Tailored electrocardiographic-based criteria for different pacing locations within the left bundle branch

Electrocardiographic (ECG)-based criteria are used to confirm left bundle branch (LBB) pacing (LBBP), but current cut-off values have never been validated for different pacing locations. To describe diagnostic performance of V6-R wave peak time (RWPT), V6-V1 interpeak interval and aVL-RWPT for different pacing sites within the LBB and to determine 100% specific values for each criterion at each pacing location. Consecutive patients with confirmed LBBP were selected. Population was divided into subgroups based on 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). A total of 147 patients with unequivocal LBB capture were analyzed. Left fascicular pacing (LFP) was more frequently achieved (82.8%) than LBTP (17.2%). Diagnostic performance of V6-RWPT, V6-V1 interpeak interval and aVL-RWPT for the discrimination of LBBP was good in all subgroups. V6-RWPT cut-off values with 100% specificity (SP) for LBBP discrimination were 75 ms in LBTP, 68 ms in LPFP, 81 ms in LAFP, and 79.5 ms in LSFP. V6-V1 interpeak interval cut-off values with 100% SP for LBBP discrimination were 35.5 ms in LBTP, 53.5 ms in LPFP, 41 ms in LAFP, and 46 ms in LSFP. In LAFP, aVL-RWPT cut-off value with 100% SP for LBBP discrimination was 68 ms, while it was 74 ms in LBTP, 74.5 ms in LSFP, and 73.5 ms in LPFP. Tailored ECG-based criteria might be useful to confirm LBBP at different pacing locations within the LBB.