(Circulation. 1995;92:2095-2101.)
© 1995 American Heart Association, Inc.
Articles |
Relation Between Ischemic Threshold Measured During Dobutamine Stress Echocardiography and Known Indices of Poor Prognosis in Patients With Coronary Artery Disease
From the Cardiology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md.
Correspondence to Dr Julio A. Panza, Director of Echocardiography, National Institutes of Health, Bldg 10, Room 7B-15, Bethesda, MD 20892.
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Abstract |
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Background Stress echocardiography has become an accepted methodology for the evaluation of coronary artery disease. One potential advantage of dobutamine over other stressors used with echocardiography is the possibility of assessing the ischemic threshold. However, whether this measurement correlates with indices associated with adverse outcome has not been established.
Methods and Results One hundred four patients (91 men and 13 women; age, 61±9 years) with coronary artery disease were studied with transesophageal echocardiography during infusion of dobutamine 2.5 to 40 µg/kg per minute. When regional dyssynergy developed, the dobutamine ischemic threshold (the dose of dobutamine at which induced regional wall motion abnormalities were first detected) was identified. The dobutamine stress echocardiogram was abnormal in 90 patients (sensitivity, 87%). The dobutamine ischemic threshold was 25.4±11.2 µg/kg per minute in patients with single-vessel disease, 14.4±7.9 in patients with two-vessel disease, and 9.1±7.9 in patients with three-vessel disease (P<.0001). The dobutamine ischemic threshold correlated with the ejection fraction response to exercise measured by radionuclide angiography: Patients with low ischemic threshold had a mean fall in ejection fraction, and patients with high ischemic threshold or normal tests had a mean increase in ejection fraction.
Conclusions In patients with coronary artery disease, the ischemic threshold measured during dobutamine stress echocardiography correlates with both the number of stenosed vessels and the left ventricular ejection fraction response to exercise. Because these variables are associated with poor prognosis, these findings provide further support regarding the utility of dobutamine stress echocardiography in the clinical evaluation of patients with chronic coronary artery disease.
Key Words: coronary disease • echocardiography • ischemia • angiography
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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In patients with coronary artery disease, transient wall motion abnormalities induced by different forms of physiological or pharmacological stressors—including exercise, dobutamine, dipyridamole, or adenosine—can be identified readily by means of cardiac ultrasound examination. Consequently, stress echocardiography has become an accepted and useful methodology for the evaluation of these patients.1 2 One potential advantage of the use of dobutamine over other forms of stress used in combination with echocardiography lies in the possibility of assessing the ischemic threshold by determining the level of myocardial oxygen demand at which ischemia develops during the infusion of incremental doses of dobutamine.
The fact that measurement of the ischemic threshold may yield important and clinically relevant information in coronary artery disease patients has been suggested by previous studies showing that the development of repolarization changes during the early stages of exercise testing is associated with a greater likelihood of cardiovascular events during subsequent follow-up3 4 and with more frequent occurrence of transient myocardial ischemia during daily life.5 In addition, measurements of ischemic threshold have been used in innumerable previous investigations to assess the efficacy of anti-ischemic medications and to unravel pathophysiological mechanisms in patients with ischemic heart disease.6
Although measurements of ischemic threshold traditionally have been derived during exercise stress testing, the inability to obtain adequate images of the left ventricle during exercise because of chest movement and hyperventilation prevents the use of echocardiography for this purpose. Similarly, thallium scintigraphy does not allow an estimation of the ischemic threshold because myocardial perfusion heterogeneity is only assessed at peak exercise. Thus, analysis of the ischemic threshold with exercise testing has been limited to the examination of ECG changes, a relatively insensitive marker of myocardial ischemia that does not provide information about the extent of induced left ventricular dysfunction. Although radionuclide angiography permits the acquisition of images throughout the performance of an exercise test, the information provided is not tomographic; therefore, measurements of the ischemic threshold rely on the assessment of either regional wall motion of only those segments visualized in a single predetermined view or impairment of global left ventricular function seen as a fall in ejection fraction.7
The infusion of graded doses of dobutamine combined with simultaneous real-time tomographic assessment of global and regional left ventricular function with echocardiography offers the unique possibility of determining the ischemic threshold by direct analysis of the functional consequences of myocardial ischemia. However, whether this measurement does indeed correlate with indices associated with adverse outcome in coronary artery disease, such as the number of stenosed vessels or the magnitude of induced myocardial ischemia, has not been established.
The purpose of the present study, therefore, was to investigate the relation between the ischemic threshold assessed during dobutamine stress echocardiography and variables that have proven to be indicative of poor prognosis in patients with coronary artery disease.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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Study Patients
One hundred four patients admitted to the Clinical Center of the National Institutes of Health for performance of coronary angiography who had
70% narrowing in the internal
diameter of at least one major coronary artery were included in
the present investigation. There were 91 men and 13 women; age was
61±9 years (range, 43 to 78 years).
Coronary angiograms were
interpreted by an independent reader
with the aid of caliper measurements. Forty-nine patients had
undergone previous revascularization
(coronary artery bypass surgery in 30 and angioplasty in 19);
in these patients, the status of the coronary vascular tree at
the time of the most recent cardiac catheterization
(performed after revascularization in all patients)
was used when classifying patients according to the presence of one-,
two-, or three-vessel disease. Patients with 50%
stenosis of the left main stem were classified in the
two-vessel or three-vessel (if the right coronary
artery had 70% stenosis) disease category.
Thirty-five of the study patients had suffered a previous myocardial infarction, but none of them in the 3 months before the study. Patients with evidence of cardiomyopathy, congenital or valvular heart disease, recent myocardial infarction, unstable angina, or uncontrolled systemic hypertension were excluded from the study. All patients were in sinus rhythm. Antianginal medications were withdrawn at least 48 hours before the performance of the studies.
The study was approved by the National Heart, Lung, and Blood Institute Investigational Review Board, and each patient gave written informed consent. In each patient, all studies were performed within 1 week.
Radionuclide Angiography
Gated cardiac blood pool studies
were performed to assess left
ventricular ejection fraction at rest and during peak
exercise with the use of red blood cells labeled in vivo with 20 to 25
mCi of technetium-99m. Patients exercised on a supine
bicycle starting at 25 W/min with increments of 25 W/min every 2
minutes. Imaging was accomplished using a conventional Anger camera
equipped with a high-sensitivity parallel-hole collimator, as
previously described.8 The left ventricular
ejection fractions during baseline conditions and at peak exercise were
derived by computer analysis of the scintigraphic data. The
lower limit of normal for ejection fraction by our technique is
45%.
Exercise Testing
Patients underwent a symptom-limited
exercise test using the
standard Bruce protocol,9 the National Institutes of
Health combined protocol,5 or the Naughton
protocol.10 Twelve-lead ECGs were obtained at rest, at
every minute during exercise, and at peak exercise. On the ECG, lead
aVR was replaced by CM5. The exercise was terminated when
chest pain, ST segment depression 4 mm, a decrease in blood pressure
20 mm Hg, ventricular tachycardia, extreme
fatigue, or shortness of breath developed during the test. The test was
considered positive when planar or downsloping ST segment depression
1 mm, at 0.08 seconds after the J-point, was observed. In patients
with positive exercise tests, the ECG ischemic threshold was
identified as the heart rate at the onset of 1-mm ST segment
depression.
Transesophageal Dobutamine Stress
Echocardiography
Transesophageal echocardiograms were performed
with a Hewlett-Packard biplane (34 patients) or omniplane (70 patients)
5-MHz probe. The studies were performed in the left lateral decubitus
position. The oral pharynx was anesthetized with aerosol
benzocaine spray. Intravenous sedation with the use of
midazolam hydrochloride was administered before introduction of the
probe and during the study as needed (total dose of midazolam used per
patient was 7±3 mg). For introduction of the probe, patients were
sedated to the point at which they were on the verge of falling asleep
but still able to follow commands such as swallowing when asked to.
This was usually accomplished with a dose of midazolam of 1.5 to 2.5
mg, depending on the patient's age and weight. During the procedure,
patients were maintained at a level of sedation at which they could
comfortably tolerate the study and report the development of symptoms
such as chest discomfort. This was achieved by additional 1- or 2-mg
doses of midalozam as needed. Continuous monitoring of heart rate and
oxygen saturation was performed during the study. A 12-lead ECG and
measurements of systemic blood pressure were recorded at the end of
each stage of the dobutamine protocol while the
echocardiographic images were obtained.
Dobutamine was infused starting at 2.5 µg/kg per minute. After 5 minutes, the dose was increased to 5 µg/kg per minute. Subsequently, the dose was increased by 5 µg/kg per minute increments every 5 minutes to a maximum of 40 µg/kg per minute. Two-dimensional views were acquired during the last 2 minutes of each stage. The stress test was terminated when the maximum dose of dobutamine was reached or if severe chest pain, severe increase in systolic blood pressure (to >250 mm Hg), clinically significant arrhythmias, extensive wall motion abnormalities, or intolerance to the probe developed. A fall in blood pressure not accompanied by development of extensive wall motion abnormalities was not considered a criterion for termination of the test.11 12 Sublingual nitroglycerin, sublingual nifedipine, and intravenous propranolol were available.
At baseline and at each stage of the dobutamine infusion, transgastric short-axis and transesophageal long-axis, four-chamber, and two-chamber views were obtained following the same sequence in all patients.13 First, the transgastric short-axis view was obtained both at the papillary muscle and the mitral valve levels. Subsequently, the probe was pulled out to the esophagus, and the long-axis, four-chamber, and two-chamber views were recorded. Immediately after completion of the image acquisition, the dose of dobutamine was increased to the next level and the probe was gently advanced again across the cardias and into the stomach in order to start with the transgastric short-axis view during the next stage. The long-axis view was obtained by lateral flexion of the longitudinal probe when using the biplane probe14 and by rotating the transducer 135° from the horizontal position when using the omniplane probe.15 During the acquisition of the transesophageal views, particular attention was paid to avoid foreshortening of the left ventricular cavity, which would result in poor visualization of the apical segments. This was achieved by using the maximum degree of retroflexion of the scope without losing contact with the esophageal wall. In addition, visualization of the apex was ascertained by ensuring that the length of the left ventricular cavity (from the plane of the mitral valve to the apical endocardium) was the same in all transesophageal views (ie, four-chamber, two-chamber, and long-axis).
Analysis of Echocardiographic
Images
Two-dimensional views were continuously recorded on
videotape and digitized on-line with use of a Nova Microsonics
IMAGEVUE system. The system permits the creation of a
continuous loop of a single cardiac cycle by displaying still frames
acquired at regular intervals in a continuous fashion. Twelve
sequential frames of each two-dimensional view were captured at
33-ms intervals with an ECG R wave–triggered mechanism at baseline
and at each dose of dobutamine.
Transesophageal echocardiographic
images digitized on-line during the dobutamine stress
study were transferred to optical disks for permanent storage and
review. Continuous videotape recordings were not routinely used
for analysis but were available during the review process.
Images were reviewed by two independent observers who were blinded to the results of the coronary angiography, exercise test, and radionuclide angiogram. In the first 58 study patients, the initial separate image analysis was subsequently used for assessment of interobserver variability in the measurement of the ischemic threshold. In case of disagreement, the studies were again reviewed, and consensus was reached between the two observers.
At each stage of the dobutamine protocol, the left ventricle was divided into 16 segments following the recommendations of the American Society of Echocardiography.16 Regional myocardial contractile function was graded as normal, hypokinesis, akinesis, or dyskinesis for each myocardial segment; particular attention was paid to systolic wall thickening rather than endocardial motion.
A test was considered negative when a gradual and consistent increase in systolic wall thickening with increasing doses of dobutamine was observed in each myocardial segment. A test was considered positive when regional dyssynergy developed (or worsened in segments with resting wall motion abnormalities) during dobutamine infusion in one or more myocardial segments compared with the previous dobutamine dose. A change from basal akinesis to dyskinesis was not considered indicative of myocardial ischemia.17 Evaluation of each myocardial segment was performed with the use of an integrated assessment of the different imaging planes available.13
When the test was considered positive, the dose of dobutamine at which induced regional wall motion abnormalities were first detected was identified. This dose is subsequently referred to as the dobutamine ischemic threshold. The heart rate and rate-pressure product measured at the dobutamine ischemic threshold were also used for analysis.
At baseline, at the dobutamine ischemic threshold, and at the maximum dose of dobutamine, an echocardiographic wall motion score was derived by adding up the scores of each segment (1, normal; 2, hypokinesis; 3, akinesis; 4, dyskinesis) and dividing that value by the number of segments assessed.
Statistical Analysis
Sensitivity was calculated with the use
of standard formulas.
Two means were compared with a paired or unpaired t test as
appropriate. Three or more means were compared by ANOVA. Proportions
were compared by the 
2 test. Relations were
assessed by means of Pearson's correlation coefficient (for continuous
variables) or Spearman's rank test (for categorical
variables). Data are presented as mean±SD except where
indicated. A P value <0.05 was considered significant.
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Results |
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Coronary Angiography
By selection, all 104 patients had significant stenosis of at least one major coronary artery. Forty-one patients (39%) had single-vessel disease, 36 (35%) had two-vessel disease, and 27 (26%) had involvement of all three major coronary vessels. Of the 63 patients with multivessel disease, 10 had >50% stenosis of the left main stem.
Radionuclide Angiography
In 95 of the 104 patients (91%),
optimal radionuclide images both
at rest and during exercise were obtained for measurements of ejection
fraction. Eight patients had medical conditions that precluded exercise
(osteoarthritis in 6 and neuromuscular disorders in 2); in the
remaining patient, the images acquired during exercise were of
suboptimal quality for analysis.
Resting ejection fraction for the
entire study group was 47±15%, and
it was abnormal (<45%) in 36 patients. An increase in ejection
fraction with exercise was observed in 27 patients and was 5% in 14.
A fall in ejection fraction with exercise was observed in 62 patients
and was 5% in 41. Identical ejection fractions at rest and exercise
were observed in 6 patients.
Exercise Testing
Ninety-two of the 104 patients (88%)
underwent an exercise
treadmill test with the Bruce protocol (32 patients), the National
Institutes of Health combined protocol (63 patients), or the Naughton
protocol (1 patient). The remaining 12 patients did not have
diagnostic exercise tests because they had either medical
conditions that precluded treadmill exercise (8 patients) or left
bundle branch block on the baseline ECG (4 patients). Heart rate
increased from 80±14 to 134±21 beats per minute. The test was
stopped
because of chest pain in 34 patients, shortness of breath or fatigue in
56, and significant ST segment depression in 2.
Forty-four of the 92 patients who underwent exercise testing developed ECG changes compatible with myocardial ischemia (sensitivity, 48%).
Transesophageal Dobutamine Stress
Echocardiography
The test was successfully completed in 102 of the 104
(98%)
patients. In the remaining 2 patients, the test was discontinued
because of intolerance to the probe. No major complications occurred in
any of the 104 study patients. The test was stopped because of
completion of the protocol (achievement of the maximum dose of
dobutamine) in 42 patients, severe chest pain in 23,
extensive wall motion abnormalities in 34, severe systolic
hypertension (>250 mm Hg) in 1, nonsustained ventricular
tachycardia in 1, and significant (>4 mm) ST segment
depression in 1. Dobutamine increased heart rate from
74±16 beats per minute at baseline to a peak of 139±18 beats per
minute. The maximum dose of dobutamine used during the test
was 27±12 µg/kg per minute.
The test was considered normal in 14 and abnormal in 90 patients, thus rendering a sensitivity of 87%. The sensitivity for detection of coronary artery disease increased with greater extent of coronary stenoses from 78% (32 of 41) in patients with single-vessel disease, 89% (32 of 36) in patients with two-vessel disease, and 96% (26 of 27) in those with three-vessel disease; these differences, however, did not reach statistical significance (P=.08).
Relation Between Dobutamine Ischemic Threshold
and Other Variables
There was a significant relation between the
dobutamine ischemic threshold and the number of
stenosed vessels (Fig 1
). Thus, the dose of
dobutamine at which myocardial ischemia was first
detected was 25.4±11.2 µg/kg per minute in patients with
single-vessel disease, 14.4±7.9 in patients with two-vessel
disease, and 9.1±7.9 in patients with three-vessel disease
(P<.0001). This difference was more clearly apparent when
the frequency distribution of the dobutamine
ischemic threshold was analyzed according to the extent
of coronary artery disease: Compared with patients with
single-vessel disease in whom the ischemic threshold
largely occurred at the higher doses of dobutamine,
patients with two- and three-vessel disease most commonly had
development of wall motion abnormalities at the lower doses (Fig
2).
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A similar relationship between ischemic threshold and extent of disease was observed when the ischemic threshold was expressed as the heart rate or the rate-pressure product at which wall motion abnormalities were first detected. Thus, the heart rate at the ischemic threshold was 125±17 beats per minute in patients with single-vessel disease, 108±18 in patients with two-vessel disease, and 99±18 in patients with three-vessel disease (P<.0001). The rate-pressure product was 18 290±5749 in patients with single-vessel disease, 16 847±4295 in patients with two-vessel disease, and 14 437±2958 in patients with three-vessel disease (P<.01).
Of note, the change in
wall motion score from baseline (which reflects
the extent of induced wall motion abnormalities) at the
dobutamine ischemic threshold was not different
among patients with one-, two-, or three-vessel disease (Figure
3). However, at the maximum dose of
dobutamine, patients with more extensive disease had more
pronounced changes in wall motion score, reflecting a greater magnitude
of wall motion abnormalities induced during the test (Fig 3).
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The dobutamine ischemic threshold also
significantly correlated with the ejection fraction response to
exercise measured by radionuclide angiography: patients with low
ischemic threshold had a mean fall in ejection fraction,
patients with intermediate ischemic threshold had little or no
change in ejection fraction with exercise, and patients with high
ischemic threshold or normal tests had a mean increase in
ejection fraction (Fig 4). Of note, the
echocardiographic wall motion score measured at the
point of the ischemic threshold significantly correlated with
the exercise ejection fraction measured by radionuclide angiography
(Fig 5).
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In the 44 patients with positive treadmill
exercise and
dobutamine stress echocardiography
tests, the heart rate at the onset of 1 mm ST segment depression during
treadmill exercise significantly correlated with the heart rate at the
onset of wall motion abnormalities during dobutamine
echocardiography (Fig 6).
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Interobserver Variability
In the 58 study patients in whom
echocardiographic
studies were analyzed by two blinded observers, the test was
considered positive in 51 patients and normal in the remaining 7.
Agreement between the two observers with regard to the presence of
induced regional wall motion abnormalities was found in each of the 58
studies.
There was a highly significant correlation in the assessment
of the
dobutamine ischemic threshold by each observer (Fig 7). In 33
of the 51 patients with induced regional wall
motion abnormalities, the same dobutamine ischemic
threshold was measured by both observers. In the remaining 18 patients
with discrepant measurements, the difference in the
dobutamine dose at ischemic threshold between the
two observers was 5.7±2.2 µg/kg per minute, approximately
equivalent
to one stage of the dobutamine protocol.
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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The results of the present study demonstrate that, in patients with coronary artery disease, the ischemic threshold measured during dobutamine stress echocardiography correlates with both the number of stenosed vessels and the left ventricular ejection fraction response to exercise. Thus, patients with development of regional wall motion abnormalities during the early stages of the dobutamine stress test (low dobutamine ischemic threshold) had a significantly higher likelihood of having multi-vessel disease on coronary angiography and a fall in ejection fraction with exercise measured by radionuclide angiography compared to patients with high dobutamine ischemic threshold or normal dobutamine stress test. Because the number of stenosed vessels and the left ventricular ejection fraction response to exercise are associated with poor prognosis in coronary disease, our findings emphasize the usefulness of assessing not only the presence of wall motion abnormalities but also the workload at which these abnormalities develop during the performance of dobutamine stress echocardiography.
Several previous studies have demonstrated that the number of vessels with significant stenoses is a critical determinant of survival and occurrence of non-fatal cardiovascular events (including acute myocardial infarction and unstable angina) in patients with chronic ischemic heart disease.18 19 Similarly, previous investigations utilizing radionuclide ventriculography have shown that assessment of the left ventricular ejection fraction response to exercise significantly aids in the prognostication of these patients, particularly in those with multi-vessel disease.3 20 21 22 23 24 25 These observations provide support for the use of these variables as surrogate indices of prognosis in the present investigation.
Previous Studies
Among the numerous previous reports related
to the use of
dobutamine stress echocardiography for
the assessment of patients with coronary artery disease, only a
few have included an analysis of the ischemic
threshold, and these have shown equivocal results. For example, Cohen
et al26 initially reported a lower dobutamine
ischemic threshold (both in terms of heart rate and
dobutamine dose) in patients with multi-vessel compared
to single-vessel disease. Similarly, Segar et al27
reported that the likelihood of multivessel disease among their study
patients was higher when the dobutamine stress test became
positive at a heart rate 
125 beats per minute. However, in a more
recent study from Cohen et al,28 no difference was found
in the heart rate at ischemic threshold during
dobutamine stress echocardiography
among patients with one- two- or three-vessel disease. Although the
reasons for this discrepancy are not clear, it must be pointed out that
in the latter study analysis of the ischemic threshold
was performed in only 23 patients, and that the heart rate at
ischemic threshold in their patients with one-vessel
disease was uncharacteristically low (91±7 beats per
minute),28 in sharp contrast to that observed in their
previous study (118±18 beats per minute)26 and in the
present investigation (125±17 beats per minute).
Strengths and Limitations
An important aspect of our study is
the fact that the
dobutamine ischemic threshold was assessed by means
of transesophageal
echocardiography. Although this technique may not
be amenable for the routine evaluation of all patients with
coronary artery disease, it provides a highly reliable tool for
the investigation of the myocardial response to dobutamine
and other interventions in which an accurate assessment of myocardial
function is critical. In a previous study, we have reported on the
safety, feasibility, and diagnostic accuracy of
transesophageal dobutamine stress
echocardiography in the overall population of
patients with known or suspected coronary artery
disease.13 In agreement with the findings of that study,
and those of other investigations related to the use of
transesophageal echocardiography
during different forms of
stress,29 30 31 32 the
technique was
well tolerated by the vast majority of patients, and in only two cases
did the study have to be discontinued because of intolerance to the
probe.
It must be acknowledged that the present report does not include follow-up information to document a direct relation between low dobutamine ischemic threshold and the occurrence of adverse cardiovascular events in our study patients. This limitation, however, is common to all studies that include an unselected population of patients with chronic coronary artery disease because those variables indicative of poor prognosis are the same ones that are used to decide the best therapy for each individual patient. Consequently, those patients presenting with a constellation of findings associated with adverse outcome (eg, patients with left main stenosis, three-vessel disease and inducible ischemia, or two-vessel disease, depressed left ventricular systolic function and inducible ischemia) are advised to undergo revascularization to diminish the risk of suffering an acute event during subsequent follow-up.3 18 19 20 21 22 23 24 25 For this reason, it is currently not feasible to conduct a follow-up study of these patients once the coronary anatomy and the left ventricular ejection fraction response to exercise are known. In fact, based on these criteria, 38 of the 104 (36%) study patients underwent revascularization following their evaluation; in addition, 15 other patients (14%) did not undergo revascularization because they were considered to carry a prohibitively high risk or unsuitable coronary anatomy for either bypass surgery or angioplasty. This prevented us from obtaining meaningful information about the patients' follow-up to determine the direct impact of assessing the dobutamine ischemic threshold on the occurrence of subsequent acute cardiovascular events.
Implications
The findings of the present investigation may
have important
implications for the assessment of patients with coronary
artery disease. First, our results suggest that the ability of
estimating the ischemic threshold with dobutamine
may constitute an important advantage of this over other forms of
stress (such as dipyridamole or adenosine) used
in combination with echocardiography. In this
regard, it is important to emphasize that patients with different
extent of coronary artery disease did not show different
magnitude of induced wall motion abnormalities at the time that these
were first detected during infusion of dobutamine. In
contrast, a greater extent of induced wall motion abnormalities was
observed at the peak dose of dobutamine in patients with
more extensive coronary artery disease. These observations have
implications for the analysis of the progressive development of
wall motion abnormalities during the infusion of dobutamine
and indicate that: a) it is the dose of dobutamine at which
the initial abnormalities are detected that correlates with the extent
of disease and not the number of segments that show regional dyssynergy
at this point; and b) once the first wall motion abnormalities are
identified, it is important to achieve higher doses of
dobutamine to more conclusively recognize the presence
of multivessel disease by means of inducing regional dyssynergy in more
extensive areas of the myocardium. It must also be pointed
out that the echocardiographic wall motion score at the
dobutamine ischemic threshold significantly
correlated with the exercise left ventricular ejection
fraction. This reflects the fact that both measurements are influenced
not only by the magnitude of induced regional dyssynergy but also by
the presence and extent of wall motion abnormalities during resting
conditions. Second, the present study findings indicate that
analysis of the results of dobutamine stress
echocardiography can be used not only for detection
of coronary disease but also for the risk stratification of
these patients. Third, our observations provide support for the use of
dobutamine stress echocardiography in
investigational studies that include measurements of ischemic
threshold. Finally, the induction of ischemia at low doses of
dobutamine, observed in a sizeable proportion of our
patients with multi-vessel disease, may help explain why myocardial
segments with depressed systolic function and preserved
thallium uptake may not show a positive inotropic response to
dobutamine.33
Conclusions
The results of the present investigation
demonstrate that, in
patients with coronary artery disease, the ischemic
threshold measured during dobutamine stress
echocardiography significantly correlates with the
number of stenosed vessels and the left ventricular
ejection fraction response to exercise. Because these variables
have important prognostic implications, our findings provide further
support regarding the utility of dobutamine stress
echocardiography in the clinical evaluation of
patients with chronic coronary artery disease.
Received February 7, 1995; revision received April 6, 1995; accepted May 22, 1995.
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