#lot-crt #left-bundle-branch-area-pacing #cardiac-resynchronization-therapy #conduction-system-pacing #heart-failure

LOT-CRT (Left Bundle Branch Area Pacing–Optimized Cardiac Resynchronization Therapy)

Definition

LOT-CRT is a hybrid resynchronisation strategy in which a left bundle branch area pacing (LBBAP) lead replaces the right ventricular lead of a conventional CRT system, while a coronary sinus lead continues to pace the left ventricular epicardium. The LBBAP lead is usually connected to the RV pace/sense port (with the original RV lead capped, or with the defibrillation coil used only for shocking), and the coronary venous lead to the LV port. The intended mechanism is complementary: direct engagement of the proximal left conduction system plus pre-excitation of the LV lateral wall, covering both proximal conduction block and distal intramyocardial delay. (sources/lot-crt-hrs-2021, rating: medium) (sources/lot-crt-circep-2024, rating: high)

The related HOT-CRT substitutes His bundle pacing for LBBAP; it achieves greater QRS narrowing in some patients but has higher capture thresholds and more complex device connections. (sources/lot-crt-hrs-2021, rating: medium)

Key Concepts

Rationale — why a second LV lead is still needed

Proximal LBB capture cannot restore physiological lateral-wall activation when the delay is distal — in the distal left bundle, the LV Purkinje network, or the myocardium. In the original LOT-CRT cohort the mean V6 R-wave peak time during LBBAP was 99.6 ± 21 ms, indicating residual LV conduction delay despite proximal capture. (sources/lot-crt-hrs-2021, rating: medium)
Conventional BVP is limited by the desynchronising effect of RV myocardial pacing, single-site epicardial LV pacing, latency, and suboptimal LV lead position. (sources/lot-crt-hrs-2021, rating: medium)
Combining the two addresses both: direct conduction-system engagement from the septal lead, and lateral-wall pre-excitation from the coronary venous lead. (sources/lot-crt-hrs-2021, rating: medium) (sources/lot-crt-circep-2024, rating: high)
Computational modelling predicts that LOT-CRT adds most when the LV His-Purkinje system is severely slowed (conduction velocity reduced to 35% of healthy), where LBBP alone leaves residual delay; it adds little when the myocardium is slow but the conduction system is intact. (sources/scar-csp-jce-2023, rating: medium)

Electrical resynchronisation

In the foundational international cohort (n = 112; 42% LBBB, 22% IVCD, 23% RV-paced, 12% RBBB), LOT-CRT narrowed QRS from 181 ± 26 to 144 ± 22 ms, better than BVP (170 ± 30 ms) or LBBAP alone (162 ± 23 ms) (both P < .0001). Lack of QRS narrowing occurred in 20.6% with BVP vs 4.4% with LOT-CRT. (sources/lot-crt-hrs-2021, rating: medium)
In IVCD patients (n = 85), LOT-CRT reduced QRS by 42.7 ± 17.4 ms vs 21.9 ± 21.5 ms with BiV-CRT (P < .0001); within the LOT-CRT group, LOT-CRT achieved a narrower QRS (140.0 ± 17.6 ms) than BVP mode (168.2 ± 19.6 ms) or LBBAP alone (155.5 ± 21 ms). (sources/lot-crt-circep-2023, rating: medium)
In the CSPOT acute study (n = 48; 60% IVCD), LOT-CRT produced the greatest QRS shortening — 29.5 ms vs BVP 18.5 ms, unipolar LBBAP 11.9 ms, and bipolar LBBAP 11.7 ms. (sources/lot-crt-circep-2024, rating: high)
The QRS advantage is therefore consistent across observational and acute haemodynamic studies; it is the most reproducible finding for LOT-CRT.

Acute haemodynamics — the electrical advantage does not fully translate

In CSPOT, BVP and LOT-CRT produced similar improvements in LV dP/dtmax (26.4% vs 25.8%; P = .45), both greater than unipolar LBBAP (19.3%) or bipolar LBBAP (16.4%). (sources/lot-crt-circep-2024, rating: high)
The incremental haemodynamic value of LOT-CRT over unipolar LBBAP was concentrated in patients with baseline QRS ≥171 ms and deep septal pacing (DSP): +14.5% LV dP/dtmax and 20.8 ms more QRS shortening. In successful LBBAP with narrower QRS, the added LV lead contributed little. (sources/lot-crt-circep-2024, rating: high)
Anodal capture during bipolar LBBAP, present in 54% of patients, reduced the haemodynamic benefit (18.6% vs 23.7% with unipolar LBBAP; P < .001). LOT-CRT protocols that require bipolar LBBAP may therefore underestimate the strategy's true haemodynamic potential. (sources/lot-crt-circep-2024, rating: high)

Echocardiographic and clinical response

Original cohort (n = 91 successful implants, mean follow-up 7.8 months): LVEF 28.5% → 37.2%, LVEDD 62.0 → 59.1 mm, LVESV 149.5 → 110.6 mL, NT-proBNP 5668 → 2561 pg/mL; echocardiographic response 62.8%, super-response 24.4%, clinical response 76%. (sources/lot-crt-hrs-2021, rating: medium)
IVCD cohort (n = 30 LOT-CRT vs 55 BiV-CRT, 24 months): LVEF 37% vs 30.5% at 2 years; echocardiographic response at 6 months 60.0% vs 31.6%; composite of cardiovascular mortality or HF hospitalisation 6.7% vs 25.5% (HR 0.33, 95% CI 0.14–0.77; P = .035). (sources/lot-crt-circep-2023, rating: medium)
CSPOT echocardiographic substudy (n = 34, propensity-matched to 34 BVP controls): LVEF +16.1% vs +6.1%, LVESV −43.5% vs −20.9%; adjusted differences +7.5% and −18.4% remained significant. Response 79%, super-response 56%. Benefit was greatest with baseline QRS ≥171 ms. (sources/lot-crt-hrs-2025, rating: medium)
LEADR LBBAP (n = 143 LOT-CRT, 6 months): QRS 170.6 → 157.5 ms, LVEF 29.7% → 38.1%, LVESVi 53.8 → 40.5 mL/m², KCCQ +14.2 points, CRT response 82%. In the non-LBBB subgroup QRS did not change but LVEF still improved. (sources/leadr-lbbap-hrs-2025, rating: high)
No randomised trial of LOT-CRT versus BVP has been completed; the clinical outcome data are observational, non-randomised, or derived from single-arm devices trials. (sources/lot-crt-circep-2023, rating: medium) (sources/leadr-lbbap-hrs-2025, rating: high)

Capture type — LBB capture versus LV septal or deep septal pacing

In the original cohort, LOT-CRT with confirmed LBB capture produced a narrower paced QRS (141 ± 20 vs 152 ± 25 ms), greater LVEF improvement (+11.1 vs +4.7 points), higher echocardiographic response (71% vs 45%) and higher clinical response (82% vs 61%) than LOT-CRT with LV septal capture only. (sources/lot-crt-hrs-2021, rating: medium)
In the CSPOT echocardiographic substudy, however, "deep septal optimized therapy" (DOT-CRT) had outcomes similar to successful LOT-CRT (LVEF +20.7% vs +13.5%; P = .14), though DOT-CRT patients had more dilated hearts and longer baseline QRS. The authors caution that ECG-based capture classification may misclassify concealed conduction-system engagement. (sources/lot-crt-hrs-2025, rating: medium)
The LEFT-BUNDLE-CRT trial's exploratory analysis also found more reverse remodelling and functional improvement in patients with confirmed LBB capture than in those with LV septal capture. (sources/left-bundle-crt-ehj-2026, rating: high)

Timing and programming

AV optimisation is as important for LOT-CRT as for BVP: a 60 ms deviation from optimal AV delay reduced LV dP/dtmax benefit by about 30%. (sources/lot-europace-2026, rating: high)
Optimal paced AV delay by LV dP/dtmax: LBBAP 152 ms, LOT-CRT 171 ms, BVP 167 ms; by QRS duration the three were similar (164, 160, 165 ms). (sources/lot-europace-2026, rating: high)
A patient-specific rule outperforms fixed delays: PAV ≈ 0.56 × Ap–LBBs + 7.7 ms for LOT-CRT (R² = 0.69), versus 0.54 × Ap–LBBs + 3.8 ms for LBBAP and 0.48 × Ap–RVs + 28.0 ms for BVP. (sources/lot-europace-2026, rating: high)
Simultaneous biventricular activation (VV = 0) was optimal for LOT-CRT and BVP in the CSPOT cohort; pacing LBBAP first by 30 ms reduced LV dP/dtmax. The optimal VV delay may differ when the mechanism is predominantly conduction-system versus intramyocardial delay. (sources/lot-europace-2026, rating: high)
Unipolar LBBAP should be preferred when possible because anodal capture during bipolar pacing can be haemodynamically detrimental despite a similar QRS. (sources/lot-crt-circep-2024, rating: high)

Safety

Original cohort: 5 early complications (2 lead dislocations, 1 septal perforation, 2 pocket haematomas); no long-term complications beyond 1 infection, 1 CS threshold rise and 1 atrial lead dislodgement. (sources/lot-crt-hrs-2021, rating: medium)
CSPOT echocardiographic substudy: 5 complications in 4 patients (12%), all procedure-related and all recovered. (sources/lot-crt-hrs-2025, rating: medium)
A case report describes ventricular fibrillation on the first post-implant day after LOT-CRT in a severely remodelled ventricle, with QT prolongation and T-wave inversions, no reversible trigger, and no recurrence after propranolol. (sources/lot-crt-vt-ane-2026, rating: low)
The LEADR LBBAP trial showed stable electrical performance and 96.8% freedom from lead-related major complications at 12 months with a dedicated 4.7-F lumenless defibrillation lead in the LBBA position. (sources/leadr-lbbap-hrs-2025, rating: high)

When to choose LOT-CRT

The evidence converges on a tailored indication rather than a universal strategy:

Favours LOT-CRT: wide baseline QRS (≥171 ms), non-specific IVCD or advanced/distal conduction disease, deep septal pacing or failed LBB capture, ischaemic cardiomyopathy with residual lateral-wall delay, and patients who remain non-responders to BVP or LBBAP alone. (sources/lot-crt-circep-2024, rating: high) (sources/lot-crt-circep-2023, rating: medium)
Favours LBBAP alone: typical LBBB with successful LBB capture and adequate QRS narrowing; adding an LV lead contributes little and adds hardware. (sources/lot-crt-circep-2024, rating: high)
Favours CRT/BVP: extensive septal scar, where CSP cannot bypass the distal block; computational modelling predicts CSP is ineffective and CRT remains effective. (sources/scar-csp-jce-2023, rating: medium)

Contradictions / Open Questions

Electrical superiority does not equal haemodynamic superiority. LOT-CRT consistently produces the narrowest QRS, but in CSPOT it did not improve LV dP/dtmax more than BVP. Whether this reflects the high prevalence of DSP and anodal capture, the acute metric, or a genuine ceiling effect is unresolved. (sources/lot-crt-circep-2024, rating: high)
Capture type matters in some datasets but not others. The original LOT-CRT cohort and the LEFT-BUNDLE-CRT exploratory analysis favour confirmed LBB capture, whereas the CSPOT echocardiographic substudy found DOT-CRT outcomes similar to successful LOT-CRT. The disagreement may reflect different classification methods and different patient substrates. (sources/lot-crt-hrs-2021, rating: medium) (sources/lot-crt-hrs-2025, rating: medium)
No randomised outcome trial exists. All clinical benefit estimates come from observational comparisons or single-arm trials; the ongoing randomised landscape is dominated by CSP-versus-BVP trials, not LOT-CRT-versus-BVP. (sources/lot-crt-circep-2023, rating: medium)
Who should receive the extra LV lead? The CSPOT subgroup analysis suggests QRS ≥171 ms plus DSP, but the subgroups are small and the threshold was derived post hoc. (sources/lot-crt-circep-2024, rating: high)
Proarrhythmia risk is poorly characterised. A single case report raises the possibility of early post-implant ventricular arrhythmia after LOT-CRT; the incidence and mechanisms are unknown. (sources/lot-crt-vt-ane-2026, rating: low)
Long-term lead durability and extraction of a defibrillation lead placed in the LBBA position remain under study (LEADR PAS). (sources/leadr-lbbap-hrs-2025, rating: high)
MRI compatibility and device configuration are compromised in some LOT-CRT setups because the RV pace/sense lead is capped or omitted.

Connections

concepts/Left-Bundle-Branch-Area-Pacing — the pacing lead that replaces the RV lead
concepts/Conduction-System-Pacing — the broader family, including HOT-CRT
concepts/Cardiac-Resynchronization-Therapy — the indication and comparator
concepts/Electrical-Resynchronization-Metrics — QRS duration, LV dP/dtmax and AV timing
concepts/Late-Gadolinium-Enhancement — scar substrates where CSP fails and CRT may still work
concepts/Pacing-Induced-Cardiomyopathy — a common upgrade indication
entities/CRT — device and clinical context
entities/ICD — defibrillator integration with an LBBA lead