Functional testing for variant prioritization in a family with long QT syndrome.

Next-generation sequencing platforms are being increasingly applied in clinical genetic settings for evaluation of families with suspected heritable disease. These platforms potentially improve the diagnostic yield beyond that of disease-specific targeted gene panels, but also increase the number of rare or novel genetic variants that may confound precise diagnostics. Here, we describe a functional testing approach used to interpret the results of whole exome sequencing (WES) in a family presenting with syncope and sudden death. One individual had a prolonged QT interval on electrocardiogram (ECG) and carried a diagnosis of long QT syndrome (LQTS), but a second individual did not meet criteria for LQTS. Filtering WES results for uncommon variants with arrhythmia association identified four for further analyses. In silico analyses indicated that two of these variants, KCNH2 p.(Cys555Arg) and KCNQ1 p.(Arg293Cys), were likely to be causal in this family's LQTS. We subsequently performed functional characterization of these variants in a heterologous expression system. The expression of KCNQ1-Arg293Cys did not show a deleterious phenotype but KCNH2-Cys555Arg demonstrated a loss-of-function phenotype that was partially dominant. Our stepwise approach identified a precise genetic etiology in this family, which resulted in the establishment of a LQTS diagnosis in the second individual as well as an additional asymptomatic family member, enabling personalized clinical management. Given its ability to aid in the diagnosis, the application of functional characterization should be considered as a value adjunct to in silico analyses of WES.

What have we learned in the last 20 years? A comparison of a modern era pediatric and congenital catheter ablation registry to previous pediatric ablation registries.

BACKGROUND: Since the onset of pediatric catheter ablation, the pediatric electrophysiology community has reported outcomes via various registries (PAPCA [Prospective Assessment After Pediatric Cardiac Ablation], PCAR [Pediatric Catheter Ablation Registry]). Most recently, a modern era pediatric and congenital ablation registry (MAP-IT [Multicenter Pediatric and Congenital EP Quality Initiative]) was developed for eventual incorporation into the National Cardiovascular Data Registry (NCDR) IMPACT (Improving Pediatric and Adult Congenital Treatment) registry. OBJECTIVE: The purpose of this study was to describe initial findings from the MAP-IT pilot registry and to compare these findings to earlier registries. METHODS: Before entering the NCDR IMPACT registry, MAP-IT was active at 12 centers (11 in the United States) between October 2014 and April 2016. All electrophysiological studies for patients younger than 21 years and for patients of all ages with structural congenital heart disease were included. We compared the acute success, fluoroscopy and procedural times, and frequency of complications between MAP-IT and the earlier registries. RESULTS: Acute success rates have improved from the initial PCAR registry for both accessory and slow pathway substrates. Both fluoroscopy and procedural times have significantly decreased across the time periods (fluoroscopy time 47.6 ± 40 minutes to 7.0 ± 9.2 minutes; P <.001; procedural time 257 ± 157 minutes to 166 ± 84 minutes; P <.001). CONCLUSION: Acute success rates and fluoroscopy and procedural times in pediatric ablation all have improved over the last 25 years.

Development of paediatric electrophysiology standards for Florida Children's Medical Services.

The Florida Children's Medical Services (CMS) has a long-standing history of ensuring that providers of multiple paediatric subspecialties abide by the highest standards. The cardiac sub-committee has written quality standard documents that participating programmes must meet or exceed. These standards oversee paediatric cardiology services including surgery, catheterisations, and outpatient services. On April, 2012, the cardiac sub-committee decided to develop similar standards in paediatric electrophysiology. A task force was created and began this process. These standards include a catalogue of required and optional equipment, as well as staff and physician credentials. We sought to establish expectations of procedural numbers by practitioner and facility. The task force surveyed the members of the Pediatric and Congenital Electrophysiology Society. Finding no consensus, the task force is committed to generate the data by requiring that the CMS participating programmes enrol and submit data to the Multicenter Pediatric and Adult Congenital EP Quality (MAP-IT™) Initiative. This manuscript details the work of the Florida CMS Paediatric Electrophysiology Task Force.

Arrhythmia management in patients with a common arterial trunk and d-transposition of the great arteries.

Arrhythmias in patients with congenital heart disease present a challenge to the care of these patients and can result in significant morbidity and mortality. Transposition of the great arteries and common arterial trunk are no exceptions. It is important to identify risk factors for arrhythmia development in the peri-operative period. The peri-operative arrhythmia burden may relate to the underlying congenital heart disease, haemodynamic perturbations, operative events, and potential residual lesions. In addition, these patients are at risk for developing arrhythmias later in life, and non-invasive and potentially invasive arrhythmia surveillance should be a routine part of the care of these patients. This article highlights important strategies to manage arrhythmia development and prevention in this patient population.

Management of children undergoing cardiac transplantation with high Panel Reactive Antibodies.

Highly sensitised children in need of cardiac transplantation have overall poor outcomes because of increased risk for dysfunction of the cardiac allograft, acute cellular and antibody-mediated rejection, and vasculopathy of the cardiac allograft. Cardiopulmonary bypass and the frequent use of blood products in the operating room and cardiac intensive care unit, as well as the frequent use of homografts, have predisposed potential recipients of transplants to allosensitisation. The expansion in the use of ventricular assist devices and extracorporeal membrane oxygenation has also contributed to increasing rates of allosensitisation in candidates for cardiac transplantation. Antibodies to Human Leukocyte Antigen can be detected before transplantation using several different techniques, the most common being the "complement-dependent lymphocytotoxicity assays". "Solid-phase assays", particularly the "Luminex® single antigen bead method", offer improved specificity and more detailed information regarding specificities of antibodies, leading to improved matching of donors with recipients. Allosensitisation prolongs the time on the waiting list for potential recipients of transplantation and increases the risk of complications and death after transplantation. Aggressive reduction of antibodies to Human Leukocyte Antigen in these high-risk patients is therefore of vital importance for long-term survival of the patient and cardiac allograft. Strategies to decrease Panel Reactive Antibody or percent reactive antibody before transplantation include plasmapheresis, intravenous administration of immunoglobulin, and specific treatment to reduce B-cells, particularly Rituximab. These strategies have resulted in varying degrees of success. Antibody-mediated rejection and cardiac allograft vasculopathy are two of the most important complications of transplantation in patients with high Panel Reactive Antibody. The treatment of antibody-mediated rejection in recipients of cardiac transplants is largely empirical and includes the use of high-dose corticosteroids, plasmapheresis, intravenous administration of immunoglobulins, anti-thymocyte globulin, and Rituximab. Cardiac allograft vasculopathy is believed to be secondary to chronic complement-mediated endothelial injury and chronic vascular rejection. The use of proliferation signal inhibitors, such as sirolimus and everolimus, has been shown to delay the progression of cardiac allograft vasculopathy. In some non-sensitised recipients of cardiac transplants, the de novo formation of antibodies to Human Leukocyte Antigen after transplantation may increase the likelihood of adverse clinical outcomes. The use of serial testing for donor-specific antibodies after cardiac transplantation may be advisable in patients with frequent episodes of rejection and patients with history of sensitisation. Allosensitisation before transplantation can negatively influence outcomes after transplantation. A high incidence of antibody-mediated rejection and graft vasculopathy can result in graft failure and decreased survival. Current strategies to decrease allosensitisation have helped to expand the pool of donors, improve times on the waiting list, and decrease mortality. Centres of transplantation offering desensitisation are currently using plasmapheresis to remove circulating antibodies; intravenous immunoglobulin to inactivate antibodies; cyclophosphamide to suppress B-cell proliferation; and Rituximab to deplete B-lymphocytes. Similar approaches are also used to treat antibody-mediated rejection after transplantation with promising results.

Lessons learned from 119 consecutive cardiac transplants for pediatric and congenital heart disease.

BACKGROUND: This manuscript reviews all patients who underwent orthotopic heart transplantations (OHT) at our program (116 patients underwent 119 OHT) to describe their diagnostic characteristics and to assess risk factors for mortality. METHODS: Median age at OHT was 179 days (mean, 1,446.6 ± 188.9 days [4.0 ± 0.5 years]; range, 5 days to 7,125 days [19.5 years]; 15 neonates, 68 infants). Median weight at OHT was 5.5 kg (mean, 17.2 ± 2.1 kg; range, 2.2 to 113 kg). Diagnoses were cardiomyopathy (n = 37), primary transplantation for hypoplastic left heart syndrome (HLHS) or HLHS-related malformation (n = 29), transplantation after prior cardiac surgery for HLHS or HLHS-related malformation (n = 9), non-HLHS congenital heart disease (n = 39), and retransplant (n = 5). RESULTS: Overall Kaplan-Meier 5-year survival was 72.7%. Operative mortality was 12.6% (15 patients). Late mortality was 13.4% (16 patients). Eighty-five patients survived, with a mean follow-up of 5.76 ± 0.48 years (median, 5.1 years; range, 0.12 to 14.0 years). Total follow-up was 507.0 years. No survival difference was seen among the five diagnostic subgroups (p = 0.20). Univariate association between risk factors and survival was assessed for the following variables: age (p = 0.91), weight (p = 0.86), sex (p = 0.47), race (p = 0.40), insurance classification (p = 0.42), high PRA (p = 0.20), pretransplant mechanical circulatory support (p < 0.001), posttransplant mechanical circulatory support (p < 0.001), redo sternotomy (p = 0.07), heterotaxy (p = 0.02), cardiopulmonary bypass time (p = 0.01), and donor heart cross-clamp time (p = 0.02). CONCLUSIONS: Excellent results are expected for children undergoing OHT regardless of diagnostic classification. Pretransplant mechanical circulatory support, posttransplant mechanical circulatory support, cardiopulmonary bypass time, donor heart cross-clamp time, and heterotaxy are risk factors for decreased survival.

Clinical heterogeneity in sodium channelopathies. What is the meaning of carrying a genetic mutation?

BACKGROUND: Mutations in the SCN5A gene have been linked to a variety of diseases causing sudden cardiac death, with important variability in expressivity and phenotypic overlap. With the availability of genetic testing family members may now be diagnosed as carriers based solely on the presence of the genetic defect. Clinical decision making in this situation is complex and generates important ethical and medicolegal issues. METHODS: We describe two families, 24-328 and 24-588, originally diagnosed with Brugada syndrome after the probands experienced cardiac arrest and we performed clinical and genetic analysis in their members. RESULTS: Both families had members with various electrocardiographic abnormalities including some with Brugada syndrome, long QT syndrome and conduction system disease. Both families had an important family history of sudden cardiac death. Direct sequencing of exons and exon-intron boundaries of the sodium channel gene SCN5A identified mutations in both families. CONCLUSIONS: These two families illustrate an increasingly common scenario when encountering families with ion channelopathies. Because a defibrillator is the only available therapeutic option at present in Brugada syndrome, physicians will be faced with extremely difficult therapeutic decisions that also have important legal, social and ethical implications, especially in children. These data indicate the need to develop guidelines on how to approach the results of genetic testing, especially in asymptomatic individuals.

Rescue cardiac transplantation for failing staged palliation in patients with hypoplastic left heart syndrome.

OBJECTIVE: Orthotopic heart transplantation is considered a rescue option for children with failing staged palliation or repair of hypoplastic left heart syndrome. We present our strategy for management, and outcomes, for these complex patients. METHODS: We transplanted 68 consecutive children, with diagnoses of hypoplastic left heart syndrome in 31, cardiomyopathy in 20, and post-operative complex congenital heart disease in 17. Of these patients, 9 (13.2%) were neonates, and 46 (67.6%) were infants. Median age was 118.5 days. Operative technique involves bicaval cannulation and anastamoses with continuous low flow bypass, and either short periods of circulatory arrest or continuous low flow antegrade cerebral perfusion for reconstruction of the aortic arch. Initial reperfusion of the donor heart utilizes glutamate and aspartate substrate enriched white blood cell filtered cardioplegia. Immunosuppressive therapy includes induction (pulse steroids, gamma globulin, and polyclonal rabbit antithymocyte globulin) and initial maintenance (calcineurin inhibitor, an anti-proliferative agent, and a weaning steroid protocol). Of the 31 patients with hypoplastic left heart syndrome, 23 underwent primary transplantation, and 8 underwent rescue transplantation from failing staged palliation in seven, or attempted biventricular repair in one. Of the seven patients who had failing staged palliation, three had undergone only the Norwood Stage 1 operation, 2 had undergone a Norwood Stage 1 operation and a Glenn superior cavopulmonary anastomosis and two had undergone a Norwood Stage 1 operation, a Glenn superior cavopulmonary anastomosis, and a completion Fontan operation. RESULTS: The group undergoing primary transplantation was younger (p equals 0.007), weighed less (p equals 0.003), and waited longer for an appropriate donor heart (p equals 0.021) compared to those requiring rescue transplantation. No significant difference exists between the groups with regards to donor heart ischaemic time or post-transplant length of hospital stay. Thirty day survival (p equals 0.156) and overall survival (p equals 0.053) was better in those having primary transplantation, although these differences were not statistically significant when a p value of less than 0.05 is considered to be significant. In those having primary transplantation, no patients had elevated panel reactive antibody greater than 10%. Half of the 8 requiring rescue transplantation had panel reactive antibody greater than 10%, and this subgroup did especially poorly. CONCLUSION: Cardiac transplantation can offer children with failing staged palliation their only chance of survival. Transplantation, however, carries a high risk in this subgroup, especially in the setting of elevated panel reactive antibody.

Pediatric cardiac transplantation in children with high panel reactive antibody.

BACKGROUND: Elevated panel reactive antibody (PRA) may be considered a risk factor precluding pediatric orthotopic heart transplantation. We retrospectively reviewed our management strategy and outcome data for children undergoing heart transplantation with high PRA (> 10%). METHODS: Sixty consecutive children (median age = 130.5 days) underwent heart transplantation. Diagnoses included hypoplastic left heart syndrome (HLHS) (30 patients), cardiomyopathy (18 patients), and postoperative complex congenital heart disease (CCHD) (12 patients). Standard induction immunosuppressive therapy included pulse steroids, gamma globulin, and polyclonal rabbit antithymocyte globulin. Initial immunosuppression is a calcinurin inhibitor and an antiproliferative agent. Eight children exhibited elevated PRA (group P). Fifty-two exhibited nonelevated PRA (group N). Immunosuppression was modified in group P as follows: preoperative intravenous immunoglobulin G (IVIG) and/or cyclophosphamide or mycophenolate mofetil and preoperative and postoperative exchange transfusions or plasmapheresis. In group P, cyclophosphamide was the initial antiproliferative agent. RESULTS: Group P = 4 HLHS patients (all status post [s/p] prior cardiac surgery) and 4 postoperative CCHD patients. Group N = 26 HLHS patients (4 patients s/p prior cardiac surgery), 18 cardiomyopathy patients, and 8 postoperative CCHD patients. Group P patients were older and weighed more than group N patients. Waiting time for donor heart, cardiac ischemic time, and length of hospital stay were similar in both groups. Thirty-day mortality for group P was 25% and for group N it was 7.9% (p = 0.178). Overall mortality for group P was 50% and for group N it was 15.4% (p = 0.043). CONCLUSIONS: Although heart transplantation can offer children with end-stage heart failure and elevated PRA their only chance of survival, these patients remain high risk despite aggressive immunosuppression.

Prenatal molecular genetic diagnosis of congenital long QT syndrome by strategic genotyping.

We demonstrate how genetic testing enabled a molecular prenatal diagnosis of congenital long QT syndrome in a 20-week fetus presenting with fetal bradycardia in the setting of maternal beta-blocker therapy. Before prenatal testing, strategic genotyping, based on a family history of a near drowning, was performed on a 3-generation family with clinically diagnosed long QT syndrome in which the affected mother was pregnant.

Acute myocardial infarction in a 15-year old secondary to myxomatous embolisation.

We present a 15-year-old white male who presented with an acute myocardial infarction secondary to embolisation of tissue from a left atrial myxoma. He successfully underwent resection of the myxoma, and embolectomy of the fragments of tumour lodged in the coronary artery.

A novel SCN5A arrhythmia mutation, M1766L, with expression defect rescued by mexiletine.

OBJECTIVE: Mutations in the cardiac sodium channel gene, SCN5A, cause congenital long QT syndrome (LQT3), Brugada syndrome, idiopathic ventricular fibrillation, and conduction disease by distinct cellular and clinical electrophysiological phenotypes. METHODS: Postmortem molecular analysis of SCN5A was conducted on an infant who presented shortly after birth with self-terminating torsades de pointes. The infant was treated with lidocaine, propranolol, and mexiletine and was stable for 16 months manifesting only a prolonged QT interval. The infant collapsed suddenly following presumed viral gastroenteritis, was found in 2:1 AV block, and was subsequently declared brain dead. Genomic DNA was subjected to SCN5A mutational analyses and DNA sequencing revealing a novel, spontaneous germline missense mutation, M1766L. The M1766L mutation was engineered into the hH1a clone by site-directed mutagenesis, transfected into embryonic kidney cells (HEK-293), and studied by voltage clamp. RESULTS: The M1766L mutation caused a significant decrease in the sodium channel expression. Co-expression with beta1 subunit, incubation at low temperature, and most effectively incubation with mexiletine partially 'rescued' the defective expression. In addition to this pronounced loss of function, M1766L also showed a 10-fold increase in the persistent late sodium current. CONCLUSIONS: These findings suggest that M1766L-SCN5A channel dysfunction may contribute to the basis of lethal arrhythmias, displays an overlapping electrophysiological phenotype, and represents the first sodium channelopathy rescued by drug.