Diagnostic role of strain imaging in atypical myocarditis by echocardiography and cardiac MRI

Background The diagnosis of myocarditis presenting as isolated acute chest pain with elevated troponins but normal systolic function is challenging with significant drawbacks even for the gold-standard endomyocardial biopsy. Objective This study aimed to evaluate the diagnostic role of strain imaging by echocardiography and cardiac MRI in these patients. Materials and methods This was a retrospective review of children with cardiac MRI for acute chest pain with elevated troponins compared to normal controls. Echocardiographic fractional shortening, ejection fraction, speckle-tracking-derived peak longitudinal, radial, and circumferential strain were compared to cardiac MRI ejection fraction, T2 imaging, late gadolinium enhancement, speckle-tracking-derived peak longitudinal strain, radial strain, and circumferential strain. Results Group 1 included 10 subjects diagnosed with myocarditis, 9 (90%) males with a median age of 15.5 years (range: 14-17 years) compared with 10 age-matched controls in group 2. All subjects in group 1 had late gadolinium enhancement consistent with myocarditis and troponin ranged from 2.5 to >30 ng/ml. Electrocardiogram changes included ST segment elevation in 6 and abnormal Q waves in 1. Qualitative echocardiographic function was normal in both groups and mean fractional shortening was similar (35 +/- 6% in group 1 vs. 34 +/- 4% in group 2, P=0.70). Left ventricle ejection fraction by cardiac MRI, however, was lower in group 1 (52 +/- 9%) compared to group 2 at (59 +/- 4%) (P=0.03). Cardiac MRI derived strain was lower in group 1 vs. group 2 for speckle-tracking-derived peak longitudinal strain (-12.8 +/- 2.8% vs. -17.1 +/- 1.5%, P=0.001), circumferential strain (-12.3 +/- 3.8% vs. -15.8 +/- 1.2%, P=0.020) and radial strain (13.6 +/- 3.7% vs. 17.2 +/- 3.2%, P=0.040). Echocardiography derived strain was also lower in group 1 vs. group 2 for speckle-tracking-derived peak longitudinal strain (-15.6 +/- 3.9% vs. -20.8 +/- 2.2%, P<0.002), circumferential strain (-16 +/- 3% vs. -19.8 +/- 1.9%, P<0.003) and radial strain (17.3 +/- 6.1% vs. 24.8 +/- 6.3%, P=0.010). Conclusion In previously asymptomatic children, myocarditis can present with symptoms of acute chest pain suspicious for coronary ischemia. Cardiac MRI and echocardiographic strain imaging are noninvasive, radiation-free tests of immense diagnostic utility in these situations. Long-term studies are needed to assess prognostic significance of these findings.