Review Question - QID 108824

A 42-year-old male presents to his primary care physician complaining of a 3 hour history of dizziness and shortness of breath. He says that his symptoms started this morning while he was helping his girlfriend move out of her apartment. He also endorses fatigue, lightheadedness, and low back pain. His past medical history is significant for psoriasis which is treated with topical steroids and asthma which is treated with an albuterol inhaler. He tried using his inhaler during this episode without notable improvement. His temperature is 99°F (37.2°C), blood pressure is 102/68 mmHg, pulse is weak at 50/min, and respirations are 24/min with an oxygen saturation of 95% on room air. On physical exam, he has mild bilateral lower extremity edema. An EKG is performed and the results are shown in Figure A. The patient is given a permanent ventricular pacemaker. During a 1 month follow-up visit, he reports improvement of his cardiopulmonary symptoms but complains of persistent low back pain. He says that the symptoms have increased to the point where he “can hardly get out of bed in the morning.” What is the most appropriate next diagnostic test for this patient's condition?