A total of 94 participants were included in this study. The majority of the procedures, 55.3%, was performed as part of a pace-and-ablate strategy due to refractory atrial fibrillation. The LLL group included 31 participants (33.0%), compared with 63 participants (67.0%) in the SDL group. There were no significant differences in baseline characteristics between both groups. Baseline left ventricular systolic function did not differ significantly between both groups, P = 0.577. The majority (55.3%) had a normal systolic function, with only few participants (6.4%) with severe left ventricular dysfunction. All baseline patient characteristics and pacing indications are summarized in Table 1.
Mean first follow-up was 10 ± 7 weeks with no significant differences between both groups, P = 0.950. Mean last follow-up was significantly longer in the LLL group, P < 0.001, with 45 ± 18 weeks versus 22 ± 12 weeks for SDL.
Twenty-five LLL participants (80.6%) received a RV lead in the same procedure, compared to 58 (92.1%) in the SDL group, with no significant differences, P = 0.344. Considering previously implanted transvenous systems, all participants in the SDL group had a functional RV lead as backup lead, where 26/31 (83.9%) in the LLL group had a backup RV lead. Procedural success, defined as adequate positioning of the LBBA lead and reliable pacing parameters < 24 h post-implantation, did not differ significantly between both groups, P = 0.553. Of all the procedures, one LLL procedure was not successful, due to inability to screw the lead in the right position with adequate capture, despite successful His mapping. One SDL procedure did not show LBB pacing on post-implantation ECG and no LBB potential during implantation and was, therefore, considered as unsuccessful. 33.0% of the participants showed LBB potential during implantation, with no significant differences between LLL and SDL (P = 0.576). Mean number of deployments was significantly lower in the SDL group compared with the LLL group (2 ± 2.3 versus 4 ± 3.4, P = 0.003). There was no correlation between number of deployments and paced QRS duration (P = 0.250) and number of deployments and lead impedance (P = 0.476). LBBA lead implantation time and procedural times were comparable between both the groups, although fluoroscopy duration was shorter in the SDL group (21 ± 14 min for LLL versus 15 ± 11 min for SDL, P = 0.025). All the procedural characteristics are shown in Table 2. Figure 2 shows examples of paced ECG and fluoroscopy images during implantation with both LLL and SDL.
Paced ECG characteristics
As shown in Table 3, left ventricular activation time (LVAT) and latency were comparable between both groups, respectively, 80 ± 10.6 ms (ms) and 33 ± 9.6 for LLL versus 81 ± 13.4 and 32 ± 8.2 for SDL (P = 0.587, P = 0.271). The mean paced QRS duration was significantly shorter in the LLL group versus SDL group, respectively, 101 ± 11.8 ms and 114 ± 15.0 ms, P = 0.001. 87.2% of the post-implant ECGs showed a dominant R-wave in V1, with no significant differences between LLL and SDL (P = 0.576). The majority of the LLL procedures, 64.5%, showed an inferior axis on the ECG, whereas the majority of SDL procedures showed a superior axis (P < 0.001).
At implantation, the LLL group had a significantly higher impedance of the LBBA lead: 616 ± 227 Ohm versus 458 ± 216 Ohm in the SDL group, P = 0.001. At first and last follow-ups, there was no significant difference in lead impedance, caused by a significant decrease of lead impedance in the LLL group, P = 0.001, which remained stable at last follow-up. Pacing thresholds were low in both groups, although the LLL group had significantly lower pacing thresholds at implantation: 0.7 ± 0.30 V for LLL versus 0.9 ± 0.29 V for SDL, P = 0.026. At first follow-up, pacing thresholds were comparable and remained low (0.7 ± 0.39 V for LLL versus 0.7 ± 0.50 V for SDL, P = 0.220). The pacing threshold in the SDL group was significantly decreased at first follow-up, P < 0.001. Last follow-up showed stable pacing thresholds in the SDL group compared with first follow-up, P = 0.589, with thresholds of 0.6 ± 0.20 V, although it was significantly lower compared with implantation, P < 0.001. Compared with SDL, the LLL group had significantly higher pacing thresholds at last follow-up: 0.8 ± 0.30 V, P = 0.017. There were no significant differences in LLL pacing thresholds during follow-up, P = 0.352. Lead parameters and differences between groups are shown in Table 3.
For both leads, threshold pulse width was significantly lower at first follow-up compared with acute values at implantation. Sensing values did not differ significantly between both groups at implantation and follow-up, with a R-wave sense of 12 ± 5.4 for LLL and 13 ± 4.9 for SDL at last follow-up, P = 0.284. The percentage of ventricular pacing did not differ between both groups at implantation, first follow-up and last follow-up, with mean ventricular pacing percentages of, respectively, 63, 69 and 92% (P = 0.762, 0.153, 0.479).
All complications, including the follow-up period, were registered and are specified in Table 2. The total amount of complications was four in the LLL group (12.9%) and ten in the SDL group (15.9%), with no significant differences, P = 1.000. In both groups, half of the complications were considered as major, the other half as minor. Major complications consist of possible life-threatening complications or complications requiring intervention or prolonged hospital admission. Complications that were conservatively treated and did not result in prolonged hospital admission were considered as minor complications. The complications that required intervention were a severe pocket infection in the SDL group, resulting in successful extraction of the complete transvenous system, two dislocated RV leads in the SDL group of which one was revised, and one pneumothorax in the SDL group requiring pleural drain insertion. One of the participants with the dislocated RV lead lost capture before the first follow-up. Although no specific problems were reported during the implantation, the procedure consisted of removing an old, dislocated RV lead as well. The other participant showed a decrease in RV sense the first day of follow-up (23.6–3.5 mV), without any problems reported during the implantation. Since the participant also experienced pain complaints of the pacemaker generator, lead and pocket revision were performed. Two of the patients in the LLL group lost capture of the LBBA pacing lead during His bundle ablation, both with a backup RV lead. One LBBA lead was successfully revised. Since the other patient had a normal left ventricular ejection fraction, a conservative approach was adopted. In the SDL group, one participant lost LBBA pacing due to dislocation of the LBBA lead, presumably due to a trauma 2 weeks after implantation. Lead explantation has been performed safely.
Considering the participants with LBBA lead dislocation and LBBA lead damage during follow-up, success rates at mean follow-up of 30 weeks were 96.8% in the SDL group and 90.3% in the LLL group, P = 0.199. This resulted in an overall success rate of 94.7%. Procedural success rate was higher: 98.4% in the SDL group compared with 96.8% in the LLL group, with an overall procedural success rate of 97.9%.