Left Bundle Branch Pacing

Authors, Journal, Affiliations, Type, DOI

• Authors: Shu Zhang, MD, PhD; Xiaohong Zhou, MD; Michael R. Gold, MD, PhD
• Journal: J Am Coll Cardiol 2019;74(24):3039–49 (December 17, 2019). JACC Review Topic of the Week. Manuscript received 12 August 2019; revised 15 October 2019; accepted 28 October 2019
• Affiliations: State Key Laboratory of Cardiovascular Disease, Arrhythmia Center, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing (Zhang); Cardiac Rhythm and Heart Failure Division, Medtronic, Dublin (Zhou); Division of Cardiology, Medical University of South Carolina, Charleston (Gold)
• Type: Narrative review — a Review Topic of the Week, not a trial or systematic review. No formal evidence grading; the underlying evidence is observational series and case reports
• DOI: 10.1016/j.jacc.2019.10.039
• Disclosures: Dr. Zhou is an employee of Medtronic, a manufacturer of pacing leads and delivery systems for this indication; Dr. Gold received consulting fees and honoraria from Medtronic and Boston Scientific. Dr. Zhang reported no relevant relationships

Overview

This is the paper that introduced left bundle branch pacing (LBBP) to the wider electrophysiology literature, and it is written as a solution to a specific failure rather than as a new technique in search of an indication. Right ventricular apical pacing causes electrical and mechanical dyssynchrony and increases the risk of heart failure and atrial fibrillation; biventricular CRT reduces dyssynchrony but leaves many non-responders and remains nonphysiological; and His bundle pacing — though genuinely physiological — fails in precisely the patients who most need resynchronisation, because QRS cannot be normalised in nearly half of LBBB patients. LBBP's insight is geometric: advance a lead across the interventricular septum to pace the left bundle distal to the site of block, bypassing the pathological or disease-vulnerable segment. The review assembles the early observational evidence, defines the technique's electrical signatures — RBBB-pattern delay in V1–V2, a recordable LBB potential, and a fast left ventricular activation time — and is notably candid about how little was known in 2019: no prospective registries, use only since 2017, no dedicated leads or sheaths, undefined implantation criteria, and a cohort of LBBB patients whom the technique cannot help.

Keywords

The article provides an abbreviations and acronyms list rather than author keywords: AV, atrioventricular; CRT, cardiac resynchronization therapy; ECG, electrocardiographic; HBP, His bundle pacing; IVS, interventricular septum; LBB, left bundle branch; LBBB, left bundle branch block; LBBP, left bundle branch pacing; LV, left ventricular; RBB, right bundle branch; RBBB, right bundle branch block; RV, right ventricular; RVAP, right ventricular apical pacing.

Key Takeaways

The Problem LBBP Was Designed to Solve

• Right ventricular apical pacing (RVAP) has been used for >50 years but causes electrical and mechanical dyssynchrony, and is associated with increased risk of heart failure and atrial fibrillation. Pacing at alternative RV sites (septum, outflow tract) has not been shown superior
• CRT with biventricular pacing promotes LV reverse remodelling, improves exercise tolerance and reduces HF hospitalisation and mortality — but a significant proportion of patients are non-responders, and the modality is nonphysiological, activating ventricular myocardium rather than the specialised conduction system. Paced QRS duration therefore remains prolonged even when reduced
• His bundle pacing is physiological — selective HBP gives normal biventricular activation — but has specific limitations: the His bundle is only ~1–2 mm in diameter and difficult to locate; high and unstable thresholds in 5–10% of patients; low R-wave amplitude or large atrial signals complicating programming; risk of damage to the His bundle during implantation; and potential limitations in long-term performance
• The critical failure: in patients with bundle branch block — especially LBBB with heart failure, where HBP could be a CRT alternative — HBP success rates are lower and the output required to correct LBBB is high. The His-SYNC study showed QRS duration cannot be normalised in almost half of patients with LBBB, suggesting the block cannot be overcome by HBP in that subset

The LBBP Concept and Its Origins

• The hypothesis behind HBP in LBBB is that increased output penetrates the LBBB region beyond the area of block and directly excites the LBB. Pacing the LBB was pioneered by El-Sherif et al. in acute studies using HBP at ~20 V
• Huang et al. reported the first direct LBBP during pacemaker implantation: standard HBP at very high output (10 V) failed to correct LBBB, but advancing the pacing tip toward the ventricle resolved LBBB at a low capture threshold (0.5 V). The patient's LV ejection fraction rose from 32% to 62% with reduction in LV volume. Pacing produced RBBB on the surface ECG at a short paced AV interval (40 ms), and the QRS normalised with AV delay prolongation — demonstrating LBBP synchronised with intrinsic RV activation
• Chen et al. developed the transventricular septal approach in a series of bradycardia patients. With the tip on the right side of the interventricular septum (IVS), the paced ECG showed an LBBB pattern; advancing to the left side of the IVS produced an RBBB conduction-delay pattern, indicating LBB pacing. Recording an LBB potential during intrinsic rhythm provided strong evidence the pacing site was at the LBB, supported by 3-dimensional echocardiography showing the tip in or near the left-sided subendocardium
• The headline QRS comparison (Chen et al.): paced QRS 111.85 ± 10.77 ms with LBBP versus 154.80 ± 9.85 ms with RV septal pacing and 165.50 ± 17.80 ms with RVAP — with comparable pacing capture threshold
• Notably, both LBBB and RBBB could be corrected by LBBP at low capture threshold
• A technique that is probably not LBBP: Mafi-Rad et al. used a custom electrode and transseptal approach to pace the left side of the IVS, achieving QRS shortening to 144 ± 20 ms — longer than the ~110–130 ms seen with true LBBP, and without recording LBB or Purkinje potentials, presumably because the pacing location is more apical. This technique likely does not achieve LBB activation, though the relative clinical benefit is unknown

Implantation Technique

• Place the pacing lead perpendicular to the ventricular septum, approximately 15–20 mm below the tricuspid valve annulus, under fluoroscopy using right anterior oblique 30° and/or left anterior oblique 30° projections. This makes it relatively simple to advance the helix to the left side of the IVS
• The ECG transition guides lead advancement:
  1. Pacing the right side of the IVS produces an LBBB pattern
  2. As the lead advances, the LBBB pattern gradually diminishes
  3. An RBBB pattern appears, suggesting the pacing site is at the LBB
  4. At this point a fast LV peak activation time of ~80 ms should be noted
  5. When the lead is near or at the LBB, an LBB potential can be recorded
• Once these electrical characteristics are observed, no further lead advancement should be performed, to avoid perforation

Electrical Characteristics of LBBP

1. RBBB conduction delay or block in ECG leads V1 and V2 — indicating activation of the LBB without excitation of the RBB
2. An LBB potential recordable in approximately 50–80% of implants. The interval from LBB potential to ECG QRS onset is 15–30 ms — shorter than the His potential to QRS onset interval of typically ~50 ms
3. A fast LV peak activation time of ~80 ms, indicating fast activation propagation through the LV specialised fascicules

• Mechanistic studies (Zou et al.; 3-dimensional activation mapping) showed LBBP with a recorded LBB potential generates ventricular synchrony similar to HBP, and Li et al. (33 patients with AV block) found LBBP preserved LV mechanical synchrony alongside stable low thresholds and narrow paced QRS

Selective vs Nonselective LBBP

• Nonselective LBBP: no isoelectric segment before the onset of the paced QRS, indicating direct myocardial activation in addition to LBB capture
• Selective LBBP: a distinct isoelectric segment before the paced QRS onset
• LBBP often causes incomplete RBBB (RBB conduction delay) rather than complete RBBB. The review considers why and notes that retrograded activation seems improbable (since RBB delay also occurs in patients with complete LBBB); virtual stimulation and cell-to-cell conduction between LBB and RBB are offered as candidate mechanisms
• RBBB with LBBP can often be avoided by programming an AV delay to achieve fusion of LBBP with intrinsic RBB activation, or by bipolar pacing in which the cathodal helix excites the LBB while the anodal ring excites the RBB area
• When LBBP alone does not fully correct LBBB, LBBP fused with LV epicardial pacing via the coronary sinus can further shorten paced QRS

Adoption (as of 2019)

• The technique was rapidly adopted in China. The Chinese Society of Pacing and Electrophysiology centralised registry recorded approximately 5,000 conduction system pacing cases in 2018, of which ~80% were LBBP
• Use elsewhere was less well established; the first US experience in 100 patients had recently been reported (Vijayaraman et al.)

Clinical Implications

• The pacing site can be distal to the pathological or vulnerable region — the AV node, His bundle, or proximal LBB — and the transventricular septal approach makes LBBP easier to perform than HBP, requiring less precision for lead placement
• Potential alternative to conventional CRT in heart failure with ventricular dyssynchrony, and possibly an optimal choice in typical LBBB. Zhang et al. reported LBBB correction, electrical and mechanical resynchronisation, and improved clinical outcomes in 11 consecutive CRT-indicated patients
• In patients with systolic heart failure, no pacing indication and narrow QRS, CRT is deleterious — so LBBP or HBP may be better choices, using the native conduction system rather than pacing two nonphysiological sites. Whether LBBP equals or exceeds biventricular CRT requires prospective randomised trials
• LBBP bypasses infra-Hisian block or iatrogenic AV node block after AV node ablation, and offers more physiological activation than RV pacing in bradycardia with either LBBB or RBBB
• Paced QRS is typically <130 ms, rather than the complete RBBB complex initially expected
• Advantages over HBP: lower and more stable capture threshold (pacing site in septal tissue) improving device longevity and possibly avoiding a backup lead; higher sensed R-wave amplitude simplifying programming; often simpler and faster implantation because LBB fascicules are widely spread in the left-sided subendocardium; and a logical choice after failed HBP

Unknowns and Future Investigation

• Long-term safety is not adequately studied — the technique had been widely used only since 2017, with no prospective registries
• Procedural complications: LV perforation from advancing through the septum; theoretical thrombus if the lead tip remains in the LV chamber; RBB injury and possible septal artery injury from repeated attempts or manipulation within the septum; the number of safe lead-repositioning attempts is unknown. Vijayaraman et al. reported acute lead dislodgement in 3 of 97 patients
• Long-term threshold data are limited, especially where low output is used for selective LBB capture. The effect of the distal lead body inside the septum on local myocardial contractility has not been studied, and there are no studies on lead extraction from this location
• Implantation criteria and the specific target location remain poorly defined — acceptable QRS duration and configuration, and LV activation time, all require consensus. An LBB potential is recorded in only 50–80% of patients and the RBBB ECG pattern is often atypical. Imaging methods for locating the pacing site should be explored
• Post-implantation, pacing parameters and mode need optimisation to achieve synchrony, particularly when LBBP must be synchronised with another modality or with intrinsic rhythm; when to use bipolar stimulation is also unresolved
• Which heart failure patients are best suited to LBBP versus HBP or conventional CRT is unknown. Critically, a study found LBBB with intact Purkinje activation in ~36% of 72 investigated patients with LBBB — so LBBP alone is unlikely to benefit that group, making it important to relate surface ECG characteristics to the presence of true discrete LBBB
• The technique is best studied in non-ischemic heart disease; criteria for ischemic cardiomyopathy — which constitutes most CRT patients — remain to be established, as do those for patients in whom LBBP produces an unresolvable RBBB
• No dedicated leads, delivery tools or sheaths exist for LBBP — the systems used were designed for RV pacing

Limitations of the document

Stated and evident in the review itself

• This is a narrative review without formal evidence grading. It is a Review Topic of the Week, not a systematic review or meta-analysis; there is no search strategy, no risk-of-bias assessment, and no quantitative synthesis. Every clinical claim rests on observational series and case reports, most of them small
• The evidence base at the time was extremely thin. The technique had been in wide use only since 2017; there were no prospective registries and no randomised trials. The largest supporting series cited are the Chinese registry (~5,000 conduction system pacing cases, ~80% LBBP — a procedural census rather than an outcome study), a 100-patient US experience, 33 patients with AV block, and 11 consecutive CRT-indicated patients. The review's own conclusions call for prospective trials and mechanistic investigation
• Two of three authors have device-industry relationships, and one is a manufacturer employee. Dr. Zhou is employed by Medtronic, which makes the pacing leads and delivery systems discussed, and Dr. Gold received consulting fees and honoraria from Medtronic and Boston Scientific. The review's central claim — that LBBP is simpler, has better thresholds and is a logical choice after failed HBP — concerns a procedure performed with those manufacturers' hardware. This is disclosed, and it does not make the technical description wrong, but the enthusiasm should be read with it in view
• The technique's defining electrical criteria are themselves unreliability-prone. An LBB potential is recordable in only 50–80% of implants, so in one-fifth to one-half of cases the operator lacks the single most specific confirmation of LBB capture. The review states that the criteria for successful implantation "need to be confirmed"
• A substantial fraction of the target population may not benefit. The finding that ~36% of LBBB patients have intact Purkinje activation means the block is not where LBBP assumes it is for a third of patients — and the review offers no way to identify them prospectively
• The comparison against CRT is uncontrolled. The claim that LBBP may be an alternative to biventricular pacing rests on single-arm series and one 11-patient experience. The review states plainly that this "needs to be confirmed in prospective randomized clinical trials"
• Safety data are procedural and short-term. Lead dislodgement in 3 of 97 patients is the only quantified complication in the review; perforation, thrombus, RBB injury, septal artery injury and extraction risk are described as theoretical or unstudied
• Publication date. 2019. The field has moved substantially since — later consensus criteria for defining and confirming LBB capture, larger comparative series, and randomised comparisons against biventricular CRT all postdate this review. This source is the foundational framing, not current technique standards

Key Concepts Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — the technique this review introduced to the wider literature; supplies its foundational 2019 evidence
• concepts/His-Bundle-Pacing — the physiological predecessor whose specific failure in LBBB motivated LBBP
• concepts/Conduction-System-Pacing — the umbrella category
• concepts/Cardiac-Resynchronization-Therapy — the established comparator; LBBP is positioned as a potential alternative in typical LBBB and possibly preferable where CRT is deleterious (narrow QRS)
• LBB potential — the most specific marker of LBB capture, recordable in 50–80% of implants, 15–30 ms before QRS onset
• Left ventricular activation time (LVAT) — ~80 ms with LBBP; the fast time indicates conduction-system rather than myocardial activation
• Selective vs nonselective LBBP — distinguished by an isoelectric segment before the paced QRS
• RBB conduction delay / incomplete RBBB — the expected ECG signature of LBBP, and the reason its mechanism is debated
• Transventricular septal approach — the implantation route, and the reason LBBP is easier than HBP
• Virtual stimulation — proposed mechanism for incomplete RBBB during LBBP

Key Entities Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — primary concept page
• Medtronic — employer of one author and manufacturer of the leads and delivery systems discussed
• Fuwai Hospital / Chinese Academy of Medical Sciences — the group behind the first reported LBBP and the Chinese registry
• Medical University of South Carolina — corresponding author's institution (Michael R. Gold)
• Huang et al. — first reported direct LBBP; Chen et al. — transventricular septal approach and the QRS comparison; El-Sherif et al. — earliest LBB pacing attempts; Teng et al. — distal His placement hypothesis; Mafi-Rad et al. — left-sided IVS pacing that is probably not LBBP; Zou et al. / Li et al. — mechanistic and synchrony studies; Vijayaraman et al. — first 100 US patients
• His-SYNC and Chinese Society of Pacing and Electrophysiology registry — the two named data sources framing the problem and the adoption

Wiki Pages Updated

• Created: wiki/sources/lbbap-jacc-2019.md
• Updated: wiki/concepts/Left-Bundle-Branch-Area-Pacing.md
• Updated: wiki/concepts/Conduction-System-Pacing.md
• Updated: wiki/concepts/His-Bundle-Pacing.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md