A 72-year-old man with long-standing hypertension and type 2 diabetes is found to be in atrial fibrillation during a routine visit. He is asymptomatic. ECG confirms non-valvular atrial fibrillation with a ventricular rate of 90 beats/min. Echocardiogram shows normal valves and left ventricular function. His CHA2DS2-VASc score is 3. Renal function is normal. What is the most appropriate strategy to reduce his stroke risk?