Established risk factors for coronary artery disease may not be as relevant for black populations as for white populations. The objectives of this study were to examine the distribution of risk factors in blacks and whites, as well as the relationship between race and the presence and extent of coronary artery disease (CAD) in the Coronary Artery Surgery Study (CASS) patient population.

The CASS registry includes individuals who underwent coronary angiography for CAD during the period from July 1974 through May 1979 in fourteen U.S. clinics and one Canadian clinic. Patients with previous bypass surgery and those other than blacks and whites were excluded. There were a total of 573 blacks and 22,781 whites.

There were several differences by race in the prevalence of risk factors. With regard to demographic variables, blacks were younger; more frequently female; more likely to be forced to quit work because of CAD; more likely to be employed as manual laborers; and less likely to be employed in professional positions than whites. With regard to the three major risk factors for CAD, higher percentages of black men were current smokers (almost 50% of black men versus 30.6% of white men were current smokers), but white men were heavier smokers. A similar racial pattern held for women. Higher percentages of blacks had elevated blood pressure (24.5% of black men and 20% of black women were hypertensive compared with about 16% of white men and 16% of white women), although the differences between blacks and whites were not statistically significant. Racial differences with respect to serum cholesterol were not statistically significant. With regard to other risk factors, several racial differences were noted. A lower percentage of blacks had an early family history of angina or myocardial infarction and had prior documented myocardial infarction compared with whites. However, a high percentage of blacks had a history of hypertension, and a higher percentage of black women had diabetes mellitus, higher relative body weight, and congestive heart failure at baseline. A higher percentage of blacks had abnormal left ventricles on chest roentgenograms. There were no significant differences in the level of recreational activity for blacks and whites.

The presence of chest pain was the major reason why blacks and whites were studied angiographically. Fewer blacks had probable or definite angina. Generally, blacks had less CAD than whites. Three-vessel disease was less prevalent in blacks among men, but was equally distributed across racial groups among women. Blacks had a lower prevalence of LMCA disease and a higher percentage had normal left ventricles (although the racial difference for more severely impaired left ventricles was not apparent). Finally, black men were more likely to have left-dominant coronary circulation than were white men.

Multivariate analyses were conducted only among persons whose data on risk factors were complete (approximately 50% of the total population). In these analyses, male sex, increased age, elevated cholesterol, current or former smoking history of diabetes, family history of CAD, non-labor occupation, sedentary recreational activity, lack of full or part time employment, and history of hypertension were associated with one or more diseased vessels. Additionally, being black was associated with absence of CAD. This race finding held even after controlling for the important risk factors for CAD such as age, sex elevated cholesterol and current or former smoking. A similar set of risk factors was associated with the presence of significant CAD and one or more disease coronary artery for both race groups.

Given the high levels of risk factors for blacks in the CASS data set, the authors had difficulty explaining why they had lower levels of CAD. They note that previous research has suggested that blacks have protective factors for CAD that might explain this finding. They additionally suggested that protective factors might include higher levels of HDL, higher work exercise levels, lower triglyceride levels, higher alcohol intake, lower prevalence of type A personality and a genetic disposition that protects blacks from coronary atherosclerosis. However, none of these factors were measured in this study.

The authors also note that it is possible that increased risk due to hypertension and cigarette smoking resulted in stroke or cancer-related deaths, which may have precluded blacks from being studied for coronary atherosclerosis. They conclude, however, that in the CASS sample, for whatever reasons, being black was associated with the absence of atherosclerotic disease.

The authors argue that further efforts must be made to reduce cigarette smoking and control hypertension in the black population. "It is apparent that the diagnosis and treatment of black patients with chest pain can be problematic in that many blacks have chest pain despite having normal coronary arteries. The finding of normal coronary arteries may lead to a false sense of reassurance to both doctor and patient. [A better] understanding of the etiology of chest pain in blacks is required. Studies of predominantly black populations for different regions of the country are [also] needed to clarify these findings from the CASS study."