Left bundle branch pacing with normal paced QRS axis produce more physiological left ventricular lateral wall depolarization than its pacing resulting in heart axis deviation

Abstract

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Ministry of Health of the Czech Republic Background Left bundle branch pacing is defined as the pacing of the trunk or its proximal fascicles, usually with septal myocardial pacing at low output. It preserves physiological left ventricular activation; however, it is unknown if there is a difference between captures with normal or deviated axes and pacing in proximal vs. distal locations. Objective To study ventricular activation during nonselective LBB pacing (nsLBBp) resulting in different paced QRS axes and proximal vs. distal pacing positions using ultra-high-frequency ECG (UHF-ECG). Methods This was a retrospective analysis of patients with bradycardia in which nsLBBp was archived during an implant procedure, and UHF-ECG analysis of ventricular activation was performed. nsLBBp captures were classified according to paced QRS axis as with superior (-30°;-90°), normal (-29°;60°), or inferior (61°;120°) axis deviation and proximal (LBbpo to ventricular EGM signal distance ≥ 26 ms) vs. distal (LBBpo to ventricular EGM signal distance < 26 ms). UHF-ECG electrical dyssynchrony parameters – e-DYS (difference between the first and last ventricular activation), local depolarization durations in precordial leads (V1-V8d), and their mean value (Vdmean) were calculated. Results We have studied 79 nsLBBp, of which 35 had superior, 28 normal, and 16 had inferior paced QRS axes. There was no difference in LBBpo to V distance, QRSduration, V5 RWPT, or e-DYS (-27 ms vs. – 22 ms vs. -25 ms for superior vs. normal vs. inferior axes; p = NS) between them. However, nsLBBp with normal paced QRS axis had shorter Vdmean (43 ±6 ms) compared to captures with superior (48 ± 7 ms) and inferior axis deviation (48 ± 6 ms); p < 0.05. It was mainly due to shorter V7-8d during nsLBBp with normal axis (mean difference of - 10 ms; p < 0.05) than in captures with superior or inferior axes. No difference in any of the studied parameters was noted when comparing proximal vs. distal pacing locations. Conclusion Nonselective capture of the left bundle branch resulting in normal paced QRS axis produces more physiological LV activation compared to captures with superior or inferior axes deviations.