Electrophysiological characteristics of lead position–dependent electrogram uninterrupted transition during left bundle branch pacing

Authors, Journal, Affiliations, Type, DOI

• Authors: Jiabo Shen, MD; Longfu Jiang, MD; Hao Wu, MD; Lu Zhang, MD; Hengdong Li, MD; Lifang Pan, MD
• Journal: Heart Rhythm 2025;22(5):1279–88 (May 2025). © 2024 Heart Rhythm Society. Open access under CC BY-NC-ND
• Type: Single-centre, observational, prospective cohort study of a procedural technique — 105 consecutive patients undergoing pacemaker implantation. No comparator arm, no randomisation
• DOI: 10.1016/j.hrthm.2024.10.062
• Note on dating: the DOI and copyright carry 2024; the issue of record is May 2025, volume 22(5). The raw filename says 2024

Overview

The conventional way to confirm left bundle branch capture is interruptive: the operator stops screwing the lead, tests pacing output, reads the ECG and electrogram, then advances again. That stop-start approach means the continuous transition of the paced ECG and intracardiac electrogram as the lead crosses the septum is never observed — only sampled, with the risk that subtle transitions are overlooked or misinterpreted. This study used a continuous pacing-and-recording technique enabled by a rotatable connector to watch those transitions in real time through lead advancement, in 105 patients. The principal finding is that the ventricular current of injury (COI) — the unfiltered unipolar injury signal at the lead tip — changes predictably with radial septal depth, peaking within the interventricular septum, and that a discrete COI component may serve as a novel marker of selective LBBP. The practical claim is that continuous COI and Stim-V6RWPT monitoring tells the operator where the lead is while it is being advanced, which both simplifies implantation and may allow earlier detection of septal perforation.

Keywords

Left bundle branch pacing; Continuous recording technique; Unfiltered unipolar electrogram; Current of injury; Septal perforation

Key Takeaways

Background and Objectives

• The interrupted technique limits continuous monitoring of paced ECG and intracardiac electrogram (EGM) transitions, "which may result in overlooked or misinterpreted subtle transitions"
• Objective: explore the electrophysiological characteristics of lead position–dependent EGM continuous transitions, to evaluate lead depth and investigate the clinical significance of transseptal pacing modalities

Methods

• A continuous pacing and recording technique enabled by a rotatable connector, allowing real-time monitoring of progressive changes in paced EGM and electrocardiographic morphology, using a transseptal pacing lead
• Observations recorded whether there were significant changes in the amplitude and morphology of the ventricular current of injury (COI), and in the R-wave peak times in leads V1 and V6 (Stim-V1RWPT and Stim-V6RWPT)
• Stim-V6RWPT = stimulus to V6 R-wave peak time; Stim-QRSd = stimulus to QRS end duration; PoLBB = left bundle branch potential; COI = current of injury

Definitions of LBB Capture — the two strict criteria

Dynamic paced QRS transition is the criterion for LBB capture diagnosis. LBB capture is confirmed by a paced QRS morphology showing right bundle branch conduction-delay pattern plus these criteria:

1. If the paced QRS morphology changes with a transition in lead V1, and the Stim-V6RWPT for 2 adjacent paced QRS complexes abruptly decreases by ≥10 ms with a constant output (2 V/0.5 ms) during lead screwing, and remains shortest and constant at low and high outputs → confirms LVSP has changed to NSLBBP
2. If the paced QRS morphology changes with a transition in lead V1, and an isoelectric interval and discrete component appear on the EGM with fixed Stim-V6RWPT → confirms NSLBBP has changed to SLBBP

• The ≥10 ms threshold is stated in the body text as "an abrupt shortening of Stim-V6RWPT by at least 10 ms"

Statistical Analysis

Bland-Altman statistics assessed interobserver agreement of the Stim-V6RWPT and COI amplitude measurements (reported in the Online Supplemental Results and Figure 1)

Results — Baseline Characteristics (Table 1)

• 105 patients underwent pacemaker implantation
• Mean age 73.7 ± 9.1 years; 51 male (58.0%)
• Pacing indication: atrioventricular block 56 (63.6%); sick sinus syndrome 31 (35.2%); atrial fibrillation with bradycardia 4 (4.5%); heart failure 5 (5.7%)
• Comorbidities: hypertension 53 (60.2%); diabetes mellitus 23 (26.1%); atrial fibrillation 22 (25.0%); coronary heart disease 14 (16.0%); cardiomyopathy 4 (4.5%)

Results — Pacing Modalities Achieved

• Nonselective LBBP (NSLBBP) in 94 patients (89.5%) — of whom 88 (83.8%) went on to achieve selective LBBP (SLBBP)
• Left ventricular septal pacing (LVSP) confirmed in 11 patients (11.5%)
• The 94 NSLBBP patients "displayed an abrupt shortening of Stim-V6RWPT by at least 10 ms"

Results — Lead Position–Dependent Parameters (Tables 2 and 3)

Procedure-related parameters (Table 2, n = 88):

Position-dependent electrophysiology (Table 3, by pacing modality):

• Ventricular COI amplitude changed predictably with radial septum depth and peaked within the interventricular septum at 26.3 ± 11.3 mV
• COI amplitude: right ventricular septal pacing (RVSP) 10.4 ± 5.8 mV versus SLBBP 11.7 ± 6.3 mV — no significant difference
• Impedance: RVSP 943.4 ± 186.3 Ω; "first" LVSP 984.5 ± 157.9 Ω; NSLBBP 926.7 ± 165.8 Ω. A significant difference was noted between "first" LVSP and NSLBBP (P < .05)
• Stim-V6RWPT: RVSP 103.2 ± 17.0 ms versus "first" LVSP 84.5 ± 13.3 ms — significant difference (P < .05). No significant difference between "first" LVSP and "last" LVSP (84.5 ± 13.3 ms vs 82.0 ± 12.0 ms)

Discussion

• "First" LVSP: the study distinguishes the initial transition through left ventricular septal pacing from the subsequent state, and shows that once first LVSP is reached, further advancement does not significantly shorten Stim-V6RWPT — so the interval does not track depth beyond that point
• Left subendocardial pacing lead localization and perforation: the continuous technique is proposed to help localise the lead relative to the left subendocardium and to prevent or detect perforation early; 3 perforations occurred (3.4%)
• SLBBP: the study's principal novel claim — "the emergence of a discrete ventricular COI may serve as a novel characteristic of SLBBP" — i.e. the injury-current morphology, not only the ECG criteria, can identify the selective state
• The authors contrast their work with Jastrzebski et al., who delineated 2 distinct transseptal ECG transition patterns to differentiate LVSP from LBBP. This study instead characterised the electrophysiological features of NSLBBP and SLBBP. They note a lower percentage of patients demonstrated Stim-V6RWPT shortening ≥10 ms in Jastrzebski's series and that COI amplitude also differed, speculating that filter-setting variations or ethnic disparities may explain it

Conclusion

• The continuous recording technique provides a more detailed understanding of pacing lead radial depth throughout implantation
• COI amplitude and morphology variations can identify different pacing modalities, particularly in recognising SLBBP
• The technique enables observing a broader array of electrophysiological phenomena during septal traversal, providing more insight, simplifying implantation, and facilitating prevention or early detection of perforations

Limitations of the document

Authors' own stated limitations

• Single centre, small sample size — "may limit the generalizability of our findings to broader populations and different clinical settings"
• Observational design precludes causality determination; the authors state that randomised controlled trials are required
• Further studies are needed to confirm the broader utility of the technique

Additional limitations evident in the study

• No comparator group and no clinical outcome endpoint. The study measures electrophysiological signals at the time of implantation; it does not test whether using the continuous technique improves lead position, reduces perforation, changes capture thresholds at follow-up, or affects any clinical outcome. The claim that it "simplifies implantation procedures, and facilitates the prevention or early detection of perforations" is inferential — 3 perforations still occurred
• The key novel claim rests on a difference that was not statistically significant. COI amplitude in RVSP (10.4 ± 5.8 mV) versus SLBBP (11.7 ± 6.3 mV) showed no significant difference, yet the conclusion proposes discrete COI morphology as an SLBBP marker. This is a morphological/qualitative observation rather than a quantitative discriminator, and it is not validated against an independent standard
• The population is not the population of interest. 63.6% had AV block and only 5.7% had heart failure; no patient group here is a CRT-indicated LBBB cohort, so the findings speak to pacemaker implantation technique rather than to resynchronisation outcomes
• Trainee/operator learning curve and filter settings are uncontrolled, and the authors themselves raise filter-setting variation as the likely explanation for disagreement with the Jastrzebski data. If filter settings materially change the COI signal, the technique's generalisability depends on matching those settings — which the paper does not standardise
• The rotatable connector enabling the technique is not characterised — its availability, cost, and whether the same observations can be reproduced with conventional equipment are not addressed
• Follow-up data are absent from the extracted content. Lead depth at implant is reported, but nothing on whether leads stayed put, threshold stability over time, or perforation sequelae
• Rating rationale: single-centre observational study, no comparator, no clinical endpoint, principal claim not statistically significant — hence medium rather than high. Its value is technical and descriptive

Key Concepts Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — the technique; this study addresses how capture is confirmed during implantation
• concepts/Conduction-System-Pacing — the umbrella category
• Current of injury (COI) — the unfiltered unipolar injury signal at the lead tip; its amplitude tracks radial septal depth and peaks in the interventricular septum, and its morphology is proposed as an SLBBP marker
• Stim-V6RWPT — stimulus to V6 R-wave peak time; the ≥10 ms abrupt shortening is the criterion for LVSP→NSLBBP transition
• PoLBB — left bundle branch potential, recorded in 75.0% here
• Selective vs nonselective LBBP — SLBBP distinguished by an isoelectric interval plus a discrete EGM component at fixed Stim-V6RWPT
• Rotatable connector / continuous recording technique — the methodological innovation; allows uninterrupted observation during lead screwing
• Septal perforation — 3.4% in this series; the target of the technique's safety claim

Key Entities Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — primary concept page
• Jastrzebski et al. — prior work delineating 2 transseptal ECG transition patterns to distinguish LVSP from LBBP; the study contrasts its findings with theirs
• Shen J, Jiang L, Pan L et al. — the investigating group (single centre)
• Heart Rhythm Society — publishing society; 2024 copyright

Wiki Pages Updated

• Created: wiki/sources/coi-lbbap-hrs-2024.md
• Updated: wiki/concepts/Left-Bundle-Branch-Area-Pacing.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md