Immune Checkpoint Inhibitor-Related Myocarditis: A Single Center Observational Registry

Introduction: Immune checkpoint inhibitors (ICIs) are associated with myocarditis, which is rare but has a high mortality. This study aimed to describe cases of ICI-related myocarditis at the University of Iowa Hospitals & Clinics and, in doing so, provide valuable insights into patient characteristics, treatment, and outcomes. Methods: This single-center observational registry included cases of ICI-related myocarditis identified from 2009 to 2024. Data were collected retrospectively from electronic medical records and included demographics, cardiovascular risk factors, medications, and cancer characteristics. Between-group comparisons for continuous data were conducted using unpaired Student's t-tests or the Wilcoxon rank-sum test. Categorical data were analyzed with Fisher's exact test. Results: Eighteen patients were included. The mean age was 74 ± 9.4 years with 61% being male. Compared to controls, patients with ICI-related myocarditis had a significantly higher prevalence of coronary artery disease (36.8% vs. 7.5%, p = 0.01) and obstructive sleep apnea (33% vs. 10%, p = 0.03). They were less likely to have a normal sinus rhythm on baseline electrocardiogram (50% vs. 70%, p < 0.01) and more likely to suffer from a major adverse cardiac event (MACE) (38.9% vs. 2.5%, p < 0.01). Twelve (66.7%) of patients with ICI-related myocarditis also had myasthenia gravis-like overlap syndrome and 9 (50%) had myositis/rhabdomyolysis. Conclusions: ICI-related myocarditis at a tertiary care center is rare with a calculated incidence of 0.48%. Despite this, the disease has a high incidence of MACE. Patients with pre-existing cardiovascular disease are at higher risk of developing ICI-related myocarditis. Careful cardiovascular monitoring in patients undergoing ICI therapy is warranted.