A 64-year-old man with long-standing hypertension develops sudden, severe “tearing” chest pain radiating to his back while in the cardiac catheterization lab for evaluation of exertional angina. He becomes diaphoretic and hypotensive. On exam, there is a new high-pitched, blowing decrescendo diastolic murmur at the left sternal border. Shortly after, he has transient loss of consciousness and a right-sided facial droop. Which of the following is the most appropriate next diagnostic study to confirm the suspected diagnosis in this patient?

(Assume no prior contrast allergy.)