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Stents are used in more than 500,000 U.S. heart procedures a year to help prop open clogged coronary arteries that cause severe chest pain and can lead to lifethreatening heart attacks. The new experimental device works by trapping the debris from tiny blood clots and the bits of plaque that get shaved off the vessel wall when a stent or an angioplasty balloon is deployed during an artery-opening procedure. The device removes the arterial gunk before it can flow downstream, when it can obstruct vessels and cause serious health problems.

Today, researchers will report results of the first large-scale clinical trial of such a device, announcing that it reduced by half the number of heart attacks suffered by a group of patients who were particularly prone to complications caused by downstream debris. Some scientists are convinced that the device will become widely used whenever doctors seek to clear obstructed arteries, not only in the heart but also in the brain, kidney and other sites.

"The study sets the stage for routine use of some sort of protection device" in a variety of blood-vessel interventions, says Donald S. Baim, a professor at Harvard Medical School and a cardiologist at Brigham and Women's Hospital, both in Boston. He is the principal investigator for the study, which he is presenting today in Washington at a cardiology meeting known as Transcatheter Cardiovascular Therapeutics.

The new report comes amid a flurry of recent research that is challenging some strongly held assumptions about the risks and benefits of treatments doctors use for patients with advanced heart disease, the Western world's leading killer. Another significant study will be presented today at the same meeting, which is sponsored by the nonprofit Cardiovascular Research Foundation, New York. It strongly suggests that coronary stents, generally used during elective procedures when patients are stable, may also be effective in treating patients who arrive at emergency rooms with heart attacks. This study, which is at odds with earlier research, could expand the market for the devices to a new category of patients.

The report on the clot-capturing device reflects a relatively recent concern among doctors about the potential downstream consequences of stents and balloons. If it leads to wide use of such tools, it would add to an ever-growing array of gadgets and drugs that cardiologists are employing to try to fend off the ravages of heart disease. "It's not that one technology has been replacing another one," says Dr. Baim. The gadgets "give us progressive leverage" against the problems of treating heart disease and "are improving the durability of the outcome for patients."

For years, doctors assumed that if stents or balloons dislodged anything, the materials left the body without causing any harm. But autopsy results and other studies have shown that bits of blood clots and other gunk sometimes get stuck in smaller, downstream heart vessels, plugging them up and choking off the blood supply to lower regions of the heart muscle, thereby causing a heart attack.

Early experiments with two types of devices to trap and remove the material have only heightened concern about the problem. "People are staggered by the amount of stuff that comes out," says David Holmes, a cardiologist at the Mayo Clinic in Rochester, Minn.

Sensing a significant market, more than 20 companies, including Johnson & Johnson and Kensey Nash Corp., are scrambling to develop the products. The most common approach, researchers say, is a tiny filter device that is threaded into the coronary artery past the point of obstruction and opened before doctors deploy the balloons and stents to do their work. The filter acts like a fish net to capture most of any debris and is withdrawn with its contents after the procedure is completed.

But a small, closely held Sunnyvale, Calif., company called PercuSurge Inc. is closest to market with a different idea. Its device is a tiny balloon that is inflated downstream from the procedure to completely block the flow of blood into the heart's smaller vessels. Then, after the stent has been deployed, the trapped blood and any debris are sucked out before the balloon is deflated.

It was the PercuSurge device that Dr. Baim tested in a group of 550 patients who were particluarly good candidates for the kind of protection it was intended to provide. All had previously undergone bypass surgery in which veins harvested from the leg were used to reroute blood around at least one of their obstructed coronary arteries.

Such vein grafts aren't designed to withstand the constant pressure of a beating heart, and on average 50% of them fail within 10 years by getting clogged. Indeed, in earlier studies of such patients treated with stents or balloons, about 17% suffered heart attacks as a result, and they were often either fatal or caused massive damage to the heart muscle.

In the study, which included patients at 40 sites in the U.S. and Canada, the PercuSurge device didn't only successfully remove fatty deposits trapped by the balloon. It also cut the heart-attack rate in half. Indeed, the device was so effective that the study, which had called for the enrollment of 800 patients, was halted early by an independent monitoring board. The company says it plans to submit the results to the Food and Drug Administration soon in a bid for approval to market the device.

"Once you've established that material has been released-and that you can remove it and lower the incidence of complications-that becomes a very compelling case to use it in all vein grafts," Dr. Baim says. Since patients with clogged vein grafts make up about 100,000 of the 700,000 U.S. stent and angioplasty patients each year, they are a sizable market all by themselves. But Dr. Baim and other researchers believe that, assuming the devices win marketing approval, the concept of protecting against procedure-related downstream debris will quickly spread to other patients.