Because the atria are not actively contracting during AF, blood may not swirl around as much when it passes through the heart, predisposing it to clotting.
Warfarin is the most commonly used medication to prevent clotting.
The study of 1,044 people with AF concluded that warfarin alone was a superior treatment option in patients at high risk for stroke, reducing its occurrence by about 75 percent. Researchers had hoped that the combination of aspirin and warfarin would help prevent both heart attack and stroke based on their effects on different aspects of clotting. People with the condition have about six times the risk of stroke compared with healthy people of the same age. Studies have shown that most people with atrial fibrillation benefit from warfarin or aspirin to prevent stroke. By using preventive therapies pioneered by the SPAF studies, over 40,000 strokes in the U.S. could be prevented each year.