Anticoagulation for atrial fibrillation and stroke prevention.

Nonvalvular atrial fibrillation (NVAF) has a prevalence of about 1% in the 60- to 70-year age group, increasing to above 4% in persons older than 80 years. The yearly stroke incidence in NVAF patients is 3-8%, which is 5-7 times higher than that in age-matched persons in sinus rhythm. In five independent studies of stroke prevention in NVAF patients, anticoagulation therapy resulted in a risk reduction of stroke of about 65%. The risk of intracerebral hemorrhage was 0.3% per year during warfarin therapy compared with 0.1% in the placebo group. In one study aspirin reduced the risk of thromboembolic events by 42% while another study found a nonsignificant effect of aspirin. The following variables were identified as risk factors for stroke in the individual studies: prior myocardial infarction, increasing age, mitral annular calcification, history of hypertension, congestive heart failure and previous arterial thromboembolism. A pooled analysis of risk factors in the placebo-treated patients of the five studies is ongoing.