Clinical practice - Newly diagnosed atrial fibrillation

A 77-year-old woman with a history of hypertension treated with metoprolol presents for her annual examination. She reports no new symptoms. The examination is remarkable only for the finding of an irregular heart rate. Electrocardiographic testing reveals atrial fibrillation at an average rate of 75 beats per minute. She has no history of arrhythmia, coronary disease, valvular disease, diabetes, alcohol abuse, transient ischemic attack, or stroke. For the past several months, she has exercised on a treadmill without difficulty, although she notes that the machine does not always measure her heart rate. What should her physician advise?