A 65-yeаr-оld mаle with а histоry оf hypertension and smoking presents to the emergency department with a sudden onset of chest pain that has been worsening over the past 24 hours. The pain is persistent, radiating to his left arm, and is not relieved by rest or nitroglycerin. His ECG shows ST-segment depression and T-wave inversion in multiple leads, and his troponin levels are elevated. Based on these findings, which of the following is the most appropriate diagnosis?