A 62-year-old man with long-standing hypertension undergoes diagnostic cardiac catheterization for evaluation of exertional angina. Two hours later, he develops sudden onset of severe, sharp “tearing” chest pain that radiates to his back. He becomes diaphoretic and anxious. Blood pressure is 190/110 mm Hg in the right arm and 155/95 mm Hg in the left arm. On exam, he has cool extremities and appears uncomfortable. Which of the following is the most likely underlying diagnosis and a key life-threatening complication if the dissection extends proximally?

(A single best answer.)