Cardiac magnetic resonance abnormalities in patients with acute myocarditis proven by septal endomyocardial biopsy

Background: Previous studies suggest low diagnostic sensitivity of cardiac magnetic resonance (CMR) imaging based on Lake Louise criteria (LLC) to identify patients with complicated presentations of acute myocarditis (AM). We evaluated classic and updated LLC in patients with AM proven by right ventricular septal endomyocardial biopsy (RVS-EMB). Methods: From an initial population of 499 patients with clinically suspected AM from a multicenter retrospective cohort, we included 74 patients with histologically proven myocarditis on RVS-EMB and available CMR within 30 days since admission. The prevalence of total and septal CMR abnormalities [namely, T2-weighted images (T2W), late gadolinium enhancement (LGE), T2 and T1 mapping, and extracellular volume (ECV)] were assessed in patients with complicated vs. uncomplicated AM. Results: Among 74 patients [mean age 38 ± 15 years, 65% males, left ventricular ejection fraction (LVEF) 40 ± 18%] with RVS-EMB-proven AM, 53 (72%) had a complicated presentation. The classic LLC were positive in 56/74 patients (76%), whereas the updated ones were positive in 41/41 of cases (100%). Septal involvement, documented in 48/74 patients (65%) by conventional T2W/LGE and in 39/41 cases (95%) by mapping techniques (p < 0.001), was more common in patients with complicated AM. In the 41 patients undergoing both evaluations, CMR sensitivity for myocarditis was 85% for the classic LLC vs. 100% for the updated LLC (p = 0.006). Conclusion: In patients with myocarditis on RVS-EMB, CMR using updated LLC has high sensitivity in the detection of AM when performed within 30 days. Septal abnormalities are more common in patients with complicated AM.