Differences of creatine kinase MB and cardiac troponin I concentrations in normal and diseased human myocardium.

The diagnosis of myocardial infarction (MI) is established in patients with chest pain and equivocal electrocardiogram changes by demonstrating a rise in blood levels of creatine kinase MB (CK-MB) and/or an increase in cardiac troponin I (cTnI) or cardiac troponin T (cTnT). Previous studies have shown that levels of CK-MB are increased in the left ventricle of individuals with heart disease; however, it has not been established whether there are differences in the ventricular myocardium concentrations of cTnI in diseased compared to healthy hearts. Using a simple extraction technique, concentrations of CK-MB and cTnI were measured in the left ventricle (LV) of six hearts obtained at autopsy from individuals ranging in age from 25 to 79 yr, with and without evidence of cardiac disease. The results show an 86-fold higher concentration of CK-MB and 7.7-fold lower concentration of cTnI in left ventricular myocardium of older men with and without cardiac disease, compared to that of younger men (< age 35 yr) without heart disease. These data suggest that age may need to be considered when setting cutoff limits for these markers for the diagnosis of myocardial infarction.