Review Question - QID 215113

A 65-year-old man presents to the emergency department with chest pain. He was seated at his desk at work when he experienced sudden-onset, severe chest pain that radiated to his back. The patient has a history of diabetes, hypertension, and chronic kidney disease. He is non-compliant with his medications, which include amlodipine and metformin. He smokes 1 pack of cigarettes per day and has a 55-pack-year smoking history. The patient’s temperature is 98.8°F (37.1°C), blood pressure is 132/78 mmHg in the right arm and 156/86 mmHg in the left arm, pulse is 104/min, and respirations are 18/min. On physical exam, the patient appears to be in acute distress and moans in pain. Cardiac auscultation reveals a soft, 2/6 diastolic decrescendo murmur over the left lower sternal border. Which of the following is the most appropriate next step to confirm the diagnosis?