Introduction
The adverse effects of His bundle pacing (HBP) have been realized,
including the higher capture thresholds, risks of acute loss of capture,
early battery depletion, and lower R-wave amplitudes1. Some studies have reported that the left bundle
branch pacing (LBBP) has lower capture thresholds, higher success rate
and stability, and larger R-wave amplitudes 2,3.
Therefore, LBBP has emerged as a novel technique that can directly
capture the left bundle branch (LBB) or LBB area by a transventricular
septal approach 4. Different from HBP, LBBP induced a
right bundle branch block (RBBB) morphology while shortening the
stimulus-peak left ventricular activation time (stim-LVAT), which
represents the negative effect of LBBP on right ventricular activation5. However, there is only limited information about
LBBP performed on patients with RBBB. In practice, we observe that the
QRS complex is narrower than the intrinsic one in almost all patients
with RBBB after implantation of LBBP (Figure 1). In this article, we
describe the changes in the QRS complex in patients with RBBB after LBBP
and discuss the possible mechanisms for this situation.