(Circulation. 1999;100:II-269.)
© 1999 American Heart Association, Inc.
Aortic and Peripheral Vascular Surgery |
Perioperative Prognostic Value of Dipyridamole Echocardiography in Vascular Surgery
A Large-Scale Multicenter Study in 509 Patients
From the CNR Institute of Clinical Physiology, Pisa, Italy.
Correspondence to Rosa Sicari, MD, PhD, CNR Institute of Clinical Physiology, Via Savi, 8, 56100 Pisa, Italy. E-mail rosas{at}ifc.pi.cnr.it
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Abstract |
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Background—Patients undergoing major vascular surgery are at a relatively high risk of cardiac events, and pharmacological stress echocardiography is increasingly used for perioperative risk stratification. The aim of the current study was to evaluate the value of dipyridamole echocardiography test (up to 0.84 mg/kg over 10 minutes) in predicting cardiac events in a large-scale, multicenter, prospective, observational study design.
Methods and Results—Five hundred nine patients (mean age 66±10
years) were studied before vascular surgery by
dipyridamole stress
echocardiography in 11 different centers. All
patients underwent preoperative clinical risk assessment according to
the American Heart Association guidelines. No major complications
occurred during dipyridamole stress
echocardiography. Technically adequate images were
obtained in all patients; however, in 4 patients only the low
dipyridamole dose (0.56 mg/kg over 4 minutes) was given
for limiting side effects. Eighty-eight (17.3%) had a positive test.
Perioperative events occurred in 31 (6.1%) patients: 6
deaths, 11 myocardial infarctions, and 14 episodes of unstable angina.
Sensitivity and specificity of dipyridamole stress
echocardiography for predicting spontaneous cardiac
events were 81% and 87%, respectively, with a positive predictive
value of 28% and negative predictive value of 99%. By
multivariate analysis, the difference between
wall motion score index at rest and peak stress (
wall motion score
index), test positivity, and ST-segment depression during
dipyridamole infusion were independent predictors of
any perioperative cardiac event.
Conclusions—Dipyridamole stress echocardiography is safe and well tolerated in patients undergoing major vascular surgery and provides an effective preoperative screening test for the risk stratification of these patients, mainly because of the extremely high negative predictive value, which is a potent predictor of complication-free procedure.
Key Words: echocardiography • trials • stress • risk factors • surgery
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Introduction |
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Perioperative cardiovascular complications such as myocardial infarction, unstable angina, pulmonary edema, and serious ventricular arrhythmias are major causes of morbidity and death in surgical patients. This is particularly important in patients undergoing major vascular surgery, who have a relatively high rate of cardiovascular complications.1 A variety of methods and noninvasive diagnostic procedures to predict perioperative risk have been evaluated over the last decade, including multifactorial clinical scoring systems,2 3 4 ambulatory ECG monitoring,5 radionuclide ventriculography,6 and pharmacological myocardial perfusion imaging.7 8 9 10 11 12 13 14 15 16 17 It has been suggested that the most accurate information can be derived by adding clinical data to those obtained by dipyridamole–thallium-201 myocardial perfusion imaging,9 which remains the most extensively studied noninvasive approach to the risk stratification of patients undergoing noncardiac surgery. Recently, stress echocardiography with dobutamine18 19 20 21 22 or dipyridamole23 24 25 26 has been proposed for risk stratification in these patients. Pharmacological stress echocardiography proved to be a safe and sensitive technique for predicting perioperative cardiac events, with an excellent negative predictive power. The widespread availability and the relatively low cost of the technique make it a most appealing one for risk stratification. This study represents the extension of a previously reported multicenter prospective study with dipyridamole stress echocardiography in 136 patients undergoing major vascular surgery.24 The aim of the study was to confirm the value of dipyridamole stress echocardiography as an effective preoperative screening test for risk stratification before noncardiac vascular surgery in a substantially larger patient population and to show the incremental value, if any, of the technique over conventional clinical variables.
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Methods |
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Patient Population
Initially, 532 patients (mean age 66±10 years) scheduled for elective noncardiac surgery, with a technically acceptable acoustic window, were prospectively enrolled in 11 different centers. Twenty-three patients were excluded from the study because of the presence of high-risk stress echocardiography response (dipyridamole time <5 minutes and/or a peak wall motion score index >2), which influenced the decision of the attending physician to either cancel or postpone the surgical intervention, so the final number of patients that were enrolled in this study was 509.
Dipyridamole Stress Echocardiography
The standard protocol for dipyridamole stress
echocardiography (cumulative dose 0.84 mg/kg over
10 minutes) was used.24 During the procedure,
2-dimensional echocardiographic, 12-lead ECG, and blood
pressure monitoring were continuously performed. Regional wall motion
was assessed according to the recommendations of the American Society
of Echocardiography with a 16-segment
model.27 In all studies, segmental wall motion was
semiquantitatively graded as follows: normal, normal wall motion at
rest, with normal/increased wall motion after
dipyridamole (score 1); hypokinetic, marked reduction
in endocardial motion (score 2); akinetic, virtual absence of inward
motion (score 3); and dyskinetic, paradoxical wall motion away from the
left ventricular center in systole (score 4). Test
positivity was defined as the occurrence of 
1 of the following
conditions: (1) new dyssynergy in a region with normal rest function
(ie, normokinesia becoming hypokinesia, akinesia, or dyskinesia); and
(2) worsening of rest dyssynergy (ie, hypokinesia becoming akinesia or
dyskinesia; rest akinesia becoming dyskinesia was not considered a
positivity criterion).28 The wall motion score index
(WMSI) was derived by dividing the sum of individual segments by the
number of interpretable segments. Aminophylline (up to 240 mg over 3
minutes) was given at the end of the test.
Echocardiographic monitoring was performed throughout
dipyridamole infusion and up to at least 5 minutes
after the end of the infusion. Two-dimensional
echocardiographic images were recorded at baseline
and at the end of each dipyridamole dose. In negative
tests, the dipyridamole time (ie, the time between
start of infusion and the onset of a regional dyssynergy) was
arbitrarily assumed to be 17 minutes (when aminophylline was
given).
Quality control of stress echocardiography performance and reading in enrolled centers was previously described in depth.29 Briefly, the reader from each recruiting center met the predefined criteria for stress echocardiography reading. At that point, the center could start recruiting patients and reading of stress echocardiography from recruiting center was directly entered in the data bank.
Preoperative Risk Assessment
Preoperative risk assessment was evaluated according to the
American College of Cardiology/American Heart
Association Task Force guidelines.30 Patients were
evaluated according to the presence of clinical predictors of increased
perioperative cardiovascular risk and
to the risk inherent to the type of noncardiac surgical procedure.
Postoperative Follow-Up
Patients were followed up throughout their hospital stay. During
the first 3 days after surgery and when clinically indicated, serum
levels of creatine kinase with isoenzymes were measured and a 12-lead
ECG recorded.
Events were defined as cardiac-related death, nonfatal myocardial infarction, and unstable angina. The definition of in-hospital cardiac-related death required documentation of significant arrhythmias, cardiac arrest, or both, or death attributable to congestive heart failure or myocardial infarction in the absence of any other precipitating factor. Myocardial infarction was diagnosed in the presence of the development of new ECG changes and cardiac enzyme level increases (MB fraction >5%). Unstable angina was defined by accelerating anginal symptoms with no enzyme level elevation or new wall motion dyssynergy on the resting echocardiogram or new Q waves on the resting ECG.
Statistical Analysis
Values are expressed as mean±SD.
The individual effect of certain variables on event-free survival was evaluated with the use of the Cox regression model (SPSS software package for Windows, 1995). The analysis was performed according to the unmodified forward selection stepwise procedure. In this case, the variables were entered into the model on the basis of a computed significance probability; accordingly, the variable that has the most significant relation to dependent outcome is selected first for inclusion in the model, and a solution to the functional form of the equation is computed. At the second and subsequent steps, the set of variables remaining at each point is evaluated, and the most significant is included if it improves the prediction of the outcome (dependent variable), but in this case this probability is conditional on the presence of the variable already selected. The algorithm ceases to select variables when there is no further significant improvement in the prediction of the whole model. We also analyzed the data according to a modified stepwise procedure, in which the significant individual variables were included in the model in the same order in which they are actually considered by the cardiologist (historic and clinical data first, preoperative risk variables second, and the dipyridamole stress echocardiography variables third).
Variables selected for examination were age, sex, previous
myocardial infarction, history of angina, history of coronary
revascularization, hypertension, smoking, diabetes,
WMSI at baseline, WMSI at peak stress, the variation between rest and
stress WMSI (WMSI), test positivity, dipyridamole
time (ie, the time from the beginning of infusion to the development of
regional dyssynergy at echocardiography), ECG
modification during dipyridamole infusion, and angina
during dipyridamole infusion.
Continuous variables were compared by the unpaired 2-sample
t test. Proportions were compared by the
2 statistic; a Fisher’s exact test was used
when appropriate. A value of P<0.05 was considered
statistically significant
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Results |
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Type of Surgery
Two hundred seventy (53%) patients underwent abdominal aortic aneurysm repair, 125 (24%) aortoiliac and aortofemoral reconstruction, and 114 (22%) carotid artery thromboendarterectomy.
Patient Characteristics
The study included 509 patients (450 men, 59 women, mean age
66±10 years), with a history of previous myocardial infarction in 103
(20%), angina pectoris in 63 (12.3%), diabetes mellitus in 54 (11%),
hypertension in 249 (52%), and 51 (10%) with a history of previous
coronary artery bypass surgery or percutaneous
transluminal coronary angioplasty. Two hundred four (40%)
patients reported either past or current smoking habit. According to
the guidelines for preoperative risk assessment, the patient population
comprised 394 (77.4%) with a high risk and 115 (22.6%) with an
intermediate risk of developing perioperative cardiac
events (Table 1
). Nineteen percent
of the patients were receiving antianginal therapy during the test
(nitrates and/or calcium-channel blockers and/or ß-blockers).
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Resting Echocardiographic Findings
Resting WMSI was 1.11±0.25. Regional wall motion abnormalities
were present in the baseline examination in 131 (26%) patients.
Mean ejection fraction was 56±10%.
Stress Echocardiographic Findings
By inclusion criterion, technically adequate images were obtained
in all patients. No major complications occurred during the test. In 4
patients, only the low dipyridamole dose (0.56 mg/kg
over 4 minutes) was given for limiting side effects. The feasibility of
the test was 99%. The dipyridamole
echocardiography test was positive in 88 (17.3%),
and negative in 421 (82.7%). WMSI at peak dipyridamole
was 1.5±0.37 in positive versus 1.10±0.26 in negative tests,
(P<0.0001).
Follow-Up Data
Perioperative cardiac events occurred in 31 (5%)
patients: 6 deaths, 11 myocardial infarctions, and 14 episodes of
unstable angina.
Twenty-five (81%) of the 31 who had cardiac events had a positive dipyridamole stress echocardiography test. Sensitivity and specificity of the test for predicting spontaneous cardiac events were 81% and 87%, respectively. The positive predictive value of the test was 28%, with a negative predictive value of 99%.
Cardiac-Related Death
When cardiac-related death was considered, all the 6 deaths
occurred in patients with a positive test (Table 2). By univariate
analysis, dipyridamole time
(2 11.1, P<0.0008), WMSI at peak
stress (2 12.7, P<0.0003), and
peak WMSI (2 18.8, P<0.0000)
reached the highest value. By stepwise analysis, only WMSI
(hazard ratio [HR] 973.5, 95% CI 43.3 to 21.874,
P<0.0000) was an independent predictor of cardiac death
(Table 3). When variables were
entered into the model according to an interactive clinically realistic
approach, clinical variables and perioperative risk
were not able to predict the adverse outcome; when considering stress
echocardiography parameters, the model
was able to predict cardiac death through the WMSI (global
2 33.504, df 4,
P<0.0001).
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Hard Cardiac Events
When only hard cardiac events (cardiac death and nonfatal
myocardial infarction), were considered, there were 6 cardiac-related
deaths and 9 nonfatal myocardial infarctions in patients with positive
test results versus no cardiac death and 2 nonfatal myocardial
infarctions in those with negative test results (17% vs 0.5%,
P<0.000). By univariate analysis,
angina during dipyridamole test
(2 11.0, P<0.0009), ST-segment
depression during dipyridamole test
(2 16.0, P<0.0001), WMSI at peak
stress (2 12.9, P<0.0003),
dipyridamole time (2 22.3,
P<0.0000), test positivity (2
24.3, P<0.0001), and WMSI (variation between rest and
stress WMSI) (2 33.3, P<0.0000)
were the best predictors of adverse outcome. By stepwise
analysis, only test positivity (HR 38.8, 95% CI 8.56 to 175.8,
P<0.001) was an independent predictor of hard cardiac
events.
Spontaneous Events
Patients with positive test results had a higher incidence of
spontaneous events than those with negative results (28% vs 1.4,
P<0.05; 6 cardiac-related deaths, 9 nonfatal myocardial
infarctions, 10 episodes of unstable angina in patients with positive
results vs no cardiac-related death, 2 myocardial infarctions, 4
episodes of unstable angina). By univariate
analysis, angina during dipyridamole test
(2 17.4, P<0.0000), ST-segment
deviation during dipyridamole test
(2 30.2, P<0.0000), WMSI at peak
stress (2 30.3, P<0.0000),
dipyridamole time (2 37.8,
P<0.0000), test positivity (2
48.7, P<0.0000), and peak WMSI
(2 53.3, P<0.0000) were the best
predictors of spontaneous events. By stepwise analysis,
ST-segment deviation during dipyridamole test (HR 2.64,
95% CI 1.0 to 6.9, P<0.0479), test positivity (HR 5.46,
95% CI 1.25 to 23.8, P<0.0237), and peak WMSI (HR 38.1,
95% CI 2.0 to 726.9, P<0.0154) were independent predictors
of adverse outcome. With an interactive procedure, we analyzed
the predicitivity of the model considering the variables in
clinical order: historic parameters first, preoperative
risk assessed on clinical grounds, and stress
echocardiographic parameters (Figure 1); still stress
echocardiographic parameters added
significant prediction to the model compared with historic and clinical
variables.
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Discussion |
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The current study confirms in a larger patient population the results of a previous report24 on the risk stratification power of dipyridamole stress echocardiography in patients undergoing noncardiac vascular surgery. In this analysis, test positivity identified as the variation between rest and stress WMSI (peak
WMSI) was the
best predictor of perioperative in-hospital cardiac
death. Stress echocardiographic results outperform the
clinical variables routinely used to estimate the risk in this set
of patients. Moreover, the current study demonstrates that the
dipyridamole echocardiography test
is safe and well tolerated in a population of consecutive patients
enrolled on a multicenter basis who are undergoing major vascular
surgery, providing an effective preoperative screening for the risk
stratification mainly as a result of the extremely high negative
predictive value.
Comparison With Previous Studies
These results are consistent with previous reports that
used pharmacological stress echocardiographic imaging
techniques to predict perioperative ischemic
events in patients undergoing noncardiac vascular surgery. The
experience of several groups with either
dobutamine18 19 20 21 22 or
dipyridamole indicates,23 24 25 26 in univocal
terms, that these tests have a very high negative predictive value
(between 90% and 100%): A negative test is associated with a very low
incidence of cardiac events and allows a safe surgical procedure. Much
lower is the positive predictive value (between 25% and 45%). In the
series by Poldermans et al,21 the presence of a new wall
motion abnormality was a powerful determinant of an increased risk for
perioperative events after multivariate
adjustment for different clinical and echocardiographic
variables. The same group31 reported that
dobutamine stress echocardiography is
the most powerful predictor of late cardiac events after major vascular
surgery and is superior to simple clinical risk assessment. In fact,
multivariate analysis indicated that the extent
of ischemia was an independent predictor of late cardiac
events.31 The lower positive predictive value of the test
in the current study compared with the study by Poldermans et al is
probably caused by the fact that referring physicians were not blinded
to stress echocardiographic results in our study. This
situation was the only feasible one in our setting because of ethical
and practical reasons. In this way, patients with "high-risk"
dipyridamole stress
echocardiography response are excluded because they
are either referred to revascularization or
vascular surgery is postponed. This ultimately deflates the predictive
value of a positive test. Myocardial perfusion imaging with
dipyridamole has been used widely for the preoperative
evaluation of patients before vascular surgery. The positive predictive
value of thallium redistribution ranged from 4% to 20% in reports
that included >100 patients.9 10 12 13 14 15 16 17 The negative
predictive value of a normal scan remains high, at 99% for myocardial
infarction and/or cardiac death. Recently Baron et al16
raised the need for caution in routine screening with
dipyridamole thallium stress testing of all patients
before vascular surgery. In this review of 457 patients undergoing
elective abdominal aortic surgery, the presence of definite
coronary artery disease and age >65 years were better
predictors of cardiac complications than perfusion imaging. In a recent
meta-analysis of 15 studies32 comparing
intravenous dipyridamole–thallium-201
imaging and dobutamine echocardiography
for risk stratification before vascular surgery, it has been
demonstrated that the prognostic value of noninvasive stress imaging
abnormalities for perioperative ischemic events
is comparable between available techniques but that the accuracy varies
with coronary artery disease (CAD) prevalence. The results
obtained with dipyridamole stress
echocardiography were added to the previous
meta-analysis: The current study shows comparable results but a
narrower confidence interval because of the large patient population
analyzed (Figure 2).
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Clinical Implications
Risk stratification in noncardiac vascular surgery recently has
become a major clinical issue in clinical practice. Several large
studies have demonstrated that perioperative cardiac
morbidity is particularly high in patients who undergo vascular
surgery, especially when they are 70 years old, with an incidence of
angiographically significant CAD as high as 75%.33
Patients who require vascular surgery appear to have an increased risk
for cardiac complications as the result of different factors: First,
many of the risk factors contributing to peripheral
vascular disease are also risk factors for coronary artery
disease; second, the usual presentation for CAD may be
obscured by exercise limitations imposed by advanced age, intermittent
claudication, or both; third, major arterial operations may
be associated with substantial fluctuations in intravascular fluid
volumes, cardiac filling pressures, systemic blood pressure, or heart
rate. The need of risk stratification for the preoperative assessment
of CAD in peripheral vascular patients is well established,
and guidelines from the AHA/ACC Committee have been drawn to focus this
clinical problem.30 The diagnostic-prognostic
algorithm takes into consideration patients at high, intermediate, and
minor cardiovascular risk who should undergo any type
of vascular surgery considered as a high-risk procedure. In the current
conceptual and practical framework, the evidence of inducible
ischemia during noninvasive stress imaging is a crucial
determinant of future risk, whereas clinical variables do not
provide an adequate power of stratification. Pharmacological stress
echocardiography might play a central role in the
workup of the vascular patient, mainly through the information on the
extent and severity of inducible ischemia. Moreover,
pharmacological stress echocardiography is a
low-cost, widely available technique, highly suited for routine
clinical risk stratification. On the basis of the current data, a
negative stress echocardiography test is associated
with a very low incidence of cardiac events and allows a safe surgical
procedure. In the presence of a positive stress
echocardiography test, the approach should be
weighed from case to case and on the basis of the stress
echocardiography response, which should not be read
as a "yes or no" gate-keeper to vascular surgery. In fact, a stress
echocardiography response has different shades of
severity, taking into consideration the time of appearance of the wall
motion abnormalities (the shorter the time the higher the probability
of an extensive CAD), the extent of wall motion abnormalities (a high
number of the segments is related to an extensive disease), and the
severity of the inducible dyssynergy. Therefore, on the basis of these
parameters, it is possible to grade the response and
consequently the therapeutic approach to the patient, which is
different from case to case because patients with a high-risk stress
echocardiography result should (and this was our
approach for ethical reasons) undergo coronary angiography and
postpone cardiac surgery; on the other end, a low-risk stress
echocardiography positivity (small extent of the
inducible ischemia and/or high dose threshold) is not
sufficient to cancel the surgical procedure but should indicate a more
aggressive medical approach. Nonetheless, not all patients should
undergo risk stratification. The decision to recommend further testing
for the individual patient must take into consideration the estimated
probabilities of effectiveness versus risk. It is possible that in the
stratification process, the risks from the tests and treatments may
offset the potential benefit of evaluation. To date, in the absence of
prospective randomized trials, it appears reasonable to perform
coronary revascularization before
peripheral vascular surgery in the presence of a markedly
positive result of stress echocardiography and to
adopt a more conservative approach-with a watchful cardiological
surveillance coupled with through pharmacological protection-in
patients with less severe ischemic responses during
stress.34
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