Heterogeneity in clinical judgment of septal lead position and capture type in left bundle branch area pacing.

Background: Determining capture type and septal lead location during left bundle branch area pacing (LBBAP) relies on criteria obtained during implantation. However, during follow-up, the interpretation of left bundle branch (LBB) capture largely depends on QRS morphology, which is not so straightforward in LBBAP.

Objective: This study aimed to investigate the inter- and intraobserver agreement, as well as the accuracy of clinical judgment of the electrocardiogram (ECG) in determining LBB-capture and septal lead position in patients undergoing LBBAP implantation. In addition, the role of vectorcardiographic QRS-area in determining LBB-capture was evaluated.

Methods: Unipolar paced ECGs during LBBAP implantation from 50 patients with baseline narrow QRS were collected. LBB-capture was attempted in all patients and assessed using MELOS (Multicentre European Left Bundle Branch Area Pacing Outcomes Study) criteria and the European Heart Rhythm Association (EHRA) consensus statement. Eight blinded cardiologists classified 100 ECGs for capture type and septal location.

Results: The interobserver and intraobserver agreement for capture type had a Light's kappa of 0.43 and 0.62, respectively. Concordance between clinical judgment and intraprocedural confirmation averaged 72%. Interobserver and intraobserver agreement for septal lead position had a Light's kappa of 0.43 and 0.77 respectively. QRS-area was significantly higher for left ventricular septal pacing (LVSP) than nsLBBP, whereas QRS duration was not. A QRS-area cutoff of 26 mV.ms had 77% accuracy in distinguishing LVSP from nsLBBP. Clinical judgment accuracy averaged 72%.

Conclusion: Interobserver agreement and correlation with intraprocedural confirmation (gold standard) are only moderate, whereas intraobserver agreement on ECG-based differentiation of capture type and septal lead location is substantial. Vectorcardiographic QRS-area slightly outperforms clinical judgment in distinguishing capture types and may be a useful objective alternative.