A 72-year-old man with poorly controlled hypertension and chronic obstructive pulmonary disease presents to the emergency department with sudden-onset severe anterior chest pain radiating to the neck and jaw. He is anxious and diaphoretic. Blood pressure is 185/110 mmHg, heart rate 112 bpm, and respiratory rate 28/min. On auscultation, there is an early diastolic murmur at the left sternal border. A portable chest X-ray shows widening of the mediastinum. An urgent bedside transthoracic echocardiogram shows a dilated ascending aorta with severe aortic regurgitation. What is the most appropriate immediate management?