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Background: Permanent pacing in children with isolated congenital complete atrioventricular block may cause left ventricular dysfunction. To prevent it, alternative pacing sites have been proposed: left ventricular epicardial or selective right ventricular endocardial pacing. Aims: To compare the functional outcome (left ventricular systolic function and synchrony) in paediatric patients with congenital complete atrioventricular block and left ventricular apical epicardial or right ventricular transvenous mid-septal pacing. Methods: Retrospective study. Epicardial leads were implanted by standard surgical technique, transvenous leads by 3D electroanatomic mapping systems. 3D mapping acquired 3D right ventricular local pacing map and defined the narrowest paced QRS site. 3D mapping guided screw-in bipolar leads on that ventricular site. Electrocardiogram (ECG) (QRS duration) and echocardiographic data (synchrony: interventricular mechanical delay, septal to posterior wall motion delay, systolic dyssynchrony index; contractility: global longitudinal strain, ejection fraction) were recorded. Data are reported as median [interquartile ranges]. p < 0.05 was significant. Results: There were 19 transvenous systems (age 8.8 [6–14] years; right ventricular mid-septum) and 17 epicardial systems (0.04 [0.001–0.6] years; left ventricular apex). Post-implantation QRS significantly widened either in endocardial or in epicardial patients. Most patients reached 4-year follow-up. One-year and 4-year ejection fraction and global longitudinal strain were mostly within normal limits and did not show significant differences between the two groups and between the same endocardial/epicardial group. Synchrony parameters were within normal limits in the two groups. Conclusions: Left ventricular apical epicardial pacing and 3D mapping-guided right ventricular mid-septal pacing preserved left ventricular contractility and synchrony in children and adolescents with congenital complete atrioventricular block at short-/mid-term follow-up, without relevant significant differences between the two groups.

Aims In congenitally corrected transposition of the great arteries (CCTGA) the right ventricle (RV) is systemic. Atrioventricular block (AVB) and systolic dysfunction are frequently observed. Permanent pacing of the subpulmonary left ventricle (LV) may worsen RV dysfunction. The aim of this study was to seek out if LV conduction system pacing (LVCSP) guided by three-dimensional-electroanatomic mapping systems (3D-EAMs) can preserve RV systolic function in paediatric CCTGA patients with AVB. Methods and results Retrospective analysis of CCTGA patients who underwent 3D-EAM-guided LVCSP. Three-dimensional-pacing map guided lead implantation towards septal sites with narrower paced QRS. Electrocardiograms (ECGs), echocardiograms, and lead parameters (threshold, sensing, and impedance) were compared at baseline (pre-implantation) and at 1-year follow-up. Right ventricle function was evaluated by 3D ejection fraction (EF), fractional area change (FAC), RV global longitudinal strain (GLS). Data are reported as median (25th–75th centiles). Seven CCTGA patients aged 15 (9–17) years, with complete/advanced AVB (4 with prior epicardial pacing), underwent 3D-guided LVCSP (5 DDD, 2 VVIR). Baseline echocardiographic parameters were impaired in most patients. No acute/chronic complications occurred. Ventricular pacing was &gt;90%. At 1-year follow-up QRS duration showed no significant changes compared with baseline; however, QRS duration shortened in comparison with prior epicardial pacing. Lead parameters remained acceptable despite ventricular threshold increased. Systemic RV function was preserved: FAC and GLS improved significantly, and all patients showed normal RV EF (&gt;45%). Conclusion Three-dimensional-EAM-guided LVCSP preserved RV systolic function in paediatric patients with CCTGA and AVB after short-term follow-up.

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&lt;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.