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Myocarditis is a rare complication of the COVID-19 mRNA vaccine. We previously reported a case series of 15 adolescents with vaccine-associated myocarditis, 87% of whom had abnormalities on initial cardiac magnetic resonance (CMR), including late gadolinium enhancement (LGE) in 80%. We performed follow-up CMRs to determine the trajectory of myocardial recovery and better understand the natural history of vaccine-associated myocarditis. Case series of patients age 19 years admitted to Boston Children's Hospital with acute vaccine-associated myocarditis following the BNT162b2 vaccine who had abnormal CMR at the time of initial presentation, and underwent follow-up testing. CMR assessment included left ventricular (LV) ejection fraction, T2-weighted myocardial imaging, LV global native T1, LV global T2, extracellular volume (ECV), and late gadolinium enhancement (LGE). Ten patients (9 male, median age 15 years) with vaccine-associated myocarditis underwent follow-up CMR at a median of 92 days (range 76-119) after hospital discharge. LGE was persistent in 80% of patients, though improved from prior in all cases. Two patients (20%) had abnormal LV global T1 at presentation, which normalized on follow-up. ECV decreased between acute presentation and follow-up in 6/10 patients; it remained elevated at follow-up in 1 patient and borderline in 3 patients.CMR performed ~3 months after admission for COVID-19 vaccine-associated myocarditis showed improvement of LGE in all patients, but persistent in the majority. Follow-up CMR 6-12 months after acute episode should be considered to better understand the long-term cardiac risks.• Myocarditis is a rare side effect of COVID-19 mRNA vaccine. •Late gadolinium enhancement is present on most cardiac magnetic resonance at the time of acute presentation.•Late gadolinium enhancement improved on all repeat cardiac magnetic resonance at 3-month follow-up. •Most patients still had a small amount of late gadolinium enhancement, the clinical significance of which is yet to be determined.

Initial reports on COVID-19 described children as largely spared from severe manifestations, with only 2-6% of children requiring intensive care treatment. However, since mid-April 2020, clusters of pediatric cases of severe systemic hyperinflammation and shock epidemiologically linked with COVID-19 have been reported. This condition was named as SARS-Cov-2-associated multisystem inflammatory syndrome in children and showed similarities to Kawasaki disease. Here, we present a narrative review of cases reported in literature and we discuss the clinical acute and follow-up management of these patients. Patients with SARS-Cov-2-associated multisystem inflammatory syndrome frequently presented with persistent fever, gastrointestinal symptoms, polymorphic rash, conjunctivitis, and mucosal changes. Elevated inflammatory markers and evidence of cytokine storm were frequently observed. A subset of these patients also presented with hypotension and shock (20-100%) from either acute myocardial dysfunction or systemic hyperinflammation/vasodilation. Coronary artery dilation or aneurysms have been described in 6-24%, and arrhythmias in 7-60%. Cardiac support, immunomodulation, and anticoagulation are the key aspects for the management of the acute phase. Long-term structured follow-up of these patients is required due to the unclear prognosis and risk of progression of cardiac manifestations.Conclusion: Multisystem inflammatory syndrome is a novel syndrome related to SARS-CoV-2 infection. Evidence is still scarce but rapidly emerging in the literature. Cardiac manifestations are frequent, including myocardial and coronary involvement, and need to be carefully identified and monitored over time. What is Known: • Multisystem inflammatory syndrome in children (MIS-C) has been described associated with SARS-CoV-2. What is New: • Patients with MIS-C often present with fever, gastrointestinal symptoms, and shock. • Cardiac involvement is found in a high proportion of these patients, including ventricular dysfunction, coronary artery dilation or aneurysm, and arrhythmias. • Management is based on expert consensus and includes cardiac support, immunomodulatory agents, and anticoagulation. • Long-term follow-up is required due to the unclear prognosis and risk of progression of cardiac manifestation.