A 62-year-old man with long-standing hypertension presents to the emergency department with sudden onset of severe “tearing” chest pain radiating to his back that began 45 minutes ago. He is diaphoretic and anxious. Vital signs: T 36.8°C, HR 112/min, BP 198/92 mm Hg in the right arm and 162/80 mm Hg in the left arm, RR 22/min, SpO2 97% on room air. Physical examination reveals a new decrescendo diastolic murmur best heard along the left sternal border. Peripheral pulses are asymmetric. ECG shows sinus tachycardia without ischemic ST-segment changes. Which of the following complications best explains the new heart murmur in this patient?