"Our findings suggest the need for greater understanding of factors influencing coronary events in diverse populations," says Jeffrey Whittle, M.D., MPH, associate professor of medicine at the Medical College of Wisconsin in Milwaukee, and lead author of the study. "Overall, I believe that as we better understand the mechanism of disease, we'll see that different factors are important for different individuals." Dr. Whittle practices at the VA Medical Center in Milwaukee.
Five U.S. Department of Veterans Affairs Medical Centers participated in the study. The researchers compared the coronary anatomy between 311 African American and white veterans who had coronary angiography following a positive nuclear perfusion imaging study. This non-invasive stress test, when positive, suggests the possibility of blocked coronary arteries. One manifestation of coronary artery disease (CAD) is the complete or partial obstruction of the arteries that supply blood to the heart muscle (the coronary arteries).
Prior to an angiogram or x-ray examination of these coronary arteries, the patient's physician was asked to estimate the probability of coronary obstruction. On average the estimated likelihood of CAD in white and African American males was similar, 83 percent vs. 79.5 percent probability, respectively. However, when results of angiography were evaluated, white men had more severe obstructions.
"In short, although the doctors thought the African American and white men were equally likely to have obstructions, white men had a greater number of severe obstructions," Dr. Whittle says.
The results raise more questions than they answer, points out Dr. Whittle. "They're paradoxical. If African American men have less severe obstructions, why are they dying more frequently? Are nuclear imaging studies less accurate among African American patients? Were there clinical risk factors that we did not measure? Perhaps African Americans are less likely to have the kind of coronary obstructions that are suitable for revascularization."
"Heart attacks are not usually caused by the kind of severe obstructions that were measured in our study. Rather, heart attacks are caused when a clot forms suddenly, typically at the site of a less severe obstruction," says Dr. Whittle. He suggests that this may explain the apparent paradox. Different individuals may differ in their propensity for developing severe obstruction and also differ in their tendency to develop sudden clots.
Dr. Whittle cautions that although this study shows that whites, on average, were more likely to have severe obstructions, many African Americans also have important obstructions. "Differences between racial groups are much smaller than differences among individuals within those groups."
While research techniques and approaches increasingly emphasize studying diverse populations, Dr. Whittle and colleagues point out that much of modern clinical practice is guided by studies done primarily in white men. "Previous studies delivered conclusions that may not apply equally to everyone in the general public. And there are many differences between population groups which future research needs to take into account, including access to quality health care, differences in health habits, health status, and experiences with the health care system," Dr. Whittle says.
Dr. Whittle and his colleagues are planning future studies to better understand the differences they observed in the present study.
The principal investigator of the study that provided the data for this paper is Nancy R. Kressin, Ph.D., research career scientist at the Center for Health Quality, Outcomes and Economic Research, Edith Nourse Rogers Memorial Veterans Hospital in Bedford, Mass. Other co-authors also at the Center include Professor Mark Glickman, Ph.D., and Michelle Orner, MS; Professor Eric D. Peterson, M.D., MPH, a cardiologist at the Durham VA Medical Center and Duke University Medical Center; Associate Professor Laura A. Petersen, M.D., MPH, at the Houston VA; and Marco Mazzella, M.D., formerly a cardiology fellow at the University of Kansas.
The study was funded by the Department of Veterans Affairs Health Services Research & Development Service.