Among LBB area pacing (LBBAP), it has been reported that left ventricular (LV) septal
pacing (LVSP), which refers to a pacing approach that only captures the LV septal
myocardium, produces homogeneous electrical propagation in the septum and leads to
delayed LV lateral wall activation. Although large randomized trials are lacking, small
observational studies have shown more preserved physiological ventricular depolarization,
or superior electrical and mechanical synchrony of the LBB capture over LVSP.

During the implantation of a device, the most commonly used method to distinguish LVSP
from the LBB capture is to pace with different pacing outputs. A transition will be found
in the ECG morphology with changes in the LV activation time if the pacing capture
threshold (PCT) of the local myocardium is different from that of the LBB (i.e.,
LBB-PCT), indicating a transition between capturing the LBB and LVSP without any LBB
capture. So far, there is no systematic investigation on the EGM characteristics or
correlation between ECG and EGM characteristics at different conduction system capture
status. Findings from this study will help to better characterize EGM characteristics and
to develop an optimal LBBAP modality to differentiate LBB capture.