(Circulation. 1995;91:1044-1051.)
© 1995 American Heart Association, Inc.
Articles |
Sex Differences in Perioperative and Long-term Cardiac Event–Free Survival in Vascular Surgery Patients
An Analysis of Clinical and Scintigraphic Variables
Presented at the Annual Scientific Sessions of the American College of Cardiology, Anaheim, Calif, March 1993, and the Society of Nuclear Medicine, Toronto, Ontario, Canada, June 1993.
From the Division of Cardiology, Department of Medicine, Northwestern University Medical School, Chicago, Ill (R.C.H.); the Cardiac Unit, Massachusetts General Hospital, Boston (M.H.C., G.J.L'I., J.B.N., S.D.P., K.A.E.); and the Department of Nuclear Medicine, University of Massachusetts Medical Center, Worcester, Mass (J.A.L.).
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Abstract |
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Background Little information is available regarding the occurrence of perioperative and late cardiac events in women with vascular disease. The current study was performed to examine whether sex-specific differences exist in these outcomes in a large population of vascular surgery patients and to determine the value of clinical and dipyridamole thallium variables in predicting myocardial infarction and cardiac death.
Methods and Results Preoperative dipyridamole thallium imaging was performed in 567 vascular surgery patients, including 380 men and 187 women. The incidence of nonfatal myocardial infarction and cardiac death was noted during the perioperative period and during a follow-up period of 50±5 months. Fixed and reversible thallium perfusion abnormalities were more common in men than in women (P<.001 and P=.004, respectively). Perioperative cardiac event rates were similar in men and women, 8.4% and 7.5%, respectively (P=.07). A transient thallium defect was associated with an increased risk of cardiac events by 3.9-fold in men (CI, 1.5 to 10.2) and 5.5-fold in women (CI, 1.4 to 22). Various clinical factors also were predictive of events but demonstrated substantial sex differences. For example, dipyridamole-induced ST-segment depression was strongly associated with perioperative events in men but not in women. There were 22 nonfatal myocardial infarctions and 29 cardiac deaths in men during the follow-up period, with comparable event rates noted for women. Cardiac event–free survival rates also were similar for men and women (P=.40). Multivariate analysis demonstrated that a history of heart failure was an important prognostic variable for both sexes, as was a fixed thallium defect. Significant sex differences in the predictive value of other clinical factors for late cardiac events was apparent.
Conclusions The present study demonstrates that (1) thallium perfusion defects are more common in men; (2) transient thallium defects are associated with perioperative myocardial infarction and cardiac death in both sexes; (3) long-term survival rates after vascular surgery are similar between men and women; (4) a fixed perfusion defect is predictive of late cardiac events in women, with a trend noted in men; and (5) sex-specific differences were noted with regard to the prognostic value of various clinical risk factors. Therefore, dipyridamole thallium plays a significant role in the assessment of perioperative and long-term prognosis for both male and female vascular surgery patients. On the basis of these observations, modifications in risk stratification based on sex may be appropriate for men and women with vascular disease.
Key Words: coronary disease • dipyridamole • surgery • prognosis • imaging
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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Ischemic heart disease is the most frequent cause of mortality in American women, accounting for more than 500 000 deaths each year.1 Additionally, the survival rates in women after myocardial infarction (MI)2 3 or coronary revascularization3 4 5 are reduced compared with those for men. Although the risks of coronary artery disease are well documented for women, little information is available regarding differences between the sexes for other atherosclerotic processes, such as vascular disease.3 During the past 10 years, no reports have been published regarding potential sex-related differences among vascular disease patients in either perioperative or long-term cardiac event–free survival rates.
Recent studies have demonstrated that many clinical trials exclude or substantially underrepresent women in population studies of coronary artery disease.6 7 8 Furthermore, despite the high prevalence of ischemic heart disease in postmenopausal women and their relatively worse outcome compared with men, there is evidence that diagnostic testing and therapeutic procedures are underutilized in women with suspected or documented coronary artery disease.4 9 10 11 12 This may stem in part from the belief that the diagnostic accuracy of such procedures as exercise testing13 14 15 16 and dipyridamole perfusion imaging17 is reduced in women. However, there is ample evidence to support the value of exercise stress testing in women for the diagnosis of coronary artery disease, especially in conjunction with thallium scintigraphy.14 18 19 20 21 22
Although thallium scintigraphy after dipyridamole infusion allows for the accurate detection of coronary stenoses,23 24 significant differences between the sexes have recently been shown to exist in the diagnostic value of this test.17 In addition to its diagnostic applications, dipyridamole thallium imaging also has been used successfully for perioperative risk stratification in patients undergoing vascular surgery.25 26 27 28 29 Furthermore, this modality has been shown to have long-term prognostic value for patients after MI,30 in vascular surgery survivors,28 and in a general unselected population.31
While previous analyses of the prognostic utility of dipyridamole thallium imaging compared outcomes of men versus women, only one study32 has specifically evaluated which factors are predictive of cardiac events for men or women. Other reports have analyzed clinical and test parameters for the entire population, without consideration for the sex of the patient. This "sexless" analysis of coronary artery disease patients is compounded by the small number of women included in most series, which makes it difficult to identify risk factors specific to women. Accordingly, we evaluated a large population of patients scheduled to undergo major vascular surgery to determine whether differences between sexes are present for the prediction of both perioperative and long-term postoperative cardiac mortality and morbidity. We hypothesized that MI and cardiac death may occur with equal frequency in men and women but that the clinical and scintigraphic factors predictive of these events would be different for each group.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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We analyzed 567 patients who underwent dipyridamole thallium scintigraphy before elective vascular surgery. The dipyridamole thallium studies were performed according to standard techniques at the Massachusetts General Hospital and University of Massachusetts Medical Center between 1984 and 1991, as previously reported.25 30 Briefly, dipyridamole (0.14 mg/kg per minute) was infused over 4 minutes. Between 2 and 7 minutes after the infusion, 2.0 to 3.0 mCi 201Tl was injected intravenously. Aminophylline was administered when severe ischemia or symptoms were present, usually at least 1 minute after administration of thallium. Blood pressure, heart rate, and ECG were continuously monitored. Planar imaging was performed in three views shortly after thallium injection and repeated 2.5 to 4 hours later. These scans were interpreted qualitatively by an experienced nuclear cardiologist who was unaware of the patient's clinical course. Reinjection or late imaging was not performed.
Perioperative data were obtained through careful medical record review. After hospital discharge, follow-up information was obtained by telephone contact with the patient or his or her family. If the data collection remained incomplete, the patient's physicians were contacted and hospital records and death certificates were reviewed.
Statistical analysis was performed with 
2
analysis for comparison of dipyridamole thallium results between
men and women. Clinical variables and scintigraphic results were
analyzed with respect to early and late cardiac events with
2 analysis and Fisher's exact test. Logistic
regression analysis (BMDP-LR;BMDP) was used to examine the value of
various clinical and scintigraphic variables for predicting a
perioperative cardiac event, which was defined as MI or death from a
cardiac cause (congestive heart failure, arrhythmia, or MI). For
multivariate analyses, variables that were predictive of outcome at a
value of P=.1 were selected for use in the models. The late
follow-up period consisted of late cardiac events, defined as those
events occurring 1 month or later after the operation or after hospital
discharge, which were examined by the Cox proportional hazards model.
Life-table analyses with the Kaplan-Meier method examined the
differences between men and women in long-term cardiac event–free
survival and were used to determine the effects of scintigraphic
abnormalities on outcome for each sex. Differences in survival curves
were compared by the Mantel-Cox statistic. A value of P<.05
was considered significant in all analyses.
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Results |
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TopAbstractIntroductionMethods Results Discussion References |
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Patient Population
The study cohort was composed of 567 patients, including 187 women and 380 men. Patient characteristics are displayed in Table 1
.
More than one third of the patients of each sex were
>70 years old, and the prevalence of diabetes and history of angina or
congestive heart failure were similar in the two groups. More prior MIs
and ECG Q waves were noted in men than in women, as was a slight
increase in the frequency of prior coronary artery bypass surgery.
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Dipyridamole Thallium
The results of dipyridamole thallium
imaging are displayed in
Table 2. Perfusion abnormalities, defined as any defect
or transient or fixed abnormality, were more common in men than in
women (P<.001). In contrast, the development of significant
ST-segment changes was equally dispersed between men and women.
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Perioperative Events
In the female cohort, 14 perioperative
cardiac events (event rate,
7.5%) occurred, including 10 cardiac deaths and 4 nonfatal MIs. Among
the men, 16 cardiac deaths and 16 nonfatal infarctions (4.2% for each
event) occurred. No differences were associated specifically with
either sex in these cardiac events (P=.70). The type of
surgery did not influence outcome, although there was a slightly higher
cardiac event rate in patients undergoing infrainguinal procedures.
The
clinical and scintigraphic variables associated with perioperative
events by univariate analyses are presented in Table 3. Among
both sexes, perfusion abnormalities were more
common in patients who sustained a cardiac event. Among several
clinical factors in men, a history of congestive heart failure, Q waves
on the ECG, and/or ST-segment changes after the dipyridamole infusion
were significant predictors of cardiac events. In contrast, only a
history of angina or diabetes correlated with such events in women.
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The
data depicted in Table 4 reveal that the presence of
transient dipyridamole thallium defects has good sensitivity (men,
81%; women, 79%) and acceptable specificity (men, 68%; women, 66%)
for both sexes regarding the occurrence of perioperative MI or cardiac
death.
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Multivariate analysis with use of stepwise logistic regression
analysis demonstrated that the presence of transient thallium
perfusion defects was correlated with an increase in relative risk of
sustaining a perioperative cardiac event by 3.9-fold in men (95% CI,
1.5 to 10.2) and 5.5-fold in women (95% CI, 1.4 to 22). As shown in
Table 5, transient defects were the only predictor
included in the multivariate model for both men and women. Several
other clinical variables were significantly associated with
perioperative cardiac events, but these were specific to one sex or the
other.
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Late Events
Complete data were available in 98% of the
patients after
vascular surgery, with an average follow-up period of 50±5 months. In
men, 22 (6.4%) nonfatal MIs and 29 (8.4%) cardiac deaths occurred,
for an overall event rate of 14.8%. Similar values were noted for
women, with nonfatal MI occurring in 6 patients (3.6%) and cardiac
death in 14 (8.3%), for a total event rate of 11.8%. Cardiac
event–free survival rates were similar between men and women
(P=.40), as displayed in Fig 1.
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Variables associated with late cardiac events by univariate
analysis are depicted in Table 6. Only the history
of angina or congestive heart failure was associated with cardiac
events in women. For men, several clinical variables and fixed thallium
defects were associated with late cardiac events. Besides the high
negative predictive value of scintigraphic abnormalities for a late
event, only fair sensitivity and specificity were noted (Table
4
).
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As shown in Table 5, the Cox
proportional hazards model demonstrated
the importance of a history of congestive heart failure in women for
late MI or cardiac death, raising the relative risk of these events by
more than eightfold (95% CI, 2.9 to 25.3). In men, several other risk
factors besides a history of heart failure contributed to the
prediction of a late cardiac event, including a history of diabetes and
angina. A fixed thallium perfusion defect increased the risk of
subsequent cardiac events in women with a relative risk (RR) of 2.9,
with a similar trend noted in men (RR, 1.8).
Life-table analysis
indicates a reduction in long-term cardiac
event–free survival rates in both men and women with an abnormal
preoperative dipyridamole thallium scan (Fig 2; men,
P=.029; women, P=.008). When persistent
thallium
defects were specifically examined, event-free survival was decreased
for both men (P<.001, Fig 3) and women
(P=.038, Fig 4).
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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This report demonstrates that the perioperative and long-term cardiac event–free survival rates for women with vascular disease are roughly equivalent to those of men. Previous studies of patients with vascular disease have not examined the effect on outcome of differences related to the sex of the patient in this population.3 Despite the similarity of prognosis, however, the present study also demonstrates that there are significant differences between sexes regarding the various clinical and scintigraphic variables that are predictive of MI and cardiac death.
Differences Between Sexes in Diagnostic Testing
Sex-specific
differences in diagnostic accuracy have been
reported with a variety of noninvasive procedures. Exercise ECG has
demonstrated a reduced ability to detect coronary stenoses in women
compared with men, even when disease prevalence is taken into
account.13 14 15 16 However,
the accuracy may be substantially
improved for women when exercise testing is combined with thallium
imaging.14 18 19 20 21 33
In the most extensive examination to
date of exercise thallium scintigraphy in women, Chae et
al18 studied exercise thallium single-photon emission
computed tomographic imaging in 243 women and demonstrated that
high-risk angiographic coronary artery disease can be identified by
thallium scintigraphy. In this report, the perfusion data were more
useful for identifying significant coronary artery disease than the
available clinical and ECG information.18
In the only sex-specific comparison of dipyridamole thallium scintigraphy, Kong and colleagues17 demonstrated similar overall diagnostic accuracies for men and women. However, in the subgroup of patients with single-vessel disease, this technique had only 60% sensitivity in women compared with 94% sensitivity in men. Furthermore, although dipyridamole perfusion imaging was safe for both men and women, more adverse effects were reported in women, especially severe ischemia and dizziness. Information regarding the adverse effects of the dipyridamole infusion was not available for analysis in the present study.
Recently, Shaw et al32 examined a cohort of 840 patients (47% women) undergoing either exercise or dipyridamole thallium stress testing. In contrast to our data demonstrating more perfusion defects in men than in women, similar frequencies of perfusion abnormalities were noted, although the defects were often larger in men. Since this study is based on a population of patients referred for myocardial imaging for a variety of reasons, the differences noted in our results may reflect variations in coronary artery disease prevalence, severity, or distribution.
Sex-Specific Prognostication in Vascular Patients
While the
diagnostic value of exercise and dipyridamole
thallium scintigraphy in women has been well demonstrated, our report
is the first to show the value of dipyridamole thallium scintigraphy
for assessing short- and long-term prognoses in women with vascular
disease. The majority of prior prognostic studies were performed
predominantly in
men.25 26 27 28 29 30 31
We have demonstrated that
myocardial perfusion imaging provides important prognostic information
regardless of the sex of the patient; the presence of a myocardial
perfusion defect is associated with a worse outcome in both sexes.
Many previous studies have demonstrated that a reversible thallium defect after dipyridamole is associated with an increased likelihood of a perioperative event.25 26 27 28 29 Our data indicate that this is true regardless of the sex of the patient. A transient perfusion defect was associated with a risk of perioperative MI or death of 3.9-fold in men and 5.5-fold in women. A fixed perfusion defect was an important univariate predictor of perioperative cardiac events but, in multivariate analysis, failed to provide any independent value beyond that of the presence of a transient defect.
Fixed perfusion defects have been associated with a reduced long-term cardiac event–free survival rate,28 a finding also demonstrated by the present study. However, while a persistent thallium defect elevates the risk of a late cardiac event by almost threefold in women, the magnitude of this effect was less important than in men. The explanation of this finding is unclear and awaits further investigation.
Sex-Specific Differences in Clinical Risk Factors
The
relation of clinical risk factors to outcome also reveals
differences between men and women. In men, the presence of ECG Q waves
and a history of heart failure are independent predictors of both
perioperative and late events. In contrast, for women, Q waves were of
no prognostic value and a history of heart failure was associated only
with late events.
Perhaps the most striking sex-specific discordance is the relation between dipyridamole-induced ST-segment depression and prognosis. This finding was strongly associated with perioperative cardiac events in men but not in women. Previous studies of dipyridamole stress testing have shown that ST-segment depression occurs in 7.5% to 34% of patients,34 35 but the prognostic value of this finding was unclear. Several authors found no correlation between dipyridamole-induced ST-segment depression and cardiac events.24 25 30 However, one report demonstrated the high specificity of this finding for the presence of coronary artery disease despite limited sensitivity.36 As with exercise testing,13 15 33 our study suggests that stress-induced ST-segment changes have a lower predictive value in women than in men.
As previously shown,26 27 the combination of clinical assessment and dipyridamole thallium stress testing is an effective method by which to stratify perioperative and long-term cardiac risks. The method appears to be useful for both men and women. Within this context, however, several points of emphasis regarding clinical markers and stress test results are relevant. First, in women, prior angina is predictive of perioperative events, whereas a history of heart failure is predictive of long-term events. For men, perioperative risk is more related to Q waves on the ECG and previous heart failure, whereas diabetes, angina, heart failure, and Q waves are predictive of late events. Diabetes did not confer an increased risk in women. Dipyridamole-induced ST-segment depression is quite useful for identifying elevated perioperative risk in men but not in women. For both sexes, transient thallium defects are predictive of perioperative events, whereas fixed defects are predictive of late events, as previously shown.28
Limitations
The present report contains several limitations.
First, data
were collected retrospectively. However, precise follow-up data were
obtained in the majority of patients. Second, the patient cohort was
somewhat biased, since patients were excluded if emergency surgery was
performed or if myocardial revascularization was performed before
vascular surgery. Additionally, the scintigraphic data were provided to
physicians, which may have affected patient management. Furthermore,
dipyridamole thallium imaging was somewhat limited in that neither
quantitative nor tomographic data were available for interpretation.
Finally, although this report presents the results of a large
patient population, these data have not been validated elsewhere and
should therefore be regarded as preliminary.
Conclusions
In conclusion, the outcomes of men and women
undergoing
vascular surgery are similar and may be predicted by clinical
evaluation and dipyridamole thallium scintigraphy. It is readily
apparent that dipyridamole thallium imaging plays a significant role in
the assessment of cardiac risk for both male and female vascular
disease patients. However, differences exist in the specific clinical
factors predictive of MI or death in men and women. These sex-specific
clinical variables have important prognostic value with regard to the
perioperative cardiac event rate and long-term morbidity and mortality.
Our data suggest that modifications in risk stratification based on the
sex of the patient may be appropriate for both men and women with
vascular disease.
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Acknowledgments |
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The authors wish to thank Bernard Villegas, MD, and Steven Whitfield, MD, for their assistance with the data collection. Additionally, we are most appreciative for the thoughtful comments provided by Robert O. Bonow, MD.
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Footnotes |
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Reprint requests to Robert C. Hendel, MD, Northwestern University Medical School, 250 E Superior St, Suite 726, Chicago, IL 60611.
Received July 8, 1994; revision received September 19, 1994; accepted September 28, 1994.
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