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BACKGROUND His bundle pacing (HBP) is the most physiologic form of pacing but associated with higher thresholds and lower success in patients with His-Purkinje conduction disease. Recent reports have described transvenous left bundle branch area pacing (LBBAP). OBJECTIVE We aimed to prospectively evaluate the feasibility and the electrophysiologic and echocardiographic characteristics of LBBAP. METHODS Patients requiring pacing for bradycardia or heart failure indications (failed left ventricular [LV] lead) were prospectively enrolled. LBBAP was performed with a Medtronic 3830 lead. Presence of left bundle branch (LBB) potential, paced QRS morphology/duration, and peak LV activation time (pLVAT) were recorded at implant. Pacing threshold and sensing was assessed at implant and follow-up. Echocardiography was performed to assess the approximate lead location and impact on tricuspid valve function. RESULTS LBBAP was successful in 93 of 100 (93%) patients. Mean age was 75 6 13 years; men 69%, left bundle branch block 24%, right bundle branch block 25%, intraventricular conduction defect 8%. Indications for pacing were atrioventricular (AV) block 54%, sinus node dysfunction 23%, AV node ablation 7%, cardiac resynchronization therapy 11%, HBP lead failure 7%. Baseline QRS duration was 133 6 35 ms. Paced QRS duration was 136 6 17 ms. LBB potentials were observed in 63 patients with left bundle branch-ventricle (LBB-V) interval of 27 6 6 ms. pLVAT was 75 6 16 ms. Pacing threshold at implant was 0.6 6 0.4 V @ 0.5 ms and R waves were 10 6 6 mV and remained stable at median follow-up of 3 months. The lead depth in the septum was approximately 1.4 6 0.23 cm. CONCLUSIONS LBBAP was feasible in a high percentage of patients with low thresholds during acute follow-up. HBP and LBBAP may significantly increase the overall success of physiologic pacing.

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Background - Left bundle branch pacing (LBBP) is a novel pacing method and has been observed to have low and stable pacing thresholds in prior small short-term studies. The objective of this study was to evaluate the feasibility and safety of LBBP in a large consecutive diverse group of patients with long-term follow up. Methods - This study prospectively enrolled 632 consecutive pacemaker patients with attempted LBBP from April 2017 to July 2019. Pacing parameters, complications, ECG, and echocardiographic measurements were assessed at implant, and during follow-up of 1, 6, 12 and 24 months. Results - LBBP was successful in 618/632 (97.8%) patients according to strict criteria for LBB capture. Mean follow-up time was 18.6±6.7 months. 231 patients had follow-up over 2 years. LBB capture threshold at implant was 0.65±0.27 mV@0.5ms and 0.69±0.24 mV@0.5ms at 2-year follow-up. A significant decrease in QRS duration was observed in patients with LBBB (167.22 ± 18.99ms vs. 124.02 ± 24.15ms, p<0.001). Post implantation left ventricular ejection fraction improved in patients with QRS≥120ms (48.82±17.78 % vs. 58.12±13.04 %, p<0.001). The number of patients with moderate and severe tricuspid regurgitation decreased at 1-year. Permanent right bundle branch injury occurred in 55 (8.9%) patients. LBB capture threshold increased to more than 3 V or loss of bundle capture in 6 patients (1%), 2 patients of them had loss of conduction system capture. Two patients required lead revision due to dislodgement. Conclusions - This large observational study suggests that LBBP is feasible with high success rates and low complication rates during long term follow up. Therefore, LBBP appears to be a reliable method for physiological pacing for patients with either a bradycardia or heart failure pacing indication.