Evolution of Myocarditis Incidence at a Large Healthcare System Before and During COVID-19 Pandemic

Abstract Background Myocarditis is a recognized complication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Emerging studies further suggest an associated risk of myocarditis following administration of messenger RNA (mRNA) COVID-19 vaccinations. coronavirus disease 2019 (COVID-19) vaccinations. We investigated the incidence of myocarditis throughout the COVID-19 pandemic across a large healthcare system in the Washington, DC, metropolitan area. Methods This retrospective analysis of patients admitted from 2017-2022. Myocarditis cases were temporally divided into two cohorts based on year of admission (pre-pandemic 2017-2019; pandemic 2020-2022), which were compared for overall myocarditis incidence. The primary endpoint was in-hospital mortality. Results The cohort included 573 myocarditis patients (pre-pandemic=208, pandemic=365). From 2017-2019, the total number and rate of myocarditis cases was consistent. Overall cases of myocarditis increased during the pandemic (97, 126, 142 patients in 2020, 2021, 2022, respectively). Interestingly, the rate of myocarditis cases not related to COVID-19 or the vaccines stayed consistent (0.0674%, 0.0676%, 0.0807%), but the rate of myocarditis related to COVID-19 or the vaccines myocarditis increased each year (0.0210%, 0.0416%, 0.0480%). In-hospital mortality was similar between the two pre-pandemic and pandemic cohorts (5.35% versus 7.7%, 0.276). Conclusion Among hospitalized patients, during the COVID-19 pandemic, the incidence of myocarditis increased as compared to the pre-pandemic era. It appears this increase is associated with either the SARS-CoV-2 infection or COVID-19 vaccination. In-hospital outcomes did not differ during the pandemic, but ongoing research is needed to evaluate the long-term impact of myocarditis during the pandemic.