Feasibility of contrast-enhanced ultrasound in confirming intranodal needle position for dynamic contrast-enhanced magnetic resonance lymphangiography in children.

This report demonstrates the feasibility and safety of using contrast-enhanced ultrasound (CEUS) to confirm intranodal needle position in children requiring dynamic contrast-enhanced magnetic resonance lymphangiography (DCMRL). A total of 7 patients were evaluated using CEUS after nodal puncture on a detachable magenetic resonance table, with 2 nodes cannulated in each patient, resulting in a combined evaluation of 14 nodes. The nodal cannulation success rate using CEUS was 85.7% (12/14 nodes). DCMRL was performed successfully in all patients with good contrast opacification of the central conducting lymphatics. Out of the 14 nodes, 2 nodes in the same patient demonstrated persistent extravasation on CEUS despite needle readjustment, requiring conversion to fluoroscopic lymphangiography. No adverse event related to the injection technique or CEUS was reported.

Evaluating High-Confidence Genes in Conotruncal Cardiac Defects by Gene Burden Analyses.

Background In nonsyndromic conotruncal cardiac defects, the use of next-generation sequencing for clinical diagnosis is increasingly adopted, but gene-disease associations in research are only partially translated to diagnostic panels, suggesting a need for evidence-based consensus. Methods and Results In an exome data set of 245 patients with conotruncal cardiac defects, we performed burden analysis on a high-confidence congenital heart disease gene list (n=132) with rare (<0.01%) and ultrarare (absent in the Genome Aggregation Database) protein-altering variants. Overall, we confirmed an excess of rare variants compared with ethnicity-matched controls and identified 2 known genes (GATA6, NOTCH1) and 4 candidate genes supported by the literature (ANKRD11, DOCK6, NPHP4, and STRA6). Ultrarare variant analysis was performed in combination with 3 other published studies (n=1451) and identified 3 genes (FLT4, NOTCH1, TBX1) to be significant, whereas a subgroup analysis involving 391 Chinese subjects identified only GATA6 as significant. Conclusions We suggest that these significant genes in our rare and ultrarare burden analyses warrant prioritization for clinical testing implied for rare inherited and de novo variants. Additionally, associations on ClinVar for these genes were predominantly variants of uncertain significance. Therefore, a more stringent assessment of gene-disease associations in a larger and ethnically diverse cohort is required to be prudent for future curation of conotruncal cardiac defect genes.

Single-pass albumin dialysis and hemoadsorption for bilirubin and bile acids removal for a child with hyperbilirubinemia after ventricular assist device implantation.

We report the successful management of hyperbilirubinemia using two different modalities of extracorporeal bilirubin removal therapy for a pediatric patient. A 13-year-old boy with dilated cardiomyopathy requiring veno-arterial extracorporeal membrane oxygenation (VA-ECMO) developed acute kidney injury and was dependent on continuous renal replacement therapy. He developed hyperbilirubinemia with a peak total bilirubin level of 786 µmol/L after implantation of biventricular assist device (BiVAD). Extracorporeal bilirubin and bile acids removal using single-pass albumin dialysis (SPAD) with 4% albumin as dialysate brought down the bilirubin level to 672 µmol/L after 21 h of therapy. Subsequently, he was started on two sessions of hemoadsorption using the Cytosorb® column which further lowered the total bilirubin level to 306 µmol/ in 24 h and 173 µmol/ after the treatment. No complication was encountered. Our case illustrated that both SPAD and hemoadsorption can effectively and safely reduce the serum bilirubin and bile acid levels in pediatric patients with BiVAD implantation. The ease of set-up, faster rate of bilirubin decline and capability of cytokine removal make hemoadsorption a favorable alternative to albumin dialysis.

Trends in contemporary advanced heart failure management: an in-depth review over 30 years of heart transplant service in Hong Kong.

Background: The year 2022 marks the 30th anniversary of heart transplant service in Hong Kong (HK). In this study, we describe prevailing trends and outcomes of advanced heart failure (AHF), including heart transplantations (HTx), in HK over the past 30 years. Methods: Trends in heart failure prevalence in HK from 1993 to 2021 were analyzed based on data from the Hospital Authority Clinical Data and Reporting System. All AHF patients referred for HTx consideration between 1992 and 2021 were reviewed. The bridge-to-transplant (BTT) utilization of short-term mechanical circulatory support (ST-MCS) devices, including venoarterial extracorporeal membrane oxygenation (VA-ECMO) and durable left ventricular assist devices (LVADs), from 2010 to 2021 was reviewed. Results: Overall, 237 heart transplants were performed in HK, with 10-year posttransplant and median survival of 68.1% and 18.7 years, respectively. An increase in AHF clinic referrals was correlated with increasing heart failure prevalence (R2=0.635, P<0.001). In total, 146 referrals were made for ST-MCS, and an observed increase in ST-MCS referrals was correlated with increasing VA-ECMO utilization (R2=0.849, P<0.001). Among 62 patients accepted for AHF therapy, those with durable LVAD implementation had better 1-year survival (71.5%) than those receiving an extracorporeal CentriMag (Levitronix) device as BTT (40%, P=0.008). In total, 143 LVADs were implanted, with 130 as BTT or bridge-to-candidacy (BTC) methods. The survival rate among the 130 BTT/BTC LVAD patients resembled that of HTx recipients (73.8% vs. 69.8% at 9 years, P=0.296). Conclusions: The burden of AHF management has increased and gained complexity over the past 30 years in Hong Kong.

Emerging roles of left ventricular assist device therapy as bridge to transplant in an Asian city with scarce heart transplant donor.

BACKGROUND: Left ventricular assist device (LVAD) has been increasingly used in patients with advanced heart failure. This study aimed to assess the impact of implementation of LVAD therapy on heart transplantation (HTx) service in Hong Kong (HK). METHODS: LVAD program was started in 2010 in HK and patients who had been put on HTx waiting list since the start of HTx program in HK from 1992 to 2020 were included for analysis. Survival on HTx waiting list between pre-LVAD era 1992-2009 and post-LVAD era 2010-2020 were analyzed by Kaplan-Meier method and compared by log-rank test. Multivariate analysis by time-dependent Cox-proportional hazard model was used to identify independent predictors of HTx waiting list mortality. RESULTS: A total of 478 heart transplant listing episodes involving 457 patients were included for analysis. There were 232 heart transplantations (HTxs), including one re-transplantation, during the study period. There were 110 patients who received LVAD as bridge to transplantation (BTT) and 30 of them had undergone subsequent HTx. The 1-, 2- and 3-year survival on waiting list were 82.3%, 61.7% and 43.0% respectively in the pre-LVAD era (n=178), while the 1-, 2- and 3-year survival were significantly improved at 85.7%, 81.8% and 78% respectively in the post-LVAD era (n=300), (P=0.003). Time-dependent multivariate analysis revealed that LVAD support was independently associated with significant reduction of waiting list mortality [odds ratio (OR): 0.21; 95% confidence interval (CI): 0.10-0.44, P<0.001]. There was no significant difference when comparing survival after LVAD as BTT and survival after HTx up to 8 years (76.1% vs. 72% at 8 years respectively, P=0.732). CONCLUSIONS: Waiting list survival improved in the post-LVAD era driven by the implementation of LVAD service. Long-term survival for LVAD recipients as BTT were comparable to heart transplant recipients in HK.

Successful Treatment of Rhabdomyolysis-Associated Acute Kidney Injury with Haemoadsorption and Continuous Renal Replacement Therapy.

We report two children with rhabdomyolysis-associated acute kidney injury who were successfully treated with a haemoadsorption column CytoSorb® in addition to continuous renal replacement therapy (CRRT). A 14-year-old girl with multiorgan failure requiring extracorporeal membrane oxygenation developed rhabdomyolysis due to reperfusion injury. Her creatine kinase (CK) and lactate levels continued to escalate despite high-dose CRRT. A haemoadsorption column was therefore added post-CRRT filter, which brought down the CK level from 264,500 IU/L to 97,436 IU/L after 8 hours of therapy. Another 4-year-old boy with epilepsy and cerebral palsy who was admitted for gastroenteritis with dehydration developed acute kidney injury and rhabdomyolysis with a peak CK level of 946,060 IU/L. He was initially treated with CRRT for 40 hours, which reduced his CK level to 147,580 IU/L. Two sessions of haemoadsorption were then performed in addition to the CRRT, which further lowered his CK level to 32,306 IU/L in 48 hours. Both patients demonstrated enhanced reduction of CK levels when the haemoadsorption column was used in addition to the CRRT, and no specific complication related to the haemoadsorption therapy was reported. Our cases showed that haemoadsorption can be considered as an adjunctive therapy for children with severe rhabdomyolysis-associated acute kidney injury.

Migrated Avalon-Elite cannula in an infant transcatheter repositioning without interruption of ECMO flow.

Inadvertent migration of Avalon-Elite cannula in patients receiving veno-venous extracorporeal membrane oxygenation (VV-ECMO) support is often difficult to manage. Cannula repositioning conventionally requires temporary discontinuation of the ECMO support which is often poorly tolerated in small infants with poor pulmonary reserve. We reported a case of a small infant weighing 3.9 kg requiring VV-ECMO support with a 13Fr Avalon-Elite cannula for respiratory failure secondary to severe pneumonitis, complicated by 2 episodes of cannula migration which were both successfully managed by transcatheter repositioning in the cardiac catheterization laboratory without interruption of ECMO flow.

Long term CentriMag biventricular support using hybrid cannulation as a bridge to transplant in a pediatric patient.

Paracorporeal continuous-flow ventricular assist devices designed for short-term support can also potentially provide long-term circulatory support as bridges to transplantation in children. We describe the long-term use of the CentriMag biventricular assist device with multiple pump changes in a 9-year-old boy with idiopathic-dilated cardiomyopathy. The initially implanted Berlin Heart EXCOR pumps were replaced by CentriMag due to thromboembolic complications. The CentriMag pumps were exchanged 15 times due to clot and fibrin formation or when the pumps reached their expiration dates. Connecting CentriMag to Berlin Heart EXCOR cannulae effectively served as an alternative long-term hybrid bridge to transplantation for 235 days. The patient successfully underwent a transplant after 284 days. Judicious pump monitoring and timely pump exchanges can potentially overcome device-related complications and extend the duration on support.

Rapid whole-exome sequencing facilitates precision medicine in paediatric rare disease patients and reduces healthcare costs.

BACKGROUND: Rapid whole-exome sequencing (rWES) offers the potential for early diagnosis-predicated precision medicine. Previous evidence focused predominantly on infants from the intensive care unit (ICU). This study sought to examine the diagnostic and clinical utility, and the economic impact on clinical management of rWES in patients beyond infancy and ICU setting. METHODS: rWES was performed on a prospective cohort of patients with suspected monogenic disorder referred from territory-wide paediatric ICUs and non-ICUs in Hong Kong urging for rapid genetic diagnosis. All eligible families were invited. We aimed to achieve a rapid turnaround time (TAT) of 14 days. Clinical utility and costs associated with clinical management were assessed in diagnosed cases. Actual quantitative changes in healthcare utilisation were compared with a counterfactual diagnostic trajectory and/or with matched historical control whenever possible. FINDINGS: rWES were offered to 102 families and 32/102 (31%) patients received a molecular diagnosis, with a median TAT of 11 days. Clinical management changed in 28 of 32 diagnosed patients (88%), including but not limited to modifications in treatment, avoidance of surgeries, and informing decisions on redirection of care. Cost analysis was performed in eight patients. rWES was estimated to reduce hospital length of stay by 566 days and decrease healthcare costs by HKD$8,044,250 (GBP£796,460) for these eight patients. The net cost-savings after inclusion of rWES costs were estimated to be HKD$5,325,187 (GBP£527,246). INTERPRETATION: This study replicates the diagnostic capacity and rapid TAT of rWES in predominantly Chinese patients, and demonstrates diagnosis-predicated precision medicine and net healthcare savings. Findings were corroborated by evidence from multinational cohorts, combined as part of a meta-analysis. rWES merits consideration as a first-tier diagnostic tool for patients with urgent needs in the clinical setting. FUNDING: Health and Medical Research Fund, HKU Seed Fund for Basic Research, The Society for the Relief of Disabled Children, and Edward and Yolanda Wong Fund.

Pediatric ventricular assist device therapy for advanced heart failure-Hong Kong experience.

Ventricular assist devices (VADs) are life-saving options for children with heart failure unresponsive to medical therapy as a bridge to transplantation or cardiac recovery. We present a retrospective review of 13 consecutive children who underwent implantation of VAD between 2001 and 2018 in our center. The median age was 12 years (1-17 years), weight was 45 kg (10-82 kg). Etiologies of heart failure were dilated cardiomyopathy (CMP) (n = 8), myocarditis (n = 2), ischemic CMP (n = 1), restrictive CMP (n = 1) and congenital heart disease (n = 1). Pre-implantation ECMO was used in 5, mechanical ventilation in 4, renal replacement therapy in 2 and IABP in 1. Devices used were: Berlin Heart EXCOR left VAD (LVAD), biventricular VAD (BIVAD) (n = 5, 2), CentriMag LVAD, BIVAD (n = 1, 2), HeartWare (n = 2), HeartMate II (n = 1). Median duration of support was 45 days (3-823 days). Overall survival was 85%. Four patients were successfully bridged to transplantation, 2 died while on a device, 4 remain on support and 3 were weaned from VAD. Late death occurred in 2 transplanted patients. Complications included bleeding requiring reoperation in 1, neurologic events in 3, driveline infections and pericardial effusion in 2 each. In one patient, CentriMag BIVAD provided support for 235 days, which is longest reported duration on such a VAD in the Asia Pacific region. Survival for pediatric patients of all ages is excellent using VADs. Given the severity of illness in these children morbidity and mortality is acceptable. VADs could potentially be used as a long-term bridge to transplantation in view of the donor shortage in the pediatric population.

Preoperative Venovenous Extracorporal Membrane Oxygenation for Transposition of Great Arteries With Severe Pulmonary Hypertension in a Newborn.

Severe persistent pulmonary hypertension in a newborn combined with transposition of great arteries increases the risk of early death before the arterial switch operation. We report the case of a newborn with transposition of great arteries and ventricular septal defect associated with severe pulmonary hypertension. Profound hypoxemia, despite successful balloon atrial septostomy and conventional supportive measures with mechanical ventilation, inhaled nitric oxide, and inotropes, led to the use of venovenous extracorporeal membrane oxygenation to rapidly stabilize the child preoperatively. Different from most reported cases on this scenario, we intentionally opted for a venovenous mode of support despite the presence of circulatory compromise.

A fatal case of COQ7-associated primary coenzyme Q10 deficiency.

BACKGROUND: Primary coenzyme Q10 (CoQ10) deficiencies are clinically and genetically heterogeneous group of disorders associated with defects of genes involved in the CoQ10 biosynthesis pathway. COQ7-associated CoQ10 deficiency is very rare and only two cases have been reported. METHODS AND RESULTS: We report a patient with encephalo-myo-nephro-cardiopathy, persistent lactic acidosis, and basal ganglia lesions resulting in early infantile death. Using whole exome sequencing, we identified compound heterozygous variants in the COQ7 gene consisting of a deletion insertion resulting in frameshift [c.599_600delinsTAATGCATC, p.(Lys200Ilefs*56)] and a missense substitution [c.319C>T, p.(Arg107Trp), NM_016138.4]. Skin fibroblast studies showed decreased combined complex II + III activity and reduction in CoQ10 level. CONCLUSION: This third patient presenting with lethal encephalo-myo-nephro-cardiopathy represents the severe end of this ultra-rare mitochondrial disease caused by biallelic COQ7 mutations. The response to CoQ10 supplement is poor and alternative treatment strategies should be developed for a more effective management of this disorder.

Achieving biventricular circulation in patients with moderate hypoplastic right ventricle in pulmonary atresia intact ventricular septum after transcatheter pulmonary valve perforation.

OBJECTIVE: Transcatheter valve perforation for pulmonary atresia intact ventricular septum is the standard of care for patients with mild right ventricular hypoplasia. However, its role in moderate right ventricular hypoplasia has been less well defined. We sought to report the long-term outcome of patients with moderate hypoplastic right ventricle who had undergone the procedure. DESIGN, SETTINGS, AND PATIENTS: We performed a retrospective analysis on patients who had undergone transcatheter pulmonary valve perforation from January 1996 to January 2015 at our institution. The procedures would be carried out irrespective of the right ventricular size, as long as there were no absolute contraindications. INTERVENTION AND OUTCOME MEASURES: Demographic and procedural data were correlated with outcome measures. Outcomes analyzed included procedural success, reintervention rates, final circulation type, and functional class. Multivariate analysis and receiver operator curve were used to identify for parameters in predicting biventricular circulation. RESULTS: The procedural success rate was 92% (33 out of 36) in this group with moderate right ventricular hypoplasia (tricuspid valve z score -4.2 ± 3.0, 69.4% of patients with z score <-2.5). Early reintervention rate was 39%, mostly being insertion of modified Blalock-Taussig shunt. Overall reintervention-free survival was 53%, 30%, and 19% at 1, 6, and 12 months postintervention. Despite no significant catch-up right ventricular growth, majority of survivors (84%) enjoyed a biventricular circulation with good functional status. A tricuspid to mitral valve ratio >0.79 was a good predictor of biventricular outcome. (specificity of 100%, positive predictive value 100%) CONCLUSION: Encouraging long-term results with biventricular circulation and functional status were demonstrated with transcatheter pulmonary valve perforation in patients even with moderate hypoplastic right ventricle, which is comparable to that with mild right ventricular hypertrophy. The baseline tricuspid to mitral valve ratio was identified as a potentially useful tool in predicting biventricular circulation.

NGS identifies TAZ mutation in a family with X-linked dilated cardiomyopathy.

We reported a family with two male siblings affected with infantile dilated cardiomyopathy (DCM). Extensive evaluation failed to identify the underlying cause for the DCM. Next generation sequencing (NGS) with targeted enrichment identified a hemizygous variant c.718G>C (p.Gly240Arg) in the TAZ gene. This variant has been reported in three other families with X linked infantile DCM and is therefore likely pathogenic. NGS allows efficient screening of a large number of uncommon genes in complex disorders like DCM, in which there is substantial genetic and phenotypic heterogeneity. The identification of TAZ mutation has major impact on their medical care as the surveillance needs to be expanded to cover for the Barth syndrome, a severe metabolic phenotype also caused by TAZ mutation, in addition to DCM.

Left ventricular torsional mechanics and diastolic function in congenital heart block with right ventricular pacing.

BACKGROUND: The effects of right ventricular (RV) pacing on left ventricular (LV) diastolic function are unknown. This study aimed to test the hypothesis that right ventricular (RV) pacing is associated with LV diastolic dysfunction and impairment of LV torsion in children and young adults with congenital heart block. METHODS: Eighteen patients aged 20 ± 7 years and 12 healthy controls aged 19 ± 7 years were studied. Transmitral and mitral annular diastolic velocities and global longitudinal diastolic strain rate were determined and compared between the 2 groups. Parameters of LV torsion including peak systolic basal and apical rotations, and systolic twisting and diastolic untwisting velocities were further determined by speckle tracking echocardiography. In 12 patients, these parameters were compared before and after interruption of RV pacing. RESULTS: Compared with controls, patients had significantly lower mitral early diastolic annular velocity (p=0.007), LV global diastolic strain rate (p<0.001), basal (p<0.001) and apical (p=0.002) rotations, peak systolic torsion (p<0.001), and peak systolic twisting velocities (p=0.009). In patients, the peak diastolic untwisting velocity correlated with peak systolic torsion (r=0.64, p=0.004) and peak systolic twisting velocity (r=0.74, p<0.001). No significant improvement in LV diastolic function or torsion was observed during pacing interruption (all p>0.05). CONCLUSION: Right ventricular pacing in childhood is associated with LV diastolic dysfunction and impaired LV torsion, which do not improve with pacing interruption.

Management of symptomatic congenital tracheal stenosis in neonates and infants by slide tracheoplasty: a 7-year single institution experience.

OBJECTIVE: Congenital tracheal stenosis (CTS) is rare. When it presents early in life, its management can be challenging. Of the surgical techniques that have been devised to correct long-segment CTS, slide tracheoplasty (ST) appears to be superior. We present our 7-year-experience of ST for the treatment of symptomatic CTS in neonates and infants. METHODS: The hospital records of all 14 neonates and infants who underwent ST between 2001 and 2008 at our hospital were retrieved. Patient characteristics, trachea morphology, co-existing anomalies, operative procedures, techniques, outcomes and clinical courses were reviewed. RESULTS: Patients underwent ST at age 4 days to 22 months (median: 2.4 months). Five (36%) required intermittent ventilator support prior to surgery. All ST was done under cardiopulmonary bypass. The associated cardiovascular anomalies in 10 infants (71%) were also corrected at the same operation. All survived the initial surgical procedures. The in-hospital mortality for the group was 14.3%. The median periods of postoperative intensive care unit and hospital stay of the 12 children, who were successfully extubated within 7 postoperative days, were 9 days (range: 6-28 days) and 28 days (range: 14-375 days), respectively. Follow-up of all 12 midterm survivors was complete, ranging from 5 months to 5.6 years (median: 40 months). A total of four patients had been found to have tracheobronchial malacia postoperatively and were managed with stenting. Of the remaining 10 survivors who had no residual or recurrent airway problems, and no cardiovascular residuum or sequela, two had gross developmental delay. CONCLUSIONS: In the management of symptomatic infants with CTS, our limited experience suggests that meticulously performed ST together with vigilant pre- and postoperative care can provide satisfactory short and midterm solution to the airway problem. Some incidental residual clinical problems appear to be unavoidable.

Impact of temporary interruption of right ventricular pacing for heart block on left ventricular function and dyssynchrony.

BACKGROUND: The increasing data suggest an association between chronic right ventricular (RV) and left ventricular (LV) dysfunction. We sought to determine the effect of temporary interruption of long-term RV pacing on LV function and mechanical dyssynchrony in children and young adults with complete heart block. METHODS: Twelve patients aged 20.0 + or - 7.4 years with congenital heart block (group I) and six patients aged 22.7 + or - 11.0 years with surgically acquired heart block (group II) with RV pacing were studied. The pacing rate was reduced to less than patient's intrinsic heart rate and maintained for 5 minutes. The LV ejection fraction (EF), three-dimensional systolic dyssynchrony index (SDI), two-dimensional global longitudinal strain and strain rate, and Doppler-derived isovolumic acceleration before and after interruption of RV pacing were compared. RESULTS: The LVEF and GLS increased while QRS duration decreased after the pacing interruption in both the groups (all P < 0.05). While SDI decreased in both groups I (6.8 + or - 2.3%- 3.8 + or - 0.8%, P = 0.001) and II (9.2 + or - 4.1%-5.0 + or - 1.6%, P = 0.032), it remained higher in group II than in group I (P = 0.046) after the pacing interruption. The prevalence of LV dyssynchrony (SDI > 4.7%) decreased in group I (83%-25%, P = 0.006) but not in group II (67%-50%, P = 0.50). The %increase in LVEF correlated positively with %reduction of LV SDI (r = 0.80, P = 0.001). CONCLUSIONS: Temporary interruption of chronic RV pacing acutely improves LV dyssynchrony and systolic function in children and young adults, the magnitude of which is greater in patients with congenital than those with surgically acquired heart block.

Impact of right ventricular pacing on three-dimensional global left ventricular dyssynchrony in children and young adults with congenital and acquired heart block associated with congenital heart disease.

The aim of this study was to determine the effect of long-term right ventricular pacing on left ventricular (LV) mechanical dyssynchrony in children and young adults with congenital and acquired heart block. Eighteen patients aged 19 +/- 7 years with congenital heart block (group I), 9 aged 21 +/- 11 years with acquired heart block after congenital heart surgery (group II), and 15 healthy control subjects (group III) were studied. The LV volumes, ejection fractions, and systolic dyssynchrony index (SDI) values, as determined using 3-dimensional echocardiography, were compared among groups. Groups I (6.68 +/- 2.44%) and II (9.43 +/- 4.44%) had significantly greater SDI values than group III (3.88 +/- 0.63%) (p = 0.011 and p <0.001, respectively). The prevalence of LV mechanical dyssynchrony (SDI >5.14%, mean + 2 SDs of controls) in groups I and II was 72% and 67%, respectively. In 27 patients with right ventricular pacing, LV SDI values were correlated negatively with the LV ejection fractions (r = -0.74, p <0.001). The times to minimum regional volume were significantly longer in lateral, posterior, and inferior segments in group I and septal and inferior segments in group II compared to those in group III (p <0.05). Compared to patients without LV dyssynchrony, patients with LV dyssynchrony had lower LV ejection fractions (p <0.001), had shorter RR intervals (p <0.001), and tended to have dual-chamber pacing (p = 0.088) but had similar durations of pacing, QRS durations, and positions of pacing wires (epicardial vs endocardial). In conclusion, permanent right ventricular pacing in childhood has a negative effect on LV systolic function through the induction of mechanical dyssynchrony, the magnitude and pattern of which differ between congenital and acquired heart block.