Narrowing the QRS, Expanding the Function: Left Bundle Branch Pacing in Dilated Cardiomyopathy.

Left bundle branch block (LBBB) is a key driver of electrical and mechanical dyssynchrony in heart failure with reduced ejection fraction (HFrEF). Conventional cardiac resynchronization therapy improves outcomes, yet up to one-third of patients is non-responders, partly due to nonphysiological ventricular activation. Left bundle branch pacing (LBBP) has emerged as a physiological alternative by directly recruiting the His-Purkinje system. We describe the case of a 62-year-old woman with nonischemic dilated cardiomyopathy, severely reduced left ventricular ejection fraction (30%), and complete LBBB (QRS 162 ms) who remained symptomatic despite maximally tolerated guideline-directed therapy. Multimodality imaging was central to decision-making: echocardiography demonstrated severe mechanical dyssynchrony and impaired strain, while cardiac magnetic resonance (CMR) excluded ischemic scar and revealed diffuse interstitial fibrosis, supporting the indication for physiological pacing. LBBP was successfully achieved, resulting in QRS narrowing to 118 ms and stable electrical parameters. At a 6-month follow-up, the patient showed marked symptomatic improvement (New York Heart Association I-II) and significant reverse remodeling, with left ventricular ejection fraction rising to 54%, global longitudinal strain improving from -8.2% to -18.8%, reduced mechanical dispersion, and regression of functional mitral regurgitation. This case highlights the value of advanced imaging for candidate selection and for quantifying structural and functional recovery. Emerging translational data suggest that LBBP may also favorably influence molecular remodeling, including connexin-mediated gap-junction coupling. LBBP represents a promising strategy for physiological resynchronization in HFrEF with LBBB and warrants further prospective evaluation.