A nurse is caring for a client who has pneumonia and tells the nurse, "I feel like an elephant is sitting on my chest." The client is weak and unable to walk. After the nurse initiates chest pain protocol, which of the following is the priority diagnostic test?

A. A chest x-ray is important to assess pneumonia but is not the priority when chest pain suggesting a cardiac event is present. B. A 12-lead ECG is the priority to assess for myocardial ischemia or infarction, given the client’s description of chest pain. C. Serum potassium is important for cardiac health but not the immediate priority in this scenario. D. PT and INR are relevant for coagulation but do not address the immediate concern of potential myocardial infarction.