His Bundle Pacing
Definition
His bundle pacing (HBP) is a form of conduction system pacing that captures the atrioventricular bundle, activating all His bundle fibres directly. The pacing lead is positioned near the tricuspid valve summit (atrial or ventricular side of the tricuspid annulus) with a His potential-to-QRS interval ≥35 ms. sources/csp-ehra-2023
Key Concepts
Anatomy
- His bundle: ~20 mm long, encapsulated in fibrous tissue insulating it from atrial and ventricular myocardium; therefore, recording a His potential does not guarantee capture sources/csp-ehra-2023
- Proximal His (atrial aspect of tricuspid annulus): selective capture more common; sensing issues more frequent (low R-wave, atrial/His oversensing)
- Distal His (ventricular aspect of tricuspid annulus): non-selective capture more common; superior electrical parameters
Implantation Technique
- Mapping in 20–30° RAO view; target: near-field (sharp) His signal + absent/small atrial EGM + larger ventricular EGM
- Pace mapping at 5 V@1 ms as alternative when His EGM not visible (useful in AV block)
- Lead fixation: counter-clockwise rotation with forward force; torque build-up (not number of rotations) indicates adequate tissue penetration
- Current of injury (COI) of His potential + negative deflection of His potential = adequate tissue contact and predictor of stable thresholds sources/csp-ehra-2023
- Absent COI after fixation → repeat rotation with stronger torque
- Lead stability test: withdraw sheath 5–8 cm, gently pull/push lead, two additional rotations
Confirming His Capture
- Primary method: Output-dependent transitions in QRS morphology during threshold testing
- ns-HBP → s-HBP → loss of capture (or ns-HBP → myocardial capture → loss of capture)
- Paced QRS with LBBB-like pattern (notch/slur in I, V4–V6; stimulus-V6RWPT >110 ms) = non-physiological; not acceptable
- Secondary method: Pacing stimulus-to-V6RWPT vs His-potential-to-V6RWPT difference <12 ms (accuracy 96.7%) sources/csp-ehra-2023
- Testing at shorter pulse widths (0.2–0.3 ms) enhances threshold divergence between His and myocardium
- Programmed stimulation useful when threshold testing inconclusive
Electrical Targets
- Optimal threshold: ≤1.5 V/0.5 ms; acceptable up to 2.0–2.5 V@0.5 ms in HF/CRT scenarios
- In patients with long HV or HV block: demonstrate 1:1 conduction at cycle lengths ≤400 ms at working output
- Bipolar sensing: ideally >2.0 mV (or unipolar >4 mV)
- Check for atrial and His bundle oversensing — fatal risk in complete heart block
Selective vs Non-Selective HBP
- Both achieve equivalent LV synchrony and clinical outcomes sources/csp-ehra-2023
- ns-HBP preferred: back-up ventricular capture present, superior sensing parameters
- s-HBP: may be preferable if ns-HBP produces broad QRS (LBBB pattern); use shorter pulse widths to widen selective zone
Complications
- Threshold rise / loss of capture: Most frequent HBP complication; occurs in up to 17% of patients; lead revision required in up to 11% sources/csp-ehra-2023
- Sensing issues: Atrial/His oversensing, ventricular undersensing
- Slitting precautions: Implant all other leads first; maintain adequate lead slack; check thresholds after slitting
Back-up Ventricular Lead Indications
- Pacemaker dependency
- High-grade AV block or infra-nodal block
- High capture threshold
- Poor sensing
- Planned AV junction ablation (risk of HBP threshold rise with both RF and cryo ablation) sources/csp-ehra-2023
Hemodynamic Evidence
- HBP vs RVP (Keene et al., n=18): HBP produced –56 ms shorter QRS (95% CI –67 to –46 ms; P<0.0001) and +5.0 mmHg acute systolic BP improvement (P<0.0001) sources/csp-jaccep-2023
- Myocardial perfusion (Zanon et al.): HBP significantly better than RVP by Tc-MIBI scintigraphy at 3 months (perfusion score 0.44 vs 0.71; P=0.011) sources/csp-jaccep-2023
- HBP-CRT vs BVP-CRT (n=18/23): HBP-CRT shortened LVAT by 26 ms more than BVP-CRT and produced ~60% greater improvement in acute systolic BP (+4.6 mmHg; P=0.04) when LBBB corrected sources/csp-jaccep-2023
- HOPE-HF trial (n=167, crossover): AV-optimised HBP in long PR + LV impairment + narrow QRS/RBBB — no change in peak VO₂ or LVEF at 6 months; significant QoL improvement; HBP preferred by clear majority sources/csp-jaccep-2023
Fluoroless and 3D Mapping Techniques
- HBP feasible without fluoroscopy in 31/39 patients (79%); guided purely by intracardiac electrograms (Zanon et al.) sources/csp-jaccep-2023
- 3D electroanatomical mapping (Sharma et al., Richter et al.): safe, feasible with dramatically reduced radiation exposure; precise localisation of His bundle region
- Particularly useful in challenging anatomy: congenital heart disease, enlarged RA, or pregnancy
Special Considerations
- In atrial fibrillation: avoid His mapping site with large atrial EGM (>0.5 mV); begin mapping from ventricular side of membranous septum
- 3D electroanatomical mapping useful in challenging anatomy, congenital heart disease, or pregnancy
- Follow-up: in-person every 6 months (ESC 2021 Class IIa, LOE C) due to high incidence of late threshold rises; automatic capture detection limited reliability
Contradictions / Open Questions
- AV junction ablation and HBP: Both RF and cryo ablation can cause rise in HBP thresholds. LBBAP preferred when AVJ ablation is planned. sources/csp-ehra-2023
- Long-term performance: Medium-term safety and efficacy data available; large RCTs with long-term follow-up still lacking.
- HOPE-HF paradox: AV-optimised HBP in long PR + LV impairment improves QoL and is preferred by patients, but did not improve peak VO₂ or LVEF in RCT. Mechanism of symptomatic benefit without objective haemodynamic improvement is unclear. sources/csp-jaccep-2023
- nsHBP vs sHBP synchrony: UHF-ECG confirms equivalent ventricular e-DYS; both equivalent to intrinsic narrow QRS. However, nsHBP produces wider surface QRS — whether this matters in specific subgroups is unresolved. sources/csp-jaccep-2023
Connections
- Related to concepts/Conduction-System-Pacing
- Related to concepts/Left-Bundle-Branch-Area-Pacing
- Related to entities/Heart-Failure (HOT-CRT)
- Related to entities/Atrial-Fibrillation (AVJ ablation planning)