Progressed Atrioventricular Block in Immune Checkpoint Inhibitor Induced Myocarditis: A Case Report.

Immune checkpoint inhibitor (ICI) has demonstrated promising results in treating various cancers, but its associated cardiotoxicity, especially ICI-associated myocarditis, presents a serious concern. We reported a case of a 63-year-old male who complained of progressive dyspnea after tislelizumab, a novel humanized anti-PD-1 monoclonal antibody, for hepatocellular carcinoma. Upon diagnosing ICI-related myocarditis, corticosteroid therapy was initiated immediately. The elevated biomarkers quickly decreased, but the atrioventricular block progressed from first-degree to third-degree, necessitating pacemaker implantation. This is the first report of complete AVB consecutive to tislelizumab-induced myocarditis, highlighting the importance of early corticosteroid therapy and continuous electrocardiography monitoring.