TRPM4 -Related LBBB-Induced Cardiomyopathy Reversed by Left Bundle Branch Area Pacing-based Cardiac Resynchronization Therapy: A Case Report

Abstract Background Progressive cardiac conduction disease (PCCD) is a rare inherited disorder characterized by degeneration of the His–Purkinje system. Although primarily considered an electrical disease, chronic left bundle branch block (LBBB) may result in mechanical dyssynchrony and reversible cardiomyopathy. Case summary A 59-year-old man presented with progressive left ventricular (LV) dilation and systolic dysfunction. Electrocardiography showed complete LBBB with a QRS duration of 165 ms. Ischemic and infiltrative cardiomyopathies were ruled out. Cardiac magnetic resonance imaging revealed LV enlargement without late gadolinium enhancement but with marked mechanical dyssynchrony. Genetic testing identified a likely pathogenic TRPM4 c.393G > C variant, considered contributory to the conduction phenotype. LBBB-induced cardiomyopathy and heart failure with reduced ejection fraction were diagnosed. The patient underwent left bundle branch area pacing (LBBAP)-based cardiac resynchronization therapy. The QRS duration narrowed to 115 ms, and follow-up echocardiography demonstrated marked reverse remodelling with LV ejection fraction improving from 26% to 48%. Discussion This case suggests that TRPM4-related PCCD may present with isolated LBBB leading to dyssynchrony-mediated cardiomyopathy. LBBAP can effectively restore electrical synchrony and promote reverse LV remodelling. This favorable response highlights the importance of timely physiological resynchronization in potentially reversible LBBB-related cardiomyopathy.