MARILYNN MARCHIONE AP Medical Writer ORLANDO, Fla. (AP) — Taking the blood thinner Plavix along with aspirin helped prevent strokes and heart attacks in people with a common heartbeat abnormality that puts them at high risk of these problems, doctors reported Tuesday. The treatment is for atrial fibrillation, a rhythm disorder that 2.2 million Americans have. It occurs when the upper parts of the heart quiver instead of beating properly. This allows blood to pool and form clots that can travel to the brain, causing a stroke. The usual treatment is the blood thinner warfarin, sold as Coumadin and in generic form. But finding the right dose is tricky — too little and patients can have a stroke; too much and they can have life-threatening bleeding. Patients on the drug must go to the doctor often for blood tests to monitor their dose. For these reasons, as many as half of patients take aspirin instead of warfarin, even though aspirin is much less effective at preventing strokes. Dr. Stuart Connolly of McMaster University in Hamilton, Ontario, led a study testing whether adding clopidogrel, sold as Plavix by French-based Sanofi-Aventis SA, could help. The study involved 7,554 patients in the United States and 32 other countries who were not able or chose not to take warfarin. All were treated with aspirin; half also were given Plavix. After nearly four years of followup, the dual drug treatment lowered a combined measure — heart attacks, heart-related deaths, strokes and blood clots — by 11 percent. There were 924 of these problems in patients on aspirin alone but only 832 in those also getting Plavix. However, the combination treatment raised the risk of serious bleeding — 251 cases versus 162 for those on aspirin alone. Doing the math, patients still come out ahead on the combination, Connolly said. For every 1,000 patients treated for three years, it would prevent 28 strokes and six heart attacks, and lead to 20 bleeding cases. Bleeding often is treated with transfusions and is not as likely to prove fatal. "For the first time in 20 years, there's a new treatment for atrial fibrillation," Connolly said. Results were presented Tuesday at an American College of Cardiology conference and published online by the New England Journal of Medicine. The study was sponsored by Sanofi, and Connolly and other authors have consulted for the company. Plavix costs about $4 a day. "Warfarin was, and remains, first-line therapy — this does not change that," said Dr. Richard Page, cardiology chief at the University of Washington School of Medicine in Seattle and an American Heart Association spokesman. But for those who can't tolerate it, the Plavix-aspirin combo gives a better option than aspirin alone, he said. Page has consulted for Sanofi in the past. On Saturday, other doctors at the cardiology conference reported on another potential treatment for atrial fibrillation — an experimental heart device called the Watchman aimed at preventing clots from reaching the brain. A federal Food and Drug Administration panel meets to consider it on April 23.