Utilization of coronary angiography and revascularization after acute myocardial infarction in men and women risk stratified by the American College of Cardiology/American Heart Association guidelines

Methods

Data from all patients (n = 462) diagnosed with AMI at Cook County Hospital between 1994 and 1997 were prospectively collected and entered into a data base. The criteria used for the diagnosis of AMI were elevation of creatine kinase MB fraction in conjunction with a clinical presentation and/or electrocardiographic evidence consistent with a diagnosis of AMI. Twenty-three patients undergoing primary angioplasty (6 women and 17 men) were excluded from the present study, leaving a final study group of 439 patients. Data were initially abstracted from patient charts by trained nursing personnel and were audited for accuracy by two cardiologists who reviewed the medical records and coronary angiograms, when necessary.

Clinical data collected included age, gender, traditional coronary risk factors (e.g., hypertension, diabetes mellitus, hyperlipidemia, smoking, family history of early CAD), Q wave versus non–Q wave MI and complications. Patients were risk stratified according to the ACC/AHA guidelines published in 1990 (14). (Although new guidelines were issued in 1996 [15], the 1990 criteria were in force during most of this study period.) Patients were considered to have a stronger (class I or IIa) indication for coronary angiography if any of the following clinical features were present: hemodynamic instability or shock, recurrent ischemia, evidence of ischemia by noninvasive testing, mechanical complication (acute mitral regurgitation due to papillary muscle dysfunction or rupture, ventricular septal defect, pseudoaneurysm), congestive heart failure, left ventricular ejection fraction <40% or malignant arrhythmia. Patients were considered to have a weaker (class IIb) indication for angiography if they did not meet any of the criteria outlined earlier and if they had received thrombolytic therapy, had experienced a non–Q wave MI or were <45 years old. No patients were included in the present study in whom angiography was categorized as class III (not indicated) according to ACC/AHA criteria.

Angiographic data were obtained from the final procedure report (and from review of angiograms, when necessary) and included the presence and extent of CAD (defined as >50% diameter stenosis) and left ventricular ejection fraction. Performance of percutaneous transluminal coronary angioplasty and coronary artery bypass graft surgery was determined from chart review, catheterization laboratory records and cardiovascular surgery records.

Categoric variables were compared using the chi-square test or Fisher exact test. Continuous variables were compared using two-sided t tests. Multiple logistic regression analysis was performed using all variables with a univariate p value <0.10. A p value <0.05 was considered significant. This study was approved by the Scientific Committee at Cook County Hospital.

Results

The clinical characteristics of the patients are shown in Table 1. Women were significantly older than men, and more women were hypertensive or diabetic; a trend toward lower prevalence of smoking was noted in women. No significant differences between men and women were noted in the proportion of patients with Q wave or non–Q wave MIs, in the percentage of patients with anterior infarction or in frequency of thrombolytic use.

There was no significant difference between the proportions of men and women who were classified as having strong (class I/IIa) or weaker (class IIb) indications for coronary angiography according to ACC/AHA guidelines (Table 2), nor were the specific indications for angiography different. Overall angiography rates were nearly identical in men and women (Table 2).

Table 3summarizes the characteristics, angiographic findings and revascularization rates for patients with ACC/AHA class I/IIa indications for angiography. There were no significant differences in angiography rates between men and women, and there were no differences in the presence or extent of CAD between men and women who underwent angiography. Rates of coronary angioplasty, bypass surgery and overall revascularization were very similar in the men and women found to have significant CAD.

Table 4summarizes the characteristics, angiographic findings and revascularization rates for patients with ACC/AHA class IIb indications for angiography. The women in this category were significantly older than the men. There were no significant differences in angiography rates between men and women or in the presence or extent of CAD. Finally, there were no significant differences in the rates of coronary angioplasty, bypass surgery or overall revascularization between men and women found to have significant CAD. At the rates of coronary angiography found in this study, the power to detect important differences (>20%) in utilization between men and women was >80% for the overall group and for each ACC/AHA class.

After adjustment for baseline clinical characteristics, there were still no significant differences in catheterization rates between men and women, in the overall group (Table 5)or when the patients were risk stratified according to ACC/AHA criteria (Tables 6 and 7). ⇓⇓Although younger patients were less likely to undergo angiography, there was no significant interaction between age and gender; for example, angiography rates in men and women older or younger than age 65 years were not significantly different (p = 0.76).

The overall in-hospital mortality rate was 7.8%. There was no significant difference in mortality between men and women (9.1% vs. 5.7%, p = 0.27). The mortality rate in patients with a class I/IIa indication for angiography was 14.4%, as compared with 1.0% in patients with a class IIb indication (p < 0.0001). There were no significant differences in mortality rates between men and women in class I/IIa (16.5% vs. 11.2%, p = 0.36) or class IIb (1.5% vs. 0%, p = 0.72).

Discussion

A number of studies have found that women are less likely than men to undergo coronary angiography and revascularization procedures after AMI. Studies from a national data base of Medicare patients with AMI (1–3,5) and from the National Hospital Discharge Survey (4) found that women admitted to the hospital for AMI were significantly less likely than men to undergo catheterization, coronary angioplasty or bypass surgery.

Angiography has also been demonstrated to be utilized less often in women in other clinical settings as well. One study of nearly 400 patients with suspected CAD undergoing exercise nuclear testing at four different New York City hospitals found that women with abnormal nuclear stress results were only one-tenth as likely as men to be referred for angiography (8), and other studies have also found lower rates of procedures in women as compared with men (7). Large, state-wide studies of hospital discharges (6,16) have found that women were significantly less likely to undergo coronary angioplasty and bypass surgery. In patients without AMI, the gender disparity in angiography rates may be attributed to clinical differences. Women are more likely to present with atypical symptoms (12). Coronary artery disease is less prevalent even in women with typical angina (11), and abnormal stress tests (including abnormal imaging studies) are more likely to be false positives (12). Women develop CAD at a later age than do men and often have more coronary risk factors and comorbid conditions, and age has been shown to be independently associated with rates of procedure utilization (13). Finally, it is possible that women may prefer less invasive treatment strategies (17).

Other, usually more recent studies have found no differences in procedural rates between men and women. After controlling for clinical characteristics, Mark et al. (9) found no differences in referrals for angiography between men and women. Krumholz et al. (10) controlled for age and found no differences in angiography rates between men and women with AMI. Wong et al. (18) found that in-hospital angiography rates were similar for men and women.

In the Survival and Ventricular Enlargement (SAVE) trial, women had lower rates of coronary angiography before the index MI, despite reporting symptoms consistent with greater functional disability (19). However, after the index AMI, rates of angiography and revascularization procedures were similar for women and men (19). This has been termed the “Yentl” syndrome; once a woman has a documented infarct and behaves like a man, she may be treated like a man.