Comparative outcomes of LBBAP vs. RV pacing in patients with a high ventricular pacing percentage

Background Left bundle branch area pacing (LBBAP) has emerged as a physiologically favourable alternative to conventional right ventricular (RV) septal/apical pacing. However, comparative evidence regarding clinical outcomes in real-world populations remains limited. Purpose To compare clinical outcomes between LBBAP and conventional RV septal/apical pacing in patients with a high pacing percentage (≥40%). Methods This single-center, retrospective study included patients who underwent pacemaker implantation between September 2022 and July 2024 and achieved ≥40% ventricular pacing during follow-up. QRS duration at baseline and under pacing was measured, and specific LBBAP parameters were recorded. Left ventricular ejection fraction (LVEF) was assessed at baseline and at follow-up when available. Clinical outcomes included heart failure (HF) hospitalization, HF-related emergency department (ED) visits, and a composite endpoint of these events. Statistical analysis was performed using SPSS 31.0 software. Cox regression was used to compare clinical outcomes. Results A total of 663 patients were included: 257 (38.8%) received LBBAP and 406 (61.2%) RV septal/apical pacing. Median age was 80.0 years (IQR 12.0), 68.3% were male, and median follow-up was 26.9±6.6 months. Indications for pacing were mostly third (41.9%) or second-degree (21.3%) atrioventricular block. Median pacing percentage was 99.0% (IQR 7.3) in the LBBAP group and 96.5% (IQR 22.0) in the RV pacing group (p>0.001). Most patients were in sinus rhythm (62.3%). Baseline QRS duration was wider in the LBBAP group (146.4±33.0ms vs. 128.3±28.1ms, p<0.001), whereas paced QRS was significantly narrower (120.0±16.1ms vs. 155.8±19.5ms; p<0.001). QRS variation differed markedly between groups (LBBAP: −27.5±30.7ms vs. RV: +26.7±28.8ms; p<0.001). Mean LVAT in LBBAP was 79.7±10.5ms, and the V6–V1 interval was 42.1±10.4ms. LBBAP was associated with an improvement in LVEF after pacing (+5.0±9.2%), whereas RV pacing resulted in a decline (−4.72±8.6%) (B=−9.667, 95% CI -11,924 to -7,409, p<0.001). The proportion of patients who lost LVEF after pacing was significantly higher in RV pacing (43.5% vs. 9.3%, p<0.001). RV pacing was associated with higher rates of HF-related ED visits (HR 1.998, 95% CI 1.159–3.444; p=0.013) and with a higher risk of the composite clinical endpoint (HR 1.777, 95% CI 1.054–2.995; p=0.031). No significant differences were found in HF hospitalizations (HR 1.381, 95% CI 0.680-2.807; p=0.372). Conclusion In patients with ventricular pacing ≥40%, LBBAP was associated with narrower paced QRS complexes, improved left ventricular systolic function, and fewer HF-related ED visits compared with RV septal/apical pacing. These findings reinforce the physiological advantages of conduction system pacing in routine clinical practice.