Warfarin for the prevention of systemic embolism in patients with non-valvular atrial fibrillation: a meta-analysis

Background: Warfarin for stroke prevention in patients with atrial fibrillation (AF) is well documented. However, it has not been examined in the prevention of systemic embolism. Objectives: To evaluate the efficacy of warfarin in preventing systemic embolism (embolism to limbs or viscera) in patients with AF. Methods and results: A combined Medline, Embase, Cochrane Library and SveMed+ search were made. Fifteen studies were included. Warfarin was better than antiplatelet agents for preventing systemic embolism with a 50% reduction of risk (odds ratio (OR)= 0.50, 95% CI 0.33 to 0.75) without increasing the risk of major bleeding (OR= 1.07; 95% CI 0.85 to 1.34). Warfarin compared with placebo resulted in a risk reduction of 71% (OR= 0.29; 95% CI 0.08 to 1.07) with higher risk of major bleeding with warfarin (OR= 3.01; 95% CI 1.31 to 6.92). Results of a comparison of warfarin with low-dose warfarin (OR= 1.52; 95% CI 0.40 to 5.81) or low-dose warfarin with aspirin (OR= 1.00; 95% CI 0.17 to 5.81) were inconclusive. Conclusions: Warfarin not only reduces the risk of stroke but is also better than placebo and antiplatelet agents in prevention of systemic embolism in patients with nonvalvular AF. Warfarin increases the risk of major bleeding compared with placebo but not compared with antiplatelet agents.