Left Ventricular Pacing‐Associated Cardiomyopathy Revealing Myocardial Vulnerability in Congenital Complete Heart Block

ABSTRACT Background Mechanisms underlying cardiac manifestations of immune‐mediated congenital complete heart block (CCHB) remain unclear. Dilated cardiomyopathy (DCM) in immune‐mediated CCHB has been associated with RV pacing, whereas reports of LV pacing‐associated DCM are lacking. Case summary A girl with immune‐mediated CCHB showed endocardial fibroelastosis (EFE) at 20 weeks of gestation before heart block developed at 22 weeks. After LV basal‐lateral pacing, she developed DCM with LV dyssynchrony. Cardiac resynchronization therapy (CRT) improved LV function and induced reverse remodeling. Conclusions Myocardial injury may precede conduction system involvement in immune‐mediated CCHB. Subclinical immune‐mediated myocardial vulnerability and pacing‐related dyssynchrony may contribute to DCM progression.