Severe vs Nonsevere Immune Checkpoint Inhibitor-Induced Myocarditis: Contemporary 1-Year Outcomes

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BackgroundThe long-term contemporary outcomes of patients with immune checkpoint inhibitor (ICI) myocarditis, spanning the spectrum of clinical severity, are undetermined. ObjectivesWe sought to investigate the characteristics and cardiovascular outcomes of patients with severe and nonsevere ICI myocarditis. MethodsThis was a retrospective cohort study of patients with suspected ICI myocarditis at Massachusetts General Brigham Health System conducted between 2015 and 2022. Cases were classified as severe, nonsevere, and negative based on the International Cardio-Oncology Society criteria. One-year cardiovascular mortality, all-cause mortality, and cardiovascular readmissions were evaluated. We also evaluated 1-year ICI resumption and left ventricular ejection fraction over a median follow-up of 18 (Q1-Q3: 8-67) weeks. ResultsThe study included 160 patients: 28 severe, 96 nonsevere, and 36 negative cases. Patients with severe myocarditis had an increased risk of 1-year cardiovascular mortality, particularly in the early post-myocarditis period (29% vs 5%; HR: 6.52; 95% CI: 2.2-19.6; P < 0.001). Patients with nonsevere myocarditis had a cardiovascular mortality rate similar to negative cases (HR: 0.61; 95% CI: 0.14-2.54). One-year all-cause mortality did not differ between severe, nonsevere, and negative cases (P = 0.74). Rates of 1-year cardiovascular readmissions and long-term left ventricular ejection fraction were also similar among the 3 groups. ICI resumption was low, even in negative cases. ConclusionsIn a contemporary analysis of patients with suspected ICI myocarditis, severe ICI myocarditis was associated with increased 1-year cardiovascular mortality, which was lower than previously reported. Patients with nonsevere ICI myocarditis had outcomes similar to negative cases. The optimal management strategies for nonsevere ICI myocarditis need to be re-evaluated.