A 58-year-old man with no prior cardiac history presents with retrosternal chest pain starting at rest and lasting 30 minutes. The pain radiates to the left arm and is associated with diaphoresis and dyspnea. His blood pressure is 150/90 mm Hg, pulse 100/min, the heart sounds are normal, and the lungs are clear to auscultation. Which of the following is the next most appropriate investigation?

This man has acute coronary syndrome (ACS) until proven otherwise. The ECG is the most useful initial investigation since it identifies individuals with ST-segment elevation who may be candidates for either thrombolysis or primary angioplasty (PCI). The troponins are important in diagnosing myocardial necrosis. The other investigations may be important in looking for alternate causes of chest pain once ST-elevation MI has been ruled out.