Non-invasive assessment of early and acute myocarditis in a rat model using cardiac magnetic resonance tissue tracking analysis of myocardial strain

Background: Myocardial strain analysis can provide diagnostic and prognostic information for myocarditis. The aim of the present study was to assess early and acute myocarditis in a rat model using cardiac magnetic resonance tissue tracking (CMR-TT) for myocardial strain analysis. We compared the strain’s findings with the histological and immunohistochemical results. Methods: Experimental autoimmune myocarditis (EAM) was induced by footpad injections of porcine cardiac myosin. The rats were examined by 7.0T preclinical CMR at day 14 (n=15) and day 21 (n=16) after EAM induction and the two control groups (each n=15) were also examined at day 14 and day 21, respectively. Using CMR-TT, we found a global peak systolic radial strain (Err SAX ) and a circumferential strain (Ecc SAX ) from the short-axis cine views and a radial strain (Err LAX ) and a longitudinal strain (Ell LAX ) from the long-axis cine views, which were calculated by dedicated TT software. Subsequently, histological and immunohistochemical evaluations were performed. Results: Ell LAX significantly decreased in early myocarditis compared with the control (–23.40%±1.48% vs . –22.02%±0.81%, P<0.05). Err SAX , Ecc SAX , Err LAX , and Ell LAX values significantly reduced in acute myocarditis compared with the controls (Err SAX : 34.27%±9.80% vs . 49.76%±4.97%, Ecc SAX : –18.98%±3.69% vs . –24.13±1.23, Err LAX : 33.21%±10.24% vs . 49.59%±5.69%, and Ell LAX : –17.75%±3.58% vs . –23.39%±1.48%; P<0.001, respectively). The receiver operating characteristic curve showed that myocardial strain analysis had a good diagnostic performance in early and acute myocarditis. The pathological evaluation revealed that inflammatory lesions began to appear in early myocarditis and peaked in acute myocarditis. Conclusions: The CMR-TT strain analysis allowed accurate and reliable evaluation of early and acute myocarditis in a rat model, and has the potential to serve as a diagnostic indicator for the assessment of myocardial dysfunction in myocarditis.