A 78-year-old woman presents with new-onset palpitations and mild dyspnoea. ECG shows atrial fibrillation with a ventricular rate of 110 beats/min. She has hypertension and heart failure with preserved ejection fraction, but no history of stroke or transient ischaemic attack. Her creatinine is normal and she is independently mobile. Her CHA₂DS₂-VASc score is 4. What is the most appropriate stroke prevention strategy?