Direct and indirect capture of the left bundle branch: Dynamic retrograde atrial potential abrupt and gradual decrease

Interesting phenomena during threshold testing of conduction system pacing: What is the mechanism?

“…Due to the battery depletion, the patient's pacemaker was upgraded from right ventricular pacing to left bundle branch When the stim-LVAT was abruptly decreased by 14 ms (changed from 62 to 48 ms) (Figure 1G, H) and remained shortest and constant at low and high outputs (2 V/0.5 ms and 8 V/0.5 ms), the LBB capture was confirmed (Figure 2A, B). 6,7 We stopped screwing the electrode and performed an initial threshold testing (Figure 2C-E). Selective LBBP (SLBBP) was characterized by appearance of an isoelectric interval…”

“…When the stim‐LVAT was abruptly decreased by 14 ms (changed from 62 to 48 ms) (Figure 1G, H) and remained shortest and constant at low and high outputs (2 V/0.5 ms and 8 V/0.5 ms), the LBB capture was confirmed (Figure 2A, B). 6,7 We stopped screwing the electrode and performed an initial threshold testing (Figure 2C–E). Selective LBBP (SLBBP) was characterized by appearance of an isoelectric interval and local EGM discrete from the pacing artifact at 0.3 V/0.5 ms with stim‐LVAT of 60 ms (Figure 2E).…”