NS-HBP Group:
Acute RBBB=4, Chronic RBBB=14
These patients showed only NS-HBP. The baseline characteristics were similar to NS-S group however the capture threshold of the pre-excitation wave now occurred at lower pacing voltage of 1.3±0.5V compared to 2.4±0.8V in NS-S HBP group. The mean H-V interval was 52±5 ms. The HVAT at baseline was 98±6 ms and decreased to 89±5 ms with 5V pacing.
All 4 patients with acute RBBB showed complete resolution of RBBB at 5V pacing 2 of the 4 showed partial recurrence of RBBB at lower voltage.
Of 14 patients with chronic RBBB, 9 had complete resolution at 5V and 5 had incomplete resolution at both high and low voltage pacing. In 9 patients with complete resolution at 5V, 6 developed partial recurrence at lower voltage during NS-HBP.
Thus in 8 patients (2 acute and 6 chronic), RBBB showed a voltage effect where complete resolution was seen at 5V however the only partial correction at lower voltage.
S-HBP Group:
Acute RBBB=2, Chronic RBBB=2.
Only 4 patients showed S-HBP at both high and low pacing voltages.
The mean H-V interval was 57±12 ms, the baseline HVAT interval was 108±19 and decreased to 97±15 ms with S-HBP.
Acute RBBB (2 patients): Only 1 patient with acute RBBB resolved completely with 5V although NS-HBP could not be ruled out. Complete RBBB recurred at 3.5V (Fig.5).
Chronic RBBB (2 patients). Neither complete nor incomplete resolution of RBBB was seen at any voltage (Fig. 5).
Figure 5: Effect of 5V pacing on RBBB in S-HBP