November 13, 2000

BIRMINGHAM, AL — Surprise findings by researchers at the University of Alabama at Birmingham (UAB) indicate that white stroke patients may have a higher incidence of atherosclerotic plaques than black stroke patients.

The study is being presented Tuesday, November 14, at the American Heart Association's 73rd Annual Scientific Sessions in New Orleans.

Researcher Navin Nanda, M.D., director of UAB's Heart Station and Echocardiography Laboratories, said the data was so surprising because other research has shown that blacks are more likely than whites to have high blood pressure, one of the key risk factors for coronary atherosclerosis. "This study is clearly pointing out the opposite of what's being said in the literature," he said. According to the American Heart Association, blacks' risk of stroke is twice that of whites.

Atherosclerosis is caused when cholesterol combines with other substances in the bloodstream to form plaque, which thickens inside the arterial walls, narrowing the inner channel of the artery and impeding blood flow. Plaque can rupture, leading to blood clots that can block the vessel entirely. When plaque clogs arteries leading to the brain, particularly the upper areas of the aorta, part of the brain dies — causing ischemic stroke.

Nanda and colleagues examined 1,692 patients, 57.7 percent of whom were whites and 42.3 percent of whom were blacks. The stroke patients received transesophageal echocardiograms so that doctors could look for holes or loose clots in the heart which may have caused the stroke. The echocardiograms allowed researchers to get a detailed image of the loops and corridors along the aorta, which stems from the top of the heart and then arches down toward the legs, carrying oxygenated blood to the entire body.

Researchers classified the plaques as simple or complex and studied their frequency in relation to three sections of the aorta. "We found that whites had significantly higher frequency of plaques when compared to blacks in the ascending aorta, the aortic arch and in the descending aorta," Nanda said. "We also found significantly higher numbers of complex plaques in whites as compared to blacks in the aortic arch, but not in the other segments of the aorta."

Nanda added that typically the more complex a plaque, the more likely it is to rupture and become mobile. He also added that a mobile plaque in the arch of the aorta is more likely to lead to stroke because it is where arteries branch off and lead to the brain.

The next step is to check for risk factors to help determine the cause of the racial differences. "We're not sure why this is happening," he said. "We need to check for risk factors such as high blood pressure, smoking, diabetes, obesity and family history of heart disease to see if there are any relationships between the number of risk factors and the racial differences."

Strokes are the third leading cause of death in the United States, behind heart attacks and cancer.