Autonomic Pharmacology USMLE Step 1 Practice Question

A 62-year-old man with a history of hypertension and stable angina pectoris is started on antihypertensive therapy. Two weeks later, he presents to clinic complaining of progressive fatigue, dizziness, and exertional dyspnea. His wife notes he has been unusually lethargic. Vital signs reveal blood pressure 92/56 mmHg, heart rate 48 bpm, respiratory rate 14/min, and temperature 37.2°C. Physical examination shows cool extremities, mild peripheral edema, and no acute distress. The patient reports that his current chest pain symptoms have improved, but he is unable to climb stairs due to shortness of breath. An ECG demonstrates normal sinus rhythm with PR interval of 240 ms and normal QRS duration. Laboratory studies show serum creatinine 1.1 mg/dL, potassium 5.2 mEq/L, and glucose 128 mg/dL. Which of the following medications most likely caused this clinical presentation?