Acute myocardial infarction releases more troponin per unit of late gadolinium enhancement mass compared to acute myocarditis

BackgroundBoth acute myocardial infarction (AMI) and acute myocarditis are characterised by cardiac troponin release as a marker of cardiomyocyte injury. While peak troponin is widely accepted as a surrogate marker for infarct size in AMI, its relationship with myocardial injury in acute myocarditis is unclear. This study aimed to quantify and compare the association between peak high-sensitivity cardiac troponin and cardiovascular magnetic resonance (CMR) late gadolinium enhancement (LGE) extent in patients with AMI versus acute myocarditis. MethodsPatients undergoing CMR imaging and measurement of high-sensitivity cardiac troponin I during hospital admission were retrospectively included. LGE extent was quantified in grams using the semi-automated expectation-maximization weighted intensity algorithm (EWA). ResultsCompared to patients with acute myocarditis (n=47), patients with AMI (n=49) had higher peak troponin levels (median [interquartile range] 32,470 [3,109-104,699] vs 7,295 [1,857-22,550] ng/L, p=0.002), larger LGE extent (25 [13-56] vs 10 [6-17] g, p<0.001), and lower left ventricular ejection fraction (45 [36- 52] vs 55 [49-58] %, p<0.001). Peak troponin was moderately positively correlated with LGE extent in both AMI (rho=0.56, p<0.001) and acute myocarditis (rho=0.58, p<0.001). However, the ratio of peak troponin to LGE mass was higher in AMI compared to acute myocarditis (1,299 [419-3233] vs 909 [310-1446] ng/L/g, p=0.02). ConclusionsPeak cardiac troponin correlates positively with LGE extent in both AMI and acute myocarditis, but the magnitude of LGE and LV systolic dysfunction is greater in AMI. Also, AMI typically has an approximately 40% greater amount of troponin release per unit LGE mass compared to acute myocarditis. This suggest that troponin-based estimates of myocardial injury size estimated by LGE are not directly interchangeable between ischaemic and inflammatory myocardial diseases.