Oral anticoagulation in nonvalvular atrial fibrillation

Chronic nonvalvular atrial fibrillation is associated with an overall risk of thromboembolic complications of 4.5% per year. Advancing age, prior stroke or transient cerebral ischaemia, diabetes, hypertension, and impaired function of the left ventricle are known risk factors. Placebo-controlled trials have demonstrated that oral anticoagulant therapy with warfarin is effective for primary and secondary prevention of ischaemic stroke, reducing the risk by 68%. The effect of aspirin is still controversial, reducing the risk by 18-44%. Recent clinical trials have investigated the effect of warfarin given at a very low intensity alone or combined with aspirin. The results from the SPAF III study demonstrated that a combination of mini-intensity warfarin plus aspirin was insufficient for stroke prevention in atrial fibrillation. More trials have now confirmed that oral anticoagulation at INR-values below 2.0 is not effective for prevention of thromboembolic events in these patients. It is currently recommended that patients at a high risk of stroke are treated with warfarin at an intensity of INR 2.0-3.0. Patients younger than 65 years without other risk factors can be given aspirin 325 mg day-1.