical or scientific purposes.

I have read the above and understand it, and my questions have been answered to my satisfaction.

Subject

Physician supervising the test

Witness

Date

Exercise Training

Care must be taken to ensure that apparently healthy individuals who are beginning an exercise program do not have detectable disease and that subjects with known disease are stable with no evidence of new or changing symptoms. Medical clearance should be obtained before entry into exercise training programs unless the anticipated activity is low level (less than 50% of maximum capacity, eg, moderate walking). Exercise testing is helpful in establishing guidelines for exercise training in apparently healthy adults and is mandatory for subjects with known or suspected cardiovascular disease. Care should be taken to exclude from training subjects with evidence of unstable heart disease such as angina, uncontrolled heart failure, or arrhythmia. Training programs for subjects with cardiovascular disease should be medically supervised until safe levels of activity have been established. Physician presence is discussed under the section titled "Types of Supervised Programs."

Exercise Training of Apparently Healthy Individuals
Risks of Exercise
Exercise has both risks and benefits, and the challenge to the physician is to provide guidelines that minimize risks and maximize benefits. Screening procedures are not perfect for identifying the rare individual who is at risk, but risks can be decreased by proper screening precautions.

Many factors affect risk of exercise. Three of the most important are age, presence of heart disease, and intensity of exercise. Sudden cardiac death is rare in apparently healthy individuals. In individuals under the age of 35 years, sudden cardiac death is usually attributed to congenital heart disease, whereas CAD is a more likely cause for those over 35. The results of selected studies reporting risks of sudden cardiac arrest during exercise training are summarized in Table 9.

View this table: [in this window] [in a new window]   Table 9. Risk of Sudden Cardiac Arrest During Exercise Training

These studies indicate that in the general population, risk of sudden cardiac death during vigorous exercise is very low. Since these studies were not randomized controlled trials, the contribution of all potential variables to sudden cardiac arrest or death cannot be determined. However, it is generally believed that the benefits of exercise exceed the risks, and individuals should be encouraged to exercise prudently.

It is recommended that anyone who plans to begin an exercise program more vigorous than walking should have a current (within 6 to 12 months) physical examination. Individuals under the age of 40 years who have no symptoms of cardiovascular disease, no major coronary risk factors, and no physical findings (including murmurs and hypertension) can be considered free of disease, do not need an exercise test, and should not be restricted in their exercise program.

Individuals 40 years of age or older or those with symptoms such as chest pain, abnormal physical examinations suggesting heart disease, or two or more major coronary risk factors should have a symptom-limited, maximum exercise test (unless otherwise contraindicated) if they plan to participate in vigorous exercise (such as jogging or running). If an exercise test is not done or is abnormal, these individuals should restrict their activities to moderate intensities. Key Point: The risks of serious complications of physical activity are highest during vigorous exercise and in individuals with heart disease. Hence, screening should ensure that cardiovascular disease is not present, that physical activity is limited to low or moderate intensities (walking or the equivalent), or that activity is medically supervised.

Physiological Changes
Physical conditioning can be measured as changes in O_2max, exercise test time, submaximal heart rate response, or ability to perform a standard amount of exercise.

Maximal oxygen uptake.O_2max is the peak oxygen uptake achieved by muscular exercise. By strictest definition, O_2max cannot be exceeded despite an increase in power output. Although demonstration of the O₂ plateau against work rate is certainly a valid demonstration of O_2max, subjects often cannot achieve the plateau because of leg fatigue, lack of necessary motivation, and general discomfort. Hence, it is customary to refer to O_2max as the peak O₂ attained during volitional incremental exercise.

In clinical practice, O_2max is not usually measured during an exercise tolerance test but is estimated from the peak work intensity achieved. Data presenting O_2max equivalents for exercise test work stages are presented in Fig 4.

Increased O_2max after training is associated with an increase in the capacity of the cardiovascular system to deliver oxygen and of the muscles to use that oxygen (greater arteriovenous oxygen [aO₂] difference and use). Higher cardiac output after training is achieved solely by an increase in stroke volume, since maximal heart rate is not usually increased after training in normal individuals.⁸⁷ O₂ is the product of cardiac output and systemic aO2 difference. Some of the increase in O_2max is the result of widening of the aO₂ difference as well as an increase in maximal cardiac output.⁸⁷ Based on data in healthy subjects,⁸⁸ a training effect can be achieved in a subject in the presence of selective or nonselective ß-adrenergic blockade. However, such changes may be attenuated⁸⁹ and/or may not be detected by metabolic studies (ie, O_2max) until after the drug is withdrawn⁸⁸ ("unmasking"). Key Point: The increase in O_2max as a result of training in normal individuals is due to a higher maximum cardiac output and to greater extraction of oxygen from the systemic circulation, reflecting both central and peripheral adjustments.

Central hemodynamic changes. Although a higher maximal cardiac output can be achieved after training, submaximum values are usually unchanged.⁹⁰ Submaximal heart rate is reduced after training, with a concomitant increase in stroke volume.^{87 90} The mechanism of these changes is not known. Exercise training has resulted in an increase in myocardial contractility in animals.⁹¹ Participation in a home exercise training group (compared with a control group) by physically disabled men with CAD significantly improved peak exercise LVEF and fractional shortening between baseline and 6 months.⁵⁴ Early results of another study revealed that in men with CAD, rest to peak LVEF improved with 1 year of training only in those doing high-intensity (85% O_2max) compared with low-intensity (50% O_2max) training. This improvement occurred in subjects with both depressed (<50%) as well as those with normal (>50%) LVEF. The increase in stroke volume that occurs with short-term training is probably largely related to augmentation of blood volume and hence ventricular preload.⁹² Fig 7 depicts relations of heart rate and stroke volume before and after training. Key Point: Submaximal heart rate is reduced after training in normal individuals, but because stroke volume is increased, cardiac output remains unchanged.

View larger version (19K): [in this window] [in a new window]   Figure 7. Mean values for stroke volume and heart rate in 15 middle-aged subjects at rest (prone and upright position) and during submaximum and maximum exercise in upright position before and after physical conditioning. From Hartley et al.87

Autonomic nervous system changes. Blood and urinary catecholamine levels are lower at rest and during submaximal exercise after training,⁹³ presumably because of less sympathetic nervous system activity. Parasympathetic tone may also be increased and, with sympathetic adjustments, may account for the slower heart rate and lower arterial blood pressures seen after training.

Peripheral changes. Skeletal muscle changes after exercise training include increases in oxidative enzyme concentration, capillary density, myoglobin concentration, adaptation of muscle fiber type to a higher percentage of red (slow twitch) fibers, and muscle glycogen. All potentially contribute to greater capacity to use oxygen and to better endurance.⁹⁴ Key Point: Greater oxidative potential in the skeletal muscles after training contributes to more endurance.

Submaximal endurance capacity. Endurance training enhances the individual’s ability to perform exercise at both submaximal and maximal intensities,⁹⁵ as demonstrated either by the ability to exercise longer at a similar work intensity or by doing more exercise in a given time. Improvements in endurance may be due to several factors, including greater availability of oxygen to the exercising muscles, greater use of aerobic processes (the most efficient energy sources), lower blood lactate levels, and/or greater anaerobic capacity. Adaptation to submaximal exercise is associated with a lower rate-pressure product (systolic blood pressure multiplied by heart rate) for a standard exercise task.

Changes in the skeletal muscles tend to improve accessibility to oxygen from the blood because of the higher myoglobin concentration and the greater capillary density, both of which enhance oxygen transport.

A greater concentration of oxidative enzymes allows muscles to obtain a larger share of their energy from aerobic rather than anaerobic sources. In so doing, the amount of high-energy phosphates generated from each mole of substrate metabolized is much greater, resulting in increased efficiency of substrate use. Lactate accumulation is also decreased, and the metabolic anaerobic threshold is increased.

Available muscle glycogen is a determinant of endurance time at higher submaximal work intensities. Since muscle glycogen is higher after training, the time required to deplete it would be expected to increase, which has been shown to augment endurance.⁹⁶ Key Point: Submaximal endurance is increased with training due to changes in the muscle cells that allow more aerobic activity and provide more glycogen for anaerobic energy.

Preventive Value of Exercise Conditioning
Habitual exercise eliminates one of the risk markers associated with a higher incidence of CAD. Physical inactivity has also been designated by the AHA as a major modifiable coronary risk factor, along with cigarette smoking, hypertension, and hyperlipidemia.⁹⁷ Other risk factors include age, gender, obesity, diabetes mellitus, and family history. Of these, hypertension, hyperlipidemia, obesity, and diabetes mellitus may be favorably affected by proper physical exercise. The Centers for Disease Control and Prevention have also proclaimed that inactivity is a major risk factor, with an overall weight for preventive value similar to high total cholesterol, cigarette smoking, and high blood pressure.⁹⁸ Some of the preventive value of exercise is related to associated improvements in other risk factors, but exercise exerts an independent effect as well.

Specific changes that accompany exercise training include the following:

• Decrease in blood pressure

• Increase in high-density lipoprotein cholesterol level

• Decrease in triglyceride level

• Augmentation of weight reduction efforts

• Beneficial psychological effects —Less depression —Reduced anxiety

• Improved glucose tolerance

Although no randomized, controlled studies have been performed, several prospective population studies have reported lower heart attack and death rates in active, apparently healthy populations compared with their sedentary counterparts. This association has been observed during leisure activity,^{99 100} total daily activity,¹⁰¹ and occupational activity.¹⁰² One significant longitudinal study¹⁰³ followed up 10 224 men and 3120 women for 8 years after a baseline exercise evaluation. Those who demonstrated a low functional capacity had the greatest subsequent mortality. Age-adjusted relative risks for low- compared with high-conditioning level were approximately 9 in women and 8 in men. Some of this protection is no doubt due to modification of risk factors, but some is an independent effect of exercise. The mechanism of the independent effect is not known. Whatever the mechanism, the benefits of exercise appear to outweigh the risks of even vigorous exercise.¹⁰⁴ Key Point: Sedentary lifestyle is a key independent risk factor for developing CAD.

Exercise Needed for an Optimum Effect
Any activity performed for training should be assessed in terms of intensity, frequency, duration, mode, and progression. The intensity of activity needed to improve physical conditioning varies among individuals and may be as little as 50% of O_2max for 20 minutes three times per week. An exercise intensity-duration relation is likely, so low-intensity exercise requires more time to increase functional capacity than higher intensity exercise. From a health and conditioning standpoint, the major advantage of moderate- and low-intensity exercise is less likelihood of complications, whereas vigorous exercise has the advantage of accomplishing the goal in less time.

Total work performed is usually expressed as kilocalories. Experience with normal populations suggests that activity equal to or greater than 700 kcal (2940 kJ) per week is associated with higher maximal working capacities. Morbidity and mortality from heart attacks may also be related to amount of exercise. One group concluded that individuals whose activity score was 28 or less had a higher incidence of CAD (MIs, angina pectoris, and sudden death) than those whose score was higher.¹⁰¹ Activity score in this study was determined by weighting activity by intensity and time so that 1 unit of score approximated 1 hour multiplied by 1 MET. Studies of college alumni whose jobs were sedentary concluded that mortality and morbidity were lowest in those whose activities required an average of 2000 or more kcal (8400 kJ) per week.¹⁰⁰ More recent studies have shown advantages of physical activities conducted at 35% to 40% of O_2max but with greater frequency and duration.¹⁰⁵ Table 10 lists the energy requirements of various activities.

View this table: [in this window] [in a new window]   Table 10. Estimated Energy Requirements of Selected Activities*

Activities that are 60% of O_2max are generally categorized as moderate. Body weight must be used to calculate calories since METs are corrected for weight. The following conversion formula is used: calories per minutex(METsx3.5xbody weight in kilograms)/200.

A threshold of intensity is probably required to achieve benefit, although the exact value is not known and may vary from one person to another. Although a threshold cannot be defined from available information, much of the exercise described in published reports and associated with good health is moderate in intensity, such as walking. Thus, exercise likely need not be of high intensity to be beneficial; the total amount of activity is more important for health than high-intensity exercise.

Vigorous exercise such as jogging and running also seems beneficial. In one study,¹⁰⁴ individuals who regularly performed vigorous exercise had an overall lessened likelihood of sudden death. More orthopedic injuries and higher dropout rates are associated with high-intensity exercise compared with low- to moderate-intensity programs. However, this does not mean that better guidelines could not reduce the risk of vigorous exercise further, providing an even greater overall benefit. Hence, these recommendations are directed toward minimizing risk and maximizing benefit.

Occupational Activity
Early studies of longshoremen suggest that occupational activity can provide protection from CAD.¹⁰² Occupational activity was also considered a part of overall activity in another study.¹⁰⁰ The level of physical effort required of longshoremen was heavy and is rarely duplicated in the United States today because of widely available mechanical devices.

An operational definition of heavy occupational activity is a job that requires lifting loads of 20 pounds or more at least once an hour throughout the day or constantly moving loads of any size from one place to another without mechanized transportation. In the longshoremen and other studies, frequent walking or standing had no protective value, although other studies suggest that individuals who walk for long periods of time (such as postal employees) obtain protection. It is likely that unless individuals walk for 1 hour or more each day (low to moderate intensity), they should supplement that activity with leisure-time exercise.

Exercise Recommendations for Men and Women
Gender is an important factor in formulating risk for CAD, and much additional research is needed to define the exercise needs of women. Women require approximately the same intensity, frequency, and duration of exercise as men to increase O_2max.¹⁰⁶ Most reported studies of heart disease prevention have focused on men because of the higher incidence of CAD in men; nevertheless, CAD is a major cause of mortality and morbidity in women. The requirements and recommendations for the prevention of heart disease in women may differ somewhat from those developed from data collected on men, but until more research is complete, the same guidelines for exercise must be recommended for both men and women.

Recommendations for Maintenance of Cardiovascular Health
Occupational activity. Unless an individual’s occupation meets minimum requirements of heavy exercise, a leisure-time exercise program should be followed. Occupational activity is defined as heavy (and adequate) if it requires continual climbing of stairs or inclines, lifting loads of 20 pounds or more each hour, or carrying loads of any size continuously throughout the day. Because of automation and the use of mechanized lift devices, very few jobs require such energy expenditure today.

Leisure-time activity. Leisure-time activity for minimum conditioning and health benefits should consume a minimum total of 700 kcal/wk; the necessary activity should be performed on three or more nonconsecutive days (the amount associated with improved conditioning). Individuals should be encouraged to engage in activities requiring up to 2000 kcal/wk for maximum health benefits. Walking 20 miles each week is one way to accomplish this goal. Key Point: Regular physical activity is important for health maintenance. Walking appears to be as beneficial as more vigorous activities. Some benefit is apparently derived from as little as 20 minutes of low-intensity exercise performed three times per week. However, incremental benefits appear to accrue from up to 2000 kcal/wk (20 miles of walking or jogging). There is no evidence of a health benefit at more than 2000 kcal/wk. Occupational activity provides adequate health benefits only when a job requires sustained heavy activities. The same recommendations are made for men as women, but more research is needed for women.

Exercise Training Techniques
Activities that cause the greatest increase in O_2max have certain characteristics that, when present, are said to qualify the exercise as endurance or cardiovascular. These characteristics include dynamic exercise, alternately contracting and relaxing the muscles (as opposed to isometric or resistive exercise), and large muscle group activities such as walking or running. Exercise must be performed at least three times per week for a minimum of 30 minutes per session at a minimum intensity of 50% to 60% O_2max. In addition to walking and running, other examples of endurance or cardiovascular activities are swimming, cycling, stair-stepping, and cross-country skiing. Such activities of higher intensity should be done with care by subjects with cardiovascular disease.

Exercising at a low intensity for 5 to 10 minutes before (warm-up) and after (cooldown) the training session is a routine recommendation. Such activities help stretch and warm up muscles and ligaments in preparation for the activity session. The cooldown period also prevents hypotension, which may occur with sudden cessation of exercise.¹⁰⁷

Properly selected resistance exercises (calisthenics and weights) are helpful for promoting muscle strength and flexibility, which are important components of physical conditioning.

Resistance exercise involves activities that use low or moderate repetition movements against a resistance, generating a rise in muscle tension that ultimately yields increases in muscular strength. Weight lifting is the prototype resistance exercise. The increased muscle tension during such exercise leads to both a restriction in muscle blood flow during contraction due to compression of arterioles and capillaries that perfuse the muscle bed¹⁰⁸ and a centrally mediated pressor response. The blood pressure and heart rate responses during resistance exercise are proportional to the relative intensity of muscular contraction (ie, the percent of maximal voluntary contraction), the size or mass of the muscle groups involved, and the duration of the contraction.¹⁰⁹ Unlike dynamic (aerobic) exercise, which can lead to changes in skeletal muscle aerobic capacity via changes in mitochondrial number and in the enzymes necessary for glycogen and fat metabolism,¹¹⁰ the effects of long-term resistance exercise on the skeletal muscle appear limited to muscle cell hypertrophy via the synthesis of increased contractile protein and the thickening of connective tissue.¹¹¹ Subsequent increases in muscle strength (or maximal voluntary contraction) after training will lead to an attenuated heart rate and blood pressure response to a given load because that load now represents a lower percentage of the maximal voluntary contraction.¹¹² Importantly, the heart rate–blood pressure product during maximal upper body resistance exercise is lower than that observed during maximal dynamic effort,¹¹³ primarily due to a lower peak heart rate response.

Several reports documenting the safe attainment of improved muscle strength after a resistance training program in subjects with cardiac disease^{114 115 116 117 118} have alleviated previously unsubstantiated concerns about weight training in such subjects. Strength gains of 22% to 29%^{114 115 116 117 118} as well as increases in the number of repetitions in a given submaximal load¹¹⁸ have been achieved by cardiac subjects. No adverse outcomes have been reported in subjects participating in supervised light to moderate intensity resistance training in cardiac rehabilitation.

As such, resistance training is encouraged as part of the overall exercise program for most subjects with cardiac disease. Such training can be performed using a wide variety of equipment, including free weights and dumbbells, wall-mounted pulleys, or exercise machines equipped with weight stacks. Resistance exercise can and should be performed in a variety of body positions, both to isolate specific muscle groups and to ensure maximum orthopedic stability. To avoid the additive cardiovascular responses of the Valsalva maneuver, subjects should be trained to exhale during the contraction phase of the movement. Resistance training should include 8 to 10 exercises that train the major muscle groups of the body, ie, arms, shoulders, chest, abdominals, back/trunk, hips, and legs. The intensity of each weight training exercise can be adjusted by alterations in any of the following factors: weight load, number of repetitions per set, number of sets, and rest period between sets. Generally, for subjects with cardiovascular disease, 2 to 3 days per week of resistance training using one set of 10 to 15 repetitions to moderate fatigue is recommended. Once 15 repetitions can be completed, the weight can be increased an additional 5%. Initial weight training activities are usually introduced during the first 2 weeks of an outpatient program. They include the use of light calisthenics and 3- to 5-lb dumbbell weights. Later in the program, if subjects are medically stable, they can be cleared for regular weight training activities using barbells and weight machines. This sequence of range of motion exercise and strength training has been shown to be safe for use with both MI and CABS patients.¹¹⁹ During this early period, resistance training should only employ light weights. Clinical experience has shown that less than 5% of CABS subjects have any contraindications to this exercise. Key Point: Physical activity should consist of cardiovascular exercise preceded by a warm-up period and followed by a cooldown period. Calisthenics and resistance training are useful for promoting strength and flexibility but probably do not significantly contribute to cardiovascular health.

Medical Clearance for Physical Activity in Apparently Healthy Populations
Medical history. Of particular interest are data in the history that indicate unsupervised exercise may be hazardous, including CAD, significant valvular heart disease, cardiomyopathy, and congenital heart disease. If any of these heart conditions are present, the individual should follow the guidelines for individuals with heart disease in the next section. Persons taking cardiovascular medications should also follow the guidelines found in the next section. Obesity and neuromuscular disease tend to increase the risk of orthopedic injury; thus lower intensity, low-impact exercise of longer duration in such persons is preferred.

Symptoms. Symptoms suggesting cardiovascular or pulmonary disease should be evaluated to exclude the presence of such disease. They include chest discomfort, shortness of breath (after climbing one flight of stairs or less), and leg discomfort consistent with claudication.

Physical examination. Hypertension requires assessment and management. Murmurs suggesting significant valvular heart disease or other signs of cardiac disease (eg, heart failure, ischemia) should be regarded as indicating the presence of cardiovascular disease until proven otherwise.

Detection of occult disease. One of the most difficult tasks a physician may undertake is detection of occult disease. It is well known that individuals can have significant CAD in the complete absence of symptoms or signs and in the presence of a normal ECG and a normal exercise test. However, the exercise test is the best method for detecting significant occult CAD.

Medical Clearance Strata
1. A recent medical history and physical examination should be done.

a. If the history or physical examination indicates significant cardiovascular disease, the person should be treated as noted in the section "Guidelines for Exercise Training of Individuals With Cardiovascular Disease." Examples of cardiovascular disease include previous MI, CABS, angina pectoris, valvular heart disease (except most cases of mitral valve prolapse), and cardiomyopathy.

b. If the individual knows of no cardiovascular disease but has symptoms or signs that suggest the presence of significant disease or major coronary risk factors, an exercise test is needed to evaluate for the presence of a high-risk condition. If an exercise test cannot be performed, activity should be limited as outlined in the next section. Examples include intracardiac lesions of uncertain severity (septal defects, valve abnormalities), symptoms suggesting angina, and certain murmurs.

2. Age should be considered.

a. If the individual is younger than 40 years, no further workup is needed and he or she can be cleared for any activity if No. 1 above is normal.

b. If the individual is 40 years of age or older:

(1) An exercise test should be recommended if vigorous exercise is planned. If the test is normal, no further restrictions are needed. If the test is abnormal, the individual should be treated as if he or she has CAD.

(2) If the individual chooses not to undergo an exercise test, he or she should follow the activity guidelines outlined in the next section. Key Point: The medical clearance stratification enables physicians to classify individuals by activity and to give advice and options for physical activity programs.

If the medical clearance strata outlined above are used, all subjects may be placed in one of the following categories.

Activity classification. After the medical clearance stratification is complete, subjects can be classified by risk based on their characteristics. The following classifications are recommended, and subsequent ECG monitoring is advised based on this classification.

Class A: Apparently healthy. There is no evidence of increased cardiovascular risk for exercise. This classification includes (1) individuals under age 40 years who have no symptoms of or known presence of heart disease or major coronary risk factors and (2) individuals of any age without known heart disease or major risk factors and who have a normal exercise test.

Activity guidelines: No restrictions other than basic guidelines

ECG and blood pressure monitoring: Not required

Supervision required: None

Class B: Presence of known, stable cardiovascular disease with low risk for vigorous exercise but slightly greater than for apparently healthy individuals. Moderate activity is not believed to be associated with increased risk in this group. This classification includes individuals with (1) CAD (MI, CABS, PTCA, angina pectoris, abnormal exercise test, and abnormal coronary angiograms) whose condition is stable and who have the clinical characteristics outlined below; (2) valvular heart disease; (3) congenital heart disease; (4) cardiomyopathy; and (5) exercise test abnormalities that do not meet the criteria outlined in class C below.

Clinical characteristics: (1) New York Heart Association (NYHA) class 1 or 2; (2) exercise capacity over 6 METs; (3) no evidence of heart failure; (4) free of ischemia or angina at rest or on the exercise test at or below 6 METs; (5) appropriate rise in systolic blood pressure during exercise; (6) no sequential ectopic ventricular contractions; and (7) ability to satisfactorily self-monitor intensity of activity.

Activity guidelines: Activity should be individualized with exercise prescription by qualified personnel trained in basic CPR or with electronic monitoring at home.

ECG and blood pressure monitoring: Only during the early prescription phase of training, usually six to 12 sessions

Supervision required: Medical supervision during prescription sessions and nonmedical supervision for other exercise sessions until the individual understands how to monitor his or her activity.

Class C: Those at moderate to high risk for cardiac complications during exercise and/or unable to self-regulate activity or to understand recommended activity level. This classification includes individuals with (1) CAD with the clinical characteristics outlined below; (2) cardiomyopathy; (3) valvular heart disease; (4) exercise test abnormalities not directly related to ischemia; (5) previous episode of ventricular fibrillation or cardiac arrest that did not occur in the presence of an acute ischemic event or cardiac procedure; (6) complex ventricular arrhythmias that are uncontrolled at mild to moderate work intensities with medication; (7) three-vessel disease or left main disease; and (8) low ejection fractions (less than 30%).

Clinical characteristics: (1) Two or more MIs; (2) NYHA class 3 or greater; (3) exercise capacity less than 6 METs; (4) ischemic horizontal or downsloping ST depression of 4 mm or more or angina during exercise; (5) fall in systolic blood pressure with exercise; (6) a medical problem that the physician believes may be life-threatening; (7) previous episode of primary cardiac arrest; and (8) ventricular tachycardia at a workload of less than 6 METs.

Activity guidelines: Activity should be individualized with exercise prescription by qualified personnel.

ECG and blood pressure monitoring: Continuous during exercise sessions until safety is established, usually in six to 12 sessions or more.

Supervision: Medical supervision during all exercise sessions until safety is established.

Class D: Unstable disease with activity restriction. This classification includes individuals with (1) unstable ischemia; (2) heart failure that is not compensated; (3) uncontrolled arrhythmias; (4) severe and symptomatic aortic stenosis; and (5) other conditions that could be aggravated by exercise.

Activity guidelines: No activity is recommended for conditioning purposes. Attention should be directed to treating the subject and restoring him or her to class C or higher. Daily activities must be prescribed based on individual assessment by the subject’s personal physician.

The above classifications are presented as a means of beginning exercise with the lowest possible risk. They do not consider accompanying morbidities (eg, insulin-dependent diabetes mellitus, morbid obesity, severe pulmonary disease, or debilitating neurological or orthopedic conditions) that may necessitate closer supervision during training sessions. As the individual gains experience, the decision may be made to place the subject in another category. In most cases, as the safety of exercise and improvement in working capacity are demonstrated, graduation to classes nearer A and B is appropriate. Key Point: An activity classification is offered to help the physician decide on the activity guidelines, monitoring, and supervision required for various conditions.

Exercise Prescription
Exercise for individuals with cardiovascular disease should be prescribed as outlined in the section "Guidelines for Exercise Training of Individuals With Cardiovascular Disease." Guidelines for physical activity for apparently healthy individuals are recommended below.

A useful approach to activity prescription is to identify the desirable rating of perceived exertion and ask individuals to adhere to that intensity. A suggested rating of perceived exertion for most healthy individuals is 12 to 16 (moderate to heavy) on a Borg scale of 6 to 20, an approach that is both effective and acceptable.¹²⁰ See Table 6 for more details on rating of perceived exertion.¹²¹

Individual Guidelines for Cardiovascular Exercise
1. Exercise only when feeling well.

Wait until symptoms and signs of a cold or the flu (including fever) have been absent 2 days or more before resuming activity.

2. Do not exercise vigorously soon after eating. Wait at least 2 hours. Eating increases the blood flow requirements of the intestinal tract. During vigorous exercise, the demand of the muscles for blood may exceed the ability of the circulation to supply both the bowel and the muscles, depriving organs of blood, resulting in cramps, nausea, or faintness.

3. Adjust exercise to the weather.

Exercise should be adjusted to environmental conditions. Special precautions are necessary when exercising in hot weather. It is difficult to define when it is too hot to exercise since air temperature is greatly influenced by humidity and air movement (wind), which are not easy to measure. The following guidelines are recommended for a noncompetitive workout: if air temperature is over 70°F, slow the pace, be alert for signs of heat injury, and drink adequate fluids to maintain hydration. A good rule to follow is to exercise at the usual workout pace (rating of perceived exertion, 12 to 16), which may be a slower pace or lower work intensity because of environmental conditions.

Acclimatization to moderate levels of heat is gradual, requiring 12 to 14 days. Accommodation to extreme heat never occurs. Signs of heat injury may be varied at the onset; hence, any symptom should be regarded as evidence of heat overload. The following indications of heat stress are particularly likely to occur: headache, dizziness, faintness, nausea, coolness, cramps, and palpitations. If any of these symptoms are present, stop exercising immediately and go to a cooler environment. If the air temperature is over 80°F, exercise in the early morning or late afternoon to avoid the heat. Air-conditioned shopping malls are popular for walking. Exercise is tolerated better if humidity is low and a breeze is present. Exercise in the heat causes excessive fluid loss, so adequate fluid intake is important before, during, and after each session.

4. Slow down for hills.

Watch for hills. When ascending hills, decrease speed to avoid overexertion. Again, a useful guide is to maintain the same rating of perceived exertion as in a usual workout.

5. Wear proper clothing and shoes.

Dress in loose-fitting, comfortable clothes made of porous material appropriate for the weather. Use sweat suits only for warmth. Never use exercise clothing made of rubberized, nonporous material. In direct sunlight, wear light-colored clothing and a cap. Wear shoes designed for exercise (eg, walking or jogging shoes).

6. Understand personal limitations.

Everyone should have periodic medical examinations. When under a physician’s care, ask if there are limitations.

7. Select appropriate exercises.

Cardiovascular (aerobic) exercises should be a major component of activities. However, flexibility and strengthening exercises should also be considered for a well-rounded program.

8. Be alert for symptoms.

If the following symptoms occur, contact a physician before continuing exercise. Although any symptom should be clarified, these are particularly important:

a. Discomfort in the upper body, including the chest, arm, neck, or jaw, during exercise. The discomfort may be of any intensity and may be present as an aching, burning, tightness, or sensation of fullness.

b. Faintness accompanying the exercise. Sometimes brief light-headedness may follow unusually vigorous exercise or a limited cooldown period. This condition does not usually indicate heart disease and may be managed by exercising at a lower intensity with a gradual cooldown at the end of the session. If a "fainting spell" or feeling of faintness occurs during exercise, discontinue the activity until after evaluation by a physician.

c. Shortness of breath during exercise. During exercise, rate and depth of breathing should increase but should not be uncomfortable. A useful rule is that breathing should not be so difficult that an ordinary conversation is an effort, wheezing develops, or more than 5 minutes are required for recovery.

d. Discomfort in bones and joints either during or after exercise. There may be slight muscle soreness when beginning exercise, but if back or joint pain develops, discontinue exercise until after evaluation by a physician.

9. Watch for the following signs of overexercising:

a. Inability to finish. Training sessions should be completed with reserve.

b. Inability to converse during the activity. Breathing normally increases during exercise but should not be uncomfortable. When a conversation cannot be conducted during exercise because of difficulty breathing, the conditioning activity is too intense.

c. Faintness or nausea after exercise. A feeling of faintness after exercise may occur if the activity is too intense or has been stopped too abruptly. In any event, decrease the intensity of the workout and prolong the cooldown period.

d. Chronic fatigue. During the remainder of the day or evening after exercise, an individual should feel stimulated, not tired. If fatigue persists during the day, intensity and/or duration of the workout should be decreased.

e. Sleeplessness. If unable to sleep well despite feelings of fatigue, the amount of activity should be decreased until symptoms subside. Insomnia is particularly likely during distance training. A proper training program should make it easier, not more difficult, to have a good night’s rest.

f. Aches and pains in the joints. Although there may be some muscle discomfort, joints should not hurt or feel stiff. Check exercise procedures, particularly stretching and warm-up exercises, to ensure that you are using the correct technique. Muscle cramping and back discomfort may also indicate poor technique. If symptoms persist, check with a physician before continuing.

10. Start slowly and progress gradually. Allow time to adapt. Key Point: General guidelines can provide an activity prescription for apparently well individuals. The benefits of exercise outweigh the risks when such an approach is used.

Noncardiovascular Injuries
Musculoskeletal injuries are common and include direct injuries such as bruises, sprains, and strains, and indirect problems such as arthritis and back pain. The traumatic impact of exercise is usually classified as low and high impact. Low-impact exercises (walking, cycling, and swimming) cause little stress on bones and joints, whereas high-impact exercises (running and aerobic dancing) cause repeated impact on the knees, ankles, and feet.

Studies of injuries during exercise show that two important factors in determining the frequency of injuries during exercise are age and the impact nature of exercise. (See Table 11.)

View this table: [in this window] [in a new window]   Table 11. Injuries by Age and Activity

Therefore, it is recommended that any individual older than 40 should take special care to avoid high-impact activities.^{122 123} If such activities are chosen, they should be initiated at low levels and increased slowly. A day of rest between exercise periods permits the body to gradually adapt to stresses and strains. More attention should also be given to warm-up and cooldown periods with stretching, low-level calisthenics, and low-level aerobic exercises. In general, fast walking is a well-tolerated, low-impact exercise that provides excellent results. Swimming, stair climbing, rowing, and stationary cycling may also be appropriate. Several popular forms of exercise are classified by musculoskeletal impact in Table 12.

View this table: [in this window] [in a new window]   Table 12. Categories of Activity by Musculoskeletal Impact

Guidelines for Exercise Training of Individuals With Cardiovascular Disease
Types of Cardiovascular Disease
Exercise training is obviously useful in treatment of CAD subjects because the physiological changes that occur lessen ischemia at rest and during submaximal exercise. Physical activity is also associated with protection from development or progression^{124 125 126} of CAD. Certain precautions are necessary to avoid injury. In this section, the principles of surveillance for safety and expectations for improvement are largely intended for subjects with CAD but may also apply to other subjects with a variety of noncoronary cardiac, vascular, and pulmonary diseases.

Safety is the major reason for establishing special guidelines for subjects with cardiovascular disease. These recommendations should be considered appropriate for any condition associated with a higher than normal risk for sudden cardiac arrest or MI during exercise, but if carefully followed, they could benefit the individual by increasing his or her physical working capacity. With the following conditions physical working capacity increases with regular exercise conditioning and surveillance is recommended:

• Abnormal exercise test indicating ischemia

• Angina pectoris

• MI

• CABS

• PTCA

• Heart transplant

• Cardiomyopathies (including heart failure)

• Valvular heart disease

• Hypertension

• Pacemakers Key Point: Regular physical activity is beneficial in the presence of cardiovascular disease if prudent guidelines are followed.

The Elderly
Special considerations must be addressed when prescribing exercise for the elderly. In these subjects maximal end-diastolic volume increases, while maximal heart rate, LVEF, and cardiac output all decrease. In the presence of disease, these factors may affect the cardiac response to a given exercise prescription. In addition, exercise-induced arrhythmias increase in frequency in older individuals and may be of concern in cardiac rehabilitation programs.¹²⁷

Heart Failure
Medically stable subjects with compensated heart failure may participate in exercise training programs. Benefits that accrue from conditioning of the musculoskeletal system include increased skeletal muscle vascular conductance and oxygen extraction and decreased skeletal muscle lactate production.¹²⁸

Risk of Sudden Death
Individuals with cardiac disease seem to have higher risks for sudden cardiac arrest during vigorous exercise (such as jogging) than do healthy individuals. However, with judicious programs, activity is clearly beneficial. The most compelling argument for exercise training in cardiac subjects is that randomized controlled trials show a lower death rate in groups that exercised compared with sedentary groups,^{124 125 126} indicating that exercise is safe and beneficial. However, those studies were performed under strictly controlled conditions, and similar results can be expected only if careful guidelines are followed. The random incidence of sudden cardiac arrest in populations with CAD has been estimated to be 1 in 80 000 to 160 000 man-hours.¹²⁹ The type and intensity of activity and the use of monitoring apparently affect incidence of sudden cardiac arrest; Table 9 shows that in cardiac subjects, incidence is lowest during activities that are largely controlled, such as walking, cycling, or treadmill walking. Table 9 also suggests that continuously ECG-monitored activities have the lowest rates of sudden cardiac arrest compared with those that are unmonitored or only intermittently monitored.

Obviously, these studies cannot answer the questions regarding the relative contributions of each of the potential variables to sudden cardiac arrest. However, they strongly suggest that the incidence of sudden cardiac arrest in all mixed activities is similar to that expected by chance alone. This, in turn, suggests that jogging increases the incidence of sudden cardiac arrest.

The higher incidence of sudden cardiac arrest during jogging in subjects with heart disease is probably related to intensity. Jogging at even the slowest pace generates a O₂ that is from 80% to 100% of maximum for most untrained individuals. If individuals with cardiac disease jog, they should do so under medical supervision.

Monitoring is important because it helps the individual establish an appropriate exercise pace, which is about 60% to 70% of O_2max. This pace can best be learned during monitored sessions. Key Point: The risks of exercise for sudden cardiac arrest and MI are higher in individuals with known heart disease who engage in vigorous physical activity such as jogging. Hence, individuals with heart disease should either exercise under medical supervision or restrict their activity to a moderate-intensity activity such as walking. Monitoring during exercise is recommended for all individuals with heart disease until the subject’s tolerance for the activity and its safety have been demonstrated.

Physiological Changes
Although physical working capacity increases with training when heart disease is present, reported physiological changes have differed somewhat from those reported in apparently healthy individuals and are outlined below.

Maximal oxygen uptake. Subjects with CAD have an increase in O_2max with training. The magnitude of the change is less in subjects with heart disease than observed in apparently healthy individuals, but the increase is noteworthy, and maximal heart rate may be the same or slightly greater after training in those with heart disease.⁸³ The smallest increments in O_2max are seen in individuals with heart failure, but even in those subjects the improvement is of great rehabilitative value for restoring ability to perform daily activities.

Cardiac output. The increase in maximal cardiac output is due to an increase in both stroke volume and maximal heart rate, which differs from normal subjects, whose maximal heart rate usually does not change. In subjects with cardiac disease, the submaximal cardiac output may be lower, with maintenance of O₂ by widening the aO₂ difference after training.¹³⁰ Such a result suggests improved overall efficiency for delivery of oxygen to the tissues.

Decreased myocardial oxygen uptake. Exercise training has special significance for individuals with CAD because the changes promote lower myocardial oxygen uptake (MO₂). Changes associated with lower MO₂ are lower heart rate, lower systolic blood pressure, and lower circulating catecholamines.

The benefits of these adjustments can be demonstrated by the greater amount of work that can be done before angina orECG-determined ST depression occurs.¹³¹ Fig 8 reflects the positive effects of conditioning exercise on angina.

View larger version (19K): [in this window] [in a new window]   Figure 8. Change in double product before and after exercise rehabilitation. Double product (heart rate x systolic pressure) is shown at rest, during exercise, and during angina (A). After conditioning, more work can be tolerated because double product (and hence myocardial oxygen uptake) is lower. From Redwood et al.131

Collateral formation. Present knowledge does not support the concept that collateral circulation is likely to develop in the coronary arterial distribution of humans as a result of exercise conditioning. Improvement of ischemia is believed most likely to occur by reducing MO₂ rather than by increasing supply.

Improved myocardial function. Although animal studies have shown increased contractility and resistance to hypoxia with exercise training, human data have not consistently shown improved myocardial performance.¹³² However, as mentioned previously, recent studies⁵⁴ have revealed increases in LVEF in subjects with CAD after exercise training. Key Point: Individuals with heart disease increase their working capacities in much the same way as healthy subjects. A major beneficial adjustment in subjects with CAD is the lowering of MO₂ demand, which in turn lessens ischemia. Collateral formation in the coronary arterial distribution and improved myocardial performance may occur with exercise in some cases but not with regularity.

Secondary Prevention
Coronary risk profile. Exercise training induces improvement in coronary risk profile. Reductions in blood pressure, triglycerides, and body fat, improved glucose tolerance, increase in high-density lipoprotein cholesterol, and favorable changes in blood coagulation seem to occur in individuals with CAD, especially in those who can perform large amounts of exercise.

Exercise is also associated with an improved mental outlook. Specifically, standard psychological tests have documented less depression and anxiety.¹³³ Lessening of depression is particularly important in post-MI subjects, who tend to be clinically depressed. Although postinfarction depression is self-limited, regular exercise probably hastens improvement.

Morbidity and mortality. The large number of subjects required and the need for careful follow-up of those subjects for long periods of time have precluded a definitive, randomized, controlled trial of cardiac rehabilitation. Several studies have been conducted, and although most show a beneficial trend, none are large enough to draw definitive conclusions. A meta-analysis of the randomized, controlled trials that examined the influence of cardiac rehabilitation on outcome has shown a distinct benefit that seems largely the result of exercise.^{124 125 126} The significant benefit is a reduction in overall cardiovascular mortality and of sudden cardiac death; no significant reduction in reinfarction could be demonstrated.

Although exercise was an integral part of the programs of all these studies, they were multifactorial in nature. In addition, all exercise was supervised and moderate in intensity.

Return to work. The use of exercise early after infarction has also been evaluated and compared with bed rest. In many studies, physical activity soon after MI promotes earlier discharge from the hospital and a greater likelihood of the subject’s returning to usual activities.¹³⁴ Key Point: Although no reduction in frequency of MI has been shown, regular physical activity is associated with improved survival when combined with other interventions such as diet. Other benefits include earlier discharge from the hospital and greater likelihood of returning to work after MI.

Procedures and Techniques for Exercise in Cardiac Rehabilitation
Precautions. All individuals must be carefully screened for medical status before beginning an exercise program. They must also have adequate instruction and follow-up to lessen the likelihood of complications. If exercise might aggravate an existing cardiac condition, it should be avoided.

Systemic infections. Acute systemic infections can be adversely affected by activity. Even individuals with chronic infections may benefit more from rest than exercise. However, as the infection responds to treatment, exercise can begin. For example, in the treatment of bronchitis, moderate exercise can begin when the individual has normal temperature, white blood cell count, and cultures. Local infections are probably not affected by exercise as long as the activity does not irritate the lesion.

Thromboembolic disease. Thrombophlebitis, arterial embolism, or pulmonary embolism should be treated with rest, even though factors that cause clot dislodgment are not clearly defined. Low-level walking or range-of-motion exercise is probably safe as soon as the individual is in a stable treatment program and has had no recurrence of symptoms. A moderate exercise program can be started when anticoagulants have been discontinued or 6 weeks of anticoagulant therapy have passed since the last symptoms or signs of thromboembolism.

Endocarditis. Individuals with vegetative endocarditis should avoid exercise until the disease is stable. The contribution of physical activity to emboli is not known for certain, but low-to-moderate activity levels seem prudent until the course of antibiotics is completed.

Neuromuscular diseases. Neuromuscular inflammation and injuries should be evaluated by a qualified rheumatologist, orthopedist, or physiatrist to assess the desirability of physical activity and to determine the types of activities that are suitable.

Cardiovascular disease complications. HEART FAILURE. Low-to-moderate physical activity is usually beneficial to subjects with stable cardiovascular disease. In contrast, individuals with uncompensated heart failure have developed fulminant pulmonary edema with exercise. Therefore, exercise is not recommended if the subject’s condition is unstable.

MYOCARDITIS. As with any infection, activity should be maintained at low levels until the individual has no signs of active infection. When the infection has subsided, there is no evidence of harm if exercise is prescribed prudently.

ACUTE ISCHEMIA. Individuals with unstable myocardial ischemia as judged by anginal symptoms or a changing pattern in the ECG should not exercise.

ARRHYTHMIAS. Although there is some evidence that regular physical activity may be helpful for subjects with arrhythmias, most studies have focused on benign arrhythmias. The occurrence of exercise-induced high-grade ventricular ectopy (three or more sequential ventricular premature beats) may be hazardous, and vigorous exercise should be avoided. The usual strategy is to prescribe activity that generates a lower heart rate than that associated with abnormalities. In general, individuals with arrhythmias other than high-grade ventricular ectopy may exercise if they are asymptomatic and remain hemodynamically stable. Monitoring during rehabilitative sessions may be helpful for adjusting drug treatment for arrhythmias.

ELECTRONIC PACEMAKERS. If performance during an exercise test is satisfactory, individuals with pacemakers are no more prone to problems than other cardiac subjects. Although the paced rate of some pacemakers can be accelerated during exercise, many cannot. Physical activity intensities in fixed-rate pacemakers must be gauged by a method other than pulse counting, such as defining specific work- loads that are about 60% to 70% of peak working capacity on the exercise test and by using the rating of perceived exertion.

SURGICAL INCISION AFTER CABS. The extent of healing of surgical incisions from CABS is the most limiting factor. Hence, the decision to start activity is often deferred to the surgeons. Low-level activities are usually acceptable 24 to 48 hours after surgery. Chest and leg wounds usually require 4 to 8 weeks for complete healing. Upper body exercises that cause sternal tension should be avoided until healing is complete. The same precautions should be exerted for CABS subjects as for post-MI subjects.

PTCA. Subjects may begin or resume exercise 24 to 48 hours after PTCA. Care must be taken to assure that anginal symptoms are recorded and properly evaluated. Exercise testing may be of considerable value in assessing new or different symptoms.

Prescribed physical activity. Prescribed physical activity is beneficial and safe because it helps subjects restrict intensities to low-risk levels. Moderate activity actually means exercise that is about 60% to 80% of O_2max. That intensity is effective for increasing O_2max if performed on a regular basis, and it is associated with a low incidence of sudden cardiac arrest.

Exercise tests. Exercise tests are an important part of the rehabilitative process. They provide initial levels of working capacity, specific precautions, and heart rates used to prescribe activity. Tests are also useful for assigning risk stratification. Exercise tests should be performed to write the exercise prescription for post-MI subjects or subjects with chronic CAD who enter cardiac rehabilitation programs. The exercise test should be repeated annually.

Rehabilitation sessions. Rehabilitation sessions are serial sessions in which the subject is taught good health behaviors, including proper diet and lifestyle modifications such as smoking cessation and exercise. Rehabilitation sessions are conducted to teach exercise techniques of intensity, duration, frequency, mode, and progression. Activity is monitored during these sessions to ensure safety. The number of monitored sessions needed depends on the clinical circumstances. In some cases, only one or two sessions may be needed, but in others, three or four sessions per week over several months are necessary.

Monitoring of activity. Symptoms. CHEST DISCOMFORT suggesting ischemia may present as chest tightness, fullness, pressure, or dull pain in the anterior precordium and may radiate to the neck or arm.

SHORTNESS OF BREATH may suggest pulmonary congestion, and appropriate assessment for pulmonary edema is needed. Some shortness of breath and fatigue may occur because of the deconditioning effect of bed rest after a cardiovascular event or surgery. Edema on the chest x-ray film, rales, or a third heart sound on examination will clarify the presence of significant pulmonary edema.

FAINTNESS (or light-headedness) is common after a period of inactivity. This symptom does not necessarily have cardiac implications since it is often due to a contracted blood volume or loss of postural reflexes caused by inactivity or surgery. Even so, individuals who become faint usually have a fall in blood pressure that could be hazardous if unattended.

WEAKNESS is a common symptom after a confining illness and need not be a concern. The sensation of fatigue will usually improve with time and conditioning. Weakness after cardiac surgery is particularly likely to occur because of low hemoglobin and may persist, interfering with the early phases of cardiac rehabilitation. Restitution of hemoglobin to normal requires several weeks unless transfusions are administered.

Heart rate. A target heart rate should be considered when exercise is prescribed. The target heart rate is usually determined from the exercise test, but if an exercise test has not been done, a useful goal is to avoid increases of more than 20 beats per minute over the resting heart rate.

Blood pressure. Blood pressure should be under control at the start of an exercise program. Specific guidelines for resting levels are difficult to set, but in general, activity should be restrained until the clinician is satisfied with resting levels. A slight increase in systolic pressure may precede exercise training sessions due to anticipation and is not a cause for concern.

Increments in systolic blood pressure during exercise are normal. However, if systolic blood pressure falls, the reason must be determined, and therapy should be initiated before proceeding.

Physical activity after MI, CABS, or PTCA. Early exercise. Walking is recommended as the major mode of exercise for these subjects unless the individual can attend classes where other monitored activities can be provided. Walking near the bedside and to the bathroom are permitted initially. If symptoms develop, he or she can quickly return to bed. Encouraging the individual to sit up is an important part of this phase. Walking should start slowly and gradually increase as tolerated until 5 to 10 minutes of continuous movement has been achieved. Active but nonresistive range of motion of upper extremities is also well tolerated early after MI or CABS, as long as the activities do not stress or impair healing of the sternal incision.

Initial activities should be monitored, and symptoms, rating of perceived exertion, heart rate, and blood pressure should be recorded. When tolerance is documented, the activity can be performed without supervision.

The emphasis of exercise within the first 2 weeks after MI should be to avoid or offset the effects of bed rest. When the individual is stable as measured by ECG, vital signs, and symptomatic standards, he or she can begin walking. Although this activity is well tolerated and safe, certain precautions are recommended as outlined in Table 13.

View this table: [in this window] [in a new window]   Table 13. Guidelines for Helping Patients Resume Walking Soon After Myocardial Infarction

Late exercise. A symptom-limited exercise test is performed after the individual is stable and is walking without difficulty (as early as 2 to 6 weeks after hospital discharge). If more studies such as angiography are not indicated, a regular conditioning program can be initiated. Careful activity prescription is recommended.

General principles of conditioning activity. For conditioning purposes, large-muscle group activities should be performed for at least 20 minutes, preceded by warm-up and followed by cooldown, at least three times per week. The intensity of exercise should be gauged by exercise prescription.

Follow-up supervised group sessions are recommended to enhance the educational process, to ensure that the participant is tolerating the program, to confirm that progress is occurring, and to provide medical supervision in high-risk situations.

A long-term follow-up should be encouraged at infrequent intervals (every 1 to 3 months) to encourage long-term compliance and to ensure that the program is being followed properly.

General Principles of Exercise Prescription
Prescription in the absence of ischemia or significant arrhythmias.Exercise intensity should approximate 50% to 80% of O_2max, which can be ascertained by an exercise test. (If a test is not done initially, the measurement of 20 beats per minute above resting heart rate is adequate until testing is performed.) The steps in this process are as follows:

1. The target heart rate may be considered as 50% to 75% of heart rate reserve ([maximal heart rate-resting heart rate] x50% to 75%) plus resting heart rate. That heart rate can be used for the prescription of many types of dynamic leg exercise.

2. Activities can be prescribed as the target work intensity that achieves the training heart rate after 5 to 10 minutes at that workload (steady state). It may be expressed as watts on an ergometer, speed on a treadmill, or in METs.

3. If an individual wants to exercise but cannot assess intensity, then heart rate counting (manually or with a cardiotachometer) is useful. Heart rate counters are widely available and are generally fairly accurate for low to moderate intensity exercise.

4. If an individual intends to walk on a level surface, activity can be prescribed as the step rate found on a treadmill to generate the desirable heart rate.¹³⁵ The usual procedure is to determine the step rate on a treadmill and prescribe it. Step rate can be easily measured as it requires less skill than counting heart rate. If this approach is used, individuals should be cautioned about avoiding hills. Walking in shopping malls or gyms allows subjects to avoid inclement weather. Exercise should be monitored for the first few sessions while the individual begins activity. Monitoring assures that the instructions are understood and that the activity is well tolerated.

5. Individuals can also judge the intensity of exercise as the rating of perceived exertion, which can be equated to desirable heart rate during laboratory exercise and to their activities. The original scale is a 15-grade category scale ranging from 6 to 20, with a verbal description at every odd number. (See Tables 6 and 14.)

View this table: [in this window] [in a new window]   Table 14. Classification of Intensity of Exercise Based on 20 to 60 Minutes of Endurance Training

The following rating of perceived exertion values should be followed: <12 light, 40% to 60% of maximal

12-13 somewhat hard (moderate), 60% to 75% of maximal

14-16 hard (heavy), 75% to 90% of maximal

6. Activities can progress as tolerance is demonstrated. The appropriate initial intensity of training is 50% to 60% of O_2max or a rating of perceived exertion of 12 to 13 on a scale of 6 to 20. After safe activity levels have been established, duration is increased in 5-minute increments each week. Later, intensities can be increased as heart rate response to exercise decreases with conditioning.

Prescription in the presence of ischemia or arrhythmias. An exercise test is essential for this type of prescription. The manifestations of arrhythmias or ischemia that require such precautions can vary but usually include ventricular ectopic beats in sequence, an arrhythmia that is symptomatic or hemodynamically unstable, chest discomfort believed to be angina, ST depression of 2 mm or more, or a fall in systolic blood pressure of 20 mm Hg or more from baseline.

The exercise test is performed in the usual fashion, but the conditioning work intensity is derived from the heart rate associated with the abnormality. If the exercise test continues to a high level of effort, the heart rate at 50% to 60% of heart rate maximum can be used if it falls at least 10 beats per minute below the abnormal level. Otherwise, the recommended training heart rate is 10 beats per minute less than that associated with the abnormality.

Guidelines for Electrocardiographic Monitoring
Role in exercise training. Various recommendations exist regarding the number of ECG-monitored sessions that are necessary and reasonable in an exercise training program. Some programs use as few as six sessions, with progression in mode and intensity of the exercise during these periods.¹³⁶ Others have used as many as 36 sessions of ECG monitoring. The fewest possible sessions should be used, and it is recommended that the classification suggested here be used as a guideline for the number of follow-ups required. (See Table 15.)

View this table: [in this window] [in a new window]   Table 15. Guidelines for ECG Monitoring in Exercise Training

Individuals who are class A (apparently healthy) do not require ECG-monitored sessions, as the general guidelines are adequate. Class B individuals should be monitored and supervised until they understand their desirable activity levels (usually 6 to 12 sessions). Class C individuals should be medically supervised with ECG monitoring until they understand the level of activity that is safe and the medical team determines that the exercise is safe and effective. Usually six to 12 sessions or more are needed.

Monitored cardiac rehabilitation. Monitoring sessions should ideally be performed with continuous ECG monitoring by either hardwired apparatus or telemetry. The sessions should be conducted by personnel who understand the exercise principles involved and have a basic knowledge of electrocardiography. The sessions should also be supervised by either a physician or a nurse trained in emergency CPR, preferably with previous experience in intensive cardiac care. CPR capability can be demonstrated by completion of an AHA-sponsored course in advanced cardiac life support. Standing orders for management of a complication should be immediately available.

Monitored sessions should also include symptom assessment by the staff, systolic blood pressure recording, the subject’s rating of perceived exertion, and instructions to subjects about selection and proper use of exercise equipment. ECG-monitored sessions should include instruction for different modes and progressions of exercise.

Home-monitored programs. The use of transtelephonic ECG monitoring at home has been suggested as a substitute for outpatient visits to the clinic.^{137 138} Such programs have the disadvantage of lacking emergency medical care, but the advantage of requiring no clinic visit. These programs may be particularly useful in following subjects in the event clinics are not readily available.

Unmonitored home programs. In the first 1 or 2 weeks after discharge from the hospital after MI, individuals may walk at a slow, regular pace with increasing duration, starting with 10-minute periods and working up to 1 hour. Such activity need not be supervised.

Unmonitored exercise¹³⁹ can also be used for conditioning after the individual has recovered from the MI (2 weeks or more after hospital discharge) or in other cases of stable CAD, although medically supervised and monitored exercise is preferred. If cardiac rehabilitation facilities are not available, activity guidelines can still be provided to cardiac subjects, and they should be encouraged to exercise. Activity should be restricted to walking (ordinary walking, not race walking) or equivalent activities. If individuals carefully watch for signs of intolerance and are attentive to heart rate and rating of perceived exertion, this activity level is considered safe. Walking is a safe, low-impact, controllable exercise that in the majority of cases generates an intensity that is 50% to 70% of O_2max.

It is recommended that activity be monitored if possible and prescribed from the exercise test results. However, if monitoring is not available, an activity other than walking (ie, cycle ergometry) can be prescribed, provided the intensity is similar to walking and that it is dynamic (as opposed to static). Range-of-motion exercises and light calisthenics can be performed in an unmonitored setting.

Activities are considered safe and appropriate if they meet the criterion of moderate intensity as perceived by the physician or judged by an exercise test. A useful guide to moderate (or less) activity is found in Table 14.

Individuals can participate in physical training classes if they carefully follow recommended guidelines for unmonitored exercise. In some cases, classes are desirable because of the camaraderie.

Types of Supervised Programs
Medically supervised group (moderate- to high-risk subjects).These activity programs are needed to provide close medical supervision for individuals who are at particularly high risk for a complication associated with vigorous physical activity. Such individuals are largely from class C.

These classes require careful medical supervision and surveillance to ensure that the activity is well tolerated. A physician should be readily available for these classes, although the presence of a properly trained nurse in the exercise room is sufficient if a physician is not available. The qualifications of the physician may vary, but experience in internal medicine and cardiovascular disease and in treatment of subjects with heart disease is recommended. Training programs should be medically supervised until the low risk of the prescribed activity has been established. All individuals entering these programs should be screened as described in Table 16.

View this table: [in this window] [in a new window]   Table 16. Screening Process for Medically Supervised Programs for Moderate- to High-Risk Patients

The program should provide staff, space, equipment, and facilities. (See Table 17.)

View this table: [in this window] [in a new window]   Table 17. Basic Requirements for Medically Supervised Programs for Moderate- to High-Risk Patients

Medically supervised group (low-risk subjects). Low-risk subjects (class B) benefit from medically supervised programs because vigorous exercise can be conducted more safely and group dynamics often help subjects comply with good health behaviors. Immediate medical supervision of low-risk subjects can be provided by a well-trained nurse working under a physician’s standard orders. If medical supervision by a physician cannot be provided, the supervisor should have successfully completed an AHA-sponsored course in advanced cardiac life support and should be able to administer emergency medications. Well-trained cardiovascular nurses usually meet these criteria. All individuals entering these programs should be screened as outlined in Table 18. The program should provide the same basic requirements detailed for high-risk subjects in Table 17.

View this table: [in this window] [in a new window]   Table 18. Screening Process for Medically Supervised Programs for Low-Risk Patients

Nonmedically supervised group (low-risk subjects). These programs consist of activities for subjects who do not require medical supervision. They are desirable because group dynamics are helpful and because exercise professionals can assist the subjects.

Records. Cardiac rehabilitation instructors should maintain evaluation forms, records of progress in problem areas, daily logs, and careful documentation of complications in much the same way as clinic and hospital charts.

Regular exercise testing. Exercise testing is important in all programs and should be performed at regular intervals, regardless of location or type of rehabilitation program. Once a year is adequate, although more frequent tests may be necessary if the subject’s condition is uncertain. Key Point: Precautions and procedures for activity programs are outlined. Symptoms and signs, types of activity, techniques of activity prescription, guidelines for ECG monitoring, types of supervised programs, and requirements for exercise testing must all be considered. Activities and precautions are geared to the severity of the illness.

Social Service and Vocational Rehabilitation
Helping the individual return to activities and a lifestyle that is as normal as possible is the focus of rehabilitation and requires close cooperation between the subject, physician, employer, and social service agencies. Decisions about long-term goals must be made early. These goals include issues of personal safety, an acceptable standard of living for the subject, and productivity for the employer.

Since few jobs require jogging, it is difficult to know how occupational activity relates in terms of risk. The general concept of lifting no more than 20 pounds is poorly supported by facts, but it is thought that lifting may be hazardous because of the risk of acute increase in afterload on the heart. Measuring heart rate and blood pressure response is helpful but is seldom possible because of the type of work involved.

One of the most difficult tasks facing a physician is advising the subject to return to work. Heavy labor can increase afterload, increasing the risk of sudden cardiac arrest accordingly. It also poses a problem for employers who are liable for workers’ compensation if a complication of heart disease occurs on the job. Conversely, loss of employment increases feelings of anxiety.

If the subject is in a low-risk activity category (class B) and exerts reasonable precautions, the probability of a complication is very small. Hence, such subjects should be encouraged and helped to return to work. If the subject is in a high-risk category (class C), the case must be judged on its individual merits. Even so, many of these subjects can return to work if the following guidelines are followed.

• The subject should participate in an organized, medically supervised cardiac rehabilitation program to enhance strength and endurance and to provide surveillance and education during return to activity.

• Assist devices should be used to limit the amount of lifting performed.

• Good cardiovascular health should be maintained through risk factor reduction, including weight control, and regular medical follow-up.

• If the subject is required to perform lifting or "carrying" activities or lift more than 20 pounds per load, lifting should be infrequent, take place in optimum environmental conditions, and be spaced with rest periods to avoid cumulative effects. Arm or resistance training in cardiac rehabilitation programs may be particularly useful for individuals in this group. Key Point: Assessing the subject’s ability to return to work should include his or her illness and conditions of employment. Most subjects can return to work with few precautions. Cooperation with the employer is essential for optimum return to work.

The Importance of Risk Factors
It is important to encourage smoking cessation, stress management, and nutrition guidelines and good health behavior counseling as needed for individuals undergoing cardiac rehabilitation.⁹⁷ Physical activity should be regarded as a part but not the whole of cardiac rehabilitation.

Sexual Activity
Sexual activity is similar to moderate-intensity exercise for most individuals with CAD. Heart rates rarely achieve 120 beats per minute, systolic blood pressure is under 170 mm Hg, and metabolic requirements are between 5 and 7 METs.¹⁴⁰ There appears to be no particular benefit in altering positions or sexual customs. Exercise training can, however, lessen the hemodynamic stress of sexual activity.

The use of ß-blockers and other drugs may impair sexual performance. The subject should be cautioned about such adverse reactions before leaving the hospital and encouraged to report them.

An exercise test within 3 weeks after MI, CABS, or PTCA may reassure both subject and spouse as well as provide guidelines.

Sexual activity should be resumed at the same time as other activities are resumed. In general, sexual activity should be deferred until activities such as walking and driving are resumed, usually about 2 to 4 weeks after returning home.

Obtaining Informed Consent for Exercise Training

Obtaining informed signed consent before initiating an exercise training program helps to clarify the responsibilities and goals of both the physician and the subject.

Informed Consent for Exercise Training

I want to participate in the

exercise training program to improve my cardiovascular function. This program was recommended by my physician,

Dr .

I will have a clinical evaluation before I enter this exercise program. This evaluation will include a medical history and physical examination consisting of but not limited to ECG at rest and, in some instances, with effort, and measurements of heart rate and blood pressure. The purpose of this evaluation is to determine the safety of my participation in this exercise training program.

The program will follow an exercise prescription prepared by

Dr .

I understand that activities are designed to place a gradually increasing workload on the circulation in an attempt to improve its function. The reaction of the cardiovascular system to such activities cannot be predicted with complete accuracy. Certain changes may occur during or after exercise, including abnormalities of blood pressure or heart rate, ineffective heart function, and, possibly, in some instances, heart attacks or cardiac arrest.

I realize that it is necessary for me to promptly report symptoms or signs indicating any abnormality or distress to the exercise supervisor. I consent to administration of immediate resuscitation measures deemed advisable by the exercise supervisor.

I have read the above and I understand it. My questions have been answered to my satisfaction.

Subject

Physician

Witness

Date

Acknowledgments

The authors are greatly indebted to Philip Ades, MD (University of Vermont) for his special review and critique of this statement.

Footnotes

Requests for reprints should be sent to the Office of Scientific Affairs, American Heart Association, 7272 Greenville Ave, Dallas, TX 75231.

Appendix

Glossary
Testing

Arrhythmia-Dysrhythmia or abnormal heart rhythm

aO₂-Arteriovenous oxygen difference

Balke-type protocol-Constant speed (2.0-3.0 mph) variable grade treadmill exercise test

Bruce-type protocol-Variable speed and grade treadmill exercise test (incremental speed and grade increase every 3 minutes)

CAD-Coronary artery disease: coronary heart disease, myocardial infarction, coronary artery bypass surgery, coronary angioplasty, and ischemia

Calories-Kilocalorie: amount of energy required to raise temperature of 1 kg water by 1°C

Calories/minute—METsx3.5xbody weight in kilograms/200

Exercise capacity-Functional capacity, training or conditioning level, level of fitness

Isometric-Static exercise: Muscle contraction with no movement (see "Resistive" below)

Isotonic-Dynamic exercise: Muscle contraction producing movement

J-junctional depression-Depression of beginning of ST segment

Kg-Kilogram: 1000 g

Kpm-Kilopond- or kilogram-meter of work: 1 J (10 ergs)

MET-Metabolic equivalent (3.5 mL · kg^-1 · min^-1 of oxygen uptake)

MO₂-Myocardial oxygen uptake

0.1 Mv-1 mm (provided calibration is set at 10 mm/Mv)

Predictive value-Percentage of those with or without disease who are identified correctly

PTCA-Percutaneous transluminal coronary angioplasty

Rating of perceived exertion-Borg scale of 6 to 20 or 1 to 10

Resistive-Muscle contraction with limited movement

Sensitivity-Percentage of persons who are unhealthy who will have a positive test

Specificity-Percentage of persons who are healthy who will have a negative test

ST depression-Horizontal or downsloping (0.10 Mv for msec), measured from isoelectric PR level

Training-Physical activity, conditioning, leading to fitness

O₂-Oxygen uptake

O_2max-Maximal oxygen uptake Training

Aerobic-Exercise in which energy needed is provided by using oxygen inspired to combust metabolites

Anaerobic-Exercise in which energy needed exceeds oxidative processes and nonaerobic metabolism begins

Cardiac output-Volume of blood ejected from heart in liters per minute. Normal: 6 L/min at rest

Cardiovascular exercise-Predominantly dynamic exercise us ing large muscle groups

Ejection fraction-Ratio of left ventricular stroke volume to end-diastolic volume (or percentage of end-diastolic volume ejected with each cardiac contraction). Normal: 60% to 75%

Flexibility activity-Activity designed to enhance range of motion of joints

Medical supervision-Physician readily available (the presence of a properly trained nurse in the exercise room is acceptable if physician is not available in the exercise room).

NYHA-New York Heart Association classification:

Class 1: Heart disease without symptoms

Class 2: Heart disease with symptoms during ordinary activity

Class 3: Heart disease with symptoms during less than

ordinary activity

Class 4: Heart disease with symptoms at rest

Occupational activity-On-the-job activity such as a job requiring lifting of loads of 20 pounds or more at least hourly throughout the day or constantly moving any size load from place to place without mechanized aid

Strength activity-Muscular contraction against resistance

designed to increase skeletal muscle strength

Stroke volume-Amount of blood ejection from heart with each contraction. Normal: 80 to 90 mL at rest

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