A 67-year-old man with a long history of poorly controlled hypertension presents to the emergency department with abrupt onset of severe, sharp chest pain that he describes as “tearing.” The pain began suddenly while he was watching television and now radiates between his shoulder blades. He is diaphoretic and anxious. Blood pressure is 198/112 mm Hg in the right arm and 168/98 mm Hg in the left arm. On exam, he has distended neck veins and muffled heart sounds. ECG shows sinus tachycardia without ST-segment elevation. Which of the following life-threatening complications most likely explains this patient’s current physical exam findings?