Relevance of surveillance manual for the early detection of immune checkpoint inhibitor-induced myocarditis: A case series

Objective: The European Cardio-Oncology Guidelines recommend regular electrocardiography and troponin testing during immune checkpoint inhibitors (ICIs) treatment, but their efficacy for monitoring ICI treatment remains unclear. This study aimed to evaluate the effectiveness of a surveillance protocol for early detection of ICI-induced myocarditis. Methods: Between May 2014 and May 2024, patients who began treatment with ICIs at our hospital and developed ICI-induced myocarditis were included in this study. We created a straightforward management flowchart for myocarditis. The protocol was based on monitoring troponin T levels. We confirmed the efficacy of our surveillance protocol using a case series of ICI-induced myocarditis. Results: During the observation period, 3481 patients were newly started on ICIs at our hospital. Five patients were previously diagnosed with myocarditis, and five patients were diagnosed with myocarditis after the implementation of the surveillance protocol. The manual enabled the early detection of myocarditis, and the mortality rate for myocarditis at our hospital improved from 60% to 0%. The incidence of conduction system disorders significantly reduced from 100% to 0% (P < 0.01). After the surveillance protocol was initiated, there were no cases of myocarditis requiring immunosuppressive drugs beyond steroids. Conclusions: This study confirmed the relevance of a troponin-based surveillance protocol for the early detection of ICI-induced myocarditis. The implementation of the surveillance protocol reduced mortality from myocarditis and significantly reduced serious complications of conduction system disorders. Although this study is a small case series of patients who developed myocarditis, we confirm the effectiveness of surveillance for myocarditis.