Left Bundle Branch Pacing Compared to Left Ventricular Septal Myocardial Pacing Increases Interventricular Dyssynchrony but Accelerates Left Ventricular Lateral Wall Depolarization

Authors, Journal, Affiliations, Type, DOI

• Authors: Karol Curila (corresponding), Pavel Jurak, Marek Jastrzębski, Frits Prinzen, Petr Waldauf, Josef Halamek, Kevin Vernooy, Radovan Smisek, Jakub Karch, Filip Plesinger, Pawel Moskal, Marketa Susankova, Lucie Znojilova, Luuk Heckman, Ivo Viscor, Vlastimil Vondra, Pavel Leinveber, Pavel Osmancik
• Journal: Heart Rhythm 2021;18(8):1281–1289. Open access (CC BY-NC-ND)
• Affiliations: Cardiocenter, Third Faculty of Medicine, Charles University and University Hospital Královské Vinohrady, Prague; Institute of Scientific Instruments, Czech Academy of Sciences, Brno; Jagiellonian University, Kraków; Departments of Physiology and Cardiology, CARIM, Maastricht University Medical Centre; Brno University of Technology; International Clinical Research Center, St. Anne's University Hospital, Brno
• Type: Prospective mechanistic study using ultra-high-frequency ECG (UHF-ECG) during pacemaker implantation. 68 patients with bradycardia; 186 capture recordings — nsLBBp (n=35), LVSP (n=96), nsHBp (n=55)
• DOI: 10.1016/j.hrthm.2021.04.025
• Funding: Charles University Research Program Q38; UNCE/MED/002; CAS Project RVO:68081731. Disclosures: the participating institutions filed a European patent application on the UHF-ECG signal-processing method (EP 19212534.2)

Overview

Three pacing strategies look similar on the surface ECG but differ in what they do to ventricular depolarisation: nonselective His bundle pacing (nsHBp), nonselective left bundle branch pacing (nsLBBp), and left ventricular septal myocardial pacing (LVSP). This study uses ultra-high-frequency ECG — 5 kHz sampling across 14 leads, recording the high-frequency components of myocyte action potentials — to measure when each LV/RV segment activates (e-DYS, interventricular dyssynchrony) and how long each segment takes to depolarise (Vd, local depolarisation duration). The results separate the two left-septal techniques cleanly. nsLBBp produces fast LV lateral wall depolarisation identical to nsHBp (V5–V8 durations 36–43 vs 38–43 ms) but the worst interventricular dyssynchrony (e-DYS −24 ms), because the RV is activated late. LVSP produces less interventricular dyssynchrony (−12 ms) but slower LV lateral wall depolarisation (44–51 ms) regardless of V5 RWPT or V1 morphology. Both left-septal techniques depolarise the septum and RV more slowly than nsHBp. The practical conclusion: a short V5 RWPT or a pseudo-RBBB in V1 does not prove fast LV activation — LVSP can have both while still conducting slowly through working myocardium.

Keywords

Depolarization duration; Dyssynchrony; His-bundle pacing; Left bundle branch pacing; Left ventricular septal myocardial pacing; Ultra-high-frequency electrocardiography

Key Takeaways

Background and method

• Both LVSP and LBBp place the lead in the left septum and produce a pseudo-RBBB in V1; LBBp requires left subendocardial placement and confirmed LBB capture, whereas LVSP captures a larger area at shallower depth
• UHF-ECG analyses the ultra-high-frequency components of ventricular action potentials. It provides:
  • activation timing per chest lead (center of mass of the UHF-QRS envelope above 50% amplitude → M1c–M8c)
  • interventricular electrical dyssynchrony (e-DYS) = difference between the first and last activation; negative e-DYS = delayed RV
  • local depolarisation duration (Vd) = UHF-QRS width at 50% amplitude; shorter = faster local conduction
• Acquisition: VDI monitor (ISI Brno/Cardion/FNUSA), 5-kHz, 14-lead ECG, 3-nV resolution, 1.5-kHz bandwidth; V1 moved to the 5th right parasternal intercostal space for better RV lateral wall signal; recorded during 2–3 min of VVI pacing at 110 bpm
• Capture classification (during unipolar pacing, 5 V/0.5 ms, output decrement):
  • nsLBBp = pseudo-RBBB with terminal r/R in V1, reached by raising output from sLBBp or LVSP; transition from myocardial capture to nsLBBp shortens V5 RWPT by >10 ms
  • LVSP = pure left septal myocardial capture with no LBB capture up to 5 V/0.5 ms; narrower QRS than RV septal pacing, terminal R/r or rs/Rs in V1; no or minor (<10 ms) change in V5 RWPT as output falls
• Lead position measured in LAO using the 10.8 mm tip-to-ring distance of the 3830 lead as reference; septal height in RAO as a percentage of heart silhouette diameter

Results

• All three comparisons were significant at P < .001 for e-DYS; V5–V8 Vd was longer in LVSP than nsLBBp (P < .05) and the same in nsLBBp and nsHBp; Vd in V1–V8 was longer in both left-septal techniques than nsHBp
• Negative e-DYS occurred in 34/35 nsLBBp, 75/96 LVSP, and 7/55 nsHBp (in 5 of those 7 because of incomplete RBBB correction)
• LVSP's V5 RWPT overlap does not mean fast conduction. V5 RWPT ranged 52–114 ms in LVSP and 52–88 ms in nsLBBp, with 51/96 LVSP (53%) at ≤88 ms — inside the nsLBBp range. When LVSP was split by V5 RWPT quartile, the shortest quartile had more dyssynchrony (e-DYS −20 vs +8 ms, P = .007) and fewer normal axes (2/24 vs 17/24, P < .001) — but identical V1–V8 depolarisation durations. Short V5 RWPT in LVSP reflects lead position, not faster conduction
• Lead position explains the axis: LVSP with left-axis deviation (51/96) had shorter V5 RWPT (80 vs 92 ms, P < .001) and a lower RAO septal position (42% vs 50% of silhouette height, P = .004) — i.e. closer to the left posterior fascicle, shortening the distance to the lateral wall
• V1 morphology is a depth marker: terminal rs/Rs (n=21) versus r/R (n=75) meant shallower lead insertion (10 vs 12 mm, P = .01), less interventricular dyssynchrony (e-DYS +3 vs −16 ms, P < .001), and more frequent positive e-DYS (11/21 vs 10/75) — with no difference in V2–V8 depolarisation duration
• The most balanced LV–RV depolarisation was LVSP with terminal rs/Rs in V1, because shallower placement reduces transseptal left-to-right conduction time
• A visible LBB potential in LVSP is a trap: all LVSP captures with a visible potential had V5 RWPT >10 ms longer than their native LBB-potential-to-V5 interval, indicating the LBB was not captured

What the findings mean

• nsLBBp preserves physiological LV lateral wall depolarisation — its V5–V8 durations are statistically identical to nsHBp, showing that the latency between stimulus and LBB capture does not materially slow LV activation
• But it does so at the cost of interventricular dyssynchrony: rapid LV activation arrives before the RV, which is activated late by transseptal conduction
• LVSP balances the ventricles but slows the LV: the delay between left septal myocyte capture and secondary His–Purkinje activation lets the RV and LV wavefronts overlap (less e-DYS), while the LV lateral wall is depolarised cell-to-cell rather than through Purkinje fibres
• Neither left-septal technique reproduces nsHBp. Both prolong depolarisation in the septal and RV leads, reflecting the contribution of slower myocardial conduction
• The clinical corollary stated by the authors: if the goal is the most physiological LV activation, nsHBp and nsLBBp should be preferred over LVSP, because LVSP slows LV lateral wall depolarisation irrespective of V5 RWPT or V1 QRS morphology

Limitations of the document

Authors' own stated limitations

• Measured during the implant procedure, immediately after lead placement; resulting damage to conductive and myocardial tissue could have influenced the paced activation patterns
• No comparison with any other invasive or non-invasive electrocardiographic method, and no haemodynamic or echocardiographic mechanical-dyssynchrony measurement
• The only method used to confirm LBB capture was the decrease in pacing amplitude, which "could have led to misclassification of some nsLBB captures as LVSP captures"
• One patient excluded because low QRS signal quality prevented UHF-ECG map construction
• Few patients with LBBB during spontaneous rhythm, so the differences cannot be generalised to the LBBB population

Additional limitations evident in the study

• The capture classification is the study's weak link, and the authors concede it. Without direct electrophysiological or LBB-potential confirmation, the nsLBBp-versus-LVSP split rests on output-dependent V5 RWPT behaviour — the same surrogate the paper is arguing is unreliable. The finding that LVSP can have a short V5 RWPT does not resolve the circularity
• The comparison is between capture episodes, not randomly assigned patients. 68 patients contributed 186 recordings (35 nsLBBp, 96 LVSP, 55 nsHBp); most patients contributed only one capture type, so the groups differ in substrate as well as in pacing mode. The paper does not report how many patients contributed each combination, so within-patient control is limited
• UHF-ECG is a specialised, non-standard technique — a 5-kHz, 14-lead system with a relocated V1 and proprietary signal processing, developed by the authors' group, who have filed a patent on it. It is not available in routine practice, and its parameters have no established thresholds or outcome validation
• e-DYS has no clinical anchor. A more negative e-DYS is described as "greater dyssynchrony", but no study links this parameter to remodelling, heart failure events, or mortality; "better" synchrony during LVSP could in principle coexist with worse LV lateral wall function, and the study cannot say which matters
• Multiple comparisons across eight leads and several subgroups with no stated correction; the subgroup analyses (quartiles, V1 morphology, axis) are post hoc and small (21–24 per group)
• The "physiological" reference is itself a paced state (nsHBp), obtained in 55 recordings, and His capture was not independently confirmed; the comparison therefore establishes relative, not absolute, physiology
• No CRT population. The cohort was bradycardia patients with a mean LVEF of 56% and only 13% LBBB, so the finding most relevant to CRT — whether LVSP's slower LV lateral wall depolarisation matters in a failing, dyssynchronous ventricle — is not tested
• Acute only. No follow-up, no remodelling, no clinical outcomes
• The V1 lead relocation to the 5th intercostal space is non-standard and limits comparison with conventional ECG-based studies
• Rating rationale: rated high. It is a prospective, mechanistically clean study with a novel measurement that resolves a real confusion — why LVSP can look fast on V5 RWPT while conducting slowly — and it directly underpins the wiki's LVSP-versus-LBBP trade-off section. It is not very high because the capture classification is surrogate-based, the technique is proprietary and unvalidated against outcomes, the groups are not randomised, and the cohort is small, bradycardic and acute

Key Concepts Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — the technique; this paper supplies the mechanistic LVSP comparison
• concepts/Conduction-System-Pacing — the umbrella category
• concepts/His-Bundle-Pacing — the physiological reference (nsHBp)
• Ultra-high-frequency ECG (UHF-ECG) — 5-kHz, 14-lead recording of myocyte action-potential high-frequency components
• e-DYS — interventricular electrical dyssynchrony; first-to-last activation difference; negative = delayed RV
• Vd — local depolarisation duration at 50% UHF-QRS amplitude; shorter = faster local conduction
• M1c–M8c — centre-of-mass activation time under each chest lead
• V5 RWPT — pacing artefact to R-wave peak in V5; a latency- and position-dependent surrogate for LV activation
• Pseudo-RBBB in V1 — a marker that the left septum was reached, not a marker of LBB capture or optimal LV depolarisation
• Terminal r/R vs rs/Rs in V1 — deeper versus shallower LVSP lead position, with different interventricular synchrony
• Lead depth — 14 mm (nsLBBp) versus 11 mm (LVSP), measured against the 10.8 mm tip-to-ring distance
• Cancellation / wavefront overlap — the mechanism by which LVSP produces less interventricular dyssynchrony

Key Entities Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — primary concept page
• Charles University and University Hospital Královské Vinohrady, Prague — coordinating centre
• Institute of Scientific Instruments, Czech Academy of Sciences, Brno — UHF-ECG development
• Maastricht University (CARIM) — Prinzen and Vernooy
• Jagiellonian University, Kraków — Jastrzębski and Moskal
• Karol Curila; Pavel Jurak; Frits Prinzen; Kevin Vernooy — the UHF-ECG research group
• Medtronic SelectSecure 3830 and C315HIS sheath — the lead and delivery system used for all captures
• VDI monitor (ISI Brno / Cardion / FNUSA) — the UHF-ECG recording system
• European patent EP 19212534.2 — the institutions' filed patent on the signal-processing method

Wiki Pages Updated

• Created: wiki/sources/lvsp-vs-lbbp-dyssynchrony-hrs-2021.md
• Updated: wiki/concepts/Left-Bundle-Branch-Area-Pacing.md
• Updated: wiki/concepts/Conduction-System-Pacing.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md