Prevention of thromboembolism in atrial fibrillation - A meta-analysis of trials of anticoagulants and antiplatelet drugs

OBJECTIVE: Appropriate use of drugs to prevent thromboembolism in patients with atrial fibrillation (AF) involves comparing the patient's risk of stro ke and risk of hemorrhage, This review summarizes the evidence regarding th e efficacy of these medications. METHODS:We conducted a mete-analysis of randomized controlled trials of dru gs used to prevent thromboembolism in adults with nonpostoperative AF, Arti cles were identified through the Cochrane Collaboration's CENTRAL database and MEDLINE until May 1998. MAIN RESULTS: Eleven articles met criteria for inclusion in this review. Wa rfarin was more efficacious than placebo for primary stroke prevention (agg regate odds ratio [OR] of stroke = 0.30, 95% confidence interval [CI] 0.19, 0.48), with moderate: evidence of more major bleeding (OR 1.90; 95% CI 0.8 9, 4.04). Aspirin was Inconclusively more efficacious than placebo for stro ke prevention (OR 0.56, 95% CI 0.19, 1.65), with Inconclusive evidence rega rding more major bleeds (OR 0.81, 95% CI 0.37, 1.77). For primary preventio n, assuming a baseline risk of 45 strokes per 1,000 patient-years, warfarin could prevent 30 strokes at the expense of only 6 additional major bleeds. Aspirin could prevent 17 strokes, without increasing major hemorrhage. In direct comparison, there was evidence suggesting fewer strokes among patien ts on warfarin than among patients on aspirin (aggregate OR 0.64, 95% CI 0. 43, 0.96), with only suggestive evidence for more major hemorrhage (OR 1.60 , 95% CI 0.77,3.35). However, in younger patients, with a mean age of 65 ye ars, the absolute reduction in stroke rate with warfarin compared with aspi rin was low (5.5 per 1,000 person-years) compared with an older group (15 p er 1,000 person-years). CONCLUSION: In general, the evidence strongly supports warfarin for patient s with AF at average or greater risk of stroke. Aspirin may prove to be use ful in subgroups with a low risk of stroke, although this is not definitive ly supported by the evidence.