Atrial fibrillation. Thromboembolic risk and indications for anticoagulation.

The risk of embolic stroke in patients with atrial fibrillation is largely related to the underlying disorders responsible for the arrhythmia. Atrial fibrillation associated with rheumatic mitral valve disease has the highest stroke risk (about 17 times greater than unaffected controls), but even with nonvalvular heart disease, the risk is increased fivefold. The stroke risk is greater with chronic than with paroxysmal atrial fibrillation, is highest in the year after onset of the arrhythmia, and is lower in younger patients with idiopathic ("lone") atrial fibrillation. Major bleeding episodes, the most important risk of anticoagulation, occur in about 5% to 10% of patients. The decision to anticoagulate a patient with atrial fibrillation depends on the cause of the arrhythmia, especially any associated cardiovascular disease, and the individual's risk from anticoagulation. Growing evidence supports the effectiveness of anticoagulation of most patients with nonvalvular, as well as valvular, cardiac disease for the prevention of both primary and recurrent strokes.