General

Clinical Question:
What benefit does warfarin provide over antiplatelet therapy in patients with nonvalvular atrial fibrillation?

Bottom Line:
Warfarin treatment is more effective than antiplatelet treatment in preventing strokes and delaying mortality in patients with atrial fibrillation. The difference between the two approaches is greater for patients who have already had a stroke or transient ischemic attack (TIA). Using rough estimates, 1 stroke is prevented for every 40 patients (who have not had a previous stroke or TIA) treated with warfarin instead of placebo, or for every 14 patients who have had a previous event. One stroke is prevented for every 81 previous stroke or TIA patients treated with warfarin instead of antiplatelet therapy (primary prevention) or for every 24 patients who have had a previous event. (LOE = 1a)

Reference:
Hart RG, Pearce LA, Aguilar MI. Meta-analysis: Antithrombotic therapy to prevent stroke in patients who have nonvalvular atrial fibrillation. Ann Intern Med 2007;146:857-867.  [PMID:17577005]

Study Design:
Meta-analysis (randomized controlled trials)

Funding:
Self-funded or unfunded

Setting:
Various (meta-analysis)

Synopsis:
Research continues to find the best approach to preventing stroke in patients with nonvalvular atrial fibrillation. The current study is an updated meta-analysis previously performed by the authors: 13 randomized studies enrolling an additional 18,000 patients have been conducted since 1999, including 4 trials that are ongoing or have not been published. The studies were identified by searching 2 databases, contacting investigators, and searching reference lists of identified studies. The new meta-analysis included 29 studies with a total 28,044 patients comparing anticoagulation and antiplatelet therapy with placebo or each other. The study results were not homogeneous and the researchers used a random effects model to better handle the heterogeneity. In patients receiving placebo, the stroke rate was 13% per year for patients who had a previous stroke or TIA, and 4.1% per year for those who had not had a previous event. Most patients in the studies had not experienced a previous event. As compared with antiplatelet therapy alone, warfarin decreased strokes by 37%, including when compared with the combination of clopidogrel and aspirin. In absolute terms, the rate of stroke was 0.7% less per year with warfarin than with aspirin for patients without a previous event and 7% less in patients with a previous TIA or stroke. The risk of intracranial hemorrhage was higher with warfarin, though the increase was small, only 0.2% per year. Overall mortality was 9% less with warfarin than with antiplatelet treatment (absolute rate difference = 0.5% per year).