Programmed Deep Septal Stimulation: A Novel Maneuver for the Diagnosis of Left Bundle Branch Capture During Permanent Pacing

Authors, Journal, Affiliations, Type, DOI

• Authors: Marek Jastrzębski, MD, PhD; Paweł Moskal, MD; Agnieszka Bednarek, MD, PhD; Grzegorz Kiełbasa, MD; Aleksander Kusiak, MD, PhD; Tomasz Sondej, MD, PhD; Adam et al.
• Journal: J Cardiovasc Electrophysiol 2020;31:485–93. © 2020 Wiley Periodicals, Inc. Received 5 November 2019; revised 13 December 2019; accepted 23 December 2019
• Affiliations: First Department of Cardiology, Interventional Electrocardiology and Hypertension, Jagiellonian University Medical College, Kraków, Poland; Geisinger Heart Institute, Geisinger Commonwealth School of Medicine, Wilkes-Barre, Pennsylvania
• Type: Single-centre observational study of a diagnostic maneuver — 143 consecutive patients undergoing pacemaker implantation, 269 programmed stimulations. No control group, no randomisation
• DOI: 10.1111/jce.14352
• ⚠ Filename is misdated. The raw file is PES-LBBAP-JCE-2019.md, reflecting the 2019 submission dates, but the journal of record is 2020;31:485–93. The slug uses the correct year; raw_path still points at the 2019-named file
• Note on the acronym: PES in the filename denotes programmed electrical stimulation, the maneuver the paper introduces — not a pacing entity

Overview

Deep septal pacing that captures the left bundle branch is almost always accompanied by simultaneous capture of the adjacent septal myocardium, producing a fused, nonselective QRS — which makes confirming that the LBB was captured genuinely difficult, because the diagnostic signature is obscured by the very thing you are trying to distinguish it from. This paper's insight is electrophysiological rather than morphological: the myocardium and the left bundle have different effective refractory periods, so a programmed extrastimulus delivered from the deep septal lead can encroach on one before the other. When it does, the extrastimulus QRS morphology changes suddenly — and which change occurs reveals whether the LBB was being captured. Across 269 programmed stimulations in 143 patients the maneuver produced a diagnostic response in 79.7%, exposing both components of the paced QRS: the selective LBB QRS and the myocardial-only QRS. It is the same Kraków group whose later physiology-based paper used the patient's own native QRS as reference; this is the refractoriness-based counterpart.

Keywords

Effective refractory period, electrocardiogram, left bundle branch pacing, nonselective capture, refractoriness

Key Takeaways

The Problem

• Permanent deep septal stimulation with LBB capture enables maintenance or restoration of physiological left ventricular activation, with potential application in both bradyarrhythmia and heart failure
• But it is almost always accompanied by simultaneous engagement of the local septal myocardium, producing a fused (nonselective) QRS complex — so confirmation of LBB capture remains difficult
• Existing confirmation methods rely on QRS morphology or an LBB potential, both of which are degraded by the fusion

The Hypothesis

• Programmed extrastimulus technique can differentiate nonselective LBB capture from myocardial-only capture, because the effective refractory period (ERP) of the myocardium differs from the ERP of the LBB

Methods

• Consecutive patients undergoing pacemaker implantation underwent programmed stimulation delivered from the lead implanted in a deep septal position
• Responses were categorised by the sudden change in QRS morphology of the extrastimuli, observed when the ERP of the LBB or of the myocardium was encroached upon, as:
  • "myocardial"
  • "selective LBB"
  • nondiagnostic (unequivocal change of QRS morphology)
• Where LBB capture thresholds were apparently non-equal, a differential pacing output maneuver was used for comparison

Results

• Programmed deep septal stimulation was performed 269 times in 143 patients — in every patient using an 8-beat basic drive train of 600 ms, and in 126 patients also during intrinsic rhythm
• The refractory periods separate by about 55 ms, and that separation is the maneuver's entire basis:

• Responses diagnostic for LBB capture ("myocardial" or "selective LBB") were observed in 114 of 143 patients (79.7%)

Baseline Characteristics (Table 1, n = 143)

• Age 76.1 ± 11.8 years; male 77 (53.8%)
• Pacing indication: atrioventricular block 65 (45.4%); sick sinus syndrome 30 (21.0%); heart failure 28 (19.6%); atrial fibrillation with bradycardia 20 (14.0%)
• Comorbidities: hypertension 122 (85.3%); diabetes mellitus 61 (42.7%); heart failure 58 (40.8%); coronary heart disease 55 (38.5%); severe valvular disease 19 (13.5%)
• Native QRS duration 127.2 ± 30.8 ms, distributed as: narrow QRS 45 (31.5%); RBBB + LAH/LPH 26 (18.2%); RBBB 17 (11.9%); asystole/broad slow escape rhythm 16 (11.2%); LBBB 14 (9.8%); NIVCD 13 (9.1%)
• LV ejection fraction 50.9 ± 14.3%; LV end-diastolic dimension 50.5 ± 8.2 mm
• Paced QRS duration 111.9 ± 15.1 ms; LBB potential visible in only 58 (40.6%); ventricular sensing 9.0 ± 5.1 mV; capture threshold 0.6 ± 0.3 V

Discussion and Conclusion

• Discussed under myocardial QRS response during programmed stimulation, selective LBB QRS response during programmed stimulation, and clinical translation
• Conclusion: a novel maneuver for confirming LBB capture during deep septal stimulation was developed and found to enable definitive diagnosis by visualisation of both components of the paced QRS complex — the selective paced LBB QRS and the myocardial-only paced QRS

Limitations of the document

Authors' own stated limitations

• Single-centre design could result in bias both at the level of patient inclusion and in the interpretation of ECG results
• Assessors were not blinded to the results of differential pacing output, which could influence interpretation of responses. The authors argue the effect is limited because in 81% of participants the LBB and myocardial capture thresholds were apparently equal, and because the two maneuvers were assessed independently (programmed stimulation in the whole group first, then differential pacing output)
• Nondiagnostic response in 20.3% of cases. It is not known whether these represented myocardial-only capture or LBB capture with a nondiagnostic response, and this limits the practical application of programmed stimulation for diagnosing LBB capture. Crucially, "currently there is no gold standard method that we could use to confirm, with high specificity and sensitivity, LBB capture and/or myocardial capture only in these cases"
• No control group with definite septal-myocardial capture was created

Additional limitations evident in the study

• One patient in five cannot be diagnosed by this method, and this paper offers no route to resolving them. The 20.3% nondiagnostic rate is not a small residual — read on its own it is the method's operating ceiling, and since the authors acknowledge no gold standard exists, those cases cannot be adjudicated by any other means either
  • Qualified by a later paper from the same author — see sources/denker-pes-lbbap-jce-2020 (rated low). That single-case Device Rounds follow-up argues the 20.3% belongs to the 600 ms basic drive train protocol rather than to programmed stimulation as such, showing the LBB-versus-myocardium ERP gap can be driven from 55 ms to 150 ms and reversed in sign using Denker short-long-short / long-short-short sequences. The reframing is plausible and mechanism-based but is supported by one patient plus unquantified experience ("very often"), so the ceiling should now be read as probably protocol-specific and demonstrably so only in a single case — a cohort comparison of protocols is what would settle it
• The validation is internal and unblinded. The response categories were assigned by observers who knew the differential-pacing-output results. With the categories themselves being judgement calls about "sudden change in QRS morphology", the risk of circular classification is real, and the authors' mitigation (81% equal thresholds) addresses a different concern
• No external validation cohort, and no comparison against the LBB-potential or QRS-transition criteria it is meant to supplement
• The maneuver requires an electrophysiology setup and expertise — programmed stimulation with extrastimuli is routine in an EP lab but not in a standard pacemaker implant, which bears on generalisability the paper does not discuss
• Only 40.6% of patients had a visible LBB potential, so the comparator against which a new method would naturally be judged was unavailable in most of the cohort
• The population is elderly and mostly non-heart-failure (LVEF 50.9%, HF as indication in 19.6%), so the technique is not tested in the CRT population where LBB capture confirmation matters most
• Rating rationale: single-centre, unblinded assessment, no control group, no gold standard, and a 20.3% irreducible nondiagnostic rate — hence medium. Its contribution is a genuinely novel maneuver with a physiological basis, not a validated diagnostic standard

Key Concepts Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — the technique whose capture this maneuver is designed to confirm
• concepts/Conduction-System-Pacing — umbrella category
• Effective refractory period (ERP) differential — myocardium 263.0 ± 34.4 ms vs LBB 318.0 ± 37.4 ms; the physiological basis of the whole maneuver
• Programmed extrastimulus technique — the maneuver; an extrastimulus encroaching on one tissue's ERP produces a sudden QRS morphology change that identifies which tissue was captured
• Nonselective (fused) QRS — the near-universal obstacle to LBB capture confirmation in deep septal pacing
• "Myocardial" vs "selective LBB" response — the two diagnostic response categories, together with a nondiagnostic third in 20.3%
• Differential pacing output maneuver — the comparator used where capture thresholds were apparently non-equal

Key Entities Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — primary concept page
• Jastrzębski et al. — the Kraków group; this paper and sources/lbb-capture-criteria-hrs-2021 are complementary contributions from the same team, one refractoriness-based and one using the native QRS as reference
• Jagiellonian University Medical College, Kraków; Geisinger Heart Institute
• Wiley Periodicals — publisher

Wiki Pages Updated

• Created: wiki/sources/programmed-septal-stim-lbbp-jce-2020.md
• Updated: wiki/concepts/Left-Bundle-Branch-Area-Pacing.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md