Oral anticoagulants vs. antiplatelet therapy

Background: Nonvalvular atrial fibrillation carries an increased risk of stroke mediated by embolism of stasis-precipitated thrombi originating in the left atrial appendage. Oral anticoagulants and antiplatelet agents have proven effective for stroke prevention in most patients at a high risk for vascular events, but primary stroke prevention in patients with nonvalvular atrial fibrillation potentially merits separate consideration because of the suspected cardioembolic mechanism of most strokes in patients with atrial fibrillation. Objective: To characterize the relative effect of long-term oral anticoagulant treatment compared with antiplatelet therapy on major vascular events in patients with nonvalvular atrial fibrillation and no history of stroke or transient ischemic attack (TIA). Search strategy: The authors searched the Cochrane Stroke Group Trials Register (June 2006). They also searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2006), Medline (1966 to June 2006) and Embase (1980 to June 2006). The Atrial Fibrillation Collaboration and experts working in the field were contacted to identify unpublished and ongoing trials. Selection criteria: All non-confounded, randomized trials in which long-term (more than four weeks) adjusted-dose oral anticoagulant treatment was compared with antiplatelet therapy in patients with chronic nonvalvular atrial fibrillation. Data collection and analysis: Two reviewers independently selected trials for inclusion, assessed quality, and extracted data. The Feto method was used for combining odds ratios after assessing for heterogeneity. Main results: Eight randomized trials, including 9,598 patients, tested adjusted-dose warfarin versus aspirin (in dosages ranging from 75 to 325 mg per day) in patients with atrial fibrillation without prior stroke or TIA. The mean overall follow-up was 1.9 years per participant. Oral anticoagulants were associated with a lower risk of all stroke (odds ratio [OR] = 0.68; 95% confidence interval [CI], 0.54 to 0.85), ischemic stroke (OR 0.53; 95% CI, 0.41 to 0.68) and systemic emboli (OR = 0.48; 95% CI, 0.25 to 0.90). All disabling or fatal strokes (OR = 0.71; 95% CI, 0.59 to 1.04) and myocardial infarction (OR = 0.69; 95% CI, 0.47 to 1.01) were substantially, but not significantly, reduced by oral anticoagulants. Vascular death (OR = 0.93; 95% CI, 0.75 to 1.15) and all-cause mortality (OR = 0.99; 95% CI, 0.83 to 1.18) were similar with these treatments. Intracranial hemorrhages (OR = 1.98; 95% CI, 1.20 to 3.28) were increased by oral anticoagulant therapy.