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.