Review Question - QID 210788

A 58-year-old man presents to his primary care physician because he has been experiencing shortness of breath. In particular, his office decided to go bowling together, and he had to sit down after half a round because he was very fatigued. In addition, he has been experiencing palpitations and occasionally has "dizzy spells" where he feels like he is going to faint. Based on this presentation, appropriate tests are performed and the patient is started on a medication. One week later, the patient is brought to the emergency department after he passed out at work. An electrocardiogram of this patient is taken at the time of presentation and the result is shown in Figure A. Which of the following drugs was most likely responsible for this patient's emergency room presentation?