A Food and Drug Administration panel will meet on the issue Thursday and Friday. Medical journals are rushing studies into print, and powerful doctor groups are reconsidering treatment guidelines.

"It's such a huge public health issue with so many people involved," said Dr. Robert Califf of Duke University, who worked on one study to be presented to the FDA.

Doctors also worry about overreacting to a risk that appears small - five or fewer clots in every 1,000 patients.

"The benefit of having a drug-eluting stent is tremendous," said Dr. Elizabeth Nabel, director of the National Heart, Lung and Blood Institute.

Stents are used in angioplasty. Through a blood vessel in the groin, doctors push a tube to a blocked heart artery, inflate a balloon to flatten the clog, and prop the artery open with a stent.

About 652,000 Americans had angioplasty in 2003 - more than twice the 268,000 who had bypass operations, which are riskier, costlier and take far longer to heal. Angioplasty became more popular when the first drug-coated stent came out that year, virtually eliminating the procedure's main drawback: scar tissue requiring a repeat effort to reopen the vessel.

Two brands are sold in the United States ¡ª Taxus, by Boston Scientific Corp., and Cypher, by Johnson & Johnson's Cordis Corp. Labels say patients should take baby aspirin and Plavix for three months with Cypher and six months with Taxus, based on how long the stents release medication and how long doctors believed it took for the artery to repair itself by forming a new lining. Many doctors prescribe Plavix for up to a year.

Now it seems the coated stents may keep this essential artery lining from forming for a long time, maybe permanently. Without the lining or Plavix, clots can form and stick to stents.

It happened in May to David Reinhart, a 41-year-old legal secretary in Manhattan who collapsed two weeks after finishing the year of Plavix his doctor recommended.

"I feel a bit of a guinea pig," he said of the stent situation. "It's obvious there's a lot they really don't know about it yet."

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