O0017: CMR Findings of COVID-19 Vaccine Associated Myocarditis at Intermediate Follow Up: A Comparison to Classic Myocarditis and MIS-C Related Myocarditis

Background: Myocarditis has been identified as a rare but serious adverse event following mRNA COVID-19 vaccination. Many children with myocarditis have ventricular dysfunction and myocardial fibrosis that persist beyond the acute phase; however, the long-term effects of COVID-19 vaccine associated myocarditis (C-VAM) are unknown. We report cardiac magnetic resonance imaging (CMR) findings at 3-5 months after diagnosis of C-VAM and compare to studies performed in patients with classic myocarditis (viral or idiopathic) and multisystem inflammatory syndrome in children (MIS-C).

Methods: Retrospective single center study including all patients diagnosed with C-VAM from May 2021 through December 2021 who had an abnormal CMR at presentation and underwent follow-up CMR. Patients who received a follow-up CMR 2-12 months after diagnosis of classic myocarditis from January 2015 to December 2021 or MIS-C from April 2020 to June 2021 were included for the comparison groups. Demographic, clinical, and CMR data were collected from time of hospitalization through follow-up CMR. Comparison of functional data, volumetric data, parametric mapping, and late gadolinium enhancement (LGE) were made among the C-VAM, classic myocarditis, and MIS-C groups. Data were compared using the Kruskal-Wallis test or Fisher’s exact test as appropriate. A p-value of less than 0.05 was considered significant.

Results: 8 patients with C-VAM, 20 with classic myocarditis, and 61 with MIS-C myocarditis were included (Table). Patients with C-VAM (median age 16.3 years, 100% male) and classic myocarditis (median age 16.7 years, 90% male) were older and more frequently male than those with MIS-C (median age 11.9 years, 67% male). Among those with C-VAM, initial CMR performed a median of 3 days (3.0, 6.5) after diagnosis revealed 2/8 patients with LVEF < 55%, 7/7 patients with LGE indicating myocardial fibrosis, 5/8 patients with elevated native T1 values, 4/7 with elevated extracellular volume (ECV), and 0/8 with myocardial edema by T2 mapping. All C-VAM patients had a subepicardial pattern of LGE predominantly involving the inferior and inferolateral segments of the heart (Figure). Follow-up CMR was performed a median of 107 days (96.8, 177.0) after diagnosis. 3/7 patients had persistent LGE and all patients had normal ventricular systolic function, T1, ECV, and T2 values. On follow-up CMR at 3-5 months, the classic myocarditis group had a higher percentage of patients with LVEF < 55% than the C-VAM and MIS-C groups (30% vs 0% vs 6.6%, p=0.018) and higher prevalence of persistent LGE (75% vs 42.9% vs 3.3%, p< 0.001).

Conclusion: Patients with COVID-19 vaccine associated myocarditis had no evidence of active inflammation or ventricular systolic dysfunction on follow-up CMR 3-5 months after diagnosis, though some patients did have persistent myocardial fibrosis. Ventricular systolic dysfunction and myocardial fibrosis were most frequent among patients diagnosed with classic myocarditis.