Cardiac Magnetic Resonance Imaging in Biopsy-proven Myocarditis: Lack of Relationship With Clinical Presentation and Viral Etiology

Objective: Myocarditis is an inflammatory disease of the myocardium, diagnosed on endomyocardial biopsy (EMB) by histology (Dallas criteria), immunohistology and molecular techniques to identify viral genomes. Cardiac magnetic resonance (CMR) has been proposed as noninvasive diagnostic imaging tool using T2-weighted and post-contrast sequences (late gadolinium enhancement, LGE). Correlative data regarding diagnostic accuracy of CMR versus gold-standard EMB are still very early. Our aim was to evaluate the diagnostic accuracy of CMR for myocarditis compared to EMB as well as potential associations between CMR patterns and specific viral agents identified by polymerase chain reaction (PCR) on EMB. Methods: CMR was prospectically performed in 40 patients (23 male, aged 31,6±11,8 years) referred to a tertiary centre for suspected myocarditis. The CMR examination was performed including T2-weighted images for assessing myocardial edema and LGE for necrosis/fibrosis (classified as subepicardial or diffuse, multifocal and/or midmural). All patients underwent right ventricular EMB and coronary artery disease was excluded by coronary angiography. EMB diagnosis of myocarditis fulfilled histologic, immunohistologic and molecular criteria by PCR for common cardiotropic viruses. Results: Clinical presentation was with heart failure in 32,5%, arrhythmia in 15%, pseudo myocardial infarction in 30%. PCR was positive for virus in 25,5%, 73,5% had active, 26,5% had borderline myocarditis. On CMR 17 patients (42,5%) showed myocardial edema and non-ischemic LGE in 38 (95%). Compared with EMB, positive T2 images showed sensitivity (sens) of 82%, specificity (spec) of 40%, positive predictive value (PPV) of 82% and negative predictive value (NPV) of 49%; LGE showed sens. and spec. of 97% and 16%, a PPV of 87% and a NPV of 50% respectively. No associations were found between CMR patterns and viral etiology, clinical presentation or specific viral types, including parvovirus B19. Conclusion: In patients with biopsy-proven myocarditis CMR had good sens, but low spec, and failed to distinguish viral from non viral etiology. Diagnostic accuracy of CMR should be better-defined using standardized protocols comparing comprehensive CMR to current EMB criteria