A 48-year-old woman with a history of hypertension suddenly experiences severe tearing chest pain radiating to the retrosternal and epigastric regions, accompanied by profuse sweating, lasting for 1 hour without relief. Physical examination: blood pressure 200/110 mmHg, heart rate 90 bpm, no cardiopulmonary abnormalities. Electrocardiogram (ECG) shows left ventricular hypertrophy with 0.1 mV ST-segment depression in V4-V6. The most likely diagnosis is: