QRS transition during interrupted lead screwing-in to confirm left bundle branch capture during left bundle branch area pacing
Authors: Tapia Martinez M , Briongos Figuero S , Estevez Paniagua A , Sanchez Hernandez A , Heredero D , Sanchez Lopez E , Luna Cabadas A , Munoz Aguilera R 
Published: May 2024

Abstract

Background
QRS transition criteria during dynamic manoeuvers are the gold-standard for non-invasive confirmation of LBB capture, but they are seen in &lt; 50% of LBBAP procedures.

Purpose
we hypothesized that transition from LVSP morphology to LBBP morphology, when observed during lead penetration into the deep IVS with interrupted pacemapping, can suggest LBB capture.

Methods
consecutive patients with an attempt of LBBAP procedure were selected at our institution. First, we defined QRS transition from LVSP to ns-LBBP capture during interrupted lead screwing-in pacemapping. Then, we compared LVSP and ns-LBBP morphologies, according to physiologic ECG-based criteria obtained in cases in which transition was demonstrated during dynamic ECG manoeuvres using differential output pacing, with LVSP and ns-LBBP morphologies obtained in cases in which transition was observed during lead screwing-in.
QRS transition during lead screwing-in was defined as shortening of paced V6-RWPT by ≥10 ms from LVSP morphology to ns-LBBP morphology, obtained with interrupted pacemapping, during mid to deep septal lead progression at the same target area, between two consecutive pacing manoeuvres, deep and deeper, with a QR/rSR′ pattern in V1 in both (figure 1). Paced V6-RWPT had to remain short and constant in the deeper LBBP position, at high and low output pacing.

Results
305 patients with attempted LBBAP were screened. Any transition in QRS morphology occurred in 139 out of 290 successful procedures (47.9%). In 17 patients both QRS transitions (ns-LBBP to s-LBBP and LVSP to ns-LBBP) were observed. The study population consisted of 104 patients with transition from LVSP to ns-LBBP: forty-four patients with transition during lead screwing-in were compared to 60 cases with a demonstrated transition criterion during pacing manoeuvres.
Average shortening in paced V6-RWPT was similar among study groups (17.3±6.8 ms vs 18.8±4.9 ms for transition during dynamic manoeuvres and lead screwing-in, respectively; p=0.719).
Paced V6-RWPT, paced aVL-RWPT, V6-V1 interpeak interval and the recently described LBBP score, were similar for ns-LBBP morphologies in both QRS transition groups (table 1). LVSP morphologies showed longer V6-RWPT and aVL-RWPT, shorter V6-V1 interpeak interval and lower LBBP score punctuation, when compared to ns-LBBP morphologies, but no differences among the two QRS transition groups appeared.
Sixty one out of 104 ns-LBBP morphologies (58.7%) met the 100% specific criterion of V6-RWPT &lt; 75 ms or V6-V1 interpeak interval &gt; 44 ms, and it was more frequently achieved in ns-LBBP morphologies obtained during lead screwing-in compared to those obtained during dynamic manoeuvres (70.5% vs 50%, respectively p=0.036).

Conclusions
during LBBAP procedure, QRS transition from LVSP to ns-LBBP can be observed as the lead penetrates deep into the IVS with interrupted pacemapping. Shortening of at least 10 ms in paced V6-RWPT may serve as marker of LBB capture.Figure 1Table 1