LBBAP versus Biventricular CRT in LBBB-mediated cardiomyopathy: where the 2025 evidence stands

Comparative outcomes — direction is consistent, magnitude is registry-level

The 2025 evidence base is now substantial enough to say the direction of effect favors LBBAP across every endpoint that matters, but the level of evidence remains predominantly observational pending the large RCTs (Left vs Left, RAFT-CSP, and others).

I-CLAS — the largest dataset (HRS 2025, n=2,579, 34±15 mo follow-up)

LBBAP reduced the composite of death or HFH from 30.8% to 22.2%, with HFH alone falling from 20.8% to 13.6%. The earlier I-CLAS publication in JACC (n=1,778, LVEF ≤35%) showed paced QRS of 128±19 ms with LBBAP vs 144±23 ms with BVP, ΔLVEF 13±12% vs 10±12%, and HR 1.495 (95% CI 1.213–1.842) favoring LBBAP for the composite endpoint.

2025 meta-analysis (Frontiers in CV Medicine, 24 studies, n=6,538)

Pooled hazard ratios favored LBBAP for the composite endpoint (HR 0.67, 95% CI 0.59–0.75), all-cause mortality (HR 0.83, 95% CI 0.71–0.96), and heart failure hospitalization (HR 0.58, 95% CI 0.50–0.67). The mortality signal is the newest and most important addition — earlier meta-analyses (Parlavecchio, Jin) consistently showed HFH reduction without a mortality signal, and the pooled mortality benefit only emerged with longer follow-up and larger numbers.

HFmrEF (LVEF 36–50%) subgroup from I-CLAS

CSP was associated with a significant reduction in the primary composite endpoint of death from any cause or HFH compared with BVP, primarily driven by reduction in HFH — directly relevant when the question is whether to apply CRT principles to a patient with high RV pacing burden and progressive remodeling, not yet meeting the traditional ≤35% threshold.

Small RCT signal (LBB-RESYNC, n=40, NICM + LBBB)

LBBAP delivered significantly greater improvement in LVEF (mean difference 5.6%; 95% CI 0.3–10.9; P=0.039) and reductions in LV end-systolic volume and NT-proBNP than BVP-CRT. Hyper-response rates were 65% (LBBAP) vs 42% (BVP). This is the strongest randomized signal so far in the exact phenotype most likely to do well — NICM with true LBBB.

Mechanistic basis for LBBAP advantage in LBBB

The fundamental difference is electrical: BVP creates a fusion of an epicardial CS wavefront and an RV endocardial wavefront — non-physiologic, with significant transmural and interventricular delay. LBBAP recruits the distal His-Purkinje system, producing an activation pattern that approximates native conduction. The 30% non-response rate to BVP has long been attributed to the nonphysiologic electrical resynchronization between epicardial CS and RV endocardial wavefronts, suboptimal lead position, presence of LV scar, and latency due to localized conduction delay — plus a 5–7% acute procedural failure rate from anatomic challenges, high thresholds, or phrenic nerve stimulation. LBBAP bypasses these constraints when capture is true and selective.

Where traditional BiV-CRT (or hybrid LOT-CRT) still wins

This is the key clinical question, and the answer is: substrate, substrate, substrate.

1. Septal scar burden — the single most important modifier

The Fuwai cohort (n=147, NICM with pre-procedure CMR) is the cleanest demonstration: remodeling response to LBBAP and BVP is modified by septal scar burden. High septal scar burden was associated with poor clinical prognosis independent of CRT method. In low-septal-scar patients, LBBAP outperformed BVP for ΔLVEF, ΔLVEDD, and echo response rate. In high-septal-scar patients, the LBBAP advantage was attenuated — because Purkinje fibers cannot be recruited through dead tissue, but a CS lead positioned away from scar can still deliver useful resynchronization.

2. Nonspecific IVCD rather than true LBBB

The 2025 EHRA/ESC consensus and multiple expert reviews flag this group explicitly: patients with nonspecific IVCD often have underlying myocardial disease (ischemic heart disease, hypertrophic cardiomyopathy, post-myocarditis with extensive scar) where LBBAP alone may be insufficient. These cases often require BiV-CRT, with or without LBBAP, for better outcomes. The mechanism makes sense — IVCD frequently reflects diffuse myocardial conduction delay rather than true proximal left bundle block, so distal conduction system recruitment doesn't fix the problem. Intrinsic activation delay (qLV) correlates poorly with LV-paced conduction time in both ischemic (R²=0.249) and nonischemic cardiomyopathy (R²=0.364).

3. Ischemic cardiomyopathy with extensive lateral wall scar

The original I-CLAS paper showed female sex, LBBB, and nonischemic cardiomyopathy as independent predictors of echocardiographic response. ICM patients still benefit from LBBAP, but the differential advantage over BVP narrows. Practically: if the dominant electrical delay is in a scarred lateral/inferolateral wall (the typical CS lead target), neither modality fully resynchronizes and outcomes are worse regardless of approach. CRT in ICM has always produced lower super-response rates than NICM, and LBBAP doesn't reverse that.

4. Failed LBBAP capture or non-selective capture only

Where transition criteria cannot be demonstrated — V6 R-wave peak time <80 ms, qR/Qr in V1, capture transitions during threshold testing — LBBAP behaves more like deep septal pacing, and BVP (or LOT-CRT with an added CS lead) becomes preferred.

Demographic and echocardiographic modifiers

Sex effects: now nuanced and somewhat contradictory

The I-CLAS sex-specific analysis showed women had a 36% reduction in death or HFH (HR 0.64; 95% CI 0.43–0.97) and a 60% reduction in HFH alone (HR 0.4; 95% CI 0.24–0.69) with LBBAP versus BVP, with the greatest benefit among women with NICM and LBBB. The Diaz et al. multicenter registry (JACC EP 2024) showed the opposite signal: men undergoing LBBAP had lower HFH/mortality compared with BVP, while in women there was no significant difference between modalities — on the rationale that women already respond well to BVP and the ceiling for incremental gain is lower. Bottom line: women respond well to both modalities; men are where the LBBAP differential advantage may be largest in absolute terms.

QRS duration and the QRS/LVEDV ratio

A patient with QRS 130–150 ms historically falls in the equivocal CRT zone where response is heterogeneous. The MORE-CRT MPP post-hoc analysis is important here: in NICM with LBBB, increased normalized QRS duration / LVEDV in those with smaller heart sizes drives the improved CRT response rates observed in women. The association is strongest at QRS <150 ms. For LBBAP specifically, V6 R-wave peak time and degree of paced QRS narrowing (rather than baseline QRSd alone) appear more predictive of response.

Practical framework for the LBBB-cardiomyopathy patient meeting CRT criteria

Where the field has moved, codified in the 2025 ESC/EHRA Clinical Consensus Statement: in patients with reduced LVEF (≤40%), the consensus supports CSP, particularly LBBAP, as an effective alternative to BiVP — while BiVP remains the standard for CRT, LBBAP offers comparable improvements in synchrony and function with practical advantages (smaller device, fewer leads, lower complication rates). Real-world adoption confirms this: the 2025 Italian HMEA survey found 98% of centers performed at least one CSP procedure in the past year, with 95% being LBBAP.

The honest summary

The field has moved decisively toward LBBAP as first-line for LBBB-mediated cardiomyopathy meeting CRT criteria, but level-1 evidence is still pending. The Left vs Left trial (n=2,136, primary endpoint death/HFH at 5.5 years, completion 2029) and RAFT-CSP will settle it. Until then: registries are large and consistent, the 2025 EHRA/ESC consensus endorses LBBAP as a primary CSP strategy for CRT, and the residual indications for traditional BVP have narrowed to specific substrate scenarios — high septal scar, true IVCD without conduction system involvement, or failed LBBAP capture. Hybrid LOT-CRT is an increasingly appealing middle ground for incomplete responders rather than a default starting strategy.

For LBBB cardiomyopathy patients meeting conventional CRT criteria, pre-implant CMR with septal LGE quantification has become the most useful single test for tailoring the choice between LBBAP, LOT-CRT, and BVP. That has shifted from "nice to have" to "should be standard" in centers performing high LBBAP volume.