Real-time assessment of inter and intraventricular synchrony in cardiac resynchronization therapy with left bundle branch pacing using ECGi and low-frequency QRS analysis.

INTRODUCTION: Left bundle branch pacing (LBBP) is an alternative to conventional biventricular pacing for cardiac resynchronization therapy (CRT). METHODS: A 76-year-old male was referred for CRT via left bundle branch pacing (LBBP). We present the real-time characterization of the transition from intrinsic left bundle branch block (LBBB) to sequential pacing modalities: right ventricular septal pacing (RVSP), left ventricular septal pacing (LVSP), and finally LBBP. Epicardial activation maps from electrocardiographic imaging (ECGi) and low-frequency (LF) QRS analysis were used to provide complementary insights into inter- and intraventricular synchrony. RESULTS: LVSP, LBBP, and anodal capture improved activation compared with baseline, with LBBP achieving the greatest improvements in interventricular and LV intraventricular synchrony despite higher RV dispersion. CONCLUSION: These findings highlight ECGi and LF QRS as valuable tools to guide CRT.