A 76-year-old woman is seen in the office for a routine health maintenance examination. She reports intermittent palpitations which have become more frequent over the last 2 days. She has a history of hypertension. Her pulse is 120/min and blood pressure is 150/90 mmHg. Lungs are clear to auscultation. Cardiac examination shows an irregularly irregular rhythm. ECG shows no P waves and widely variable RR intervals without a repetitive pattern. An oral beta blocker is administered as a rate control strategy and her heart rate drops to 80/min. She is averse to frequent blood tests.

Considering the risk of thromboembolism in this patient, which of the following is the best management option?