Prevention of stroke in atrial fibrillation: an update.

Atrial fibrillation (AF) is associated with a substantially increased risk of ischemic stroke. Recently, five randomized clinical trials independently assessed the value of antithrombotic prophylaxis in AF patients. The rate of ischemic stroke in patients receiving a placebo averaged 5% per year. On aggregate, anticoagulation (INR 1.5 to 4.0) was shown to substantially (mean = 70%) reduce the risk of arterial thromboembolism. The effect of acetylsalicylic acid (ASA) studied in two trials was not uniform, but the efficacy of ASA was less than anticoagulation. ASA appeared to prevent nonembolic strokes better than embolic strokes in AF patients. The characterization of subgroups of AF patients who have relatively high or low absolute stroke rates determines which patients gain greater or lesser benefit from anticoagulant therapy. A multivariate analysis of a large cohort of placebo-treated patients yielded three independent clinical predictors of an increased risk of arterial thromboembolism: a history of hypertension, recent (within three months) congestive heart failure and prior transient ischemic attack (TIA) or stroke, and two echocardiographic predictors--left atrial size of greater than 4.6 cm and impaired left ventricular function. At present, anticoagulation with warfarin (INR 2 - 3) is recommended in AF patients with one or more of these risk factors. The European Atrial Fibrillation Trial studied only AF patients with prior stroke and TIA and confirmed the superiority of warfarin over ASA for secondary prevention.