Preventing systemic embolization in patients with atrial fibrillation.

Patients with atrial fibrillation have an annual risk of stroke of 4.5%. Randomized clinical trials have reliably demonstrated that for every 1000 atrial fibrillation patients treated with warfarin, there is a reduction of 31 strokes per year at a cost of 3 major bleeds per year (including cerebral hemorrhage). Aspirin therapy is also effective for the reduction of stroke, although less so than warfarin; the bleeding risk is less with aspirin. It is possible to select patients at particularly high risk of cerebral embolism based upon simple clinical and echocardiographic parameters. Ongoing clinical trials are evaluating regimens of warfarin versus aspirin, combinations of warfarin and aspirin, and low-dose warfarin.