Abstract
BACKGROUND: Coronavirus disease 2019 (COVID-19) vaccine-related myocarditis (C-VRM) is a potential adverse event following mRNA-based vaccination. Cardiac magnetic resonance imaging (CMR) is pivotal for diagnosing and monitoring myocarditis. This study compared quantitative CMR findings among C-VRM, COVID-19 myocarditis, and other myocarditis in the Korean population, and identified prognostic factors associated with adverse outcomes. METHODS: This retrospective multicenter study included patients diagnosed with various types of myocarditis who underwent CMR in four tertiary-care hospitals between October 2018 and January 2023. Clinical data and CMR findings, including cine, native T1, T2, extracellular volume (ECV), and late gadolinium enhancement (LGE) were analyzed. Differences in CMR parameters among myocarditis types were analyzed using linear regression. Predictors of adverse outcomes, defined as a composite of left ventricular ejection fraction (LVEF) of < 40% at follow-up and all-cause mortality, were assessed using logistic regression analysis. RESULTS: A total of 82 patients (mean age, 42.8 ± 19.2 years; 40 men) were included: 29 with C-VRM, 7 with COVID-19 myocarditis, and 46 with other myocarditis. C-VRM showed significantly lower native T1, T2, and ECV than other myocarditis (P = 0.001, 0.022, and 0.001, respectively), after adjustment for age, sex, and time from symptom onset to CMR. Among the 74 patients with follow-up LVEF data, seven (9.5%) experienced adverse outcomes. Maximum ECV z-score (odds ratio [OR], 1.457; 95% confidence interval [CI], 1.062-1.998; P = 0.020) and LGE extent (OR, 1.109; 95% CI, 1.029-1.194; P = 0.007) remained independent predictors after adjusting for age and initial LVEF, while myocarditis type was not associated with prognosis. CONCLUSION: In this Korean multicenter cohort, CMR markers of myocardial injury were lower in C-VRM than in other myocarditis types, whereas prognosis was more strongly associated with injury severity than with disease subtype.