Effect of His Bundle Pacing on Right Bundle Branch Block Located Distal
to Site of Pacing.
Abstract
Aims: it is generally accepted that bundle branch block (BBB) may be
corrected simply by pacing (P) the His bundle (HB) distal to site of
block. This hypothesis, based on observations with percutaneous
catheters, assumes that conduction block is in proximal HB. However,
these postulations have not been systematically studied following active
fixation of HB pacing lead. We analyzed role of pacing voltage and
capture thresholds in selective (S) and non-selective (NS) HBP in
patients with right (R) BBB. Methods: In thirty-nine patients with RBBB,
4 showed S-HBP, 18 showed NS-HBP, and 17 showed NS-HBP at
>2.40.8 V and S-HBP at lower voltage (NS-S HBP group).
Results 1. During S-HBP there was no correction of RBBB. 2. NS-HBP
either completely or partially corrected RBBB along with with a decrease
in QRS activation time (919ms from 986ms). 3. NS-HBP group with
capture threshold of 1.30.5V completely resolved RBBB in 9/14 vs 3/11
patients in NS-S HBP group with higher capture threshold of 2.40.8V. 4.
During NS-HBP higher voltage caused complete resolution of RBBB in 22/39
patients vs 10/39 at lower voltage. Conclusions: 1.) Lack of correction
with S-HBP suggests that RBBB was distal to site of HBP and yet was
corrected with NS-HBP. 2.) Voltage dependent properties in NS-HBP
suggests that conduction via a specialized parallel pathway maintains
normal ventricular activation time. 3.) Correction of RBBB in all
patients with NS-HBP, suggests that conduction block was either bypassed
or right ventricular free wall pre-excited by conduction via a parallel
pathway.