Estimating equations for cardiopulmonary exercise testing variables in Fontan patients: derivation and validation using a multicenter cross-sectional database.

Cardiopulmonary exercise testing (CPET) is a common method of evaluating patients with a Fontan circulation. Equations to calculate predicted CPET values are based on children with normal circulation. This study aims to create predictive equations for CPET variables solely based on patients with Fontan circulation. Patients who performed CPET in the multicenter Pediatric Heart Network Fontan Cross-Sectional Study were screened. Peak variable equations were calculated using patients who performed a maximal test (RER > 1.1) and anaerobic threshold (AT) variable equations on patients where AT was adequately calculated. Eighty percent of each cohort was randomly selected to derive the predictive equation and the remaining served as a validation cohort. Linear regression analysis was performed for each CPET variable within the derivation cohort. The resulting equations were applied to calculate predicted values in the validation cohort. Observed versus predicted variables were compared in the validation cohort using linear regression. 411 patients underwent CPET, 166 performed maximal exercise tests and 317 had adequately calculated AT. Predictive equations for peak CPET variables had good performance; peak VO2, R (2) = 0.61; maximum work, R (2) = 0.61; maximum O2 pulse, R (2) = 0.59. The equations for CPET variables at AT explained less of the variability; VO2 at AT, R (2) = 0.15; work at AT, R (2) = 0.39; O2 pulse at AT, R (2) = 0.34; VE/VCO2 at AT, R (2) = 0.18; VE/VO2 at AT, R (2) = 0.14. Only the models for VE/VCO2 and VE/VO2 at AT had significantly worse performance in validation cohort. Of the 8 equations for commonly measured CPET variables, six were able to be validated. The equations for peak variables were more robust in explaining variation in values than AT equations.

Barth syndrome.

First described in 1983, Barth syndrome (BTHS) is widely regarded as a rare X-linked genetic disease characterised by cardiomyopathy (CM), skeletal myopathy, growth delay, neutropenia and increased urinary excretion of 3-methylglutaconic acid (3-MGCA). Fewer than 200 living males are known worldwide, but evidence is accumulating that the disorder is substantially under-diagnosed. Clinical features include variable combinations of the following wide spectrum: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), endocardial fibroelastosis (EFE), left ventricular non-compaction (LVNC), ventricular arrhythmia, sudden cardiac death, prolonged QTc interval, delayed motor milestones, proximal myopathy, lethargy and fatigue, neutropenia (absent to severe; persistent, intermittent or perfectly cyclical), compensatory monocytosis, recurrent bacterial infection, hypoglycaemia, lactic acidosis, growth and pubertal delay, feeding problems, failure to thrive, episodic diarrhoea, characteristic facies, and X-linked family history. Historically regarded as a cardiac disease, BTHS is now considered a multi-system disorder which may be first seen by many different specialists or generalists. Phenotypic breadth and variability present a major challenge to the diagnostician: some children with BTHS have never been neutropenic, whereas others lack increased 3-MGCA and a minority has occult or absent CM. Furthermore, BTHS was first described in 2010 as an unrecognised cause of fetal death. Disabling mutations or deletions of the tafazzin (TAZ) gene, located at Xq28, cause the disorder by reducing remodeling of cardiolipin, a principal phospholipid of the inner mitochondrial membrane. A definitive biochemical test, based on detecting abnormal ratios of different cardiolipin species, was first described in 2008. Key areas of differential diagnosis include metabolic and viral cardiomyopathies, mitochondrial diseases, and many causes of neutropenia and recurrent male miscarriage and stillbirth. Cardiolipin testing and TAZ sequencing now provide relatively rapid diagnostic testing, both prospectively and retrospectively, from a range of fresh or stored tissues, blood or neonatal bloodspots. TAZ sequencing also allows female carrier detection and antenatal screening. Management of BTHS includes medical therapy of CM, cardiac transplantation (in 14% of patients), antibiotic prophylaxis and granulocyte colony-stimulating factor (G-CSF) therapy. Multidisciplinary teams/clinics are essential for minimising hospital attendances and allowing many more individuals with BTHS to live into adulthood.

Substrate metabolism during basal and hyperinsulinemic conditions in adolescents and young-adults with Barth syndrome.

BACKGROUND: Barth syndrome (BTHS) is a rare X-linked disorder that is characterized by mitochondrial abnormalities, infantile or childhood onset of cardioskeletal myopathy, and high mortality rates. It is currently unknown if BTHS related mitochondrial dysfunction results in substrate metabolism abnormalities and thereby contributes to cardioskeletal myopathy in patients with BTHS. METHODS: Adolescents and young adults with BTHS (n = 5, 20 ± 4 yrs) and age and activity matched healthy controls (n = 5, 18 ± 4 yrs) underwent an hyperinsulinemic-euglycemic clamp procedure with stable isotopically labeled tracers for measurement of lipolysis, fatty acid oxidation, glucose disposal, and whole-body proteolysis rates; dual energy x-ray absorptiometry for measurement of body composition and 2-D and strain echocardiography for measurement of left ventricular function. RESULTS: Participants with BTHS had lower fat-free mass (FFM) (BTHS: 31.4 ± 6.9 vs. CONTROL: 46.7 ± 5.3 kg, p < 0.005), lower systolic function (strain, BTHS: -15.2 ± 2.4 vs. CONTROL: -19.0 ± 2.4 %, p < 0.05), greater insulin-stimulated glucose disposal rate per kg FFM (BTHS: 96.5 ± 16.3 vs. CONTROL: 67.4 ± 17.6 µmol/kgFFM/min, p < 0.05), lower basal (BTHS: 4.6 ± 2.7 vs. CONTROL: 11.9 ± 4.4 µmol/kgFM/min, p < 0.05) and hyperinsulinemic (BTHS: 1.6 ± 0.4 vs. CONTROL: 3.6 ± 1.6 µmol/kgFM/min, p < 0.05) lipolytic rate per kg fat mass (FM), and a trend towards higher basal leucine rate of appearance per kg FFM (BTHS: 271.4 ± 69.3 vs. CONTROL: 193.1 ± 28.7 µmol/kgFFM/hr, p = 0.07) compared to controls. Higher basal leucine rate of appearance per kg FFM (i.e. whole-body proteolytic rate) tended to be associated with lower left ventricular systolic strain (r = -0.57, p = 0.09). CONCLUSION: Whole-body fatty acid, glucose and amino acid metabolism kinetics when expressed per unit of body composition are altered and appear to be related to cardioskeletal myopathy in humans with BTHS. Further studies examining myocardial substrate metabolism and whole-body substrate metabolism during increased energy demands (e.g., exercise) and their relationships to skeletal and cardiac function are recommended.

The Barth Syndrome Registry: distinguishing disease characteristics and growth data from a longitudinal study.

Barth syndrome (BTHS); MIM accession # 302060) is a rare X-linked recessive cardioskeletal mitochondrial myopathy with features of cardiomyopathy, neutropenia, and growth abnormalities. The objectives of this study were to further elucidate the natural history, clinical disease presentation, and course, and describe growth characteristics for males with BTHS. Patients with a confirmed genetic diagnosis of BTHS are referred to the BTHS Registry through the Barth Syndrome Foundation, self-referral, or physician referral. This study is based on data obtained from 73 subjects alive at the time of enrollment that provided self-reported and/or medical record abstracted data. The mean age at diagnosis of BTHS was 4.04 ± 5.45 years. While the vast majority of subjects reported a history of cardiac dysfunction, nearly 6% denied any history of cardiomyopathy. Although most subjects had only mildly abnormal cardiac function by echocardiography reports, 70% were recognized as having cardiomyopathy in the first year of life and 12% have required cardiac transplantation. Of the 73 enrolled subjects, there have been five deaths. Growth curves were generated demonstrating a shift down for weight, length, and height versus the normative population with late catch up in height for a significant percentage of cases. This data also confirms a significant number of patients with low birth weight, complications in the newborn period, failure to thrive, neutropenia, developmental delay of motor milestones, and mild learning difficulties. However, it is apparent that the disease manifestations are variable, both over time for an individual patient and across the BTHS population.

Reproducibility of echocardiographic diagnosis of left ventricular noncompaction.

BACKGROUND: Left ventricular noncompaction (LVNC) cardiomyopathy is variably defined by numerous trabeculations, deep intertrabecular recesses, and noncompacted-to-compacted (NC/C) ratio >2. Limited studies exist on the reproducibility of diagnosing LVNC. METHODS: Clinical records of patients diagnosed with LVNC by echocardiography were reviewed. Blinded review of the index echocardiogram for all patients and a 1:1 match without LVNC was performed independently by two observers, measuring the number of trabeculations and the NC/C ratio. RESULTS: A total of 104 patients with LVNC were included in the study, 52 with no congenital heart disease (NCongHD) and 52 with congenital heart disease (CongHD). The duration of follow-up was 7.2 years (range, 0.5-23.1 years) for NCongHD and 8.2 years (range, 0-33.3 years) for CongHD. Agreement between observers in determining zero to three versus more than three trabeculations was 59% (NCongHD) and 73% (CongHD). Agreement in measuring an NC/C ratio ≤ 2 versus > 2 was 79% (NCongHD) and 74% (CongHD). Agreement with the original reader in diagnosing LVNC was 67%. There was no association between the number of trabeculations or the NC/C ratio and the likelihood of a major event. Patients with moderate or severe left ventricular dysfunction at the time of diagnosis were more likely to undergo cardiac transplantation or die compared with those with normal or mild dysfunction (NCongHD, 22% vs 0%, P = .01; CongHD, 39% vs 3%, P = .001). CONCLUSIONS: The reproducibility of making measurements to diagnose LVNC by accepted criteria is poor. Heart transplantation and death are associated with significant ventricular dysfunction and not with increased trabeculations or NC/C ratios.

Impaired cardiac reserve and severely diminished skeletal muscle O2 utilization mediate exercise intolerance in Barth syndrome.

Barth syndrome (BTHS) is a mitochondrial myopathy characterized by reports of exercise intolerance. We sought to determine if 1) BTHS leads to abnormalities of skeletal muscle O(2) extraction/utilization and 2) exercise intolerance in BTHS is related to impaired O(2) extraction/utilization, impaired cardiac function, or both. Participants with BTHS (age: 17 ± 5 yr, n = 15) and control participants (age: 13 ± 4 yr, n = 9) underwent graded exercise testing on a cycle ergometer with continuous ECG and metabolic measurements. Echocardiography was performed at rest and at peak exercise. Near-infrared spectroscopy of the vastus lateralis muscle was continuously recorded for measurements of skeletal muscle O(2) extraction. Adjusting for age, peak O(2) consumption (16.5 ± 4.0 vs. 39.5 ± 12.3 ml·kg(-1)·min(-1), P < 0.001) and peak work rate (58 ± 19 vs. 166 ± 60 W, P < 0.001) were significantly lower in BTHS than control participants. The percent increase from rest to peak exercise in ejection fraction (BTHS: 3 ± 10 vs. control: 19 ± 4%, P < 0.01) was blunted in BTHS compared with control participants. The muscle tissue O(2) saturation change from rest to peak exercise was paradoxically opposite (BTHS: 8 ± 16 vs. control: -5 ± 9, P < 0.01), and the deoxyhemoglobin change was blunted (BTHS: 0 ± 12 vs. control: 10 ± 8, P < 0.09) in BTHS compared with control participants, indicating impaired skeletal muscle extraction in BTHS. In conclusion, severe exercise intolerance in BTHS is due to both cardiac and skeletal muscle impairments that are consistent with cardiac and skeletal mitochondrial myopathy. These findings provide further insight to the pathophysiology of BTHS.

Phase I trial of intramuscular injection of a recombinant adeno-associated virus serotype 2 alphal-antitrypsin (AAT) vector in AAT-deficient adults.

A phase I trial of intramuscular injection of a recombinant adeno-associated virus serotype 2 (rAAV2) alpha1-antitrypsin (AAT) vector was performed in 12 AAT-deficient adults, 10 of whom were male. All subjects were either homozygous for the most common AAT mutation (a missense mutation designated PI*Z) or compound heterozygous for PI*Z and another mutation known to cause disease. There were four dose cohorts, ranging from 2.1 x 10(12) vector genomes (VG) to 6.9 x 10(13) VG, with three subjects per cohort. Subjects were injected sequentially in a dose-escalating fashion with a minimum of 14 days between patients. Subjects who had been receiving AAT protein replacement discontinued that therapy 28 days before vector administration. There were no vector-related serious adverse events in any of the 12 participants. Vector DNA sequences were detected in the blood between 1 and 3 days after injection in nearly all patients receiving doses of 6.9 x 10(12) VG or higher. Anti-AAV2 capsid antibodies were present and rose after vector injection, but no other immune responses were detected. One subject who had not been receiving protein replacement exhibited low-level expression of wild-type M-AAT in the serum (82 nM), which was detectable 30 days after receiving an injection of 2.1 x 10(13) VG. Unfortunately, residual but declining M-AAT levels from the washout of the protein replacement elevated background levels sufficiently to obscure any possible vector expression in that range in most of the other individuals in the higher dose cohorts.

Cardiac and clinical phenotype in Barth syndrome.

OBJECTIVE: Barth syndrome, an X-linked disorder that is characterized by cardiomyopathy, neutropenia, skeletal myopathy, and growth delay, is caused by mutations in the taffazin gene at Xq28 that result in cardiolipin deficiency and abnormal mitochondria. The clinical phenotype in Barth syndrome has not been characterized systematically, and the condition may be underrecognized. We sought to evaluate extent of cardioskeletal myopathy, potential for arrhythmia, delays in growth, and biochemical correlates of disease severity in patients with this disorder. METHODS: We conducted an observational, cross-sectional study of the largest cohort of patients with Barth syndrome to date (n = 34; age range: 1.2-22.6 years). Evaluation included echocardiography, electrocardiography (standard and signal-averaged), microvolt T wave alternans analysis, biochemical and hematologic laboratory analyses, and physical therapy evaluation of skeletal myopathy. RESULTS: Family history was positive for confirmed or suspected Barth syndrome in 63%. Ninety percent of patients had a clinical history of cardiomyopathy (mean age at diagnosis of cardiomyopathy: 5.5 months; at genetic confirmation of Barth syndrome: 4.6 years). Echocardiography revealed a mean ejection fraction of 50% +/- 10%, mean fractional shortening of 28% +/- 5%, and mean left ventricular end-diastolic volume z score of 1.9 +/- 1.8. Left ventricular morphology demonstrated increased trabeculations or true noncompaction in 53%. Of 16 patients who were evaluated at > or = 11 years of age, 7 (43%) had documented ventricular arrhythmia. Growth deficiency was present (mean weight percentile: 15%; mean height percentile: 8%). Laboratory analysis revealed low total white blood cell count (absolute count: < 4000 cells per microL) in 25% of those who were not on granulocyte colony-stimulating factor. Hypocholesterolemia was present in 24%, decreased low-density lipoprotein cholesterol in 56%, low prealbumin in 79%, and mildly elevated creatine kinase in 15%. CONCLUSIONS: Our cohort demonstrated clinical variability, but most had cardiomyopathy and diminished growth velocity, with a propensity toward neutropenia and low cholesterol. There was increased incidence of ventricular arrhythmia, predominantly in adolescents and young adults. Barth syndrome should be considered when boys present with cardiomyopathy, especially when associated with increased left ventricular trabeculations, neutropenia, skeletal muscle weakness, or family history indicating an X-linked pattern of inheritance.

An institutional review of the value of computed tomographic angiography in the diagnosis of congenital cardiac malformations.

The ultra-fast, thin-cut computerised tomographic angiogram is an efficient method to diagnose extracardiac lesions associated with congenital cardiac disease. For the purposes of this review, we evaluated various facets of the technique as used in 30 patients who were referred for diagnosis of congenital cardiac disease. The technique had high diagnostic accuracy, with a sensitivity of 93 percent in 15 of these patients referred for either interventional catheterisation or surgery. There were no immediate side-effects associated with the scanning procedure. The scan was also found to be more cost-effective as compared to an alternative noninvasive modality for imaging modality, namely magnetic resonance imaging. The angiographic technique, however, does expose the child to between 2 and 2.5 rems of radiation, despite the short period of scanning, of 10 plus or minus 2 seconds.

Phase I trial of intramuscular injection of a recombinant adeno-associated virus alpha 1-antitrypsin (rAAV2-CB-hAAT) gene vector to AAT-deficient adults.

A recombinant virus vector constructed from adeno-associated virus (AAV) that has been altered to carry the human alpha1-antitrypsin (hAAT) gene expressed from a hybrid chicken beta-actin promoter with a cytomegalovirus enhancer has been developed. The construct has been shown to initiate the production of hAAT in animal models closely matching the proposed human trial. The proposed clinical trial is an open-label, phase I study administering recombinant adeno-associated virus alpha1-antitrypsin (rAAV2-CB-hAAT) gene vector intramuscularly to AAT-deficient human subjects where gene expression can be measured directly in blood samples to assess safety. Safety parameters will be measurement of changes in serum chemistries and hematology, urinalysis, pulmonary function testing, semen assay for vector genomes, immunologic response to AAT, and AAV, as well as reported subject history of any symptoms.