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African Americans Nearly Three Times as Likely to Get Blood Clots with Stents

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August 30, 2010

A new study has found that African Americans are nearly three times as likely as non-African Americans to experience life-threatening blood clots after receiving a drug-coated stent, despite taking anti-clotting medications.

The study entitled Does Black Ethnicity Influence the Development of Stent Thrombosis in the Drug-Eluting Stent Era? was published online ahead of print in the August 31 issue of Circulation: Journal of the American Heart Association.

A stent is a tiny tube placed into an artery, blood vessel, or other duct to hold the structure open.

Researchers compared data for 7,236 patients, 22% or 1,594 African Americans and 5,642 non-African American patients, implanted with stents coated with clot-preventing drugs, also called drug-eluting stents, to treat narrowing arteries between 2003 and 2008. After taking other known risk factors such as diabetes, hypertension and kidney problems into consideration, researchers found that African Americans still experienced a higher rate of thrombosis or clotting.

Being of African American race was the biggest predictor of whether a patient would have a blood clot after implantation of a drug-coated stent.

“The bottom line is this is not just because this population is sicker or less compliant, but there is something else there that needs to be explored,” said Ron Waksman, M.D., the study’s lead author, in an American Heart Association press release.

African Americans’ clotting rates compared to non-African Americans were:

  • 1.71 percent vs. 0.59 percent after 30 days;
  • 2.25 percent vs. 0.79 percent at one year;
  • 2.78 percent vs. 1.09 percent at two years; and
  • 3.67 percent vs. 1.25 percent at three years.

These increased rates of clotting were present even though the African American patients too post surgery anti-clotting medications as prescribed at a higher rate than other races. African American also had a higher death rate after three years, 24.9% versus 13.1% for non-African Americans.

“Physicians and patients need to know that African-Americans are at a higher risk of developing stent thrombosis, which is associated with heart attack or death,” said Waksman, associate director of the Division of Cardiology at Washington Hospital Center and professor of medicine and cardiology at Georgetown University.

Waksman urged further study to reduce the blood clotting risks in African Americans, whose genetic differences influence the effectiveness of the anti-clotting medication Clopidogrel.

In March 2010, the U.S. Food and Drug Administration required that a black box warning, the agency’s highest alert, be added to clopidogrel (Plavix) warning of reduced effectiveness in people who cannot metabolize the drug to convert it to its active form. “Poor metabolizers” are people who have reduced functioning of their CYP2C19 liver enzyme and cannot effectively convert Plavix to its active form, who therefore do not receive the drug’s therapeutic benefits.

Some studies have found that this genetic anomaly occurs more frequently in African American people than white people. There are blood tests and genetic testing that can determine if a patient is a “poor metabolizer” of clopidogrel.