Comparison of myocardial depolarization spreading after resynchronization with left bundle branch area pacing versus biventricular pacing
Authors: Zlahtic T , Starc V , Mrak M , Zupan Meznar A , Zizek D 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: None.

Introduction
Left bundle branch area pacing (LBBAP) is an emerging new method of cardiac resynchronization therapy (CRT) in patients with left bundle branch block (LBBB). Studies comparing LBBAP with standard biventricular pacing (BiV) have shown similar post-operative shortening of QRS duration and left ventricular activation times. Calculation of equivalent dipole (ED) trajectories from 12-lead high-resolution ECG (hrECG) provides additional insight into myocardial depolarization and may be used for further assessment of left ventricular activation.

Purpose
The aim of this study was to determine myocardial depolarization patterns with assessment of ED trajectories in patients undergoing CRT with LBBAP or BiV and to compare them to myocardial depolarization patterns of healthy controls.

Methods
Twenty-five heart failure patients in sinus rhythm and LBBB with indication for CRT were randomized in LBBAP or BiV pacing group. Five-minute supine 12-lead hrECG recordings before and one month after implantation were assessed. LBBAP group was compared to BiV group and both groups were compared to the control of healthy subjects with normal surface ECG. The QRS duration was measured manually by two independent electrophysiologists and averaged. ED trajectories were constructed with the use of inverse algorithm method. The length of ED trajectory was defined as a line between the start and the end of the ED trajectory and its orientation with azimuth and elevation angles. (Figure 1).

Results
Eleven patients received LBBAP and 14 BiV. There were no differences in baseline characteristics (72% male, 64% non-ischemic cardiomyopathy) between groups. The average baseline QRS duration was 174±20 ms in LBBAP and 180±17 ms in BiV group (p=0.42). QRS duration decreased to 134±14 ms after LBBAP (p&lt;0.01) and 137±11 ms after BiV pacing (p&lt;0.01) and was comparable in both groups (p=0.59). There was also no difference in absolute (p=0.72) or relative (p=0.72) QRS shortening. The absolute and relative ED shortening did not differ (p=0.43 and p=0.38, respectively). At follow-up, analysis of ED trajectories showed a significant difference in elevation angle in both groups (p&lt;0.01). The elevation angle in LBBAP group (6±30°) was significantly different from the angle in BiV group (-44±33°) (p &lt; 0.01), pointing more toward apex of the heart (Figure 2). Furthermore, elevation angle in LBBAP was more similar (absolute difference 49°) to healthy subjects than the elevation angle in BiV group (absolute difference 103°) (p&lt;0.01). There was no intergroup difference in azimuth angle (p=0.07).

Conclusion
Compared to BiV pacing, resynchronization with LBBAP produces significantly different ED trajectory orientation, which was more comparable to orientation in healthy controls. While both resynchronization methods result in similar QRS narrowing, LBBAP may provide more physiological depolarization of the left ventricle in comparison to BiV.