You are answering a USMLE-style medical question. Question: A 63-year-old man comes to the emergency department because of retrosternal chest pain. He describes it as 7 out of 10 in intensity. He has coronary artery disease, hypertension, and type 2 diabetes mellitus. His current medications are aspirin, simvastatin, metformin, and enalapril. He has smoked one pack of cigarettes daily for 33 years. On arrival, his pulse is 136/min and irregular, respirations are 20/min, and blood pressure is 85/55 mm Hg. The lungs are clear to auscultation. Cardiac examination shows no abnormalities. An ECG is shown. Which of the following is the most appropriate next step in management? Options: A) Coronary angiogram B) Intravenous esmolol C) Intravenous amiodarone D) Synchronized cardioversion Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.