Review Question - QID 108371

A 67-year-old man with hypertension, hypercholesterolemia, and diabetes mellitus presents to the ED with severe chest pain. The pain started suddenly a few hours ago, characterized as sharp and radiating to his back. He has never experienced pain like this before. He also has been sweaty, short of breath, and nauseous, but denies cough, fever, vomiting, or a history of trauma. He has smoked 1 pack of cigarettes per day since age 15, and currently takes lisonopril, amlodipine, metformin, and atorvastatin. In the ED, his temperature is 98.5 deg F (36.9 deg C), blood pressure is 85/50 mmHg, pulse is 115/min, and respirations are 25/min. An EKG is seen in Figure A and appears similar to an EKG obtained 1 month ago. He appears to be in moderate distress. Auscultation of his chest revealed no murmurs and his lungs are clear bilaterally. There is no tenderness to palpation along his chest wall. His abdominal exam is noteworthy for a pulsatile mass. The rest of his exam is within normal limits. Appropriate management is initiated. What is the most likely etiology of this patient's acute chest pain?