Following cardiopulmonary resuscitation (CPR) and multiple defibrillations, the client's blood is drawn for STAT analysis. The client's heart rate is 130 beats/minute with ST elevation. Which of the client's serum laboratory values is most important for the nurse to monitor?

A. Creatine phosphokinase MB (CK-MB): CK-MB is a cardiac marker that rises after myocardial injury, but it is less specific and peaks later than troponin. While it can support diagnosis, it is not the most critical marker to monitor immediately following resuscitation and ST elevation. B. Troponin: Troponin is the most sensitive and specific marker of MI. It rises within 3–6 hours of cardiac muscle damage. In a post-CPR client with ST elevation, monitoring troponin is crucial for assessing the extent of cardiac injury and guiding further treatment. C. Lactate dehydrogenase (LDH or LD): LDH is a nonspecific enzyme elevated in many conditions involving tissue breakdown. It lacks the specificity and rapid diagnostic utility needed for acute coronary syndrome assessment post-resuscitation. D. Alanine aminotransferase (ALT or SGPT): ALT is a liver enzyme and is not relevant to immediate cardiac status or post-resuscitation myocardial injury. Monitoring it does not provide useful information for evaluating acute ST elevation or cardiac ischemia.