Clinical Characteristics and Outcomes of Acute Myocarditis: An Analysis of Korean Multicenter Registry

Background and Objectives: Data are limited on the clinical manifestations and outcomes of acute myocarditis from a large-scale registry. We investigated acute myocarditis's clinical characteristics and prognosis from a large-scale, multi-center registry in the Republic of Korea. Methods: We collected data from seven hospitals between 2001 and 2021. Clinical variables and outcomes during the index hospitalization and follow-up periods were analyzed. We also evaluated inter-center and temporal differences in diagnostic and treatment patterns. Results: Eight hundred forty-one patients diagnosed with acute myocarditis were included. Common symptoms included chest pain (60.4%), followed by fever or myalgia (46.3%), and dyspnea (45.7%). Fulminant myocarditis occurred in 421 (50.1%), with 217 requiring extracorporeal membrane oxygenation (ECMO) support. Endomyocardial biopsy (EMB) was performed in 276 (32.8%) patients, and biopsy-proven diagnosis was made in 234 (27.8%). Based on the EMB results, lymphocytic myocarditis was the predominant form (69.6%), followed by eosinophilic (13.8%) and giant cell myocarditis (1.4%). Eighty-three in-hospital (9.9%) and 16 (1.9%) additional mortality during the follow-up occurred. An increase in the use of EMB, cardiac imaging, and immunosuppressive therapy was noted over time, but in-hospital mortality remained unchanged. Remarkable variations in diagnosis and treatment were observed across different centers. Conclusions: This study unveiled clinical features of acute myocarditis in the Republic of Korea, including a high incidence of fulminant myocarditis and complex cases requiring ECMO. Given the considerable inter-center variation in diagnostic and treatment patterns and prognosis, protocolized future trials are needed to clarify diagnosis and treatment in patients with acute myocarditis.