Atrial fibrillation is the most common cardiac arrhythmia. The principal significance of atrial fibrillation, both to patients and health care systems, is the fivefold increased risk of embolic stroke.1 Atrial fibrillation is associated with 15% of all strokes2 and with 36% of strokes in patients older than 80.

Renewed interest in atrial fibrillation has followed publication of randomised controlled trials showing that anticoagulation is effective in decreasing this risk of stroke.3-7 The effect size for warfarin is huge with a 68% relative risk reduction for stroke in the primary prevention trials, with annual stroke risk reduced from 4.5% to 1.4% and number need to treated (NNT) for one year of 32.8 In secondary prevention the effect size is even greater with a 66% relative risk reduction, annual risk reduction from 12% to 4%, and NNT for one year of only 12.9 The data on aspirin are less impressive, with the 21% risk reduction only just reaching significance.10 Reliable data on the newer antithrombotics in atrial fibrillation are not currently available.

Reductions in stroke risk not only have obvious benefits to patients; stroke has a high cost to all health care systems with 1000 new cases per 500 000 population per year, expending around 5% of National Health Service …