Pembrolizumab-associated myocarditis presenting as symptomatic bradycardia: A case report

An 80-year-old woman with Stage IV non-small-cell lung carcinoma developed myocarditis after two doses of pembrolizumab, an immune checkpoint inhibitor. She presented with dizziness and a slow heart rate, diagnosed as junctional rhythm. Echocardiography showed normal heart function, but cardiac MRI revealed subacute myocarditis. After treatment with atropine, a temporary pacemaker, and high-dose prednisone, her condition improved, but junctional rhythm recurred, requiring permanent pacemaker implantation. This case underscores the need for early detection and monitoring of myocarditis in patients receiving ICIs like pembrolizumab.