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 |
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
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:
- CSP anti-bradycardia pacing (replacing standard RV pacing)
- CSP-CRT (CSP replacing biventricular pacing for cardiac resynchronization)
- HOT-CRT / LOT-CRT (His-optimized or LBB-optimized CRT: CSP combined with LV lead) sources/csp-ehra-2023
Evidence Base
- MELOS registry: 2533 patients, 14 European centres — largest LBBAP outcomes registry available as of 2023
- 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
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 LBBP with coronary vein LV pacing when LBBP alone insufficient
- Multicentre series (n=112, 81% success): QRS 182→144 ms (21% reduction) vs 7% with BVP; LVEF 28.5→37.2%; NYHA 2.9→1.9 sources/csp-jaccep-2023
- Ongoing trial: CSPOT (NCT04905290)
- Both HOT-CRT and LOT-CRT remain investigational
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
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)