Conduction System Pacing
Predicting Successful LBBAP and Durable Left Bundle Branch Capture
Acute lead deployment succeeds in nearly every case. Confirmed conduction-system capture does not. Knowing which patients fall into the gap—and reading the imaging and ECG that flag them—is where pre-procedural planning earns its keep.
The endpoint that matters is the one that's hardest to reach
Lead deployment and confirmed conduction-system capture are different endpoints with different predictors. Most of patient selection is about closing—or anticipating—this gap.
The literature on left bundle branch area pacing has matured enough that we can separate two questions that are too often answered as one. The first is whether the lead can be placed with the expected paced morphology. The second is whether the left bundle is genuinely being captured—and whether that capture lasts. Registry data put acute lead implantation success around 96.6%, but confirmed LBB capture runs far lower, from roughly 55% in unselected bradycardia cohorts to 82% in more favorable series. The predictors that govern each endpoint are not the same.
01Anatomic and imaging predictors
Echocardiography first, then CT and CMR for the hard cases
The most reproducible predictors of procedural failure are anatomic and visible on a standard echo. In a multicenter bradycardia cohort, a thickened interventricular septum (OR 2.48), severe tricuspid regurgitation (OR 8.84), and intraventricular conduction delay (OR 8.16) were each independent predictors of failure. The mechanism is mechanical: the dominant failure mode was the lead's inability to penetrate deep into the septum, with failure to shorten stimulus-to-LV-activation time accounting for most of the remainder.
Severe septal hypertrophy is the scenario where imaging changes the plan rather than merely the prognosis. Above a septal thickness of roughly 18 mm, endocardial fibrosis, calcification, and scar conspire against fixation—but success rates in this subgroup improve with stylet-driven leads, whose torque transmission helps reach the target. That is an imaging finding with a direct, actionable lead-selection consequence.
Right atrial enlargement on pre-procedural echo predicts more lead-deployment attempts—likely a function of sheath reach and angulation rather than the septum itself.
For the resynchronization population, cardiac MRI scar burden is the standout imaging predictor, and it outperforms ECG-based selection. Global, septal, and lateral scar percentages each predicted echocardiographic response (AUC 0.857, 0.864, 0.822) and outperformed Strauss LBBB morphology criteria (AUC 0.696). Higher scar burden also tracked with worse long-term clinical outcomes. Pre-procedure CMR is arguably the highest-yield refinement available for selecting LBBAP-CRT responders.
02ECG and conduction predictors
Baseline QRS and a newer intra-procedural marker
Baseline conduction substrate predicts difficulty. The failure group in one stylet-driven cohort had a longer baseline QRS duration (146 vs. 127 ms), and patients with IVCD required significantly more deployment attempts. Left bundle branch block is the hardest substrate: unrecordable conduction potentials and associated structural abnormalities translate into longer procedures, more attempts, and more risk.
A newer refinement targets exactly that population. The notch/slur-to-QRS-end duration, measured during RV septal pacing, has been proposed as an intra-operative marker for predicting site-level success in LBBB. Notably, septal thickness did not differ between successful and failed sites in that analysis—the predictive "transseptal distance" appears to be both an electrophysiologic and an anatomic quantity, which is a useful reminder that anatomy alone underdetermines the substrate.
03Predictors of sustained capture
The durability question—and where threshold-watchers should look
This is where acute confirmation and long-term durability diverge. The single most important implant-time predictor of durable capture is the non-selective-to-selective (NS-to-S) transition. In long-term follow-up, failure to demonstrate the NS-to-S transition at implant—together with a higher number of deployment attempts—were strong predictors of loss of capture during follow-up. The reassuring counterpoint: overall loss of LBB capture ran around 4.6%, with only 1.5% requiring a redo, so clean capture is generally durable.
| Predictor | Endpoint affected | Reported effect |
|---|---|---|
| Thickened IVS | Procedural failure | OR 2.48 |
| Severe tricuspid regurgitation | Procedural failure | OR 8.84 |
| IVCD | Failure & ↑ attempts | OR 8.16 |
| ≤3 deployment attempts | Success & capture | p = 0.01 |
| NS-to-S transition at implant | Durable capture | protective |
| Tip-to-LV-cavity distance (CT) | Late loss of capture | predictive |
| CMR scar burden | CRT response | AUC 0.86 |
The most novel durability finding reframes capture as partly an anatomic depth question. In the IMAGE-LBBP cohort, 20.6% of patients developed new-onset loss of capture after an initially stable mid-term period, and lead-tip-to-LV-cavity distance on mid-term CT was a robust predictor. This dovetails with echo- and CT-guided work showing the tip must reach the LV subendocardial region for true LBB capture—durability is, in part, about how deep the lead actually sits.
Stimulus-to-LV-activation time isn't only a capture-confirmation criterion: it independently predicted left-ventricular end-diastolic dimension at 12 months, linking capture quality to reverse remodeling.
04A practical pre-procedural workup
What to measure, and what each measurement should change
Pulling this together: pre-procedural echocardiography should flag severe septal hypertrophy and severe TR—both of which argue for stylet-driven leads and honest counseling on lower odds. The baseline ECG characterizes QRS duration and IVCD to anticipate attempt count and procedural complexity. For the CRT population, pre-procedure CMR scar quantification outperforms QRS morphology for predicting response. Intraprocedurally, the durability levers are a clean NS-to-S transition, minimizing attempts, and confirming adequate septal depth.
One caveat belongs in front of all of this. Most predictor studies are retrospective or single-center, the working definition of "confirmed LBB capture" still varies between groups—which inflates the apparent heterogeneity in success rates—and the CT-based durability work comes from a small cohort. The direction of the findings is consistent and clinically usable; the precise thresholds are not yet standardized.
05Frequently asked questions
What separates acute LBBAP success from confirmed LBB capture?
Acute success means the lead was deployed with the expected paced morphology, achieved in roughly 86–97% of attempts. Confirmed LBB capture is a stricter electrophysiologic endpoint—requiring criteria such as an NS-to-S transition—and is documented in a lower share of cases, from about 55% to 82% depending on the cohort and the capture definition used.
Which anatomic factors most strongly predict failure?
A thickened interventricular septum, severe tricuspid regurgitation, and intraventricular conduction delay are independent predictors. Severe septal hypertrophy above 18 mm brings fibrosis and calcification that hinder lead penetration—though stylet-driven leads improve success in this subgroup.
How does pre-procedural imaging improve success rates?
Echo flags septal hypertrophy and TR that should change lead selection and counseling. In the resynchronization population, CMR scar quantification predicts echocardiographic response better than QRS morphology, and CT-measured lead-tip depth predicts durability of capture.
What predicts long-term loss of capture?
Failure to show an NS-to-S transition at implant and a higher number of deployment attempts are strong predictors of loss of capture during follow-up. Greater lead-tip-to-LV-cavity distance on cardiac CT also predicts new-onset late loss.
06References
- Kato H, et al. Predictors of implantation failure in left bundle branch area pacing using a lumenless lead in patients with bradycardia. J Arrhythm. 2023.
- Predictors of success in left bundle branch area pacing with stylet-driven pacing leads: a multicenter investigation. 2024.
- C-SING Group. Real-world adoption of left bundle branch area pacing: insights from the Conduction-System Pacing Italian Network Group. 2024.
- A novel ECG marker for predicting LBBAP success in left bundle branch block: notch/slur to QRS end duration. EP Europace. 2025.
- LBBAP in patients with severe interventricular septal hypertrophy: a multicenter study of lumenless and stylet-driven leads. Heart Rhythm O2. 2025.
- Cardiac magnetic resonance–derived myocardial scar and echocardiographic response of LBBAP for cardiac resynchronization therapy. 2023.
- Loss of capture during long-term follow-up after left bundle branch pacing. JACC Clin Electrophysiol. 2023.
- Distance from pacing lead tip to LV cavity predicts long-term loss of LBB capture: insights from the IMAGE-LBBP cohort. Can J Cardiol. 2025.