Preventing stroke in atrial fibrillation.

Atrial fibrillation, a common cardiac arrhythmia, is now recognized as a powerful risk factor for stroke. Previously, atrial fibrillation was thought to predispose persons to stroke only in the presence of rheumatic heart disease with mitral stenosis. The significant impact of nonvalvular atrial fibrillation on stroke incidence, recurrence and mortality was not fully appreciated. A series of clinical trials have confirmed that a five-fold increase in stroke incidence occurs in patients with atrial fibrillation, and that warfarin anticoagulation is efficacious in stroke prevention. This anticoagulation benefit was achieved with an acceptably low risk of serious hemorrhage.