Assessing V6 RWPT and V6-V1 interpeak time as conduction system capture criteria in non-basal LBBAP lead positions
Authors: Rijks J , Sandgren E , Lankveld T , Van Stipdonk A M W , Timmer S A J , Vernooy K , Luermans J G L M 
Published: May 2024

Abstract

Background
In left bundle branch area pacing(LBBAP) a basal septal lead position is usually aimed for. However, in clinical practice LBBAP leads might be implanted in a non-basal position. A basal lead position is characterized by a paced monophasic R-wave in lead V6, whereas a non-basal position leads to a paced Rs/rS pattern in lead V6(1). Because differences in interval from pacing stimulus to peak R-wave in lead V6(V6 RWPT) and interval between peak R-wave in lead V6 and lead V1(V6-V1 interpeak time) in non-basal positions might be observed, it is unclear if the current cut-off values for these intervals can be used for conduction system capture(CSC) verification in non-basal placed LBBAP leads.

Purpose
To investigate the differences in paced V6 RWPT and V6-V1 interpeak time between basally and non-basally implanted LBBAP leads and to identify optimal cut-off values for CSC verification in non-basally implanted LBBAP leads.

Methods
Patients implanted with an LBBAP lead were retrospectively screened and included when a paced Rs/rS was demonstrated in lead V6 &gt;20%(1) of the total QRS amplitude. A random selection of LBBAP patients without a paced Rs/rS in lead V6 implanted in the same period were included as comparator. CSC was confirmed by an output-dependent QRS transition at decremental voltage output pacing or an interval from the left-sided Purkinje potential to V6RWPT in intrinsic rhythm equal to paced V6RWPT. If none of these were present, left ventricular septal pacing was assumed.

Results
Eighty patients were included for analyses. Baseline characteristics are presented in fig. 1. Patients with non-basally implanted LBBAP leads were significantly younger(p=0.004) and showed a significantly shorter interval from left-sided Purkinje potential to QRS onset(p=0.041). Paced V6RWPT was significantly shorter in a non-basal lead position (70±12ms vs. 77±9ms, p=0.005), fig 2A. V6-V1 interpeak time was significantly longer in non-basal lead positions(52±14ms vs. 40±9 ms, p&lt;0.001), fig 2A. A V6RWPT cut-off &lt;70ms(sens. 78%, spec. 83%, AUC 0.79) was optimal for CSC confirmation in non-basal lead positions with 100% specificity achieved &lt;55ms. A V6-V1 interpeak time cut-off &gt;47ms(sens. 74%, spec. 65%, AUC 0.73) was optimal for CSC capture confirmation with 100% specificity achieved &gt;73ms, fig 2b.

Conclusion
The interval from left-sided Purkinje potential to QRS onset in patients with a paced Rs/rS in lead V6 is significantly shorter than in patients with a paced monophasic R in lead V6, suggesting a more distal lead position. This lead position leads to significant shortening of V6 RWPT and prolongation of V6-V1 interpeak time, affecting known diagnostic criteria for conduction system capture. An optimal cut-off &lt;70 ms and 100% specificity &lt;55ms for conduction system capture confirmation with V6 RWPT is suggested. An optimal cut-off &gt;47ms and 100% specificity &gt;73ms for conduction system capture confirmation with V6-V1 interpeak time is suggested.