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Effect of His Bundle Pacing on Right Bundle Branch Block Located Distal to Site of Pacing.
  • Rehan Mahmud,
  • Shakeel Jamal,
  • Brenda Harris
Rehan Mahmud
McLaren Bay Region
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Shakeel Jamal
McLaren Bay Region
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Brenda Harris
McLaren Bay Region
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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 >2.40.8 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 (919ms from 986ms). 3. NS-HBP group with capture threshold of 1.30.5V completely resolved RBBB in 9/14 vs 3/11 patients in NS-S HBP group with higher capture threshold of 2.40.8V. 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.