High-pass filter settings and possible mechanism of discrete electrograms in left bundle branch pacing

Objective The characteristics of discrete intracardiac electrograms in selective left bundle branch (SLBB) pacing (SLBBP) have not been described in detail previously. This study aimed to examine the effect of different high-pass filter (HPF) settings on discrete ventricular components in an intracardiac electrogram (EGM) and to analyze its possible mechanisms. Methods This study included 95 patients with indications of permanent cardiac pacing. EGMs were collected at four different HPF settings (30, 60, 100, and 200 Hz) with a low-pass filter at 500 Hz, and their possible mechanisms were analyzed. Results LBBP was successfully achieved in 92.6% (88/95) of patients. SLBBP was achieved in 80 patients. The occurrence rates of discrete EGM were 18.9%, 40.0%, 74.7%, and 84.2% for HPF settings of 30 Hz, 60 Hz, 100 Hz, and 200 Hz, respectively. The analysis of discrete ECG detection showed significant differences between the different HPF settings. By using the discrete EGM as the SLBB capture golden standard, the results of EGMs revealed that the 30 Hz HPF has a sensitivity of 23% and specificity of 100%. The 60 Hz HPF had a sensitivity of 48% and a specificity of 100%. The 100 Hz HPF had a sensitivity of 89% and a specificity of 100%. The 200 Hz HPF had a sensitivity of 100% and specificity of 100%. Conclusions An optimal HPF setting of 200 Hz is recommended for discrete electrogram detection. A discrete EGM should exhibit an isoelectric interval. A steep deflection and spinous ventricular EGM morphology nearly identify an intrinsic EGM morphology.