Q. A 62-year-old woman comes to the emergency department because of chest pain of 5 hours duration. The patient has experienced similar episodes previously, which are usually relieved by rest and nitroglycerin. The patient describes the pain as “heaving” and reports it is not associated with respiration. Her medical history is significant for hypertension, diabetes, and fatty liver disease. The patient’s vital signs are blood pressure 142/90 mm Hg, heart rate 100/min, and respiratory rate 15/min. Cardiac auscultation reveals no abnormalities. An ECG shows no ST segment elevations. Lab values reveal a troponin I of 0.02 ng/ml (normal less than 0.04 ng/mL), and a creatine kinase level of 54 U/L (normal 25-90 U/L). Which of the following is the most likely diagnosis?