Surgical implantation of MicraTM leadless
pacemaker
The procedure for
MicraTM leadless
pacemaker deployment has been well described before.10Briefly, patients were placed in a supine position and local anaesthesia
was administered at the right inguinal area. The femoral vein was
punctured using the modified Seldinger technique and the
MicraTM delivery sheath (27F) was inserted into the
inferior right atrium via the inferior vena cava (IVC). The delivery
catheter through the sheath was bent to cross over the tricuspid valve
annulus to the right ventricle. In the radiography group, the RV septum
was visualized via the precise right ventriculography by the operator
and the MicraTM leadless pacemaker was subsequently
implanted in the mid-septum. The specific implantation method was as
follows: a pigtail catheter (6Fr; TERUMO, Kyoto, Japan) was delivered
along a sheath to the apex of the right ventricle, and the right
ventriculography was achieved by injection of 20 cc contrast under
fluoroscopic views in the right anterior oblique (RAO) 30°±10° and left
anterior oblique (LAO) 45°±10° positions, respectively (Supplemental
Materials Figure S1). The right ventriculography under fluoroscopic
RAO30 showed the RV septum that was divided into nine subdivisions
(named zones 1-9, Figure 1A) and the initial intended implantation site
at zone 2 (the mid-septum) was chosen for deployment of
MicraTM leadless pacemaker (Figure 1C). In the
non-radiography group, regular cap injection of 10 mL contrast was
conducted, that usually showed a small region of the right ventricle
(Supplemental Materials Figure S1). In both groups, after transvalvular
access to the right ventricle, the Micra-TPS was slightly rotated
clockwise to point to the intended area in the fluoroscopic image of RAO
30, and the MicraTM pacemaker was subsequently
adjusted clockwise at the LAO view (usually at 40°). This was done to
ensure that the angle between the Micra-TPS and spinal vertebrates was
70° to 90° and the height of the TPS was adjusted according to the
spinal vertebrate positioning, which aided the anchoring of the
MicraTM leadless pacemaker to the median septum.
If the pacing parameters at the chosen site were unacceptable, the
distal delivery catheter was moved to a nearby location. After release
of MicraTM pacemaker was completed, electrical testing
of the MicraTM pacemaker, including evaluations of
pacing capture threshold, pacing impedance, and R-wave amplitude, was
performed. Pacing and sensing electrical parameters were tested at a
pulse width of 0.24 ms; the required capture threshold was ≤1.5 V, the
pacing impedance ranged from 400 to 1500 Ω, and R-wave amplitude was ≥5
mV. After satisfactory test results, the row traction test verified that
at least two hook teeth were fixed in the myocardium, then the tether
was cut after pull and hold test and the delivery system was removed,
and the puncture site was sutured
for haemostasis. The duration of the procedure was defined as the time
between the insertion of the femoral vein puncture needle into the skin
and the withdrawal of the puncture sheath after completion of pacemaker
implantation.
Data collection :
Baseline data including demographic characteristics and indications for
pacemaker implantation were collected at enrollment. Pacing parameters
including capture threshold, R-wave amplitude, and pacing impedance were
recorded at and post implantation. The echocardiography parameters
measured at enrolment and post implantation were as follows: left
ventricular ejection fraction (LVEF), left ventricular end-diastolic
internal diameter (LVEDD), right ventricular size, and tricuspid valve
regurgitation.
The procedural data collected at the implantation were as follows: the
number of MicraTM pacemaker positioning, length of
surgery, X-ray exposure time and dose, pacing parameters and 12-lead
electrocardiography (ECG) from which QRS duration and left ventricular
activation time (the interval from pacing artifact to the peak of ECG V5
or V6) were measured. Adverse events if any were documented, including
arteriovenous fistula, hematoma, incision site bleeding, persistent
lymphatic fistula, vascular pseudoaneurysm, and other complications such
as pericardial effusion and perforation, as well as leadless pacemaker
displacement and embolization.
All patients underwent a computed tomography (CT) scan of the heart with
contrast enhancement post implantation (day 2 to day 30). CT scan is a
reliable method to identify the location of a pacing
lead.11 CT scan data were processed with 64 slides
using the software Carto-Merge (Cartomerge™, Biosense Webster, Inc.,
Diamond Bar, CA, USA) to achieve 3-D cardiac reconstruction with
MicraTM pacemaker location, based on which the
positional relationship between the MicraTM pacemaker
and the location in the right ventricular septal surface was determined
(Figure 2 A-B). The CT image-based pacing location was compared to the
intended location by the operator at the implantation.