Oral anticoagulation in nonvalvular atrial fibrillation - Introduction

Chronic nonvalvular atrial fibrillation is associated with an overall risk of thromboembolic complications of 4.5% per year. Advancing age, prior stro ke or transient cerebral ischaemia, diabetes, hypertension, and impaired fu nction of the left ventricle are known risk factors, Placebo-controlled tri als have demonstrated that oral anticoagulant therapy with warfarin is effe ctive for primary and secondary prevention of ischaemic stroke, reducing th e risk by 68%. The effect of aspirin is still controversial, reducing the r isk by 18-44%. Recent clinical trials have investigated the effect of warfa rin given at a very low intensity alone or combined with aspirin, The resul ts from the SPAF III study demonstrated that a combination of mini-intensit y warfarin plus aspirin was insufficient for stroke prevention in atrial fi brillation. More trials have now confirmed that oral anticoagoulation at IN R-values below 2.0 is not effective for prevention of thromboembolic events in these patients. It is currently recommended that patients at a high ris k of stroke are treated with warfarin at an intensity of INR 2.0-3.0. Patie nts younger than 65 years without other risk factors can be given aspirin 3 25 mg day(-1).