Warfarin is most effective when the INR lies between 2.0 and 4.0

Epidemiological research has established that non-rheumatic atrial fibrillation is an important risk factor for stroke. It increases the risk about fivefold and is particularly important in elderly people, in whom the prevalence of atrial fibrillation is high.1 Randomised trials have shown that this risk is largely reversed by anticoagulation.2 3 The prescription of warfarin for stroke prevention has increased, but concerns about the risks of bleeding continue to dampen enthusiasm for its wider use.4 Targeting those with a higher risk of stroke ensures that only those with most to gain from anticoagulation are exposed to its risks.2 However, reducing the risks will require safer anticoagulation strategies. Three have been tested in recent research: very low intensity warfarin, aspirin, and a combination of these two treatments.

Information about the efficacy of these strategies is now available from both observational and experimental studies. In a case-control analysis 74 patients with non-rheumatic atrial fibrillation who suffered a stroke while taking warfarin were compared with 222 patients with atrial fibrillation who had not had a stroke while anticoagulated.5 …