CHICAGO -(Dow Jones)- Patients struck by rare but dangerous blood clots related to stent heart devices have a heightened chance of getting a second clot, and possibly more, a study released Saturday showed.

The placement of a second stent during emergency treatment for the first episode was a strong predictor of second clots, and should be avoided, investigators in the Dutch Stent Thrombosis Study concluded. The study was released during the Society for Cardiovascular Angiography and Intervention's annual conference, which started Saturday and is being held alongside the American College of Cardiology's annual meeting.

Heart stents are tiny metal devices that act as scaffolds for arteries, and drug-coated stents, which are more expensive and more commonly used in the U.S., use medication to combat renarrowing. Stent-related clots can develop on rare occasions after the devices are implanted, and also over a long period of time. Patients typically take anti-clotting medication to guard against the risk, and use the medication for a long time if they have a drug-coated stent.

Concerns emerged in 2006 that coated stents may also slightly elevate patients' risk for late-developing clots, or late stent thrombosis. Safety concerns may be abating amid recent studies indicating that coated stents don't heighten the risk for serious events such as death and heart attacks, but do help avoid repeated procedures to re-open arteries.

Boston Scientific Corp. (BSX), Johnson & Johnson (JNJ) and Medtronic Inc. ( MDT) have coated stents for sale in the U.S., and Abbott Laboratories Inc. (ABT) hopes for approval to enter the market soon. Abbott, like the other companies, is selling its coated stent overseas. It is also a top maker of bare-metal stents.

The Dutch study found that 74 of 437 patients studied, or about one in six, experienced multiple episodes of stent thrombosis. Sixty-one patients had two episodes, 12 had three episodes, and one patient had four episodes.

Among predictors of another event, researchers found that patients with an additional stent implanted were 4.2 times as likely as other patients to experience a repeat clotting episode. Patients with a prior heart attack were 2.6 times as likely to have another episode, and patients who had a clot long after the stent was implanted had 2.1 times the usual odds of another clot.

The Dutch study was led by Jochem Wouter van Werkum, a cardiologist at St. Antonius Hospital in the Netherlands. The study enrolled 437 consecutive patients who had stent thrombosis confirmed by angiography over a three-year period.

-By Jon Kamp, Dow Jones Newswires; 312-750-4129; jon.kamp@dowjones.com

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  03-29-08 1328ET
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