A 62-year-old man with a history of long-standing poorly controlled hypertension presents to the emergency department with sudden-onset, severe chest pain that he describes as “ripping” and radiating to his back. He becomes progressively dyspneic and anxious. Vital signs: T 37.0°C (98.6°F), BP 190/105 mm Hg, HR 118/min, RR 24/min, O2 sat 93% on room air. On exam, jugular venous distention is present, heart sounds are muffled, and the lungs are clear to auscultation. ECG shows sinus tachycardia without ischemic changes. The patient becomes hypotensive shortly after arrival. Bedside labs show creatinine 3.0 mg/dL (baseline unknown). Which of the following is the most appropriate next diagnostic test to confirm the suspected diagnosis in this patient?

(Assume pregnancy is not a consideration.)