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A Sticky Wicket for Heart Patients

Platelet differences indicate risk

MONDAY, July 9, 2001 (HealthDayNews) -- Researchers are talking about a new risk factor for heart problems and a new target for treatment: the stickiness of platelets, the blood elements that clump together to cause artery-clogging clots.

Platelets are disc-shaped particles that adhere to uneven or damaged surfaces in blood vessels. They are central to the blood-clotting process.

Stickiness of clot-forming platelets varies greatly from person to person, say two reports in the July 10 issue of Circulation: Journal of the American Heart Association, and persons with the stickiest platelets appear to be at higher risk of coronary trouble.

One report comes from the University of Vermont, where a study led by Dr. Samer S. Kabbani, an interventional cardiologist and soon to be assistant professor of medicine, looked at platelet stickiness in a group of hospital patients with problems requiring artery-opening treatment called angioplasty.

Using a technique of their own invention, the Vermont researchers measured reactivity, the tendency of platelets to stick together, for each patient, then looked at the incidence of problems during and after angioplasty.

"People who have highly reactive platelets are more likely to have complications during the procedure," says Kabbani. "When they go home, they are more likely to have symptoms, such as chest pain and heart attacks, and are more likely to come back to the hospital."

The research shows the same results six months after treatment, Kabbani says.

"We plan to follow these patients for at least one year, then for five years," Kabbani says. "Then we can do a larger study of people with a history of heart disease to see if those with highly reactive platelets are more likely to have heart attacks."

The finding does not yet have practical application in routine medical practice, he says. Major medical centers have the machine, called a flow cytometer, to measure platelet reactivity, but "we are the only ones using this specific assay," Kabbani says.

If platelet stickiness does turn out to be a reliable measure, "we could identify a certain group of patients who are more likely to have heart attacks or heart problems during their lives," he says. Platelet measurements also could identify patients who need more aggressive clot-dissolving therapy during treatment.

A second study, by Dr. Christopher J. O'Donnell and colleagues involved in the National Heart, Lung and Blood Institute's Framingham Heart Study, looked at an underlying genetic cause of platelet stickiness -- a gene designated PlA that is a blueprint for a receptor molecule on the surface of platelets. That receptor binds to a protein called fibrinogen that helps link platelets to form clots.

The Framingham researchers looked at two forms of the gene, PlA1 and PlA2, in 1,340 offspring of people in the study. Everyone carries two copies of the PlA gene, but laboratory studies showed more platelet clumping in people with at least one PlA2 gene compared with those with two PlA1 genes.

"The way fibrinogen affects platelet stickiness seems to be strongly influenced by this single genetic variation," says a statement by O'Donnell. "The findings could have important implications for treating people with the PlA2 form of the gene or those with higher fibrinogen levels."

Specifically, genetic tests could someday indicate patients who would benefit most from the "super aspirin" clot-busting drugs called glycoprotein Iib/IIIa inhibitors, the report says.

What To Do

It's too early in the research process for people to be tested for platelet stickiness, but it's never to early to follow the tried and true advice about reducing coronary risk: a sensible diet, not smoking, physical activity and controlling cholesterol.

The American Heart Association has a quick quiz to learn your risk for a heart attack or stroke. More advice on heart health comes from the National Heart, Lung and Blood Institute.

SOURCES: Interview with Samer S. Kabbani, M.D., interventional cardiologist, University of Vermont, Burlington; July 10, 2001 Circulation: Journal of the American Heart Association
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