A 46-year-old male with a 10-year history of hypertension presents to the emergency department with severe retrosternal pain radiating to the back for 5 hours. Physical examination: BP 200/105 mmHg, pallor, profuse sweating, cold clammy skin. Heart rate 120 bpm with regular rhythm. A grade III diastolic blowing murmur and grade II systolic blowing murmur are heard at the aortic valve area. ECG shows left ventricular hypertrophy with strain. The most likely diagnosis is: