Restoration of Cardiac Function in Left Bundle Branch Block-Induced Cardiomyopathy via Conduction System Pacing: A Case Report

BACKGROUND Left bundle branch block (LBBB) is not uncommon. In certain cases, patients with LBBB exhibit a deterioration of cardiac function, ultimately progressing to a clinical phenotype resembling cardiomyopathy in the absence of an alternative etiology, a condition referred to as left bundle branch block-induced cardiomyopathy (LIC). We present a case of a 57-year-old woman who developed LIC 1 year after the onset of new LBBB. Following conduction system pacing (CSP), her cardiac function was completely restored. CASE REPORT A 57-year-old woman presented with normal electrocardiograms (ECGs) and heart function 1 year prior. After developing LBBB, she experienced progressive dyspnea and reduced exercise tolerance over the subsequent year, during which her left ventricular ejection fraction (LVEF) declined from 55% to 31%. A comprehensive diagnostic workup revealed interventricular mechanical dyssynchrony and excluded ischemic or structural etiologies, which is consistent with LIC. Guideline-directed medical therapy was initiated; however, her symptoms persisted after 6 months of therapy. Following CSP for cardiac resynchronization therapy, the patient's LVEF improved to 54% at 6 months and further increased to 56% at 30 months, approaching normalization. CONCLUSIONS LIC is a recently identified condition wherein patients with LBBB experience left ventricular dysfunction and mechanical dyssynchrony without an alternative etiology. Emerging evidence indicates that CSP may effectively correct the electrical dyssynchrony associated with LBBB. We present a case of a patient diagnosed with LIC within 1 year of symptom onset, who exhibited significant improvement following CSP treatment. This case highlights the critical importance of early diagnosis and timely intervention.