#conduction-system-pacing #cardiac-pacing #his-bundle-pacing #left-bundle-area-pacing #cardiac-resynchronization-therapy

Conduction System Pacing

Definition

Conduction system pacing (CSP) delivers the pacing stimulus directly to the His–Purkinje conduction axis, producing more physiological ventricular activation than conventional right ventricular pacing. Capture level is determined by anatomical lead position, paced QRS morphology, and the potential-to-QRS interval. sources/csp-ehra-2023

Key Concepts

CSP Entities (Taxonomy)

CSP encompasses several distinct entities arranged by anatomical level sources/csp-ehra-2023 :

Entity	Abbreviation	Lead position	Potential-to-QRS
His bundle pacing	HBP	Tricuspid valve summit	≥35 ms
Right bundle branch pacing	RBBP	Distal His region	<35 ms
Left bundle branch pacing	LBBP	Deep septum ~1–2 cm from His	25–34 ms
Left fascicular pacing	LFP	Mid-septum 2–4 cm from His	<25 ms
Left ventricular septal pacing	LVSP	Deep septum, LV subendocardium	No CS capture
Left bundle branch area pacing	LBBAP	Umbrella: LBBP + LFP + LVSP	Variable
Deep septal pacing	DSP	Deep septum, not reaching LV subendocardium	No CS capture

Right Bundle Branch Pacing — A Third Right-Sided Target (2023)

The taxonomy above treats RBBP as a point on the His-to-LBB continuum. A dedicated analysis shows it is a distinct, identifiable modality with its own capture criteria and outcomes. (sources/right-bundle-branch-pacing-hrs-2023, rating: high)

Prevalence: 19.6% (64/326) of patients in whom HBP was intended, and 12.2% at the working output; 90.6% of those with a potential–QRS interval <35 ms versus 5.6% of the rest
Diagnostic standard: stimulus–V6RWPT exceeds potential–V6RWPT by ≥10 ms — the paced wavefront must travel RBB → His → LBB, whereas during HBP the paced and native routes are identical. Δ was 17.8 ms in RBBP versus 0.5 ms in HBP, with 100% specificity
Supporting criteria: a double QRS transition; a selective paced QRS different from native (SN 64.1%, SP 91.1%); paced latency > native RB-V latency (SN 87.2%, SP 95.3%); a small (<20 ms) V6RWPT rise on loss of capture (SN 70.5%, SP 94.8%); and equal conduction-system and myocardial thresholds (SN 31.3%, SP 95.8%)
ECG: RBBP prolongs V6RWPT by 11.6 ms and QRS by 10.5 ms versus HBP, with LV activation delay and a pseudo-delta wave; selective RBBP occurs only at low output, and RBBP is always nonselective at working output
Outcomes vs HBP (42 vs 284): sensing much better (5.6 vs 3.2 mV), thresholds equivalent, and no significant difference in echocardiographic outcomes or 3-year mortality (28.6% vs 23.2%, P = .28)
The niche: RBBP cannot correct LBBB, so it is not a standalone CRT strategy, but it avoids transseptal access (potentially easier extraction and relevant to leadless pacing) and is proposed for dual-branch pacing with LBBP — a hypothesis with no outcome data
See concepts/Right-Bundle-Branch-Pacing for the full criteria and limitations

Selective vs Non-Selective Capture

Non-selective (ns-): Simultaneous capture of conduction system + adjacent myocardium; pseudo-delta wave present; QRS onset immediately after stimulus sources/csp-ehra-2023
Selective (s-): Conduction system only; isoelectric interval in all 12 leads after stimulus (= latency period) sources/csp-ehra-2023
For HBP: ns-HBP preferred — back-up ventricular capture, superior sensing, equivalent LV synchrony to s-HBP sources/csp-ehra-2023
The original operational distinction for LBBP is electrogram-based: selective LBBP shows a discrete local component separate from the stimulus artifact on the unipolar lead electrogram; nonselective capture shows none. This is the basis for calling capture "selective", rather than the surface QRS, which differs only slightly between the two. (sources/lbbap-beginners-guide-hrs-2019, rating: high)

Training Requirements

Learning curve flattens after 30–50 cases for HBP and 110 cases for LBBP sources/csp-ehra-2023
Dedicated EP recording system recommended (12-lead ECG + filtered + unfiltered intracardiac signals)
Minimum display: leads I, II, III, V1, V5 or V6

Device Configuration

No dedicated CSP generator currently available; standard PM/ICD/CRT generators used
Three main clinical scenarios:
1. CSP anti-bradycardia pacing (replacing standard RV pacing)
2. CSP-CRT (CSP replacing biventricular pacing for cardiac resynchronization)
3. HOT-CRT / LOT-CRT (His-optimized or LBB-optimized CRT: CSP combined with LV lead) sources/csp-ehra-2023

Antitachycardia Pacing from the Conduction System

CSP leads can deliver antitachycardia pacing from the His bundle or the LBBA instead of the RV apex. Both sites have been tested only in the same canine ischaemia-reperfusion model.
His ATP: no efficacy gain over RV ATP (23 vs 25 successful trials of 64 each) but fewer VT accelerations (6 vs 14, p = 0.05) and less degeneration into VF (1 vs 7, p = 0.02); incomplete epicardial capture was less frequent (25% vs 43%, p = 0.05). (sources/his-atp-vt-jce-2023, rating: medium)
LBBA ATP: higher termination rate than RV ATP (70.2% vs 47.3%, risk ratio 1.44), without more acceleration or VF. (sources/lbbap-atp-jaccep-2026, rating: medium)
The contrast suggests the efficacy benefit is specific to left-sided Purkinje engagement rather than to conduction-system pacing as a class; neither site has human outcome data.

Why LBBAP Emerged as an Alternative to HBP

Conduction system pacing began with the His bundle, but HBP has a specific structural failure that drove the development of a distal alternative. The His bundle is only ~1–2 mm in diameter and difficult to locate; thresholds are high and unstable in 5–10% of patients; sensed R-waves are small relative to atrial signals; and the bundle can be damaged during implantation. Most consequentially, in bundle branch block the HBP success rate falls and the output required to correct LBBB rises — and His-SYNC showed QRS duration cannot be normalised in almost half of patients with LBBB, indicating that where a discrete block is present, His pacing cannot overcome it. (sources/lbbap-jacc-2019, rating: high)

Left bundle branch area pacing instead places the lead transseptally, distal to the presumed block. It is both technically simpler — less precision is required, and LBB fascicules are widely spread in the left-sided subendocardium — and electrically better, with a lower and more stable capture threshold and a larger sensed R-wave. The founding comparison gave paced QRS of 111.85 ± 10.77 ms with LBBP against 165.50 ± 17.80 ms with RV apical pacing, at comparable capture threshold.

The trade-off is an assumption. LBBAP presumes the block lies in the left bundle, and ~36% of patients with LBBB have intact Purkinje activation — they violate that assumption, and LBBAP alone is unlikely to help them. HBP makes no such assumption, but fails structurally in the same population for a different reason. (sources/lbbap-jacc-2019, rating: high)

LVSP — the Third Entity, and the Capture Distinction

Left ventricular septal pacing (LVSP) is a conduction-system-adjacent modality that is often conflated with LBBAP. The distinction: LVSP captures working myocardium on the left side of the interventricular septum; LBBP captures the left bundle branch itself. LVSP reproduces near-physiologic activation by pacing near where the Purkinje system normally exits, without requiring proof of conduction-system capture — which makes it technically easier but leaves it, by definition, not conduction-system pacing. (sources/lvsp-vs-lbbp-cepc-2022, rating: high)

The practical problem: actual LBB capture rates in the literature range from 60% to 90%, so many cohorts labelled "LBBP" contain a substantial LVSP admixture. Any LVSP-versus-LBBP comparison drawn from published series is therefore contaminated, and the distinction the two techniques rest on is not reliably recoverable from the literature
Implantation technique is similar; the difference is the verification burden — LBBP requires LVAT (spike to R-wave peak in V5/V6), QRS morphology, fixation beats or continuous pacing, a qR in V1 for deep left-sided deployment, or septal contrast angiography
Both are reported as giving (near-)physiologic electrical and mechanical activation, with promising CRT results for each, and the review's stated conclusion is that more long-term and more head-to-head studies are needed
What the two modalities trade, quantified: LVSP implants faster (38.13 ± 11.52 vs 53.52 ± 14.39 min; P < 0.001) and gives better interventricular synchrony, but reverses the intrinsic LV activation sequence — coronary sinus mapping found all LBBP patients preserved the intrinsic lateral→posterior sequence, while all LVSP patients were non-physiological. Paced QRS duration, across 15 studies, does not separate them consistently. (sources/lbbp-vs-lvsp-criteria-fcm-2022, rating: high)

Evidence Base

MELOS registry (primary source: sources/melos-lbbap-ehj-2022, rating: high): 2,533 patients at 14 European centres — the largest LBBAP outcomes registry. Implant success 92.4% bradyarrhythmia vs 82.2% heart failure; learning curve plateauing only after 250 cases; complication rate 11.7% with 8.3% specific to the transseptal route. Capture types: left bundle fascicular 69.5%, LV septal 21.5%, proximal LBB 9% — over a fifth of "LBBAP" implants captured only septal myocardium
The lead, not just the site, is a variable. LBBAP was developed with lumenless leads (Medtronic 3830, 4.1 Fr, fixed helix) and most evidence reflects them. A multicentre registry of stylet-driven leads (SDL) — 353 consecutive patients at 8 Belgian hospitals, Solia S60 (5.6 Fr, extendable helix) via a Selectra3D sheath — found success 94.6% with threshold 0.6 ± 0.4 V stable to 12 months, and, most usefully for adoption, success independent of centre volume (93–100%, p = .75; median only 25 implants per centre). The caveats matter more than the headline: only 73% achieved LBB capture (27% LVSP) under a success definition of "LBBP or LVSP", LBB potentials were seen in just 14%, 12-month data covers 67/353 patients, and septal perforation (2%) and coronary fistula (1.4%) ran above single-centre lumenless reports. Every operator was a certified electrophysiologist with >5 years' device experience — so volume-independence describes experts, not novices (sources/stylet-lbbap-jce-2022, rating: medium)
The lead families are not interchangeable in technique or in failure mode. Lumenless leads (3830) are fixed-helix, isodiametric and resist retraction, but accept no locking stylet, making extraction the main concern; stylet-driven leads allow continuous pacing from the stylet during rotation, but their extendable helix can retract, deform or fracture. Neither advantage has been tested head-to-head, and the perforation rates attributed to each depend on how systematically perforation was sought. (sources/lumenless-vs-stylet-leads-jcm-2024, rating: medium)
Capture confirmation has no single cut-off that travels. Across 15 studies the optimal Stim-LVAT ranges from 70 to 101 ms depending on baseline QRS, ventricular size and heart failure; the field's answer is within-patient comparison (ΔStim-LVAT against His pacing, V6–V1, native IDT − TCT) rather than a fixed value. (sources/lbbp-vs-lvsp-criteria-fcm-2022, rating: high)
The largest long-term LBBP registry confirms flat thresholds but exposes the selective-capture problem: 618 patients, 0.65 V at implant → 0.69 V at 2 years, LBBB QRS 167 → 124 ms, LVEF in QRS ≥120 ms 48.8 → 58.1%, but selective capture falls from 74.4% to 30.9%. (sources/longterm-lbbap-circep-2021, rating: high)
The only direct LBBP-versus-RVP comparison shows electrical superiority without clinical superiority: paced QRS 132 vs 178 ms, better thresholds and sensing, but identical complications and cardiac outcomes in a preserved-LVEF, non-CRT cohort followed 18 months. (sources/lbbp-vs-rvp-europace-2020, rating: medium)
Tricuspid regurgitation is a positional cost: worsening in 32.6% of 89 patients, predicted by a lead entry site ≤16.1 mm from the septal leaflet; this conflicts threefold with the long-term registry's 11.1%. (sources/tricuspid-regurgitation-lbbap-hrs-2023, rating: medium)
Electrical benefit is larger than the QRS change suggests: body-surface ECG-belt mapping during optimised LBBAP reduced global activation-time dispersion (SDAT) by 47% while QRS duration fell only 16%, and anodal capture narrowed QRS while worsening LVAT and LV dispersion — so QRS duration both understates and can misrank electrical resynchronisation. (sources/crp-lbbap-jice-2023, rating: low)
HBP introduced in ESC supra-ventricular arrhythmia guidelines 2019 and ESC pacing guidelines 2021
Large randomized trials with long-term follow-up still needed before CSP becomes universal first-line pacing sources/csp-ehra-2023

Hemodynamics: CSP vs RVP

HBP vs RVP: QRS shortened by 56 ms; acute systolic BP improved +5 mmHg; myocardial perfusion better by scintigraphy sources/csp-jaccep-2023
RVP causes GLS decline, LA volume index increase, and peak systolic dispersion worsening at 6 months vs stable/improved parameters with HBP sources/csp-jaccep-2023

Hemodynamics: CSP vs Biventricular Pacing (CRT)

HBP-CRT vs BVP-CRT: 60% greater acute systolic BP improvement (+4.6 mmHg; P=0.04) when LBBB corrected; 26 ms greater LVAT reduction sources/csp-jaccep-2023
LBBAP vs BVP: greater QRS reduction (–11 ms; P=0.003) and 6% greater increase in LV dP/dt sources/csp-jaccep-2023
HBP-CRT vs LBBAP-CRT: HBP achieves faster total biventricular activation; LBBAP non-inferior for LVAT reduction; delayed RV activation with LBBAP did not adversely affect hemodynamics sources/csp-jaccep-2023
Anodal capture during LBBAP: shorter QRS but no additional hemodynamic benefit (RV septal myocardial capture — not right bundle — is the mechanism) sources/csp-jaccep-2023

CSP vs BVP: Clinical Outcomes (2023–2026)

The outcome evidence has moved from small mechanistic studies to large observational cohorts and one randomised non-inferiority trial. The consistent signal is fewer heart failure hospitalisations with CSP, without a demonstrated mortality difference.

LBBAP vs BVP in LVEF ≤35% (n = 1,778, 15 centres): composite of death or HFH 21% vs 28% (adjusted HR 1.495 for BVP vs LBBAP); HFH 12% vs 19% (HR 1.494); mortality not significant after adjustment; LVEF +13% vs +10%; complications 3.8% vs 7.5%. (sources/lbbap-crt-jacc-2023, rating: high)
LBBAP vs BVP in LVEF ≤50%, propensity-matched (n = 1,560 of 2,579): composite 22.2% vs 30.8% (HR 0.81); HFH 13.6% vs 21.8% (HR 0.63); mortality 12.4% vs 18.2% (HR 0.82, P = .156); complications 3.5% vs 6.5%; LVEF +11.5% vs +8.9%. (sources/iclas-lbbap-crt-hrs-2025, rating: high)
CSP vs BVP in HFmrEF (n = 1,004): composite 22% vs 34% (HR 0.64); HFH 13% vs 23% (HR 0.64); mortality 13% vs 17% (HR 0.88, NS); LBBB subgroup composite HR 0.49. HBP and LBBAP did not differ. (sources/iclas-hfmref-hrs-2025, rating: high)
LBBP vs LVSP vs BIVP (n = 415, prospective): freedom from HFH or death 76.6% LBBP vs 48.4% LVSP vs 43.6% BIVP; LVSP and BIVP were indistinguishable. The result argues that true LBB capture, not septal pacing alone, drives benefit. (sources/lbbp-lvsp-crt-jaccep-2024, rating: high)
The only randomised trial to date — LEFT-BUNDLE-CRT (n = 176, typical LBBB): CRT response at 6 months 94.6% BiVP vs 89.7% LBBAP in the intention-to-treat analysis (RR 0.95, 95% CI 0.88–1.02), so the 10% non-inferiority margin was not met; the on-treatment analysis (92.8% vs 91.3%; RR 0.98, 95% CI 0.91–1.06) suggested comparable efficacy but was exploratory. Crossovers were 20.7% in the BiVP arm and 9.8% in the LBBAP arm. (sources/left-bundle-crt-ehj-2026, rating: high)
MRI-guided LBBP in LBBB-associated non-ischaemic cardiomyopathy (n = 225): scar burden <10% (90% of patients) treated without a defibrillator had a 6.9% composite of death, HFH or VT/VF vs 26.1% with ≥10% scar; LVEF normalised in 82.2% vs 25% at 2 years. (sources/mri-lbbap-hrs-2025, rating: high)

Hybrid CRT Approaches

HOT-CRT (His-Optimized CRT)

Combines HBP with coronary vein LV pacing; indicated when HBP alone fails to resynchronize
Observational data (n=27): QRS 183→120 ms (34% reduction vs 11% with BVP); LVEF 24%→38%; NYHA improved sources/csp-jaccep-2023
Ongoing RCT: HOT-CRT trial (NCT04561778, n=100)

LOT-CRT (Left Bundle–Optimized CRT)

Combines an LBBAP lead (in place of the RV lead) with coronary vein LV pacing when LBBAP alone is insufficient. See concepts/LOT-CRT for the full evidence base.
Multicentre series (n=112, 81% success): QRS 182→144 ms vs 170 ms with BVP and 162 ms with LBBAP alone; LVEF 28.5→37.2%; NYHA 2.9→1.9. (sources/lot-crt-hrs-2021, rating: medium)
In IVCD (n=85), LOT-CRT reduced QRS by 42.7 vs 21.9 ms and lowered the 24-month composite of cardiovascular death or HFH (6.7% vs 25.5%; HR 0.33). (sources/lot-crt-circep-2023, rating: medium)
CSPOT acute study (n=48): LOT-CRT gave the greatest QRS shortening (29.5 ms) but LV dP/dtmax improvement similar to BVP (25.8% vs 26.4%), both above LBBAP alone (19.3%). The incremental benefit over LBBAP was concentrated in QRS ≥171 ms with deep septal pacing. (sources/lot-crt-circep-2024, rating: high)
CSPOT echocardiographic substudy (n=34): LVEF +16.1% vs +6.1% and LVESV −43.5% vs −20.9% compared with propensity-matched BVP. (sources/lot-crt-hrs-2025, rating: medium)
AV timing matters as much as for BVP: a 60 ms deviation from optimal AV delay reduces haemodynamic benefit by ~30%; PAV ≈ 0.56 × Ap–LBBs + 7.7 ms; VV = 0 is optimal on average. (sources/lot-europace-2026, rating: high)
Offering a single-lead defibrillation option: the 4.7-F OmniaSecure lead in the LBBA position had stable electrical performance and 96.8% freedom from lead-related major complications at 12 months, with 82% CRT response in the LOT-CRT subgroup. (sources/leadr-lbbap-hrs-2025, rating: high)
Both HOT-CRT and LOT-CRT remain investigational; no randomised outcome trial has reported.

ACC/AHA/HRS 2018 Guideline Recommendations for His Bundle Pacing

Class IIa (B-R [SR]): In patients with AV block requiring PPM + LVEF 36–50% + expected ventricular pacing >40%: physiologic pacing (CRT or His bundle pacing) preferred over RV pacing — prevents pacing-induced cardiomyopathy (sources/bradycardia-acc-aha-hrs-2018, very high)
Class IIb (B-R [SR]): In patients with AV block at level of the AV node requiring PPM: His bundle pacing may be considered to maintain physiologic ventricular activation (sources/bradycardia-acc-aha-hrs-2018, very high)
Context: 2018 guideline was the first ACC/AHA/HRS guideline to formally recommend His bundle pacing; evidence based on systematic review "Impact of Physiologic Versus Right Ventricular Pacing Among Patients With Left Ventricular Ejection Fraction Greater Than 35%"
Recommendations denoted by [SR] = informed by systematic review; precede the 2023 EHRA CSP expert consensus

AUC 2025 Appropriateness Ratings for CSP

The ACC/AHA/HRS 2025 AUC formally evaluated CSP scenarios (sources/icd-crt-auc-2025, rating: high):

HBP or LBBAP as alternative to RV pacing (anticipated pacing burden >40%, normal LVEF): A(7) — physiological activation preferred over chronic RVP
CSP-CRT (HBP/LBBAP replacing LV coronary sinus lead in a CRT-indication patient): M(5–6) — insufficient RCT hard-outcome data to reach A despite haemodynamic superiority in observational data
LBBAP preferred over HBP at most centres: better electrical parameters, larger anatomical target, lower pacing threshold instability (sources/icd-crt-auc-2025, rating: high)
Rating upgrade expected once PROTECT-HF (n=2,600; CSP vs RVP) and Left vs Left (n=2,136; HBP/LBBAP vs BVP) report hard outcomes (sources/icd-crt-auc-2025, rating: high)

Published RCTs (as of 2023)

Seven small RCTs (29–167 patients, 6–18 months follow-up) sources/csp-jaccep-2023 :

LBBP RESYNC (n=40): LBBP superior to BVP in LVEF, LVESV, NT-proBNP
LEVEL-AT (n=70): CSP non-inferior to BVP on LVAT; greater LVAT reduction in per-protocol analysis
HOPE-HF (n=167): HBP in long PR + LV impairment — no change in peak VO₂; significant QoL improvement; HBP preferred by majority
All trials were underpowered for hard clinical outcomes

Ongoing Landmark Trials

PROTECT-HF (n=2,600): CSP vs RVP; primary: CV death + HFH + QoL + upgrade; 48-month follow-up sources/csp-jaccep-2023
Left vs Left (NCT05650658, n=2,136): HBP/LBBAP vs BVP; primary: death + HFH; 66-month follow-up sources/csp-jaccep-2023
LEAP (NCT04595487, n=470): LVSP vs RVP — directly tests whether CS capture is necessary for benefit sources/csp-jaccep-2023

Perioperative Considerations for CSP Leads

HBP leads have a higher risk of elevated pacing thresholds or microdislodgement compared with RV apical or LBBP sites in the periprocedural period (sources/periop-cied-aha-2024, rating: high)
LBBP sites have a more favourable perioperative threshold/dislodgement profile compared with HBP (sources/periop-cied-aha-2024, rating: high)
CSP leads should be interrogated after RF catheter ablation to exclude changes in sensing or thresholds from ablation catheter manipulation near intracardiac leads (sources/periop-cied-aha-2024, rating: high)

Contradictions / Open Questions

Is conduction system capture necessary for clinical benefit? Whether confirmed LBB/fascicular capture is required (vs LVSP alone) is uncertain; registry data show similar acute outcomes. LEAP trial (NCT04595487, n=470) directly addresses this. sources/csp-ehra-2023 sources/csp-jaccep-2023
Long-term LBBAP lead extraction: Established for HBP (3830 lead); not yet demonstrated for LBBAP leads in the LBB position. Special extraction tools may be needed. sources/csp-ehra-2023
HBP vs LBBAP superiority: HBP achieves maximum electrical synchrony (biventricular); LBBAP has better electrical parameters and larger target. Head-to-head hemodynamic study (Ali et al.): LBBAP non-inferior for LVAT reduction despite delayed RV activation. No outcomes RCT. sources/csp-jaccep-2023
Shorter LVAT vs narrower QRS: Distal LBBAP reduces LVAT but widens QRS (more interventricular dyssynchrony). Whether shorter LVAT or narrower QRS is more clinically important is unresolved. sources/csp-jaccep-2023
There is no agreed metric of electrical success. QRS duration, QRS area and activation-time dispersion rank the same pacing configurations differently — anodal capture shortens QRS but worsens LVAT and LV dispersion, while selective LBBP gives the longest QRS of the LBBAP capture states. Until a metric is linked to outcome, "electrically superior" pacing has no single definition. (sources/crp-lbbap-jice-2023, rating: low) (sources/lbbp-vs-lvsp-criteria-jaccep-2021, rating: medium) (sources/qrs-area-crt-jcm-2021, rating: medium)
Does lead type change who can perform CSP? Stylet-driven leads are used by most implanters and give comparable acute electrical parameters to lumenless leads, and a multicentre registry found success independent of centre volume — the main argument that CSP need not be confined to expert centres. But that registry's operators were all experienced electrophysiologists, and its complication rates (perforation 2%, fistula 1.4%) ran above lumenless single-centre reports, with the authors attributing the difference to including rather than excluding the learning curve. So the claim "anyone can do this" and the claim "this is as safe as lumenless" are each supported only by uncontrolled, cross-study comparison. (sources/stylet-lbbap-jce-2022, rating: medium)
Does lead type change anything measurable? The structural trade-off is clear — lumenless leads resist helix retraction but are harder to extract, stylet-driven leads support the septum and allow pacing during rotation but retract and fracture — yet no study randomises lead type, and no study reports extraction or fracture rates by lead type in a comparable cohort. The one quantitative fracture figure is the 3830's bench-predicted 0.02% at 10 years; the SDL excess is asserted without absolute rates, and perforation rates attributed to each (2% registry vs 10.2%/11.6% in a technical review) are defined differently, so they cannot be compared. Lead choice currently rests on procedural feel and operator familiarity, not on outcome evidence. (sources/lumenless-vs-stylet-leads-jcm-2024, rating: medium)
Is RBBP a real entity, or an ECG inference? The modality is defined by a ΔV6RWPT ≥10 ms — a physiological inference, not a direct recording of RBB capture. It was validated against a double transition in only 28 patients, and the additional 36 cases were classified by the criterion under test. No retrograde His or anterograde RBB potential has been demonstrated. The criteria were also derived and tested in the same 326 patients, and the population excluded LBBB and H-V >55 ms — precisely the patients in whom RBBP cannot help. (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
The evidence is now long-term on parameters but not on outcomes. Across the largest registry and the only direct RVP comparison, thresholds are stable, QRS is narrower, and sensing is better — yet complications, heart failure hospitalisation and mortality are unchanged. The cohorts are preserved-LVEF and non-CRT, follow-up is 18 months, and event rates are 0–1%, so the studies are structurally incapable of showing benefit. The claim that conduction-system pacing prevents pacing-induced cardiomyopathy remains an extrapolation from electrical surrogates. (sources/longterm-lbbap-circep-2021, rating: high) (sources/lbbp-vs-rvp-europace-2020, rating: medium)
The first randomised CRT trial did not establish non-inferiority. LEFT-BUNDLE-CRT's intention-to-treat analysis missed its prespecified 10% margin (94.6% BiVP vs 89.7% LBBAP; RR 0.95, 95% CI 0.88–1.02), while the on-treatment analysis met it (RR 0.98, 95% CI 0.91–1.06). The discordance is driven by a 20.7% crossover rate in the BiVP arm, which makes the ITT comparison a comparison of strategies-including-rescue rather than of pacing modalities. Whether LBBAP is truly equivalent, superior, or slightly inferior to BVP in typical LBBB remains formally unresolved. (sources/left-bundle-crt-ehj-2026, rating: high)
Observational superiority is driven by HFH, not mortality. The I-CLAS cohorts and the JACC 2023 cohort consistently show fewer heart failure hospitalisations with CSP, but mortality differences disappear after adjustment or matching. The composite endpoint can therefore look positive while overall survival is unchanged; longer follow-up and the ongoing Left vs Left trial are needed. (sources/iclas-lbbap-crt-hrs-2025, rating: high) (sources/iclas-hfmref-hrs-2025, rating: high) (sources/lbbap-crt-jacc-2023, rating: high)
Does the benefit come from LBB capture or from avoiding the RV lead? LBBP outperformed both LVSP and BIVP in a prospective registry, suggesting capture matters, but the LOT-CRT echocardiographic substudy found deep septal pacing outcomes similar to successful LOT-CRT. The two findings may reflect different substrates and different capture-classification methods. (sources/lbbp-lvsp-crt-jaccep-2024, rating: high) (sources/lot-crt-hrs-2025, rating: medium)
Proarrhythmia is a recognised but unquantified risk. CSP generally reduces ventricular arrhythmias compared with BVP in I-CLAS, yet case reports describe early VF, monomorphic VT and electrical storm after LBBAP, including one after LOT-CRT with QT prolongation. The incidence, mechanisms and predictors are unknown. (sources/lot-crt-vt-ane-2026, rating: low)
Do His and LBBA ATP produce the same thing? In the same canine model, His ATP reduced adverse outcomes without improving termination, whereas LBBA ATP improved termination without worsening safety. The two results are from separate small experiments with different endpoints, no shared control arm and non-selective capture in both; they are consistent with a site-specific effect but do not establish one. (sources/his-atp-vt-jce-2023, rating: medium) (sources/lbbap-atp-jaccep-2026, rating: medium)

Connections

Related to concepts/His-Bundle-Pacing
Related to concepts/Left-Bundle-Branch-Area-Pacing
Related to concepts/Periprocedural-CIED-Management — HBP threshold/dislodgement risk perioperatively; LBBP preferred profile
Related to entities/Heart-Failure (CSP-CRT, HOT-CRT, LOT-CRT configurations)
Related to entities/Atrial-Fibrillation (AVJ ablation: LBBAP preferred over HBP)