PMC9883728_01
Electrogram recorded from the pacing lead screwed in the left bundle branch area (left bundle branch pacing). Note the presence of a sharp potential within the ventricular electrogram (arrow). Endocardial channel filtered at 0.5-500 Hz, with 64x gain.
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The EGM of intrinsic conducted beats with LBBB displayed a sharp potential within the ventricular signal (Figure 1).
Fascicular potential visible within the ventricular potential during cycles with left bundle branch block (first and third QRS complexes). Following a long RR interval (due to an atrial extrasystole, not visible on the tracing), the QRS narrows (second cycle) and the fascicular potential is visible before the ventricular potential. Schematic representations of activation are shown below each cycle, with retrograde activation of the fascicular potential during left bundle branch block, and anterograde activation during narrow QRS. LBBP, left bundle branch pacing lead electrogram. Recording using Labsystem Pro (Boston Scientific) with endocardial signal filtering of 0.5-500 Hz and 64x gain setting.
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Blocked atrial premature beats resulted in pauses, with narrowing of the post-extrasystolic QRS complex and visualization of a presystolic fascicular potential (with a potential:QRS interval of 22 ms):see Figure 2.
Electrocardiogram showing non-selective left bundle branch capture, with intermittent selective left bundle branch capture (arrows). Note the narrow QRS cycle directly after the pause, followed by resumption of left bundle branch block.
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The LBBP capture threshold was 0.5 V @ 0.5 ms, with intermittent transition from non-selective capture to selective LBB capture (Figures 3 and 4).
Transition from non-selective to selective left bundle branch capture with decrementing pacing output. Note the rounded appearance of the R' wave in V1 and change in the left bundle branch pacing electrogram morphology with selective capture with splitting of the signal.
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The LBBP capture threshold was 0.5 V @ 0.5 ms, with intermittent transition from non-selective capture to selective LBB capture (Figures 3 and 4).