Elevations of Cardiac Troponin I Associated With Myocarditis

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Abstract
Background Endomyocardial biopsy is currently the standard method used to diagnose myocarditis. However, it is invasive and has a low diagnostic yield. Because the histological diagnosis of myocarditis requires the presence of myocyte injury, we sought to determine whether measurement of cardiac troponin I (cTnI), which is a serum marker with high sensitivity and specificity for cardiac myocyte injury, could aid in the diagnosis of myocarditis. Methods and Results To validate this approach, cTnI values were first measured in mice with autoimmune myocarditis. cTnI values were elevated in 24 of 26 mice with myocarditis but were not elevated in any of the control animals (P<.001). Next, cTnI values were measured in the sera from 88 patients referred to the Myocarditis Treatment Trial and were compared with creatine kinase–MB (CK-MB) values measured in the same patients. cTnI values were elevated in 18 (34%) of 53 patients with myocarditis and in only 4 (11%) of 35 patients without myocarditis (P=.01). In contrast, CK-MB values were elevated in only 3 (5.7%) of 53 patients with myocarditis and 0 of 35 patients without myocarditis (P=.27). Thus, elevations of cTnI occurred more frequently than did elevations of CK-MB in patients with biopsy-proven myocarditis (P=.001). Importantly, elevations of cTnI in patients with myocarditis were significantly correlated with ≤1 month duration of heart failure symptoms (P=.02), suggesting that the majority of myocyte necrosis occurs early, and thus the window for diagnosis and treatment may be relatively brief. Conclusions cTnI was superior to CK-MB for detection of myocyte injury in myocarditis, and cTnI elevations were substantially more common in the first month after the onset of heart failure symptoms.