Cardiac troponin I for accurate evaluation of cardiac status in myopathic patients

Background: Brain natriuretic peptide (BNP) and left ventricular ejection fraction (LVEF) are standard indexes for cardiac function. However, they can not reveal myocardial damage directly and they often remain normal even in advanced cardiomyopathy in immobilized patients. Myocardial markers such as MB type of creatine kinase (CK-MB), heart-type fatty acid binding protein (H-FABP) and cardiac troponins are expected to evaluate active myocardial degeneration. However, their availabilities in these patients have not been examined yet. Methods: Participants were 129 patients with dystrophinopathies; 100 Duchenne muscular dystrophy (DMD), 25 Becker muscular dystrophy (BMD) and 4 DMD/BMD carriers. Various serological cardiac indexes, including CK-MB, H-FABP, cardiac troponin I (cTnI), BNP and LVEF were measured and statistical analysis was done. Results: CK-MB and H-FABP was highly associated with creatine kinase (CK). On the contrary, cTnI, BNP and LVEF were independent from CK. In DMD, relatively high cTnI values were observed in patients with motor ability of rowing wheelchair and in their second decade. BNP and LVEF was strongly correlated. However, cTnI was independent from LVEF and only weak correlation could be detected between cTnI and BNP. Conclusion: cTnI had been proven to be expressed in myocardium exclusively. Our results also certified that cTnI can assess cardiac degeneration independently from skeletal muscle degeneration and is practical index even in myopathic patients. Our findings also suggested that cardiac degeneration was preceded to functional impairment in many cases. It indicated that cTnI enable us to detect early stage of cardiac degeneration and initiate intervention at proper stage.