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.