A 78-year-old woman, a member of your hospital board, is admitted with mild CHF responding well to diuretics. She has a history of PAF, hypertension, type 2 diabetes, and had a TIA 3 years ago. She had been treated with warfarin until 6 months ago, when she had a severely bleeding gastric ulcer. Echocardiogram demonstrates normal systolic function, mild MR, and LA of 4.5 cm