Review Question - QID 213187

A 65-year-old man is hospitalized after undergoing operative fixation of a left distal radius fracture due to a fall. On postoperative day 1, he reports having several episodes of palpitations with associated lightheadedness. He denies any chest pain and states that these episodes last for a few seconds each before resolving. On exam, his temperature is 98.4°F (36.9°C), blood pressure is 124/76 mmHg, pulse is 94/min, and respirations are 12/min. The patient is currently asymptomatic without palpitations. The patient is immediately connected to a cardiac monitor which shows normal sinus rhythm. Over the course of the night, the monitor demonstrates 3 more episodes of the rhythm shown below in Figure A, with associated palpitations and lightheadedness. Blood pressure and oxygen saturation are stable during these episodes. The patient is given intravenous magnesium. The decision is made to also start medical therapy. Which of the following medications should be started?