Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia affecting an estimated 2.2 million persons in the United States (US). In addition to being debilitating, AF has been identified as a leading risk factor for stroke. AF is often associated with structural heart disease, but a substantial number of AF patients have little or no detectable structural heart disease. A patient with AF is up to 5 times more likely to have a stroke than the general population.