Atrial Fibrillation in Stroke Prevention.

About 20% of all ischemic strokes occur as a result of an embolus to a cerebrl artery arising from the cardiac chambers or valves. Atrial fibrillation represents the most frequent cardiac source of embolus to the brain accounting for 45% or more of the cardiac causes of ischemic stroke". The remaining causes include emboli from left ventricular thrombi in the setting of an acute cardiac infarction or emboli arising from ventricular thrombi located in a ventricular aneurysm or overlying a dyskinetic ventricular wall . Other cardiac sources of emboli include rheumatic valvular disease, prosthetic valve disease and a variety of other less common cardiac abnormalities. Atrial fibrillation is the most common arrhythmia in the general population and is particularly common over the age of 60. The median age of patients with atrial fibrillation in the United States is 75 years. Atrial fibrillation has been shown to convey a 6-fold increased risk of stroke in the general population compared to similar patients without atrial fibrillation. This substantial increase has been confirmed by repeated epidemiological studies . This increased risk of stroke translates to an annual stroke risk of around 5% per year. About 15% of ischemic stroke patients have atrial fibrillation identified at the time of their stroke and about two-thirds of these will ultimately be concluded to have their ischemic stroke on the basis of an embolus arising from the left atrium. Atrial fibrillation