Atrial fibrillation is the most common sustained cardiac arrhythmia
During atrial fibrillation the atrial heart muscle contracts rapidly and erratically, for reasons that are not fully understood. This problem affects about 2.2 million people in the US. By age 75, about 12% of the population has atrial fibrillation. A patient with atrial fibrillation has a six times increased risk of stroke. Overall, about 15% of ischemic strokes are attributed to this condition.

Special populations
In seniors aged 65-85, about 70% of all strokes are attributed to atrial fibrillation.

Relationship to stroke pathogenesis
Patients with atrial fibrillation have a greatly increased risk of embolic stroke. Ineffective contraction of the left atrium allows blood to pool along its walls and increases thrombus formation. Bits of these thrombi can break free, travel through the left ventricle to enter the systemic circulation, and embolize the brain or other organs.

A little about control/treatment
In some patients, atrial fibrillation resolves spontaneously. Electrical cardioversion or pharmacologic agents may be helpful in restoring a normal cardiac rhythm. Treatment with anticoagulants such as warfarin in patients with atrial fibrillation reduces their stroke risk by about 67% compared with untreated patients. For patients who have a low overall stroke risk or for whom warfarin therapy is not an option, an antiplatelet agent like aspirin or clopidogrel is an appropriate alternative. Clinical decisions concerning the use of these therapies must be balanced by the risk of hemorrhagic complications.