Myocarditis following COVID-19 vaccination: magnetic resonance imaging study.

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To describe the cardiac magnetic resonance (CMR) imaging findings of patients who developed myocarditis following messenger RNA (mRNA) coronavirus disease 2019 (COVID-19) vaccination. The present study retrospectively evaluated patients with clinically adjudicated myocarditis within 42 days of the first Pfizer-BNT162b2 mRNA COVID-19 vaccination, between 20 December 2020 and 24 May 2021 who underwent CMR. A total of 15 out 54 patients (28%) with myocarditis underwent a CMR and were included, 100% males, median age of 32 years (interquartile range = 22.5-40). Most patients presented with chest pain (87%) and had an abnormal electrocardiogram (79%). The severity of the disease was mild in 67% and intermediate in 33%. All patients survived and one patient was readmitted during the study period. CMR was performed at a median of 65 days (range 3-130 days) following diagnosis. Median ejection fraction was 58% (range 51-74%) global- and regional wall motion abnormalities were present in one and three patients, respectively. Native T1 was available in 13/15 patients (2/3 in 3 T and 11/12 in the 1.5 T), with increased values among 6/13. Late gadolinium enhancement (LGE) was found among 13/15 patients with a median of 2% (range 0-15%) with inferolateral wall being the most common location (8/13). The patterns of the LGE were: mid-wall in six patients; epicardial in five patients; and mid-wall and epicardial in two patients. Among patients who were diagnosed with post-vaccination clinical myocarditis, CMR imaging findings are mild and consistent with 'classical myocarditis'. The short-term clinical course and outcomes were favourable.