Permanent Left Bundle Branch Area Pacing for Atrioventricular Block: Feasibility, Safety, and Acute Effect

Authors, Journal, Affiliations, Type, DOI

• Authors: Xiaofei Li, MD; Hui Li, MD, PhD (these two contributed equally); Wentao Ma, MD; Xiaohui Ning, MD, PhD; Erpeng Liang, MD; Kunjing Pang, MD, PhD; Yan Yao, MD, PhD, FHRS; Wei Hua, MD, PhD, FHRS; Shu Zhang, MD, PhD, FHRS; Xiaohan Fan, MD, PhD (corresponding)
• Journal: Heart Rhythm 2019;16(12):1766–1773. © 2019 Heart Rhythm Society, published by Elsevier. Received dates not printed in this extraction; DOI issued April 2019
• Affiliation: Department of Cardiology and Department of Echocardiography, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
• Type: Retrospective, single-centre observational cohort — 33 consecutive patients with AV block undergoing attempted LBBAP, with 3-month follow-up. The authors state it is "the first to describe the feasibility and safety of LBBAP for patients with AVB"
• DOI: 10.1016/j.hrthm.2019.04.043
• Disclosures: "The authors declare no conflict of interest"
• Why it matters here: the earliest source in this wiki dedicated to LBBAP as a bradycardia strategy rather than CRT, and the first to report LBBAP outcomes specifically in AV block — including a 90.9% success rate, a stable threshold to 3 months, the first LBBAP perforation report in this corpus, and an LBB-potential rate (26.7%) that adds to the contradiction documented on concepts/Left-Bundle-Branch-Area-Pacing

Overview

This is the Fuwai group's early case series of permanent LBBAP in 33 patients with atrioventricular block — an indication-specific extension of a technique that had until then been reported mainly as case reports and small mixed series. LBBAP succeeded in 30 (90.9%), with the other 3 falling back to LV septal pacing, and produced a low, stable threshold (0.76 ± 0.26 V at 0.4 ms at implant, 0.64 ± 0.20 V at 3 months) with a narrow paced QRS (112.8 ± 10.9 ms at implant, 116.8 ± 10.4 ms at 3 months). In the 16 patients with baseline LBBB or RBBB, bundle branch block was corrected in 11 (68.7%). The paper's value is that it reports the unglamorous parts plainly: an LBB potential was recorded in only 26.7% of successful implants, anodal capture occurred in 96.7%, lead positioning took 31.4 ± 14.1 minutes, and there was one ventricular septal perforation requiring revision. Its core limitation is stated by the authors: retrospective, single-centre, small, and only three months of follow-up.

Keywords

Atrioventricular block; Left bundle branch area pacing; Left ventricular septal pacing; Physiological pacing; Synchronization

Key Takeaways

Abstract

• Background: "Left bundle branch area pacing (LBBAP), a new pacing approach, lacks adequate evaluation"
• Objective: to assess feasibility, safety, and acute effect of permanent LBBAP in patients with AV block
• Methods: 33 AVB patients with indications for ventricular pacing. ECGs, pacing parameters, echocardiographic measurements, and complications were evaluated perioperatively and at 3-month follow-up. Successful LBBAP was defined as a paced QRS morphology of RBBB pattern in lead V1 and QRS duration <130 ms
• Results: LBBAP successful in 90.9% (30/33); mean age 55.1 ± 18.5 years; 66.7% male
  • Capture threshold 0.76 ± 0.26 V at 0.4 ms during the procedure → 0.64 ± 0.20 V at 0.4 ms at 3 months
  • Paced QRSd 112.8 ± 10.9 ms during the procedure → 116.8 ± 10.4 ms at 3 months
  • Baseline left or right bundle branch block was corrected (intrinsic QRSd 153.3 ± 27.8 ms vs paced QRSd 122.2 ± 9.9 ms) with a success rate of 68.7% (11/16)
  • One ventricular septal lead perforation occurred soon after the procedure with characteristics of pacing failure, and lead revision was successful
  • Cardiac function and LV synchrony by 2-dimensional echocardiographic strain imaging at 3 months slightly improved versus baseline
• Conclusions: "Permanent LBBAP yielded a stable threshold, a narrow QRSd, and preserved LV synchrony with few complications"

Introduction — the case for LBBAP in AV block

• The harm of RVP: it causes LV mechanical dyssynchrony, leading to systolic and diastolic dysfunction, mitral regurgitation, and increased left atrial diameter, and eventually AF, HF or cardiac death. In the Dutch FOLLOWPACE study, every 10% increase in %RVP was associated with an 8% risk of HF death
• Minimising ventricular pacing helps — but not in AV block, where RVP is "inevitable"
• HBP's three limitations, which motivate LBBAP:
  1. An increased pacing threshold may occur during follow-up, in which case RV endocardial backup pacing would be imperative, especially in advanced AVB; threshold rise can force early replacement, "one of the major causes of device infection"
  2. His lead placement is technically challenging owing to anatomy and surrounding structures
  3. For infranodal AVB — especially block in the distal His bundle — S-HBP or NS-HBP may need a high threshold or cannot be achieved at all
• The founding observations cited: Huang et al. first described peri-LBB pacing in a patient with HF and LBBB, moving the pacing site 15 mm toward the ventricle after HBP failed to correct LBBB; Chen et al. first reported clinical feasibility in 20 patients
• The anatomical rationale for the lower threshold: the LBB ramifies into three interlinked fascicles as it passes toward the apex, "which provides a relatively large area as an alternative pacing site", and the pacing site may lie distal to the His bundle area, beyond the site of block

Methods

Population

• Permanent LBBAP has been performed at Fuwai Hospital since October 2017
• Retrospective recruitment of consecutive AVB patients with indications for ventricular pacing; all enrolled patients had attempted LBBAP between 1 May and 30 September 2018
• Excluded: persistent AF, or indications for CRT or ICD
• Institutional review board approval; written informed consent

Procedure

• 3830 lead (SelectSecure, 69 cm, Medtronic) via left subclavian or left axillary vein
• C315His sheath inserted into the right atrium near the tricuspid annulus over a long guide wire
• In the RAO 30° position the lead was advanced so the distal screw sat within the catheter tip, and the sheath was advanced across the tricuspid annulus
• A His bundle electrogram was first mapped and recorded from the lead tip (unipolar)
• The tip was then moved toward the ventricle by 1.5–2 cm, and pace-mapping at 2 V/0.4 ms used to identify the ideal site, by two criteria:
  1. Paced QRSd in V1 <145 ms, or a "W" morphology with a mid notch in V1
  2. The tip directly against the septum, confirmed in LAO 45°
• The lead was screwed approximately 5–6 clockwise rotations, with the notch migrating toward the end of the QRS and the QRSd narrowing; a further 2–3 rotations were attempted until a paced RBBB pattern in V1 and an S wave in V5–V6 appeared
• Successful LBBAP was defined as a paced RBBB pattern with QRSd <130 ms
• If an LBB potential was recorded, the interval from potential to QRS onset was measured; it was expected to be identical to or less than the stimulus–ventricle interval
• ⚠ The attempt rule: "If successful LBBAP could not be achieved after 5 attempts of lead positioning or fluoroscopy duration exceeded 20 minutes, the lead was then placed in the mid-LV septum by transseptal access to achieve a relatively narrow QRSd — namely, LV septal pacing"
• S-PLVAT (stimulus-to-peak LV activation, from the ventricular stimulation signal to the R spike in V5) was measured at low (2 V/0.4 ms) and high (5 V/0.4 ms) output

Results

Population

• 33 patients: 31 with second-degree type II or complete AVB, 2 with PR >350 ms, and 12 with combined sinus node dysfunction
• Paroxysmal AF in 30.3% (10/33)
• Structural heart disease in 39.4% (13/33), including previous aortic or mitral valve replacement in 21.2% (7/33), MI/PCI in 9.1% (3/33), and congenital heart disease in 9.1% (3/33 — 1 ASD, 2 membranous septal defects with transcatheter closure)
• Baseline LBBB or RBBB in 48.5% (16/33)

Procedural and electrical outcomes

• LBBAP successful in 30 (90.9%); the other 3 ultimately received LV septal pacing after trying LBBAP
• A narrow endocardial paced QRSd (<145 ms) or a mid-notch V1 morphology was recorded in 90.0%
• ⚠ An LBB potential was recorded in only 26.7% (8/30), with a mean potential-to-QRS-beginning interval of 31.3 ± 3.1 ms
• Mean S-PLVAT 82.6 ± 15.3 ms
• Paced QRSd 113.1 ± 11.2 ms at 5 V/0.4 ms and 116.8 ± 10.4 ms at 2 V/0.4 ms
• Anodal capture at 1 V/0.4 ms in 96.7% (29/30) — a very high rate, and relevant to the wiki's note that anodal capture shortens QRS without haemodynamic benefit
• Sensed R wave 14.4 ± 5.1 mV
• Unipolar impedance: 929.9 ± 142.8 Ω endocardial → 691.7 ± 133.8 Ω after septal fixation
• Time for 3830 lead positioning: 31.4 ± 14.1 minutes
• Among the 3 failures: 2 had mitral valve replacement histories, and 1 had a membranous VSD with giant right atrium (52 × 64 mm)

Bundle branch block correction

• In complete LBBB (n=8) or RBBB (n=8), LBBAP corrected LBBB in 6 and RBBB in 5 — a successful correction rate of 68.7%
• Illustrative case: baseline complete LBBB with QRSd 196 ms corrected by unipolar LBBAP to 110 ms in V1 at 1.0 V/0.4 ms
• RBBB could be corrected by bipolar LBBAP at low output, or by unipolar pacing at relatively high output

Complications

• One ventricular septal lead perforation soon after the procedure. "The patient remained asymptomatic regarding the perforation except for having features of ventricular pacing failure." Lead revision was performed; the perforated lead was slowly withdrawn from the right ventricle, and LBBAP was successfully repeated at another endocardial site
• No other postoperative complications related to LBBAP during 3-month follow-up

Follow-up

• Mean ventricular pacing rate 79.4% at 3 months
• Pacing parameters stable over 3 months: sensing amplitude, threshold, and impedance; paced QRSd remained narrow at 3.0 V/0.4 ms
• Complete echocardiographic data at baseline and 3 months in 13 LBBAP and 3 LV septal pacing patients:
  • Left atrial diameter: 37.6 ± 7.3 → 35.8 ± 5.2 mm (downward trend)
  • LV end-diastolic diameter: 50.8 ± 7.7 → 49.2 ± 5.7 mm
  • LVEF: 62.0 ± 6.2% → 61.7 ± 6.5% (stable)
  • Mechanical dispersion: 56.8 ± 21.5 → 49.8 ± 12.3 ms — slightly improved, "especially for those patients with complete LBBB at baseline"
  • For patients receiving LV septal pacing, mechanical dispersion seemed to WORSEN

Discussion

On selective vs nonselective capture — the question is left open

• "Whether LBBAP should be additionally refined into selective or nonselective LBB pacing remains inconclusive because no unified criteria have been established for a precise definition"
• Candidate evidence for selective capture: an LBB potential with a potential-to-QRS interval <35 ms, or S-PLVAT unchanged at different outputs
• ⚠ And the counter-argument, stated plainly: "However, narrow QRSd could also be achieved by pacing both the LBB and adjacent ventricular tissues". In this study the paced QRS morphology, duration, and S-PLVAT slightly changed at different outputs in some patients, and "whether this phenomenon indicated nonselective LBB pacing remains unclear"

Advantages over HBP

• HBP has a success rate up to 80–90% but its anatomy makes fixation difficult, with "a relatively high chance of lead dislodgement"
• LBBAP offers: a large LBB area for site selection; easier fixation by screwing into the septum; more likely correction of baseline BBB because the site is beyond the block; a low and stable capture threshold; R-wave amplitudes similar to RVP; and backup pacing from adjacent septal myocardium

Complications beyond perforation

• "Coronary artery damage might be a potential major issue"
• "Another notable concern is lead fracture: because the pacing lead is screwed into the ventricular septum, long-term safety should be observed"

Mechanisms of BBB correction

• LBBB correction by unipolar low-output pacing may reflect a pacing site beyond the LBB block
• RBBB: "According to the theory of longitudinal dissociation, LBBAP could cause the RBBB pattern instead of a correction of the RBBB. However, we did observe narrowing of the complete RBBB morphology directly by unipolar LBBAP at a relatively high output", attributed to stimulation beyond the block and overcoming "the resistivity of the fibrous sheath encasing the right bundle branch"
• Incomplete RBBB can sometimes be corrected by bipolar pacing, presumably via an anodal contribution; sometimes AV delay adjustment corrects it by achieving biventricular stimulation simultaneously

Study Limitations (the authors' own)

• "A retrospective and observational study in a single center with a small sample size" — prospective multicentre studies needed
• Only 3 months of follow-up — "longer-term follow-up is necessary for the evaluation of clinical outcomes and adverse events"
• The authors nonetheless note that "few studies evaluate the feasibility and safety of LBBAP" and that this was "the first to describe the feasibility and safety of LBBAP for patients with AVB"

Conclusion

• "Permanent LBBAP yielded a stable threshold, a narrow QRSd, and preserved LV synchrony with few complications. Our preliminary results indicate that LBBAP holds promise as an attractive physiological pacing strategy for AVB"

Limitations of the document

Authors' own stated limitations

• Retrospective, observational, single centre, small sample (n=33)
• Only 3 months of follow-up, with no clinical outcomes and no long-term adverse-event data
• No comparison group — every outcome is described within the LBBAP cohort, and the 3 LVSP patients appear only in the echocardiographic substudy

Additional limitations evident in the study

• The cohort is small enough that several key results rest on single-digit denominators. Bundle branch correction is 11/16; the perforation is 1 patient; the echocardiographic substudy covers only 13 LBBAP + 3 LVSP patients. The mechanical-dispersion improvement (56.8 ± 21.5 → 49.8 ± 12.3 ms) is a within-group change with no control and no statistical test reported, and the claim that dispersion worsened with LVSP rests on 3 patients
• "Successful LBBAP" is defined by the ECG surrogate the later literature rejects as insufficient. The definition here is a paced RBBB pattern with QRSd <130 ms — while this wiki's direct-evidence study shows a paced RBBB pattern is present in 23.4–44.4% of LVSP cases and is "necessary but not sufficient" (sources/lbbp-vs-lvsp-criteria-jaccep-2021). The 90.9% "success" rate therefore describes an ECG pattern, not proven conduction-system capture, and some of these 30 patients may have had LV septal capture instead
• The LBB potential was recorded in only 26.7%, and where absent the lead was still accepted on the RBBB-pattern/QRSd definition — so capture confirmation was partly inferential in nearly three-quarters of the cohort. (For context, this figure joins a now-documented spread from 14% to 98.3%; see concepts/Left-Bundle-Branch-Area-Pacing)
• The LV septal pacing fallback is a design decision, not a measured outcome. Failure was declared after 5 attempts or 20 minutes of fluoroscopy, so the 3 patients labelled LVSP may include cases that another operator — or a longer attempt — would have converted. This is directly relevant to the live controversy over whether to keep repositioning (see Contradictions on the concept page)
• Anodal capture in 96.7% is striking and unexplained. Almost every patient had anodal capture at 1 V, and the paper does not analyse whether this contributed to the narrow QRS — despite the wiki recording elsewhere that anodal capture shortens QRS without haemodynamic benefit. The paced QRSd reported here may therefore be partly an anodal artefact
• No adjustment for the structural and valvular disease in 39.4%, including 7 patients with prosthetic valves — and 2 of the 3 failures had mitral valve replacement, which is reported as an observation but not analysed as a predictor
• The echocardiographic findings are described qualitatively ("downward trend", "seemed to worsen") and are presented as "slight improvement", which is a fair description of the effect size but is easily over-read
• Rating rationale: rated medium. It is an early, genuinely informative indication-specific series — the first for AV block — with honest reporting of thresholds, attempts, anodal capture, and a perforation, from a group that went on to become a major contributor to the field. But it is retrospective, single-centre, n=33, with a 3-month horizon, defines success by an ECG surrogate now known to be non-specific, and rests several claims on fewer than 10 patients. Consistent with how this wiki rates the other 30–45-patient observational LBBAP studies

Key Concepts Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — the technique under study
• concepts/Conduction-System-Pacing — the umbrella category
• concepts/His-Bundle-Pacing — the alternative the introduction measures LBBAP against, and the source of the "three limitations" motivating LBBAP
• Atrioventricular block as an indication — the population here, distinct from the CRT populations in most other LBBAP sources
• S-PLVAT / Stim-LVAT — stimulus to peak LV activation, measured here at 2 V and 5 V at 0.4 ms; mean 82.6 ± 15.3 ms
• Anodal capture — present in 96.7% at 1 V/0.4 ms; can shorten QRS without haemodynamic benefit
• LBB potential — recorded in 26.7%, with a potential-to-QRS interval of 31.3 ± 3.1 ms
• Mechanical dispersion / PSD — the echocardiographic strain measure used to assess LV synchrony
• Longitudinal dissociation — the theory invoked to explain why LBBAP can produce rather than correct an RBBB pattern

Key Entities Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — primary concept page
• Medtronic SelectSecure 3830 (69 cm) and C315His sheath — the lead and sheath used for every implant, the standard lumenless setup in this wiki
• Fuwai Hospital, Beijing — the single investigating centre; one of the originators of LBBP
• Huang et al. and Chen et al. — the two founding reports cited as the technique's origin
• Dutch FOLLOWPACE study — the source of the "8% risk of HF death per 10% increase in %RVP" figure
• Heart Rhythm Society / Elsevier — publisher (Heart Rhythm)

Wiki Pages Updated

• Created: wiki/sources/lbbap-avb-hrs-2019.md
• Updated: wiki/concepts/Left-Bundle-Branch-Area-Pacing.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md