A 72-year-old woman with a history of recurrent paroxysmal atrial fibrillation and structural heart disease (ejection fraction 35%) presents for long-term rhythm control. She has had two episodes of AF in the past 3 months despite rate-control therapy. Her renal function is normal (eGFR 65 mL/min/1.73 m²), and baseline QTc is 420 ms. Which antiarrhythmic agent is most appropriate for maintenance rhythm control in this patient?