Utility of whole-exome sequencing for those near the end of the diagnostic odyssey: time to address gaps in care.

An accurate diagnosis is an integral component of patient care for children with rare genetic disease. Recent advances in sequencing, in particular whole-exome sequencing (WES), are identifying the genetic basis of disease for 25-40% of patients. The diagnostic rate is probably influenced by when in the diagnostic process WES is used. The Finding Of Rare Disease GEnes (FORGE) Canada project was a nation-wide effort to identify mutations for childhood-onset disorders using WES. Most children enrolled in the FORGE project were toward the end of the diagnostic odyssey. The two primary outcomes of FORGE were novel gene discovery and the identification of mutations in genes known to cause disease. In the latter instance, WES identified mutations in known disease genes for 105 of 362 families studied (29%), thereby informing the impact of WES in the setting of the diagnostic odyssey. Our analysis of this dataset showed that these known disease genes were not identified prior to WES enrollment for two key reasons: genetic heterogeneity associated with a clinical diagnosis and atypical presentation of known, clinically recognized diseases. What is becoming increasingly clear is that WES will be paradigm altering for patients and families with rare genetic diseases.

Detection of genomic deletions of PKP2 in arrhythmogenic right ventricular cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited myocardial disease that predominantly affects the right ventricle and is associated with ventricular arrhythmias that may lead to sudden cardiac death. Mutations within at least seven separate genes have been identified to cause ARVC, however a genetic culprit remains elusive in approximately 50% of cases. Although negative genetic testing may be secondary to pathogenic mutations within undiscovered genes, an alternative explanation may be the presence of large deletions or duplications involving known genes. These large copy number variants may not be detected with standard clinical genetic testing which is presently limited to direct DNA sequencing. We describe two cases of ARVC possessing large deletions involving plakophilin-2 (PKP2) identified with microarray analysis and/or multiplex ligation-dependent probe amplification (MLPA) that would have been classified as genotype negative with standard clinical genetic testing. A deletion of the entire coding region of PKP2 excluding exon 1 was identified in patient 1 and his son. In patient 2, MLPA analysis of PKP2 revealed deletion of the entire gene with subsequent microarray analysis demonstrating a de novo 7.9 Mb deletion of chromosome 12p12.1p11.1. These findings support screening for large copy number variants in clinically suspected ARVC cases without clear disease causing mutations following initial sequencing analysis.

The congenital long QT syndromes in childhood.

Twenty-three children and young persons with a congenital long QT syndrome were identified; the median age at the time of referral was 10 years (range 4 days to 19 years) and 14 patients (61%) had a family history of the syndrome. Among the 19 patients with symptoms, the initial symptom was syncope in 13 (69%), aborted sudden death in 5 (26%) and near drowning in 1 (5%). There were three deaths during a combined follow-up period of 67 patient-years (average annual mortality rate 4.5%). Patients who did not respond to therapy with a beta-adrenergic blocker and those who died were significantly younger than the remaining patients at the time of diagnosis (p less than or equal to 0.05 for both). Analysis of 44 treadmill exercise tests performed by 16 patients revealed significant prolongation of the median corrected QT (QTc) interval in response to exercise, with maximal prolongation present after 2 min of recovery (median QTc interval 0.52 s versus a baseline value of 0.47 s, p less than 0.001). Characteristic changes in T wave configuration were noted in 8 of 15 patients on at least one occasion during ambulatory Holter electrocardiographic monitoring, including T wave alternation in two patients, both of whom died shortly afterward. It is suggested that the congenital long QT syndrome is associated with a significant mortality rate in childhood despite the use of conventional therapy in symptomatic patients. Ambulatory Holter monitoring and treadmill exercise testing may be helpful, both in confirming the diagnosis of a long QT syndrome and in monitoring the adequacy of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk factors for atrial tachyarrhythmias after the Fontan operation.

OBJECTIVES: The purpose of this study was to define the incidence and risk factors for atrial tachyarrhythmias after the Fontan operation. BACKGROUND: Atrial tachyarrhythmias cause morbidity after the Fontan operation. Causative factors may be affected by the type of systemic to pulmonary connection. METHODS: The Fontan operation was performed in 270 consecutive patients between 1982 and 1992. The mean age at operation was 7.0 +/- 4.3 years. Direct atriopulmonary connection was used in 138 patients (51%), total cavopulmonary connection in 94 (35%) and right atrial to right ventricular connection in 38 (14%). RESULTS: Atrial tachyarrhythmias were seen early postoperatively in 55 patients (20%), preoperative atrial tachyarrhythmia being the only risk factor. Follow-up was achieved for 228 early survivors (97%) at a mean interval of 4.4 years. There were 20 late deaths. Late atrial tachyarrhythmias were noted in 29% of patients who received an atriopulmonary connection, 14% of those who received a total cavopulmonary connection and 18% of those who received a right ventricular connection (p < 0.02). Significant risk factors as determined by univariate and multiple logistic regression analysis were atriopulmonary connection type (odds ratio 0.40 for total cavopulmonary relative to atriopulmonary connection [p < 0.05] and 0.37 for right ventricular relative to atriopulmonary connection [p = 0.08]), longer follow-up interval (odds ratio 1.32 for each consecutive year [p < 0.002]) and atrial tachyarrhythmia in the operative period (odds ratio 6.31 [p < 0.0001]). CONCLUSIONS: Early postoperative atrial tachyarrhythmias, length of follow-up and atriopulmonary connection are significant independent risk factors for the presence of late atrial tachyarrhythmias.

Arrhythmia and mortality after the Mustard procedure: a 30-year single-center experience.

OBJECTIVES: Our purpose was to assess the risk factors for late mortality, loss of sinus rhythm and atrial flutter after the Mustard operation. BACKGROUND: The Mustard operation provides correction of cyanosis with low surgical risk in transposition of the great vessels. However, right ventricular failure, loss of sinus rhythm, atrial flutter and death are frequent long-term complications. METHODS: Records of 534 children who underwent the Mustard operation at a single center since 1962 were reviewed for demographic, anatomic, electrocardiographic and physiologic predictors and outcomes. RESULTS: There were 52 early deaths (9.7%). Survival analysis was undertaken for 478 early survivors with a mean follow-up interval of 11.6 +/- 7.2 years. There were 77 late deaths (16.1%), with sudden death (n = 31) the most frequent cause. Survival estimates were 89% at 5 years and 76% at 20 years of age. Risk factors were an earlier date of operation, operative period arrhythmia and an associated ventricular septal defect. Risk (hazard) of late death declined in the first decade, with further peaks in the second decade. Sinus rhythm was present in 77% at 5 years and 40% at 20 years. Loss of sinus rhythm was associated with previous septectomy, postoperative bradycardia and late atrial flutter. Freedom from atrial flutter was 92% at 5 years and 73% at 20 years of age. Risk factors for atrial flutter were the occurrence of perioperative bradyarrhythmia, reoperation and loss of sinus rhythm during follow-up. Risk of atrial flutter demonstrates a late increase. CONCLUSIONS: Ongoing loss of sinus rhythm and late peaks in the risk of atrial flutter and death necessitate continued follow-up.

Five-year experience with implantable defibrillators in children.

Cardioverter-defibrillators were implanted in children aged 4 to 16 years over a 5-year period with no mortality and eventual clinically appropriate shocks in 6 of 11 patients. Both transvenous and epicardial implantable cardioverter-defibrillators were safe and effective in children resuscitated from sudden death or at high risk for sudden death.

Chronotropic competence of the sinus node in congenital complete heart block.

Electrocardiograms taken at rest of 2 children with transplacental exposure to anti-Ro antibody but 1:1 atrioventricular conduction demonstrated sinus node disease. Treadmill exercise testing of 28 patients with congenital complete heart block found 3 patients with chronotropic incompetence of the sinus node.

Clinical efficacy and safety of intravenous Amiodarone in infants and children.

The effectiveness and safety of intravenous amiodarone in children are not well established. This study reviewed its use in 30 infants and children for life-threatening tachyarrhythmias: 18 patients (19 episodes) with supraventricular tachycardia, and 12 with ventricular tachycardia. Eighteen patients had structural heart defects with arrhythmias that occurred after surgery. The mean loading dose was 5 mg/kg infused over 1 hour, with a starting maintenance dose of 5 micrograms/kg/min. In 18 treatment episodes, amiodarone was used alone or in combination with digoxin. Thirteen patients received amiodarone combined with other antiarrhythmic agents. Intravenous amiodarone was effective or partially effective in 94% of patients, achieving a therapeutic effect in a median time of 1 day (range 1 hour to 5 days). The mean effective maintenance dose was 9.5 micrograms/kg/min (13.7 mg/kg/day), and median treatment duration was 5 days (range 1 to 30). Adverse effects occurred in 18 patients (58%), however none necessitated termination of amiodarone therapy. Potentially significant electrocardiographic abnormalities occurred in 5 patients during combination antiarrhythmic therapy with propafenone. Sinus bradycardia requiring temporary postoperative pacing occurred in 3 patients treated with amiodarone alone. Intravenous amiodarone used alone or in combination therapy is an effective treatment for resistant, life-threatening arrhythmias in infants and children. Combination drug therapy with propafenone must be used cautiously. Potential bradycardia pacing may be necessary during administration of amiodarone after surgery.

Exercise capacity in children with hypertrophic cardiomyopathy and its relation to diastolic left ventricular function.

Left ventricular diastolic impairment is often seen in children with hypertrophic cardiomyopathy regardless of left ventricular outflow tract obstruction. Such impairment in diastolic filling is related to the presence of symptoms and exercise impairment.

Mortality following radiofrequency catheter ablation (from the Pediatric Radiofrequency Ablation Registry). Participating members of the Pediatric Electrophysiology Society.

Deaths have been reported following radiofrequency catheter ablation (RFCA), but the mortality rate in children has not been defined. This study sought to analyze the incidence and the factors associated with mortality related to RFCA. Ten of 4,651 cases (0.22%) reported to the Pediatric RFCA Registry resulting in death were reviewed and compared with a matched control group (n = 18). Death occurred in 5 of 4,092 children (0.12%, ages 0.1 to 13.3 years) with structurally normal hearts. Death was related to traumatic injury, myocardial perforation and hemopericardium, coronary or cerebral thromboembolism, and ventricular arrhythmia. All cases were left-sided (p = 0.019 vs right or septal) supraventricular arrhythmias with radiofrequency applications in the systemic atrium and/or ventricle, and all procedures were successful. Mortality occurred in 5 of 559 children (0.89%, p = 0.001 vs normals, ages 1.5 to 17.4 years) with structural heart disease. No new pathology except the mural radiofrequency lesions was seen at autopsy. Those with structurally normal hearts who died were smaller (32.7 vs 55.6 kg, p = 0.023) and had more radiofrequency applications (26.3 vs 8.7, p = 0.019) than those who survived. No differences were demonstrated for those with abnormal hearts. Operator experience was not different (deaths 103 +/- 106 vs controls 117 +/- 125, p = 0.41). Mortality associated with pediatric RFCA is rare, but is more frequent when there is underlying heart disease, lower patient weight, greater number of radiofrequency energy applications, and left-sided procedures. Operator experience does not appear to be a factor leading to mortality.

Accuracy of surface electrocardiograms for differentiating children with hypertrophic cardiomyopathy from normal children.

Most patients with hypertrophic cardiomyopathy have abnormal electrocardiograms. In this study of 37 matched pairs in the pediatric age group, the 12-lead electrocardiogram did not differentiate between affected and normal children reliably enough to allow it to be used as a screening test in the general population.

Coarctation of the aorta or subaortic stenosis with atrioventricular septal defect.

Thirty patients are reported with atrioventricular (AV) septal defect and either coarctation of the aorta (C of A) or subaortic stenosis (SAS) or both. All patients had normal left ventricles as assessed by angiography (21 of 30 patients) or necropsy (9 of 30). Three groups were recognized. Groups I and II included 19 patients with AV septal defect (12 complete, 7 partial) and C of A with or without SAS, 11 patients with AV septal defect (5 complete, 6 partial) and SAS. In Group I, preductal C of A was diagnosed in 16 of 19 patients. Concomitant angiographic evidence of SAS was present in 2 cases, the mechanism being exaggerated anterior displacement of the left AV valve. In Group III, at the time of diagnosis left ventricular-aortic peak systolic pressure gradients of greater than 20 mm Hg were present in 9 patients, 2 of whom had gradients greater than 50 mm Hg. Angiographic diagnoses were: discrete fibrous diaphragm in 4, fibromuscular obstruction in 5, dynamic tunnel in 1, and chordae from left AV valve to LV outflow tract in 1. Thus, SAS in AV septal defect is most often due to a discrete anatomic lesion. Hemodynamic data show that SAS can be progressive, both before and after the surgical management of the AV septal defect.

Differential effects of dexamethasone treatment on lipopolysaccharide-induced testicular inflammation and reproductive hormone inhibition in adult rats.

A single intraperitoneal injection of lipopolysaccharide (LPS) causes a biphasic suppression of testicular steroidogenesis in adult rats, with inhibition at 6 h and 18-24 h after injection. The inhibition of steroidogenesis is independent of the reduction in circulating LH that also occurs after LPS treatment, indicating a direct effect of inflammation at the Leydig cell level. The relative contributions to this inhibition by intratesticular versus systemic responses to inflammation, including the adrenal glucocorticoids, was investigated in this study. Adult male Wistar rats (eight/group) received injections of LPS (0.1 mg/kg i.p.), dexamethasone (DEX; 50 microg/kg i.p.), LPS and DEX, or saline only (controls), and were killed 6 h, 18 h and 72 h later. Treatment with LPS stimulated body temperature and serum corticosterone levels measured 6 h later. Administration of DEX had no effect on body temperature, but suppressed serum corticosterone levels. At the dose used in this study, DEX alone had no effect on serum LH or testosterone at any time-point. Expression of mRNA for interleukin-1beta (IL-1beta), the principal inflammatory cytokine, was increased in both testis and liver of LPS-treated rats. Serum LH and testosterone levels were considerably reduced at 6 h and 18 h after LPS treatment, and had not completely recovered by 72 h. At 6 h after injection, DEX inhibited basal IL-1beta expression and the LPS-induced increase of IL-1beta mRNA levels in the liver, but had no effect on IL-1beta in the testis. The effects of DEX on IL-1beta levels in the liver were no longer evident by 18 h. In LPS-treated rats, DEX caused a significant reversal of the inhibition of serum LH and testosterone at 18 h, although not at 6 h or 72 h. Accordingly, DEX inhibited the systemic inflammatory response, but had no direct effect on either testicular steroidogenesis or intra-testicular inflammation, at the dose employed. These data suggest that the inhibition of Leydig cell steroidogenesis at 6 h after LPS injection, which was not prevented by co-administration of DEX, is most likely due to direct actions of LPS at the testicular level. In contrast, the later Leydig cell inhibition (at 18 h) may be attributable to extra-testicular effects of LPS, such as increased circulating inflammatory mediators or the release of endogenous glucocorticoids, that were inhibited by DEX treatment. These data indicate that the early and late phases of Leydig cell inhibition following LPS administration are due to separate mechanisms.

Obstructive rhabdomyoma and univentricular physiology: a rare combination.

We report the successful excision of a large left atrial rhabdomyoma producing complete obstruction of both inflow and outflow to the left ventricle. Systemic perfusion was dependent on anterograde ductual flow. The resultant univentricular physiology was initially managed medically, with spontaneous tumor regression contemplated as a means of possible long-term "cure." Failure to achieve hemodynamic stability compelled urgent surgical excision. This neonate was successfully discharged home with an in-series biventricular circulation.

Massive right ventricular fibroma treated with partial resection and a cavopulmonary shunt.

Cardiac fibromas in infants and children may present as intramural or intracavitary masses. Total or partial resection as well as transplantation have been reported as treatment for symptomatic patients. We report an infant, diagnosed prenatally, who underwent partial excision of a massive obstructive right ventricular fibroma and creation of a bidirectional cavopulmonary shunt. The palliative approach has allowed the child to be followed up with the option of transplantation should the tumor continue to increase in size.

Total cavopulmonary anastomosis (Fontan) in children with Down's syndrome.

BACKGROUND: There is a paucity of information to guide the management of the child with Down's syndrome and congenital heart disease in whom biventricular repair is precluded. METHODS: Through the cardiology and cardiovascular surgery databases of The Hospital for Sick Children and Toronto Congenital Cardiac Centre for Adults, we identified patients with trisomy 21 and ventricular hypoplasia who had undergone a Fontan procedure (or modification). RESULTS: Of 533 patients who had undergone a Fontan operation between 1976 and 1997, 4 had trisomy 21. All 4 patients had unbalanced complete atrioventricular septal defect with right ventricular hypoplasia in 3 and left ventricular hypoplasia in 1. Three patients survived, and 1 died of endocarditis. The 3 survivors have done well in the short term and medium term without complications related to the pulmonary vasculature. CONCLUSIONS: We suggest that in appropriately selected patients with trisomy 21 and ventricular hypoplasia who are unsuitable for two or one and a half ventricle repair, the Fontan procedure is not contraindicated and provides short-term and medium-term benefit.

The assessment of pulmonary arterial pressures in bronchopulmonary dysplasia by cardiac catheterization and M-mode echocardiography.

Severe (Stage IV) bronchopulmonary dysplasia (BPD) has been associated with pulmonary hypertension and right heart failure, with a mortality rate of 39%. Recently, M-mode echocardiography has been used to measure right-sided systolic time intervals (the ratio of right ventricular pre-ejection period to ejection time; RVPEP/RVET), with a value greater than 0.35 predicting pulmonary hypertension. This measurement has also been used to predict outcome of BPD and response to oxygen therapy. A retrospective study of six infants with Stage IV BPD who had had cardiac catheterizations and M-mode echocardiography is reported. By catheterization criteria, four of the six had pulmonary hypertension. By echocardiographic criteria, only two of the six had unequivocally prolonged RVPEP/RVET ratios, and correlations with mean or diastolic pulmonary arterial pressures were poor (0.069 and 0.255, respectively). The validity of M-mode echocardiography in the assessment of the pulmonary vascular bed in Stage IV BPD is open to debate, and its role in predicting outcome and response to therapy is unknown.

Transposition complexes.

Transposition complex refers to the reversal of the normal connection of the ventricles to the great arteries, and includes both complete transposition of the great arteries (TGA) and congenitally corrected TGA. Adults with complete TGA usually have had an atrial switch (Mustard or Senning), procedures now abandoned in many pediatric centers in favor of the arterial switch (Jatene). The course and treatment of patients with congenitally corrected TGA is much more variable, depending on which associated lesions are present. Such patients share the tendency to complete heart block, systemic tricuspid AV valve regurgitation, and systemic RV dysfunction. Information about these conditions in adults is urgently needed to reduce our reliance on extrapolation from the pediatric experience.

Absence of the leaflets of the aortic valve in DiGeorge syndrome.

A newborn infant is described with complete absence of the leaflets of the aortic valve, interruption of the aortic arch and DiGeorge syndrome. This association has not previously been reported, nor has absence of the leaflets of the aortic valve without other features of left ventricular dysplasia. We discuss the possible influence of severe intra-uterine aortic regurgitation on development of the aortic arch.

Sudden cardiac death in the young.

This review summarizes the clinical aspects of sudden cardiac death in the pediatric population. The scope of the problem is defined by examining findings from autopsy series and from clinical series of survivors of out-of-hospital cardiac arrest. Representative lesions from different etiological categories serve as discussion points.