Review Question - QID 108894

A 68-year-old male presents with several years of progressively worsening pain in his buttocks. The pain is dull and is worse with exertion, especially when ascending the stairs. He has a history of type 2 diabetes mellitus, obesity, coronary artery disease with prior myocardial infarction, and a 44-pack-year smoking history. Current medications include aspirin, atorvastatin, metoprolol, lisinopril, insulin, metformin, and varenicline. Upon further questioning, the patient's wife states that her husband has also recently developed impotence. His temperature is 99.5°F (37.5°C), pulse is 90/min, blood pressure is 150/90 mmHg, respirations are 12/min, and oxygen saturation is 96% on room air. A physical exam reveals decreased pulses in the lower extremities bilaterally. Which of the following is the most appropriate initial step in management?