Analysis by patient groups
NS-S Group:
Acute RBBB=6, Chronic RBBB=11.
These patients transitioned from NS-HBP to S-HBP at a mean pacing voltage of 2.4±0.8V (capture threshold of NS-HBP). The capture threshold of S-HBP was 1.0±0.7 V.
The baseline H-V interval was 53±8 ms. Following transition to S-HBP the stim-q interval was 57±10 ms.
In patients who developed acute RBBB with active fixation, the RBBB was completely reversed with NS-HBP phase (from 5.0V to > 2.4±0.8V), however upon transition to S-HBP phase complete RBBB recurred in all patients in this group (Fig. 1).
In patients with chronic RBBB, either partial (8/11) or complete correction of RBBB (3/11 patients) occurred but only during the NS-HBP phase at pacing voltage > 2.4±0.8V. Like acute RBBB, in all 11 patients with chronic RBBB recurred on transition to S-HBP phase (Figures 2,3).
Of the 9 patients with complete correction of RBBB, in 2 patients with acute RBBB and 1 patient with chronic RBBB as pacing voltage was lowered, a progressive increase in rightward delay was seen (Figs. 1,4). This voltage effect was seen only with NS-HBP and not during S-HBP where abrupt recurrence of complete RBBB was seen in all patients.
Figure1: Effect of NS-HBP and S-HBP in acute RBBB