A 58-year-old male presents with palpitations and hand tremors for 3 years, worsened over 1 month. Physical exam: HR 110 bpm, BP 160/60 mmHg, weight loss, moist skin, palpable thyroid gland with vascular bruit, no jugular venous distension, normal cardiac size, irregularly irregular rhythm (HR 134 bpm) with varying heart sound intensity, clear lungs and abdomen, no lower limb edema. The preferred treatment is: