Pacemaker implantation
The left subclavian approach was preferred per study protocol. After the
venous system was reached, the atrial pacing lead was temporarily placed
in the apex of the right ventricle. Then the His bundle region was
mapped using a SelectSecure™ lead (model 3830, 69 cm, Medtronic Inc.,
Minneapolis, MN), which was delivered through a fixed-curve sheath (C315
HIS, Medtronic, Minneapolis, MN), as previously described
[8]. Once the His bundle signal was
identified, to ensure the para-hisian ventricular position of the lead
tip, it was moved to the right ventricle, behind the hinge of the septal
leaflet of the tricuspid valve. An X-ray and an electrogram (EGM) of the
atrial, His bundle, and ventricular signals were used to navigate the
lead tip to the area of the basal interventricular septum. At this
location, atrial signals significantly decreased or disappeared, but His
bundle signals were present before lead fixation - Figure 1. In case of
uncertainty, an injection of contrast agent through a C315 HIS sheath
was performed to verify ventricular lead tip placement. Once the proper
ventricular septal position of the lead tip was achieved, it was fixed
using 3–5 clockwise rotations to anchor it into the septal
‘para-hisian’ position, which was followed by pacing with outputs
between 0–5V at 0.5 ms. cSp was confirmed when a wide, notched, or
slurred QRS complexes during low output pacing, which narrowed and had a
reduced R wave peak time (RWPT) at V6 (LVAT) during high output pacing
were observed. Thereafter the atrial lead with a pre-shaped stylet was
moved from the apical position and temporarily placed in pre-specified
locations in the right ventricle (RV septum, anterior wall, and lateral
wall). For appropriate lead placement in these locations, the
SelectSecure™ lead and C315His sheath, already positioned in the basal
septal region, were used as landmarks – Supplementary Figure 1. For all
pacing locations, X-ray cine loops in two projections (RAO 20–30° and
LAO 20–30°) were generated and stored for further analysis. In patients
with an indication for a dual-chamber pacemaker, the atrial lead was
removed from the ventricular position and was fixed in the right atrium
at the end of the procedure. Stored ventricular pacing positions of the
atrial lead were later retrospectively reviewed by an experienced
physician blinded to the intended position. The exact location of the
lead tip was determined to be one of the following: RV myocardial septal
– mSp, apical, anterior wall or lateral wall. Moreover, mSp positions
were further classified as (a) the septal right ventricular inflow tract
(RVIT) or (b) the septal right ventricular outflow tract (RVOT) in the
RAO projection – Figure 2.
The distances between cardiac silhouette lines (a+b) and the lead with
cSp capture to the lower cardiac silhouette (a) were measured in mm –
Figure 2. The location of the para-hisian region with cSp capture, with
respect to the diameter of the heart silhouette, was calculated as
(a/a+b) x 100 and reported as percentages. All ECG recordings during
pacings of the right ventricular septum were reviewed retrospectively
using EP Labsystem software (Boston Scientific, MA, USA) at 25, 100, and
200 mm/s, as needed. HV intervals (calculated as the mean value between
2 consecutive beats), LVAT, the types of ventricular capture, and the
ratio between the atrial and ventricular signal amplitudes in mV (A/V
amplitude ratio) were measured after lead fixation in the para-hisian
area during spontaneous rhythm and pacing at 100 mm/s.