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Background Alternative right ventricular (RV) sites (RVAPS) have been proposed to prevent or reduce RV pacing-induced left-ventricular (LV) dysfunction. Nonfluoroscopic 3D electroanatomic mapping systems (EAM) have been developed to guide cardiac catheter navigation and reduce fluoroscopy during electrophysiological procedures or pacemaker implantations. Aim The aim of the study was to compare the results of EAM-guided permanent pacemaker implantation aiming at RVAPS with conventional fluoroscopic-guided implantation in RV apex (RVA) in children and adolescents. Methods A prospective, randomized analysis was performed on children/adolescents with complete atrioventricular block (CAVB) who underwent EAM-guided pacemaker and transvenous leads implantation into RVAPS (EAM-RVAPS) or conventional, fluoroscopic-guided implantation into RV apex (RVA). In EAM-RVAPS, a pacing map guided the implantation of ventricular leads in septal sites with narrower QRS. After implantation, LV contractility (ejection fraction [EF], Global Longitudinal Strain [GLS]) and synchrony were evaluated at 1-12 months. Results Twenty-one pediatric patients with CAVB, with (six patients) or without structural heart diseases, aged 4-16 (median 10.5) years, were divided in two groups: EAM-RVAPS (11 patients, four dual-chamber/DDD, seven single-chamber/VVIR pacemakers) and RVA (10 patients, one DDD/nine VVIR). The two groups did not show significant differences for preoperative parameters. EAM-RVAPS showed: preserved LVEF and synchrony (not significantly different than RVA), significantly lower GLS and radiation doses/exposures, in spite more complex procedures, significantly longer procedure times and narrower paced QRS than RVA. Conclusions EAM-guided procedures have been useful to reduce radiation exposure and to localize RVAPS with narrower paced QRS and lower GLS than RVA.

Aims Right ventricular (RV) apical (RVA) pacing can induce left ventricular (LV) dyssynchrony, remodeling, and dysfunction in children with complete atrioventricular block (CAVB). We compared the functional outcome of RVA with RV alternative pacing sites (RVAPS), including para-Hisian, septal, and outflow tract sites. Methods This is a single-center, retrospective study. Data were collected before pacemaker implantation (transvenous leads), postoperatively, at 6 months, and at 1–2–3–4 years. Electrocardiogram evaluation included QRS duration, axis, QTc/JTc, and QTc dispersion. Echocardiographic evaluation included 2-D/3-D assessment of ventricular dimensions (Z-score of LV end-diastolic dimension), function (ejection fraction), and synchrony. Results From 2009 to 2015, 55 patients with CAVB, aged 3–17 years, with or without other congenital heart defects, underwent RVAPS (30 patients, median age 11 years) or RVA (25 patients, median 12 years). All leads were positioned into the septum. Before implantation, no significant differences in parameters were observed, except for higher Z-score in RVAPS than in RVA. After implantation, at a median follow-up of 2.5 (range 1–6) years, the two groups showed no significant differences in LV dimensions, contractility, and synchrony. QRS intervals of RVAPS were significantly shorter than RVA. Clinical status was good and contractility/synchrony indexes were normal or adequate in all patients. Conclusions In pediatric patients, RVAPS and RVA showed no significant differences in LV dimensions, contractility, and synchrony. Preimplantation dilated patients showed LV reverse remodeling. RVAPS demonstrated shorter QRS intervals. Therefore, septal pacing sites, either RVA or RVAPS, seem to determine good contractility and synchrony at a mid-term follow-up.

Background Transcatheter cryoablation is a well-established technique for the treatment of atrioventricular nodal reentry tachycardia (AVNRT) in children. Nevertheless, atrioventricular nodal slow-pathway conduction may recur after an acutely successful procedure. The aim of this study was to evaluate the long-term outcome of acutely successful AVNRT cryoablations in pediatric patients in case of focal cryolesion and in case of need for High-Density Linear Lesion (HDLL) cryoablation due to focal failure. Methods Sixty-nine consecutive pediatric patients (30 males, mean age 12.4 ± 3.2 years; range: 5.4-18.0 years) underwent 3D-guided cryoablation for AVNRT at our institution from July 2013 to November 2014. When a focal cryoablation was acutely unsuccessful, a 3D-guided HDLL was created delivering multiple overlapping cryolesions/cryoenergy applications from the ventricular side of the tricuspid annulus to the atrial side, including the site of focal cryoablation if transiently successful. Results No permanent cryoablation-related complications occurred. Acute success rate was 98.5% (68 out of 69): in 55.9% (38 out of 68) with focal-lesion and in 44.1% (30 out of 68) with HDLL. Mean follow-up was 25.3 months and AVNRT recurrence rate was 13.2% (nine out of 68): 5.2% (two out of 38) with focal lesion and 23.3% (seven out of 30) with HDLL (P = 0.036). Conclusions In cryoablation of AVNRT in children, the need for a more aggressive protocol (HDLL), due to the failure of focal ablation, is strictly related to higher recurrence rates. Indeed, AVNRT recurrences after cryoablation in children seem to be due to a larger and deeper substrate rather than due to the type of energy used.

Background The etiological diagnosis of syncope and/or palpitations in children is often challenging. However, when noninvasive conventional examinations are inconclusive, the subcutaneous miniaturized implantable loop recorder (ILR) is recommended. The aim of our study was to evaluate the efficacy of miniaturized cardiac implantable devices in the early diagnosis of arrhythmias in children ≤6 years. Methods From March 2014 to May 2015, 21 patients (median age 5 years) underwent implantation of miniaturized ILR at our Institution after a complete cardiac work up. Median follow-up was 10 months. Results One patient underwent device removal for pocket infection and one needed a pocket revision. Eleven (52%) patients did not show any symptom and/or arrhythmia. Eight patients experienced symptoms during ILR monitoring: six had no electrocardiographic abnormalities, two had significant sinus pauses. Two patients had significant arrhythmias without symptoms and in one of these a pacemaker was implanted. The overall diagnostic yield was 47%. Conclusions Miniaturized ILR could be very useful to make a diagnosis and to decide future management strategies in small patients with undefined symptoms or severe cardiac diseases. Considering its characteristics, miniaturized ILR could start a new era in the diagnosis and follow-up of young patients with symptomatic and/or malignant arrhythmias.

Aims The subclavian vein approach has been used for 20 years in our center for pacemaker (PM) implantation in children, but it carries risks of hemothorax/pneumothorax and lead fracture, which could be reduced by axillary vein approach. Methods and Results This is a prospective study enrolling the first 48 consecutive pediatric patients (age: 12.3 ± 4.6 years) who underwent PM/implantable cardioverter-defibrillator leads implantation through axillary vein (guided by contrast venography) between 2009 and 2012 (group I). A comparison was made with the outcomes of the subclavian vein approach (group II) in 41 patients, age 12.3 ± 4.8 years, consecutively enrolled between 2006 and 2011. The two groups showed no significant differences for the variables examined except for follow-up, longer in group II, and for alternative ventricular pacing sites, more frequent in group I. Axillary vein diameter was 7.9 ± 1.7 mm and showed positive correlation with height (r = 0.77). The axillary vein approach was effective in 93.7% of patients. The unsuccessful procedures occurred in patients with significantly lower age and smaller venous diameters. The subclavian vein approach was effective in 100% of patients. Sixty-two leads were implanted in group I, 54 in group II. There were neither intraoperative complications in both the groups, nor significant differences for early and late complications. Conclusions The axillary vein approach for PM implantation in children is effective and safe for physicians skilled with subclavian vein approach. Younger patients with smaller vein diameters are at low risk for unsuccessful procedure.

Background:Automatic management of atrial stimulation by verification of atrial threshold (ACM) has recently been made feasible. We investigated circadian atrial threshold variability over the long term and the predictors of successful automatic atrial threshold measurement, in order to provide practical clues for programming ACM features, in such a way as to achieve daily threshold verification and > 99% effective atrial stimulation. Methods:Six daily attempts to measure atrial threshold were programmed in patients receiving an EnPulse™ pacemaker (Medtronic Inc., Minneapolis, MN, USA). Atrioventricular (AV) conduction was maximized by programming Search AV+ (SAV+) to a resting Paced AV delay = 400 ms in the first month, and 600 ms thereafter. Results:Seventy-six patients had a median follow-up of 12 months. Median ACM success was 77%. Concordance between automatically and manually measured thresholds was observed during the entire follow-up (Rho = 0.82, P 94% of measurements in the first trimester after implantation, and 99% of measurements thereafter, as well as any time after pacemaker replacement. Atrial threshold was measured on 86% of days: the predictors of ACM failure were AV block (AVB), high%Atrial pacing, and atrial fibrillation. Programming SAV+ to achieve 600 ms resting Paced AV decreased%Vpacing in patients with normal AV conduction and first-degree AVB, improving the ability to detect atrial threshold. Conclusions:The reliability of ACM is high over a long follow-up. On the basis of atrial threshold variability, a practical approach to ACM programming should be two daily atrial threshold measurements in patients with normal AV conduction and%Ap ≤ 40%, or with normal sinus activity and AVB, whereas 3–4 measurements should be recommended in patients with first-degree AVB and%Ap > 40% or with recurrent atrial fibrillation and AVB. The lowest adapted stimulation output should achieve at least threshold +1 V in the first trimester after implantation, then threshold +0.5 V thereafter, in order to achieve > 99.5% effective atrial stimulation.

Children with single chamber pacemakers, in adolescence and young adulthood, may be upgraded to dual chamber systems, but there are no published data about indications, timing, and complications. Upgrading was attempted in 18 patients with transvenous pacing leads. A retrospective analysis of all collected data was performed. At initial pacemaker implantation (mean +/- SD, 9.3 +/- 4.1 years), the pacing mode was VVIR (n = 13 patients) and AAI/AAIR (n = 5 patients). After 72 +/- 41 months of follow-up, at the age of 15.5 +/- 5.2 years, upgrade was undertaken because of the patient's age at elective generator replacement (n = 3 patients), ventricular dysfunction (n = 7), syncope/presyncope (n = 3) in patients with VVIR pacing, atrioventricular block (n = 2), and/or drug refractory supraventricular tachyarrhythmias (n = 4) in patients with atrial pacing. In comparison with single chamber pacemaker implantations, the average procedural time and the average fluoroscopy time were not significantly longer. All suitable preexisting leads were incorporated in the new pacing system. Leads were inserted via the ipsilateral subclavian vein in 16 patients. Venous occlusion was found in two patients: in the first the procedure was not performed; in the second, the contralateral vein was used and the old lead was abandoned. There were no procedural complications. During a follow-up of 14 +/- 11 months, ventricular dysfunction worsened in five of seven patients; other patients benefitted symptomatically. In conclusion, pacemaker upgrade is technically challenging but feasible and safe and may be beneficial for some patients.

The atrioventricular node is situated in the lower atrial septum, at the apex of the Koch's triangle. The dimensions of the Koch's triangle are studied in adult humans, while no data exist about them in pediatric age. The knowledge of the dimensions of Koch's triangle in childhood is very important for safe and correct application of radiofrequency energy during transcatheter ablation. The dimensions of Koch's triangle were determined in 69 human pediatric hearts. The median age of the children was 3 months, with a range from 1 day to 14 years, 30 were female and 39 were male. Relations between body weight (extracardiac parameter) and tricuspid valve diameter (intracardiac parameter) were determined in all hearts to show morphometric modifications with growth. The distribution of body weight was not Gaussian and no correlation could be obtained between Koch's triangle dimensions and body weight. However, it was possible to identify that the mean ratio between the cathetus of the Koch's triangle corresponding to the annulus of the tricuspid valve and the tricuspid valve diameter was 0.45 +/- 0.16, with a highly significant correlation coefficient (r = 0.653, P < 0.001). Therefore, by knowing: (1) the diameter of the tricuspid valve, and (2) the constant ratio between the cathetus of the Koch's triangle and the tricuspid valve diameter, it is possible to calculate the length of the segment of the tricuspid annulus along which the transcatheter application of radiofrequency current can be applied to ablate the slow-pathway, thus reducing the risks of damage of the atrioventricular node.

A 13-year-old male patient, who underwent Mustard operation for a very complex congenital heart disease (CHD), after palliation presented a decrease of the sinus node function, developing a tachy-brady syndrome and a mild dysfunction of atrioventricular (AV) conduction. He was successfully treated using a DDDRP pacemaker, which ensured a suitable atrial rhythm and was able to interrupt supraventricular tachycardia episodes. Until now, hospitalization related to episodes of heart failure or symptomatic arrhythmia, has not been necessary.

Single chamber rate responsive pacing offers many potential advantages over the more complex dual chamber atrial tracking pacing mode in children, and the preservation of atrioventricular synchrony could be unnecessary in selected groups of pediatric patients. Twenty-two pediatric patients (age range 9 months to 12 years; mean 6.5 years) had implantation of ventricular rate responsive (VVIR) pacemakers over a 2-year period. All patients had chronic third-degree atrioventricular block, and a normal ventricular function at rest. During the follow-up each patient underwent a 24-hour Holter monitoring, and ten performed a graded treadmill test in both ventricular fixed rate (VVI) and rate responsive (VVIR) pacing mode. Paced ventricular rates were found to be normal for age in all 22 patients; maximum rate did not reach the higher programmed rate during daily activities in any patient. Comparing the mean paced ventricular rate to the mean rates of blocked P waves, six patients showed a difference of more than 20 beats/min, which induced the pacemaker parameters to be reprogrammed. In all patients a significant correlation was found between variations of paced ventricular rate and variations of spontaneous blocked atrial rhythm (P < 0.05); this correlation persisted in the subsequent Holter controls in the ten patients with longer follow-up. Exercise tolerance resulted normal in the ten patients who performed a treadmill test either in VVIR or VVI mode, with increased maximal heart rates and maximal systolic blood pressure in VVIR mode (P < 0.0013). Rate responsive ventricular pacemakers seem to adequately respond to the physiological needs of daily life of this selected group of children requiring permanent pacing.