A 70-year-old woman with newly diagnosed non-valvular atrial fibrillation is seen in clinic. She has no prior stroke or TIA, no heart failure, no hypertension, no diabetes and no known vascular disease. She is independent in all activities of daily living. According to the Canadian Cardiovascular Society atrial fibrillation guideline CHADS-65 algorithm, what is the most appropriate antithrombotic strategy for stroke prevention?