Tailored electrocardiographic-based criteria for different pacing locations within the left bundle branch
Authors: Briongos Figuero S , Estevez A , Tapia Martinez M , Sanchez Hernandez A , Heredero D , Sanchez Lopez E , Luna Cabadas A , Munoz Aguilera R 
Published: May 2024

Abstract

Background
QRS morphology transition criteria are the current gold-standard for the confirmation of LBB capture during LBBAP, but they are seen in less than 40% of procedures. Thus, physiologic ECG-based criteria are widely used to confirm LBBP. Current CSP guidelines recommend 100% specific cut-off points (V6-RWPT&lt; 75 ms or V6-V1 interpeak interval &gt; 44 ms) to confirm LBB capture but these values were never validated for different pacing locations.

Purpose
To describe diagnostic performance of paced V6-RWPT, V6-V1 interpeak interval and paced aVL-RWPT for different pacing sites within the LBB and to determine 100% specific values at each pacing location.

Methods
Consecutive patients with an attempt of LBBAP procedure were screened at our institution. Only patients with unequivocal LBB capture according to QRS transition criteria were selected. The study population was divided into subgroups according to the site of pacing (left bundle trunk pacing (LBTP), left septal fascicular pacing (LSFP), left posterior fascicular pacing (LPFP) and left anterior fascicular pacing (LAFP)).

Results
147 patients with unequivocal LBB capture were analyzed (mean age 77.5±10.4 years, 50.3% male, 95.2% preserved LVEF, and 94.6% with bradycardia pacing indication. Non-diseased LBB (narrow QRS complex or isolated RBBB) was present in 70.7% of patients (n=104).
Left fascicular pacing was the most common type of LBB capture achieved (82.8%) while LBTP accounted for 17.2% of cases. LFSP was the most frequent fascicular capture (54.1%), followed by LPFP (36%) and LAFP (9.9%).
The ROC curves of paced V6-RWPT for the differential diagnosis of LBBP and LVSP showed good diagnostic performance among different pacing locations (figure 1). The highest AUC were found in patients with LSFP and LAFP (94.9% and 93.2%, respectively). The 100% V6-RWPT specific cut-off value was 68 ms (SN) 25%) in LPFP, 75 ms (SN 56.5%) in LBTP, 79.5 ms (SN 75%) in LSFP and 81 ms (SN 90.9%) in LAFP (figure 1).
The diagnostic performance of V6-V1 interpeak interval was also good among study subgroups (figure 2). The highest AUC were found in patients with LBTP and LSFP (89% and 89.4%, respectively). The 100% V6-V1 interpeak interval specific cut-off value was 35.5 ms (SN 65.2%) in LBTP, 53.5 ms (SN 32.5%) in LPFP, 46 ms (SN 44.1%) in LSFP and 41 ms (SN 63.6%) in LAFP (figure 2).
Diagnostic performance of paced aVL-RWPT was good among study subgroups (AUC of 93% in LAFP, 80.1% in LBTP, 84% in LSFP and 77.5% in LPFP). The 100% specific cut-off values for LBBP confirmation were 74 ms, 74.5 ms and 73.5 ms for LBTP, LSFP and LPFP patients, respectively, but it was 68 ms in patients with LAFP (SN 66.7%).

Conclusions
Diagnostic performance of the physiologic ECG-based criteria for the discrimination of LBBP, was good among different pacing locations within the LBB. Tailored cut-off values depending on the site of pacing might be useful additional tools for better LBB capture confirmation.Figure 1Figure 2