A 58-year-old man with a history of long-standing poorly controlled hypertension presents to the emergency department with abrupt onset of severe, sharp chest pain that he describes as “tearing.” The pain began while he was at rest and now radiates between his shoulder blades. He feels lightheaded. Vital signs: T 36.8°C, HR 112/min, BP 198/104 mm Hg in the right arm and 154/90 mm Hg in the left arm, RR 22/min, O2 sat 96% on room air. Physical exam reveals asymmetric upper-extremity pulses. ECG shows sinus tachycardia without ST-segment elevations. Chest x-ray shows a widened mediastinum. Which of the following is the most appropriate definitive management?