Quantitative CT Lead Localization Reveals Proximal Left Bundle Targeting Facilitates Superior Physiologic Pacing.

BACKGROUND

Implant electrical criteria for left bundle branch (LBB) capture in conduction system pacing (CSP) cannot localize the lead along the conduction axis.

OBJECTIVE

To classify CSP lead position with an observer-independent CT workflow (CARA) using two anatomic measurements - lead-to-His distance (LH) and lead-to-endocardium offset (LE) - and to test whether proximal position yields near-native paced activation.

METHODS

Of 186 consecutive CSP patients, 145 had interpretable CT anatomy. Leads were classified by prespecified rule: LVSP if LE ≤ -2.5 mm; otherwise proximal (LH ≤ 25 mm) or distal (LH > 25 mm), with 25 mm referenced to left bundle histology. Primary analysis set: sinus rhythm, native QRS <115 ms, complete paired ECGs, LE > -2.5 mm (n = 46).

PRIMARY ENDPOINT: |Δ frontal axis| ≤15° and |Δ QRS duration| ≤15 ms.

RESULTS

Classification yielded 68 proximal, 70 distal and 7 LVSP leads. The procedural label carried no positional information (48% of physician-labeled LBBP leads proximal vs 49% overall). The composite endpoint occurred in 15/24 (62%) proximal versus 6/22 (27%) distal leads (OR 4.14, 95% CI 1.23-13.96; p = 0.021; adjusted OR 5.35, p = 0.013), consistent across sensitivity analyses. The ROC-optimal LH cut-point (24.9 mm) independently reproduced the prespecified 25 mm threshold. Position was not recoverable from the surface ECG (classification AUC 0.48).

CONCLUSION

In this proof-of-concept anatomic study, a two-measurement rule classified CSP lead position objectively. Near-native paced activation requires proximal targeting (LH ≤ 25 mm), which neither the procedural label nor ECG can identify - quantitative imaging is required.