Long-term CMR Findings in Pediatric COVID-19 Related Myocarditis

Cardiac magnetic resonance (CMR) is a key modality for diagnosing and monitoring myocarditis, including cases related to COVID-19 infection and Multisystem Inflammatory Syndrome in Children (MIS-C). While acute findings are often favorable, the persistence of abnormalities over time remains uncertain. This retrospective study included 21 pediatric patients with suspected COVID-19-related myocarditis between March 2020 and July 2023. All underwent CMR as part of clinical evaluation. Imaging findings were analyzed at early (< 30 days), mid (30-364 days), and long-term (≥ 365 days) intervals. Myocarditis was defined using the 2009 Lake Louise criteria. Of the 21 patients (mean age 13.1 years, 57% male), 8 had follow-up CMRs (median time to follow-up 347 days). Etiologies included MIS-C (57%), confirmed COVID-19 (19%), and suspected COVID-19 (24%). A total of 30 CMR studies were analyzed. Initial CMR met 2009 Lake Louise criteria in 8 patients (38%). Across temporally categorized studies, LGE declined from 46% of early studies to 25% of mid-term studies and was absent on long-term studies; pericardial effusions similarly declined from 46% to 25% to 0%. EGE remained frequent across timepoints (77%, 83%, and 80%, respectively). Among patients with serial CMR, no patient had edema on follow-up, LGE persisted in 1 of 8 (13%), pericardial effusion in 1 of 8 (13%), and only 1 of 8 (13%) continued to meet Lake Louise criteria. Biventricular systolic function remained normal on follow-up imaging. Initial LGE demonstrated marked lateral wall predominance (Cochran's Q = 13.38, p = 0.004). Median clinical follow-up was 20 months (IQR 11-38), with no documented arrhythmias, heart failure symptoms, cardiac-related rehospitalizations, or mortality. In pediatric myocarditis associated with COVID-19, most CMR abnormalities improve over time, with resolution of edema and substantial reduction in LGE and pericardial effusion. Persistent EGE remains common, although its clinical significance is uncertain. Medium-term clinical outcomes were favorable. Larger prospective studies are needed to define the long-term significance of persistent imaging abnormalities.