 - Patient has a CHADS2 score 3 OR has a CHADS2 score 2 WITH at least one of the following documented: renal impairment GFR 30-60 mlmin, sleep apnea, coronary artery disease, or chronic obstructive pulmonary disease. Note: strokeTIA criterion as part of the CHADS2 score for this trial is limited to either an ischemic stroke or TIA, which occurred MORE THAN one year prior to enrollment. 