Funding Acknowledgements Type of funding sources: None. Background Left bundle branch area pacing (LBBAP) includes both left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP). The implant procedure characteristics of these two pacing modalities have not been yet fully described. We sought to compare 2 different LBBAP implant strategies: the first one accepting LVSP as a procedure endpoint and the second one aiming at achieving LBBP in every patient. Methods Consecutive patients undergoing LBBAP at our centre from January 2020 to October 2022 were included. After our initial LBBAP learning curve, LVSP was accepted as a procedure endpoint in the first 217 patients. Thereafter, LBBP was attempted in every patient with a maximum of 5 lead deployment attempts or > 30 minutes for lead implant even if LVSP had been previously achieved. Definition of LBBP or LVSP was established according to currently accepted criteria. Procedure characteristics including total procedure time, LBBAP lead implant time, radiation exposure parameters, electrical parameters and acute complications were evaluated. Results A total of 422 consecutive patients were included in the analysis (217 patients with LVSP as acceptable endpoint, and 205 patients with LBBP as final endpoint). Baseline characteristics of the patients are described in table 1. In the LVSP group, the final capture pattern was LVSP in 57.6% and LBBP in 29% whereas in the LBBP group the final capture pattern was LVSP in 19.5% and LBBP in 71.2%. Failure of LBBAP occurred in 13.4% of LVSP group and 9.3% of LBBP group. LBBAP lead position in the septum was basal in 12,5% of LVSP group vs. 23,9% of LBBP group and medium in 81.7% and 72%, respectively (Table 2). A discrete LB potential was identified in 21.2% of LVSP group patients and in 45.8% of LBBP patients, p<0.0001. The LBBP strategy was associated with significantly longer LBBAP lead implant time (19±11min vs. 17±10 min, p=0.05), higher number of lead deployment attempts (3.4±1.8 vs 2.9±1.9, p=0.004), higher number of lead turns (22.4±4.3 vs. 18.3±4,1, p<0,0001) and higher fluoroscopy time (13.2±9.5 min vs. 10.6±9.3 min, p=0.003). Incidence of septal perforation was comparable between the 2 groups (10.6% for LVSP group and 7.8% for LBBP group, p=0.4) but development of complete AV block during implant tended to be more frequent in LBBP group (3.9% vs. 1.4%, p=0.13). The final paced QRS width, measured from the pacing spike, was comparable between the 2 groups: 161±18 ms for LVSP group and 158±19 ms for LBBP group, p=0.2. Conclusions LBBP can be achieved in more than 70% of unselected patients with significantly prolonged procedure time, higher number of lead deployment attempts and higher radiation exposure. When LVSP is accepted as an outcome, LBBP can be achieved in up to 29% of cases. The final paced QRS duration is comparable between the two implant strategies. Any potential clinical benefit of LBBP over LVSP in the long-term remains to be proven.

Funding Acknowledgements Type of funding sources: None. Background Lumen-less leads (LLL) and stylet driven leads (SDL) are currently used for left bundle branch area pacing (LBBAP). We sought to evaluate the acute performance of SDL during LBBAP in comparison with LLL. Methods This is an observational retrospective study including consecutive patients undergoing LBBAP at our institution.Acute lead performance was evaluated including implant success rate,electrical parameters,ECG characteristics and lead related complications (intraprocedure LBBAP lead dislodgment after having being penetrated into the septum in an stable position needing lead repositioning, septal perforation, coronary venous fistula, development of complete AV block not previously present and LBBAP lead damage during implant).Conduction system capture criteria were assessed before patient discharge during asynchronous ventricular pacing. Ventricular lead position within the septum was evaluated using paced QRS axis, fluoroscopic orthogonal views and post-procedure TTE, and classified as basal,mid or apical septum. Results 451 consecutive LBBAP implants were included, 333 using LLL and 118 using SDL. LBBAP acute success was significantly higher with LLL (91.6% for LLL vs 79.7% for SDL,p=0.001).Among patients with successful LBBAP,LBB capture criteria were achieved in 53.2% for LLL vs 36.4% for SDL,while left ventricular septal pacing (LVSP) was achieved in 39% vs 44.1%,respectively (p<0.0001). A basal lead position was more frequently obtained with LLL (19.8% for LLL vs 13.3% for SDL),while SDL were more frequently located at mid to apical septal positions (86.7% for SDL vs 80.1% for LLL, p=0.003).Paced ECG axis was inferior in 43.9% of LLL vs 28.9% of SDL and superior in 24.5% vs 42.1%, respectively,p=0.001.Intraprocedure lead dislodgment occurred in 9.3% of SDL vs 2.1% of LLL,p=0.001.In 5 cases of SDL (4.2%),lead damage occurred during lead implant needing lead replacement due to helix entrapment or malfunction with no such cases registered among LLL patients.Acute LBBAP lead-related complications were significantly higher for SDL vs LLL (29.1% vs 12.6%, respectively, p<0.0001,table 1),none of them needing additional interventions.Among patients with LBBAP criteria at the end of the procedure,34 (7.5%) experienced loss of r prime wave in V1 with paced QRS widening before hospital discharge,more frequently in patients with SDL (17.8% vs. 9.4%, respectively,p<0.0001) indicative of lead microdislodgment. Conclusions In our experience,acute lead performance is different between LLL and SDL.LBBAP implant success rate is significantly higher with LLL with higher percentage of patients with LBB capture criteria in comparison with SDL.SDL are associated with a more mid to apical and inferior lead position in the septum.A significantly higher rate of lead related complications during the implant procedure as well as higher rates of acute microdislodgment after implantation were also seen in SDL,none of them needing acute re-intervention.

Funding Acknowledgements Type of funding sources: None. Background/Introduction Pulse field ablation (PFA) has emerged as an effective, safe and efficient tool for pulmonary vein isolation (PVI). Purpose We studied the extent of PVI, specifically the isolation of PV antrum, carina and left atria’s posterior wall after PFA with an ultrahigh density mapping (UHD). Methods We involved the first patients referred for atrial fibrillation (AF) ablation treated with a PFA multispline catheter. PFA-lesion extension was assessed with a voltage-map UHD mapping performed before and immediately after PVI. Results Sixty-one consecutive patients underwent PVI with PFA (62±10 year old, 23 women, 39 paroxysmal AF). Four out of 61 patients were excluded because their posterior wall was isolated with extra aplications on purpose. Acute results involved a 100% success of PVI and the only safety issue was a pericardial effusion in one patient managed conservatively. Mean procedure and fluoroscopy times were 59±39 min and 16±5 min, respectively. UHD immediately after PVI revealed early reconnection just in one vein (1/228 veins). PFA created wide antral circumferential lesions without electrical activity registered by UHD mapping inside the isolation area. There were no notch-like normal voltage areas at the anterior or posterior side of carinas. As a result of the PVI with this technology, it was observed the existence of a narrow corridor in the posterior wall in 8 patients (14%) and in another 8 cases right and left antral ablation converged at the posterior wall creating an unexpected isolation area. There was a significant relationship between LA posterior inter-carina distance and posterior wall´s level of isolation (77,1±7mm, no affectation; 68,8±7mm narrow corridor; 60,3±1mm posterior wall isolation (fig 1); p=0.036). Finally, it was a significant linear correlation between posterior inter-carina distance and the distance between the ipsilateral, antral levels of isolation at the posterior wall (fig 2, r=0.79, p=0.001) Conclusion(s) PFA creates wide antral circumferential PVI lesions involving the ipsilateral veins carina. Nevertheless, in small left atria it can create an undesired isolation or a narrow corridor in the posterior wall.