Durvalumab-Associated Myocarditis Initially Presenting With Sinus Bradycardia Progressing Into Complete Heart Block.

Durvalumab is a monoclonal antibody that blocks programmed cell death ligand-1 (PD-L1). It has been recently approved for the treatment of advanced urothelial and non-small cell lung cancer (NSCLC) with a more favorable side effect profile compared to traditional chemotherapy agents. We present a case of durvalumab-induced myocarditis complicated by complete heart block (CHB). A 71-year-old male with a history of atrial flutter status post ablation, type 2 diabetes mellitus, hypertension, and non-small cell lung carcinoma (NSCLC) recently started on durvalumab, presented with new sinus bradycardia on electrocardiogram (EKG). His initial labs were notable for a troponin T of 207 ng/L (normal range ≤50). Transthoracic echo (TTE) and computed tomography angiography (CTA) of the coronaries were unremarkable. The hospital course was complicated by CHB on telemetry for 15 minutes. Given hemodynamic instability, cardiac magnetic resonance imaging (MRI) could not be obtained. The patient received transvenous pacing. Electrophysiology and cardiology-oncology were consulted to evaluate for pacemaker implantation as well as management for durvalumab-induced myocarditis. Methylprednisolone 1000 mg intravenous (IV) was started with an improvement in troponin levels but without improvement in CHB. His course was further complicated by polymorphic ventricular tachycardia prompting the placement of a permanent dual-chamber pacemaker. The patient was discharged on a prednisone taper, and durvalumab was discontinued. A diagnosis of durvalumab-induced myocarditis was made based on elevated troponin levels, with the exclusion of coronary artery disease with CTA of the coronaries. The persistence of conduction abnormalities despite treatment with steroids leads to the placement of a permanent pacemaker. Durvalumab falls under the category of immune checkpoint inhibitor (ICI) therapy which are novel agents that have more favorable side effect profiles compared to traditional chemotherapeutic agents. A review of the literature shows myocarditis with arrhythmias as a potentially rare side effect of ICI therapy. Corticosteroid therapy seems to be promising as a potential therapy.