March 29 (HealthDay News) -- Despite initial concerns that stent thrombosis, a blood clot inside a stent, is more common with the drug-eluting device, there appears to be no difference in the clot risk for either drug-eluting or bare metal stents, a large new study found.

After a heart attack, many patients undergo a treatment called angioplasty, which opens the blocked coronary artery that caused the attack. With many of these procedures, the stent, a metallic mesh tube that props open the narrowed artery, is also inserted and left in place.

"We had a thrombosis rate of 3.3 percent over a year, which sounds high, but these are patients with acute [heart attacks] getting a stent," lead researcher Dr. George Dangas, an associate professor of medicine at Columbia University Medical Center in New York City, said during a Sunday morning teleconference at the American College of Cardiology's annual scientific sessions in Orlando, Fla. "So it's not that high after all."

"With any type of bare metal stent or drug-eluting stent, there was no difference after one year," Dangas added.

Bare metal stents -- as the name implies -- are bare tubes of metal mesh. Drug-eluting stents, in addition to keeping the artery open, slowly release a medication to prevent the build-up of scar tissue inside the stent.

A stent thrombosis can block blood flow through the stent and cause another heart attack or even death. Concerns have been raised that stent thrombosis might be more common in drug-eluting stents than bare-metal ones.

Dangas and his colleagues looked at data on 3,202 patients who participated in the HORIZONS-AMI trial; these patients received either bare metal stents or drug-eluting stents.

During the year after treatment, 107 patients (3 percent) developed stent thrombosis. The rate of stent thrombosis was the same for those treated with bare metal and those with drug-eluting stents, the researchers found.

Also, there was no difference in the rate of patients developing stent thrombosis whether they were taking the blood thinner Angiomax (bivalirudin) or heparin plus glycoprotein IIb/IIIa inhibitors, which also help prevent clots from forming.

Although patients treated with Angiomax had a higher rate of acute stent thrombosis, both groups had equal rates of stent thrombosis after a month, the researchers reported.

Dangas's group also collected information on factors that could lead to stent thrombosis, such as smoking, insulin-treated diabetes, implanting several stents, treatment of ulcerated lesions and complete blockage of the artery responsible for the heart attack.

For these patients, high doses of the anti-clotting drug Plavix (clopidogrel) protected against stent thrombosis.

A related presentation Saturday at the cardiology conference found that patients with coated stents had fewer cases of serious complications. The study -- the largest one ever to evaluate "real-world" stent patients -- included 217,675 patients over age 65 with coated stents and 45,025 patients with bare-metal devices, the Wall Street Journal reported.

The study found that patients with coated stents were significantly less susceptible to non-fatal heart attacks or death. And there were slightly fewer cases of repeat procedures with coated stent patients, while stroke rates were about the same in both groups of patients, the newspaper said.

SOURCES: March 29, 2009, teleconference with George Dangas, M.D., Ph.D, associate professor of medicine, Columbia University Medical Center, New York City; March 29, 2009, presentation, American College of Cardiology's annual scientific sessions, Orlando, Fla.