Funding Acknowledgements Type of funding sources: None. Background/Introduction Paediatric transvenous permanent pacing from alternative ventricular sites including conduction system pacing may prevent ventricular dyssynchrony and systolic dysfunction. These procedures may be difficult and require higher fluoroscopic exposures. The use of three-dimensional-electroanatomic mapping system (3D-EAM) may guide lead implantation toward these alternative sites and reduce fluoroscopic exposure. Purpose of this study is the outcome of 3D-EAM-guided alternative sites pacing in paediatric patients. Methods Retrospective analysis of children and young patients with congenital or acquired complete atrioventricular block (CAVB) with or without other congenital heart disease (CHD) who underwent 3D-EAM-guided transvenous pacing in alternative sites of the subpulmonary ventricle, to perform non-selective His bundle pacing (NSHBP), pacing of ventricular septum close to conduction system (VS-CSP) or outflow tract (OT). 3D-pacing map guided stylet-directed screw-in lead implantation toward septal sites with narrower paced QRS. Procedure and follow-up data were recorded. Parameters of ECG (QRS duration, left ventricular activation time, LVAT), echocardiogram (3D ejection fraction, EF, global longitudinal strain, GLS, of the systemic ventricle) and lead (threshold, sensing) were registered and compared at baseline (pre-implantation) and during follow-up (1-3-year). Data are reported as median (25th-75th centiles). P<0.05 was significant. Results 64 patients (47 females) with CAVB, of whom 11 with CHD, underwent 3D EAM-guided pacing (31 VVIR, 33 DDD) at age 12 (8-15) years, weight 44 (27-57) kg. Prior pacing (RV apex, RV and LV free wall, also biventricular) was present in 27 patients. Pacing sites were: 10 NSHBP, 5 RVOT, 49 VS-CSP (Figure 1). Procedure time was 175 (146-200) min, fluoroscopy exposure was: 3.0 (1.2-5.0) mGy and 90 (33-146) microGy/m2. Echographic parameters at baseline and follow-up are reported in Table 1. Baseline QRS duration 85 (80-130) ms, increased after implantation, 115 (100-120) ms (P=0.002), with LVAT 80 (70-81) ms (Figure 1). In patients with prior pacing, QRS shortened post-implantation: QRS 130 (120-160) vs. 120 (110-125)ms (P=0.004). Lead parameters were good post-implantation and at 3-year follow-up: threshold 0.5 (0.4-0.7) vs. 0.9 (0.7-1.2)V/0.5 ms; R-wave sensing 9 (6-12) vs. 7 (4-9)mV. Four NSHBP patients showed lead dislodgement requiring lead repositioning. Conclusions 3D-EAM-guided alternative site pacing was accomplished with low fluoroscopic exposure. Paced QRS duration was significantly broader than in junctional rhythm but it was significantly narrower than prior epi/conventional site endo pacing. This pacing approach preserved ventricular systolic function in paediatric patients with CAVB at mid-term follow-up.

Funding Acknowledgements Type of funding sources: None. Background/Introduction Transvenous implantation of pacemaker is performed with fluoroscopy for leads’ insertion and implantation in the heart. This implies radiation exposure for patients and operators. Fluoroscopy allows a two-dimensional view of lead movements, and sometimes it is difficult to implant lead in the complex heart anatomy, or in alternative right ventricular (RV) pacing sites, that often requires higher radiation doses. These alternative pacing sites may prevent pacing-induced ventricular dysfunction. They are his bundle pacing area (HBP), ventricular septum close to the conduction system area (VS), RV outflow tract (RVOT). The use of three-dimensional-electroanatomic mapping system (3D-EAM) may reduce fluoroscopy and guide lead implantation. Published median fluoroscopy data for similar procedure are: 6 mGy (1), 13 mGy and 231 microGy/m2 (2). Purpose of this study is to seek out if a 3D-EAM-guided transvenous implantation into RV alternative sites pacing in paediatric patients can be accomplished with zero or near-zero X-rays. Methods Retrospective analysis of children and adolescents with congenital or acquired (idiopathic) complete atrioventricular block (CAVB) without other congenital heart defects who underwent 3D-EAM-guided pacing in alternative RV sites. The implant procedure was divided in 4 steps: 1-contrast venography; 2- 3D mapping: with a steerable catheter (femoral vein), the 3D-EAM acquired geometric reconstruction of the right heart and a pacing map identified RV sites with narrower paced QRS; 3-axillary vein puncture; 4-lead and pacemaker implantation: 3D-EAM guided stylet-directed screw-in lead implantation toward desired RV sites. Data are reported as median (25th-75th centiles). Results 54 CAVB patients (42 females), underwent 3D EAM-guided pacing (27 VVIR, 27 DDD) at age 11.5 (7.7-14) years, weight 42 (26-54) kg. Pacing sites were: 10 HBP, 4 RVOT, 40 VS (Figure 1). Procedure time was 170 (143-193) min, total fluoroscopy exposure and that of the 4 steps are reported in Table 1. The lowest exposures were: 0.2 mGy, 8 microGy/m2 (VVIR) and 0.6 mGy, 15 microGy/m2 (DDD). Paced QRS was 115 (100-120) ms. Conclusions 3D-EAM-guided alternative RV pacing sites was accomplished with very low fluoroscopic exposure, close to zero in some cases. Therefore, with 3D-EAM we can significantly reduce radiological doses also in difficult pacing procedures in paediatric patients, thus reducing radiological risks and preserving ventricular function. The dream is becoming reality.

Funding Acknowledgements Type of funding sources: None. Background/Introduction One of the main complications of transvenous leads implanted in paediatric patients is the stretching of the lead caused by the somatic growth. It may cause pacing and sensing defects and lead dislodgement or even fracture. Absorbable lead ligature and atrial loop may reduce this risk. However, the loop may induce traction or may unroll too early and therefore impair lead function. Lead extraction and replacement is another solution, although it has some procedural risks in young patients. Lead advancement through pushing it from the pocket may solve growth-induced traction and spare the electrode throughout childhood until post-puberty. Purpose of the study is the retrospective analysis of the outcome of the transvenous lead advancement in children with a pacemaker (PM) in a single tertiary paediatric center. Methods Consecutive patients with a VVIR PM implanted for isolated congenital complete atrioventricular block (no structural heart disease) in alternative right ventricular (RV) pacing sites, with lead stretching underwent a trial of lead advancement during general anaesthesia, cefuroxime antibiotic profilaxis, from 2014 to 2021. After venous angiography showed venous patency, the PM pocket was opened, the lead was released from subcutaneous adherences and with a stylet was gently advanced to create a semi-loop in the atrium without dislodging the tip. Lead data (threshold, sensing, impedance) were compared before and after the procedure. Data are expressed as median (25th-75th centiles) Results: 7 patients underwent PM implantation at 6.9 (5.5-8.0) years of age, 20 (18-21) kg, 116 (106-120) cm, with the lead positioned at parahisian(3)/mid-septum (4 pts) sites. During a follow-up of 3 (1-5) years, advancement procedures were 2 (1-4) per patient. Between procedures, delta age was 15 (12-19) months, height 7 (6-11) cm and weight 4 (2-6) kg. All leads were successfully advanced without any procedural complications. Procedure time (skin to skin) was 91 (69-105) minutes, fluoroscopy was 0.4 (0.2-1.2) mGy, 13 (9-35) microGy/m2. Electrical lead parameters did not showed significant differences between consecutive control times. In one parahisian pacing, chronic threshold increased after 3 years (2 advancement procedures) from 0.7V to 2.6 V/0.4 ms. Conclusion the advancement of transvenous leads in children is a safe and effective procedure, without significant procedural complications and during follow-up, and with low fluoroscopy exposure. This procedure may maintain a good function of transvenous leads until growth has completed.

Funding Acknowledgements Type of funding sources: None. Background/Introduction Before bipolar epicardial leads became widely available and used by heart surgeons, unipolar epicardial leads were frequently implanted in small children requiring permanent pacing. Main complications are lead fractures causing pacing/sensing defect. Therefore, patients should undergo new epicardial or endocardial lead implantation with relevant procedural risks, especially in complex congenital heart disease (CHD). Proximal fractures, close to the generator, may be repaired using a dedicated Unipolar Lead Adapter and Extension, with reduced operative risks. Purpose of the study is the retrospective analysis of the outcome of the repair of unipolar epicardial leads in young patients (pts) in a single tertiary paediatric center. Methods Consecutive patients with proximal fracture underwent a trial of lead repair using the lead adapter/extension, during general anaesthesia, cefuroxime antibiotic profilaxis, from 2004 to 2020. Lead data (threshold, sensing, impedance) were compared before and after the repair procedure. Results 18 patients with CHD (12pts, 10 of whom complex, 6 post-Fontan) or normal structural heart (6pts), who underwent pacemaker implantation at 2.5 (0.7-5.8)years of age for congenital/postoperative atrioventricular block (11pts) and sinus node dysfunction (7pts), showed lead (7 atrial, 11 ventricular) fractures after chronic pacing. At 13 (8-17)years of age, all leads were successfully repaired without any complications. Follow-up was 4 (2-6)years. Four pts (22%) showed again fractures of the repaired lead, after 1 month, 1and 3 years (2pts). Electrical lead parameters are shown in table 1: there were not significant differences between consecutive time of controls, also in the atrial and ventricular lead subgroups. Table 1.-------------------Pre-repair;--intraprocedural;---1 month;----------1 year;-------------4 years. Threshold (V/0.4 ms):--1.1 (0.7-1.4);--1.0 (0.8-1.6);-------1.2 (0.9-1.5);-----1.2 (0.9-2.1);-------1.5 (1.1-1.8). Sensing (mV):--------- 7 (2.4-12);------5.4 (1.3-15);-------4 (1.5-11);----------5 (1.6-12);---------3 (2-10). Impedance (ohm): 343 (289-407);---350 (246-415);--346 (250-432);--374 (250-589);--362 (220-470). Conclusion The repair of fractured unipolar epicardial leads in young patients is a safe and effective procedure, with few complications during follow-up. Effective repair can delay more aggressive procedures.