Background and purpose: In ACTIVE-W, oral anticoagulation (OAC) was more efficacious than combined clopidogrel plus aspirin (C+A) in preventing vascular events in patients with atrial fibrillation. However, because OAC carries important bleeding complications, risk stratification schemes have been devised to identify patients for whom the absolute benefits of OAC exceed its risks.
Methods: Participants were risk-stratified with the widely-used CHADS(2) scheme. Treatment-specific rates of stroke and major bleeding were calculated for patients with a CHADS(2)=1 and compared to those with a CHADS(2)>1.
Results: Observed stroke rates for those with a CHADS(2)=1 were 1.25% per year on C+A and 0.43% per year on OAC (RR=2.96, 95% CI: 1.26 to 6.98, P=0.01). Among patients with a CHADS(2)>1, the stroke rates were 3.15% per year on C+A and 2.01% per year on OAC (RR=1.58, 95% CI: 1.11 to 2.24, P=0.01) (P for interaction between stroke risk category and efficacy of OAC=0.19). The risk of major bleeding during OAC was significantly lower among patients with CHADS(2)=1 (1.36% per year) compared with CHADS(2)>1 (2.75% per year) (RR=0.49, 95% CI 0.30 to 0.79, P=0.003).
Conclusions: In this clinical trial, patients with a CHADS(2)=1 had a low risk of stroke, yet still derived a modest (<1% per year) but statistically significant absolute reduction in stroke with OAC and had low rates of major hemorrhage on OAC.