Benefits and risks of oral anticoagulation for stroke prevention in nonvalvular atrial fibrillation

Nonvalvular atrial fibrillation is the most common clinically significant cardiac arrhythmia in the United States. It increases both the risk for and the severity of strokes and is associated with substantial morbidity, mortality, decreased quality of life, and related health care costs. Guidelines recommend anticoagulation therapy for the majority of patients with atrial fibrillation. Clinical trials have established that vitamin K antagonists are effective for stroke prevention for patients with atrial fibrillation for whom anticoagulation is recommended. However, vitamin K antagonists remain underutilized for a variety of reasons, including drug, physician, and patient factors. While vitamin K antagonists considerably reduce the risk of stroke, the absolute risk reduction varies according to individual patient risk factors. Accurately assessing each patient's true risk of stroke and bleeding is essential when determining which (if any) antithrombotic strategy should be used. Several stroke risk stratification schemes exist; of these, CHADS₂ is widely employed and simple. New, more sophisticated schemes may generate more precise risk estimates and better identify those patients for whom anticoagulant therapy offers a net clinical benefit. More studies are needed to determine the utility of bleeding risk stratification systems, as well as the role of surgical and interventional alternatives to anticoagulation treatment. Several novel oral anticoagulants are in (or have completed) phase 3 clinical trials. Dabigatran etexilate, approved in the United States in October 2010 for reducing the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation, now offers the first oral alternative to warfarin for patients with atrial fibrillation.