Challenges in left bundle branch area pacing in children and congenital heart disease: technical limitations, diagnostic pitfalls, and physiologic insights

Abstract Introduction Left bundle branch area pacing (LBBAP) restores physiologic ventricular activation in adults. However, paediatric implantation remains challenging due to small cardiac size and surgically altered congenital heart diseases (CHD) anatomy. Furthermore, it remains uncertain whether electrocardiographic criteria derived from adult cohorts can reliably define left bundle branch (LBB) capture in children. Purpose To evaluate the procedural success, diagnostic limitations of LBBAP in paediatric patients and to identify technical and interpretive challenges specific to this population. Methods We retrospectively reviewed all patients ≤18 years who attempted LBBAP from January 2021 to June 2025. Procedural details, fluoroscopy and intra-procedural transesophageal echocardiography (TEE) were analyzed. European Heart Rhythm Association criteria were applied to define LBB capture. Results Sixteen patients (median age 13.3 years; 8 male) were identified. Three patients had repaired CHD. Over a median 24-month follow-up, pacing and sensing thresholds remained satisfactory in all patients. Among those with structurally normal hearts, LBBAP can be achieved in 69.2% (9/13). Successful cases were significantly older (13.8 vs 7.8 years, p=0.025) and heavier (body weight: 48.1 vs 23.4 kg, p=0.034; body surface area: 1.43 vs 0.90 m², p=0.034). Early procedures using sheaths configured for adult anatomy tended to direct the lead to inferior septum, with subsequent failure in capturing the LBB. Adoption of atrial septal–oriented sheaths improved septal alignment, and enhanced the procedural success in children down to 20.2 kg. In children with normal anatomy and successful LBBAP, V6RWPT shortened significantly from 78ms pre-fixation to 66ms post-fixation (median reduction 14ms, p=0.0039), whereas no significant changes occurred in failed cases. Notably, 38% of patients, including some without LBB capture, had pre-fixation V6RWPT 75ms, underscoring the limited specificity of adult cut-offs. (Figure 1) Successful LBBAP showed improved ventricular synchronization, reflected by a shorter interventricular mechanical delay (12 vs 30ms, p=0.037) and reduced septal-to-posterior wall motion delay (42 vs 85ms, p=0.037) on echocardiogram assessment. In repaired CHD, fibrotic septa and surgical patches often hindered mid-septal fixation. Despite TEE-confirmed LV subendocardial positioning, threshold responses, QRS morphology, and time-based indices were inconsistent, reflecting altered septal geometry and conduction pathways (Figure 2). Conclusion LBBAP implantation in paediatrics has unique challenges. Perpendicular mid-septal lead placement is key to success. Adult-based criteria—especially fixed V6RWPT cut-offs—are unreliable in children and CHD. A composite approach incorporating relative V6RWPT shortening, threshold response, and imaging guidance provides a better methodology in confirming LBB capture in paediatrics.Figure 1Figure 2