Left Bundle Branch Area Pacing

Definition

Left bundle branch area pacing (LBBAP) is capture of the subendocardial area on the left side of the interventricular septum, with or without simultaneous conduction system capture. It is an umbrella term encompassing left bundle branch pacing (LBBP), left fascicular pacing (LFP), and left ventricular septal pacing (LVSP). The practical designation is used when differentiation between subtypes is impossible, uncertain, or not feasible. sources/csp-ehra-2023

Key Concepts

Sub-Types of LBBAP

All data from the MELOS registry (n=2533) sources/csp-ehra-2023 :

LFP sub-types:

• LAFP: QRS positive leads II and III
• LSFP: QRS positive/isoelectric II; isoelectric/negative III
• LPFP: QRS negative leads II and III

Implantation Technique

Localising the Insertion Site

• Use His bundle potential or tricuspid valve summit as anatomical reference in RAO 20–30° view
• Advance sheath ~15–20 mm towards RV apex after locating His; counter-clockwise torque to reach RV basal-to-mid septum
• Good initial site features: 'W' pattern (nadir notch in V1); discordant QRS in leads II and III (II slightly positive, III negative or equiphasic)
• Liu et al. sector technique: target 15–35 mm from tricuspid annulus at −10° to 30° angle (RAO 30°) sources/csp-ehra-2023
• Lead placement >16–19 mm from tricuspid annulus associated with less TR worsening

Penetrating the Interventricular Septum

• Lead orientation: 10–40° (usually 20–30°) superior to horizontal in LAO 30–40° view; confirms perpendicular septal entry
• RAO view: check for posterior course (no lead progression) or anterior course (no terminal R in V1 despite apparent progression)
• Lead behaviour during rotation:
  • Screwdriver effect (desired): smooth, steady progression into septum
  • Entanglement: torque build-up + no penetration → reposition, do not force
  • Drill effect: multiple rotations without progression → tunnel forms without secure fixation; change position or increase push/support

Monitoring Lead Depth (5 Methods)

1. Continuous fluoroscopy (LAO 30–40°): progression often subtle; not sufficient alone
2. Unipolar paced QRS: V6RWPT shortening as lead progresses; terminal R in V1 → stop and test
3. Fixation (template) beats: QR/qR/rSR' morphology in V1 = 96.5% sensitivity, 97.4% specificity for LBB area reached sources/csp-ehra-2023
4. Unipolar pacing impedance: Rises intra-septally, falls at LV endocardium; <500 Ω or >200 Ω drop = caution
5. Myocardial COI: Rises to 20–35 mV intra-septally; falls to ~10–12 mV at LV subendocardium; <3–5 mV = perforation suspected; visible LBB/fascicular potential = stop rotations sources/csp-ehra-2023

Confirming LBB Capture (Algorithm)

Step 1: QRS Transition (Gold Standard)

• Threshold test (unipolar mode): ns-LBBP → s-LBBP or ns-LBBP → LVSP
  • ns-LBBP → s-LBBP transition: V1RWPT prolongs >10 ms; EGM splitting
  • ns-LBBP → LVSP transition: V6RWPT prolongs ≥15 ms (100% specific for loss of LBB capture)
• Only 26.4% demonstrated this in MELOS; up to 75.4% at more proximal sites (acute implant)
• Programmed stimulation (S2/S3) when threshold test inconclusive

Step 2: V6RWPT Criteria sources/csp-ehra-2023

• <74 ms: 100% specific for LBB capture in narrow QRS or isolated RBBB
• <80 ms: 100% specific in LBBB, IVCD, wide escape rhythm
• Measured from pacing stimulus; add ~30 ms latency for pseudo-delta wave in ns-LBBP

Step 3: V6–V1 Inter-Peak Interval sources/csp-ehra-2023

• 44 ms: 100% specific for LBB capture

• 33 ms: likely LBB capture (sensitivity 71.8%, specificity 90.0%)

• Useful when V6RWPT prolonged (conduction disease, large hearts); uses V1 R-peak (RV activation) as patient-specific reference

Step 4: Physiology-Based ECG

• LBB potential-to-V6RWPT = stimulus-to-V6RWPT (±10 ms)
• Sensitivity 88.2%, specificity 95.4% for CS capture
• Record potential-to-V6 interval in implant report for future follow-up monitoring

Lead-Position-Dependent QRS Transition (Real-Time Capture During Rotation)

• During continuous pacing while rotating lead into septum, beat-to-beat QRS change identifies moment of LBB capture sources/csp-jaccep-2023
• Signs of LBB capture during rotation: sudden V6RWPT shortening ≥10 ms; R′ amplitude increase in V1; S waves appear in leads I, V5, V6; repolarisation normalises in V5–V6
• Requires EP recording system (real-time recognition difficult; review consecutive complexes retrospectively)
• Requires rotational adapter to maintain pacing during lead rotation (commercial or self-made options available)

Distal vs Proximal LBBAP: LVAT–QRS Trade-off

• Distal LBB stimulation: shorter LVAT (shorter local Purkinje-to-ventricle interval) but wider QRS (delayed retrograde RBB activation → more interventricular dyssynchrony) sources/csp-jaccep-2023
• Proximal stimulation: narrower QRS but longer LVAT
• Best interventricular synchrony achieved when first late r occurs in V1 (LVSP1); deeper positions improve LV activation at cost of widening QRS
• Whether shorter LVAT or narrower QRS is clinically superior is unresolved

Anodal Capture During LBBAP

• Programming anodal capture (ring electrode) produces shorter QRS via earlier RV activation sources/csp-jaccep-2023 ★
• Mechanism is RV septal myocardial capture, NOT right bundle capture (confirmed by ECGi)
• Despite shorter QRS, anodal capture provides NO additional hemodynamic benefit vs standard LBBAP
• Routine anodal capture programming is not recommended based on available evidence

Hemodynamic Evidence vs BVP

• LBBAP vs BVP (Liang et al.): LBBAP produced greater QRS reduction (–11 ms; P=0.003) and 6% greater increase in LV dP/dt (P=0.002) sources/csp-jaccep-2023
• LBBP RESYNC RCT (n=40): LBBP superior to BVP in LVEF improvement, LVESV reduction, NT-proBNP reduction at 6 months sources/csp-jaccep-2023
• LEVEL-AT RCT (n=70): CSP (predominantly LBBAP) non-inferior to BVP on LVAT; greater LVAT reduction in per-protocol analysis (23% crossover from CSP to BVP) sources/csp-jaccep-2023
• HBP-CRT vs LBBAP-CRT (Ali et al., n=19): HBP achieves faster total biventricular activation; LBBAP non-inferior for LVAT reduction; delayed RV activation with LBBAP does NOT adversely affect hemodynamic response sources/csp-jaccep-2023

LOT-CRT (Left Bundle–Optimized CRT)

• Combines LBBP with coronary vein LV pacing for patients where LBBP alone fails to fully resynchronize sources/csp-jaccep-2023
• Multicentre series (Jastrzebski et al., n=112, 81% implant success): QRS 182→144 ms (21% reduction) vs 7% BVP and 11% LBBP alone; LVEF 28.5→37.2%; NYHA 2.9→1.9
• Applicable in LBBB/IVCD with coexistent myocardial disease — CSP corrects bundle branch block while LV epicardial pacing addresses residual myocardial delay
• Remains investigational; ongoing CSPOT trial (NCT04905290)

Electrical Targets

• Acceptable capture threshold: <1.5 V@0.5 ms (ideally <1 V@0.5 ms)
• Bipolar sensing: ideally >4 mV
• Check bipolar vs unipolar QRS width (anodal capture from ring electrode may further narrow QRS)

Stylet-Driven Leads (SDLs) vs Lumenless Leads

• Most experience with lumenless leads (Medtronic 3830, 4.1 Fr)
• SDLs (≥5.5 Fr): used by >50% of implanters; success rates 87–95%; comparable electrical parameters
• SDLs: enhanced stiffness/torquability; extendable helix; but risk of helix retraction, screw damage, larger tricuspid annulus interference
• Lumenless: smaller diameter, isodiametric, fixed helix; but less torquable, smaller sheath support sources/csp-ehra-2023

Complications

• Septal perforation: 0–14.1%; recognized by COI drop, impedance fall, ring>tip COI, QS/RS COI morphology
  • Overt: reposition (do not simply withdraw); late perforation requires anticoagulation
  • Micro-perforation: observe if electrical parameters stable; no anticoagulation needed; endothelialisation protective
• Right bundle branch block: 19.9% (6.3% permanent)
• Complete heart block: 9.4% acute (2.6% permanent)
• Tricuspid regurgitation worsening: 7.3–32.6%; higher with proximal lead position
• Lead dislodgment: 0.3–1.5%; reduced with proper screwdriver effect and adequate slack
• Loss of LBB capture: 0.3–11.5%; monitor with V6RWPT on serial 12-lead ECGs
• Threshold rise >1 V: 0.3–1.8%
• Coronary artery fistula: 1.4–2.0%
• Troponin rise >3× ULN: 49.4% (mechanical septal trauma); less than most EP procedures

Follow-up

• More spaced than HBP; remote monitoring acceptable if device captures thresholds reliably
• In-person: check paced 12-lead ECG; verify V6RWPT; assess for terminal R in V1 (loss = possible micro-dislodgement)
• Loss of terminal R in V1 at follow-up reported in 4% (MELOS registry)

Contradictions / Open Questions

• Is CS capture necessary for clinical benefit? LVSP alone may provide adequate resynchronization via retrograde conduction system engagement. Not yet resolved. LEAP trial (NCT04595487, n=470) directly tests LVSP vs RVP. sources/csp-ehra-2023 sources/csp-jaccep-2023
• SDL vs lumenless lead outcomes: Possibly higher LBB capture loss rate with SDLs in early reports; likely learning curve; needs further evaluation. sources/csp-ehra-2023
• Long-term lead extraction: No established data for LBBAP leads in LBB position; special tools likely required. sources/csp-ehra-2023
• LBBAP vs biventricular pacing (RCT data): Small RCTs suggest LBBAP superiority or non-inferiority; no large powered RCT yet. Left vs Left (NCT05650658, n=2,136) will provide definitive comparison. sources/csp-jaccep-2023
• Optimal LBBAP site (proximal vs distal): Proximal captures achieve narrower QRS; distal captures achieve shorter LVAT at cost of wider QRS and more interventricular dyssynchrony. Clinical implications unresolved. sources/csp-jaccep-2023

Connections

• Related to concepts/Conduction-System-Pacing
• Related to concepts/His-Bundle-Pacing
• Related to entities/Heart-Failure (LOT-CRT, CSP-CRT)
• Related to entities/Atrial-Fibrillation (LBBAP preferred when AVJ ablation planned)

Sources

• sources/csp-ehra-2023
• sources/csp-jaccep-2023