Cardiac Magnetic Resonance Findings of COVID-19 Vaccine Associated Myocarditis at Intermediate Follow Up: a Comparison to Classic Myocarditis and MIS-C Related Myocarditis

ObjectiveTo report intermediate cardiac magnetic resonance (CMR) findings of COVID-19 vaccine associated myocarditis (C-VAM) and compare to classic myocarditis (CM) and multisystem inflammatory syndrome in children (MIS-C). Study DesignRetrospective cohort study including children diagnosed with C-VAM from 5/2021 through 12/2021 with early and intermediate CMR. Patients with CM and MIS-C with intermediate CMR were included for comparison. ResultsThere were 8 patients with C-VAM, 20 with CM, and 61 with MIS-C. Among those with C-VAM, CMR performed at median 3 days (IQR 3, 7) revealed 2/8 patients with left ventricular ejection fraction (LVEF)<55%, 7/7 patients with late gadolinium enhancement (LGE), and 5/8 patients with elevated native T1 values. Borderline T2 values suggestive of myocardial edema were present in 6/8. Follow-up CMRs performed at median 107 days (IQR 97, 177) showed normal ventricular systolic function, T1, and T2 values; 3/7 patients had LGE. At intermediate follow up the C-VAM group had a lower percentage of LVEF<55% compared to CM and MIS-C (0.0 vs 30.0 vs 6.6%, respectively, p=0.018) and an intermediate degree of LGE (42.9 vs 75.0 vs 3.3%, respectively, p<0.001). Pairwise comparisons showed fewer myocardial segments with LGE in the C-VAM group versus CM (4/119 vs 42/340, p=0.004) and more segments with LGE than MIS-C (4/119 vs 2/1020, p=0.0014). ConclusionPatients with C-VAM had no evidence of active inflammation or ventricular dysfunction on intermediate CMR although a minority had persistent LGE. Intermediate findings in C-VAM may be favorable compared to CM though LGE is more common compared to MIS-C.