African-Americans may be at an increased risk for developing life-threatening blood clots after receiving drug-coated stents that are meant to keep their arteries open, new research shows.

The study is published in Circulation: Journal of the American Heart Association.
Stents are tiny mesh cylinders that keep arteries from renarrowing after angioplasty, a procedure that widens clogged heart arteries. Stents are either bare metal or drug-coated.

While drug-coated stents were developed to prevent arteries from renarrowing, they may also increase the risk of blood clots forming at the site of implantation -- often referred to as "stent thrombosis." To reduce this risk, people with drug-coated stents must take anticlotting drugs for one year.

In the study, researchers culled information on 7,236 patients who had drug-coated stents implanted between mid-2003 and the end of 2008. Of these study participants, 22% were African-American.
The analysis showed that African-Americans were nearly three times as likely to develop clots after receiving drug-coated stents than their non-African-American counterparts. This increased risk was evident at 30 days after the procedure and extended out for three years, the study showed.

The findings held even after the researchers controlled for other known risk factors for blood clots such as diabetes, hypertension, and kidney problems. African-Americans had increased rates of stent thrombosis even though they took anticlotting medication at a higher rate than people of other races.

"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," says study researcher Ron Waksman, MD, associate director of the division of cardiology at Washington Hospital Center and professor of medicine and cardiology at Georgetown University, in a news release. "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."

Role of Genetics
Exactly why African-Americans are at higher risk for developing blood clots with drug-coated stents is not fully understood. Possible genetic differences in the way their bodies react to the anticlotting medication clopidogrel (Plavix) may play a role, the researchers speculate. Clopidogrel carries a warning stating that it may not be effective in some people whose bodies have trouble converting clopidogrel to its active form.

"All in all, the study affirms that there are likely differences amongst patients in terms of risk profile and this is likely largely based on genetics," says Stephen Ellis, MD, section head of interventional cardiology at Cleveland Clinic in Ohio, in an email.
Robert Iaffaldano, MD, an interventional cardiologist with MetroSouth Medical Center in Blue Island, Ill., says that these drug-coated stents are better than bare-metal stents in most scenarios.

"They prevent scar tissue from forming over the stent, which is what results in [renarrowing]," he explains. "But when skin or scar tissue grows over the stent, the body knows the stent is no longer a foreign object," he says. "With the drug-eluting stents, the body's natural response is to isolate foreign object by surrounding it with clot."

"Drug-eluting stents prevent scars from forming, but the price that you pay is that your body sees the stent as foreign for a longer period of time, which is why anticlotting drugs must be taken for one year," he says. With bare metal stents, anticlotting drugs are only taken for one month.