A 62-year-old man with a history of ischemic cardiomyopathy (EF 30%) presents to the emergency department with palpitations and mild shortness of breath for the past 30 minutes. He is alert and oriented, blood pressure is 110/70 mm Hg, heart rate is 180/min and regular, respiratory rate is 18/min, and oxygen saturation is 96% on room air. An ECG shows a wide-complex tachycardia at 180 bpm consistent with sustained monomorphic ventricular tachycardia. He has no chest pain, no signs of shock, and no acute heart failure findings. Which of the following is the most appropriate next step in management?