Biomarkers in acute cardiac disease.

In their state-of-the-art paper on biomarkers in acute cardiac disease (1), Dr. Jaffe and colleagues list creatine kinase-MB (CK-MB) as a “potentially outdated marker.” However, CK-MB has a specific utility in the diagnosis of reinfarction (2), and it cannot be replaced by the cardiac troponins for this purpose. By following up the time course of rise and fall of CK-MB, an interruption in the progressive decline in the level of the biomarker (to levels below upper reference limit) can be detected (2–4). Re-elevations in CK-MB by more than 50%, can be used to diagnose re-infarctions as early as 18 h after the index event (2). Both cardiac troponin T (cTnT) and cardiac troponin I (cTnI) on the other hand are continuously released from degenerating contractile apparatus in necrotic cardiomyocytes and may show persistent elevations, 7 to 10 days in the case of cTnI and up to 10 to 14 days in the case of cTnT, after the index event (2). The protracted time course of kinetic release of cTnI and cTnT limit their ability to diagnose reinfarction even several days after the index ST-segment elevation myocardial infarction (STEMI) because the cardiac troponin levels will still be on the rise during this period as a result of their normal kinetics, and it is not possible to be sure whether the rise is due to a re-infarction or not. It is because of this important difference in the kinetics between CK-MB, which shows a rapid rise and fall, and the troponins, the American College of Cardiology/American Heart Association Practice guidelines for STEMI specifically state that CK-MB is superior for diagnosing reinfarction (2). This is very relevant as recurrent chest pain is a common complaint of patients admitted for myocardial ischemia and CK-MB plays a vital role in the further evaluation of this complaint.