Implantation procedure
A single cardiologist was responsible for implantation, while other
operators participated at various stages of the procedure (venous
cannulation, atrial lead placement).
Fluoroscopy-guided cannulation of the axillary vein was the venous
access of choice, using a lumen-less 4-Fr lead (Select-Secure model 3830
69 cm, Medtronic Inc., Minneapolis, MN) through a fixed preformed sheath
(C315 HIS, Medtronic Inc.). A deflectable sheath (C304, Medtronic Inc.)
was used when it proved impossible to record the His electrogram. The
lead was connected to a digital recording system (Electrophysiology Lab
System, Boston Scientific, MA) in a unipolar configuration to measure
the intracavitary signal.
HBP was performed as described in the literature.10 In
brief, rotation and advance-retreat maneuvers were used to find the His
bundle electrogram with lowest atrial signal amplitude, evaluating the
selective and non-selective HBP with the lowest possible threshold. The
bundle block correction threshold was also considered in patients with a
wide baseline QRS.
After localization of the His electrogram in the LBBAP procedure, the
sheath was apically advanced 1–2 cm; next, if a paced QRS with “W”
morphology was obtained in lead V1, the electrode was inserted into the
septum with 5–6 clockwise turns until the notch in the paced QRS
complex migrated to the end of the QRS wave (or disappeared) and the QRS
width narrowed (Figure 1). The depth at which the lead was affixed in
the interventricular septum was guided by the impedance values and
target QRS obtained. Recording of the left bundle branch potential was
not an objective. The fluoroscopy time included the time for the
axillary puncture and for placing all of the leads.
The QRS complex was recorded before and after implantation by another
operator using a digital recording system at a speed of 100 mm/s. The
QRS duration was measured from QRS onset in the 12 leads when an
isoelectric interval was observed between pacing stimulus and QRS onset
or from stimulus to the end of the QRS when it was not. Pacing
parameters (threshold, sensed R-wave amplitude, impedance) were compared
between implantation and 3 months post-implantation.
The procedure was considered successful when a baseline QRS of
<120 ms was achieved in HPB, as recommended by the Multicenter
HBP Collaborative Working Group1, and when a QRS width
≤ 130 ms was obtained in LBBAP.12 In patients with
bundle branch block (BBB), HPB and LBBAP procedures were considered
successful when the paced QRS narrowed by ≥20% or to a QRS width of
<130ms 13. Accepted pacing parameters were a
pacing threshold of ≤ 3.5 V, an R-wave amplitude ≥ 0.8 mV, and a pulse
width of 1 ms with HBP and 0.5 ms with LBBAP.