In the past decade, much has been learned about antithrombotic prophylaxis to prevent stroke in patients with non-valvar atrial fibrillation (AF). Adjusted dose warfarin is highly efficacious, aspirin is modestly efficacious (reducing primarily non-disabling, non-cardioembolic strokes in AF), warfarin is much more efficacious than aspirin, and low intensity warfarin (international normalised ratios (INR) < 1.5) alone or combined with aspirin offers minimal protection.1The absolute risk of stroke varies widely in patients with AF, from < 1% to 12% per year, depending on age and coexisting vascular disease.2 ,3 Selection of antithrombotic prophylaxis should consider the inherent risk of stroke and the absolute risk reductions afforded. It is my view that many AF patients, including most younger than 75 years, do not substantially benefit from treatment with adjusted dose warfarin.

Two observational studies in this issue address this important, controversial issue.4 ,5 Perez and colleagues surveyed a sample of patients with AF randomly drawn from outpatient clinics.4 Applying a scheme for stratifying stroke risk, only about half of those deemed high risk and who had no apparent contraindications for anticoagulation were being treated with warfarin, while a quarter of those presumed at low risk were receiving anticoagulants. Warfarin was particularly underused among high risk AF patients older than 75 years: only about 20% were being anticoagulated. …