Continuous unipolar pacing characteristics monitoring to
guide LBBAP
Left Bundle Branch Area Pacing (LBBAP) involves deep transeptal screwing
of the lead until the LV sub-endocardium is reached. The exact number of
rapid rotations of the lead during this manoeuvre remains highly
variable and depends among other factors of the septal wall thickness,
the penetration angle of the lead in the septum, and the progression
speed of the lead through the septum. Regular control of the paced QRS
morphology and unipolar pacing impedance is key to avoid perforation in
the LV cavity and confirm engagement of the left septal conduction
system. Typically, as the pacing lead advance into the septum, the “W”
shaped QRS morphology in lead V1 gradually changes towards an incomplete
right bundle branch block morphology (qR/rsR’) in lead V1. This
indicates appropriate progression of the lead through the septum.
Simultaneously, the global QRS duration and the initial QRS slurring or
pLVAT in lead V6 decrease as the LBB area is approached. Unless a
transseptal perforation has occurred, the unipolar lead impedance
progressively rises and falls (slightly) before reaching the LV
sub-endothelium. The intermittent pace mapping strategy impose the rapid
rotations of the outer lead body to be repeatedly interrupted to connect
the programmer (via crocodile clips) to the connector pin for pacing. If
no LV cavity perforation has occurred and if criteria for LBBAP are not
met after a first initial lead engagement, the crocodile clips are
disconnected, and the lead can be carefully further advanced until next
evaluation. With the loss of momentum, the repetition of these steps may
compromise distal torque transmission. This is particularly true with
stylet-driven leads, which are non-isodiametric and more susceptible to
accumulate torsional forces. As a consequence, further lead progression
might be compromised, and late retraction of the helix can occur with
eventual loss of LBB capture or inappropriate fixation. Finally, the
repetition of the pace mapping after each set of lead rotations prolongs
the procedure and increases the risk of sheath dislodgement. Therefore
continuous monitoring of unipolar pacing characteristics without
interruption of screwing-in of the lead is highly desirable.