"One might suspect that there would be more coronary obstructions in African American compared to white men, because of the greater number of deaths among African American men due to coronary artery disease," explained Nancy R. Kressin, PhD, research career scientist at the Center for Health Quality, Outcomes and Economic Research at the Edith Nourse Rogers Memorial Veterans Hospital in Bedford, Mass. and principal investigator of the study. "But it appears, in this study, to be quite the contrary. Based on our data from men who appeared to have similar health status, white men had a greater number of severe obstructions."
Dr. Kressin, who is also an associate professor in the Health Services Department at Boston University's School of Public Health in Boston presented the study today at an American Medical Association media briefing, Cardiovascular Disease, in New York City.
Five U.S. Department of Veterans Affairs Medical Centers participated in the study, which documented information from the medical charts of 311 veterans who had a positive nuclear perfusion imaging study, a noninvasive stress test that when positive, suggests the possibility of blocked 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," said Dr. Kressin. "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, it appeared that white men had more severe obstructions.
The results pose more questions than they answer, said Dr. Kressin. "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 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," said Jeffrey Whittle, MD, MPH, associate professor at the Medical College of Wisconsin in Milwaukee, Wisc., and lead author of the study. Dr. Whittle is also a physician on staff Clement J. Zablocki VA Medical Center. He suggested that these clots may be the cause of CAD deaths in African American men.
"Overall, I believe that as we better understand the mechanism of disease, we'll see that different factors are important for different individuals," said Dr. Whittle. He 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, both researchers 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," explained Dr. Kressin. "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."
Drs. Whittle and Kressin are planning future studies to better understand the differences they observed in the present study. They agree that "treatment approaches need to be different depending on the disease factors most important for each patient...The color of the patient's skin is unlikely to be the best way to determine those factors."
Editor's Note: Dr. Kressin has received grant support from the Department of Veterans Affairs, National Institutes for Health, National Institute for Dental and Craniofacial Research and the National Heart, Lung and Blood Institute. Dr. Kressin has received an honorarium from the American Medical Association to speak at today's conference.