WARFARIN VERSUS ASPIRIN FOR PREVENTION OF THROMBOEMBOLISM IN ATRIAL-FIBRILLATION - STROKE PREVENTION IN ATRIAL-FIBRILLATION-II STUDY

Warfarin is an established treatment for prevention of ischaemic strok e in patients with atrial fibrillation, but the value of this agent re lative to aspirin is unclear. In the first Stroke Prevention in Atrial Fibrillation (SPAF-I) study, direct comparison of warfarin with aspir in was limited by the small number of thromboembolic events. SPAF-II a ims to address this issue and also to assess the differential effects of the two treatments according to age. We compared warfarin (prothrom bin time ratio 1.3-1.8, international normalised ratio 2.0-4.5) with a spirin 325 mg daily for prevention of ischaemic stroke and systemic em bolism (primary events) in two parallel randomised trials involving 71 5 patients aged 75 years or less and 385 patients older than 75; we so ught reductions in the absolute rate of primary events by warfarin com pared with aspirin of 2% per year and 4% per year, respectively. In th e younger patients, warfarin decreased the absolute rate of primary ev ents by 0.7% per year (95% Cl - 0.4 to 1.7). The primary event rate pe r year was 1.3% with warfarin and 1.9% with aspirin (relative risk [RR ] 0.67, p = 0.24). The absolute rate of primary events in low-risk you nger patients (without hypertension, recent heart failure, or previous thromboembolism) on aspirin was 0.5% per year (95% Cl 0.1 to 1.9). Am ong older patients, warfarin decreased the absolute rate of primary ev ents by 1.2% per year (95% Cl - 1.7 to 4.1). The primary event rate pe r year was 3.6% with warfarin and 4.8% with aspirin (RR 0.73, p = 0.39 ). In this older group, the rate of all stroke with residual deficit ( ischaemic or haemorrhagic) was 4.3% per year with aspirin and 4.6% per year with warfarin (RR 1.1). Warfarin may be more effective than aspi rin for prevention of ischaemic stroke in patients with atrial fibrill ation, but the absolute reduction in stroke rate by warfarin is small. Younger patients without risk factors had a low rate of stroke when t reated with aspirin. In older patients the rate of stroke (ischaemic a nd haemorrhagic) was substantial, irrespective of which agent was give n. Patient age and the inherent risk of thromboembolism should be cons idered in the choice of antithrombotic prophylaxis for patients with a trial fibrillation.