Background: Currently, splitting of electrogram (EGM) or electrocardiogram (ECG) under threshold test are used as the gold standard to assess Left bundle branch (LBB) capture in LBB area pacing. However, discrete intracardiac ventricular EGM has not been reported until now. This study aims to explore the clinical significance and possible mechanism of different pacing ventricular EGM morphologies in selective LBB pacing. Methods: Only patients with evidence of selective LBB pacing (splitting of EGM under threshold test) were included. According to the differences between intrinsic and paced ventricular EGM morphologies, the participants were further divided into three groups: concordant EGM (CE) group, similar EGM (SE) group and discordant EGM (DE) group. Baseline characteristics, indications for pacing, pacing parameters, and V6 R-wave peak time were analyzed. Results: 274 patients (85.6%) achieved successful selective LBB pacing. After excluding 34 LBBB patients, LBB potential was recorded in 192 (80%) of 240 patients. In patients with LBB potential, the correlation between V-V6(P) RWPT and V-V6(S) RWPT in CE group (r=0.083, P<0.0001) and SE group (r=0.766, P<0.0001) were strong. V-V6(S) RWPT was significantly shorter than V-V6(P) RWPT (38.14±9.42 vs. 43.68±6.72, P<0.01) in DE group. In patients without LBB potential, V-V6(S) RWPT was significantly shorter than V-V6 RWPT (38.14±11.60 vs. 46.15±11.81, P<0.05) in DE group. There was a strong correlation (r=0.943, P<0.0001) between V-V6 RWPT and V-V6(S) RWPT in CE group, a possible correlation (r=0.564, P=0.07) in SE group, while poor correlation (r=0.259, P=0.27) in DE group. Conclusion: The continuous recording technique combined with High Pass-200 Hz filter setting was feasible and effective for confirming selective LBB pacing by discrete EGM. Concordant or similar intrinsic and pacing ventricular EGM indicated that the electric conduction shared the same pathway, while discordant intrinsic and pacing ventricular EGM indicated that the electrical stimulation is conducted through different pathway.

The authors have declared no competing interest.

This work was supported by Zhejiang Provincial Public Service and Application Research Foundation (LGF22H020009), Medical Scientific Research Foundation of Zhejiang Province, China (2023RC260), Ningbo Major Research and development Plan Projects (2024Z235), and National Nature Science Foundation of China (No.81900340).

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The study protocol was approved by the Ethics Committee of the Ningbo No 2. Hospital.

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