Complete heart block and subsequent sudden cardiac death from immune checkpoint inhibitor–associated myocarditis

Immune checkpoint inhibitors (ICIs) are being increasingly used for the treatment of certain advanced cancers. Each drug targets a specific signaling pathway to reduce inhibition of the antitumor immune response and thus activate the body’s immune cells against cancer cells. Nivolumab, most often used in treatment of melanoma, renal cell cancer, and non–small cell lung cancer, is a human immunoglobulin G4 monoclonal antibody that selectively inhibits the programmed cell death-1 (PD-1) receptor.1 Cardiotoxicity from ICIs is thought to result from the loss of T-cell regulation and subsequent dysregulated autoimmune response to cardiac antigens.