Randall M. Bryant

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 ≥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 μL) 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.

Ventricular Arrhythmia in the X-linked Cardiomyopathy Barth Syndrome

Barth syndrome is an X-linked disorder characterized by dilated cardiomyopathy, cyclic neutropenia, skeletal myopathy, abnormal mitochondria, and growth deficiency. The primary defect is a mutation in the TAZ gene on the X chromosome at Xq28, resulting in abnormal phospholipid biosynthesis and cardiolipin deficiency. To date, there has been no systematic evaluation of the cardiac phenotype. We report five cases of cardiac arrest and/or placement of an internal cardiac defibrillator with documented ventricular arrhythmia. We suggest that ventricular arrhythmia is part of the primary phenotype of the disorder and that patients should be screened accordingly.

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.

Cardiac transplantation in children and adolescents with long QT syndrome

BACKGROUND Long QT syndrome (LQTS) is a potentially lethal, yet highly treatable, cardiac channelopathy. Cardiac transplantation has been reported anecdotally for patients with severe LQTS refractory to standard therapies. OBJECTIVE The purpose of this study was to evaluate the incidence of and risk factors for cardiac transplantation in children evaluated and treated in an LQTS specialty center. METHODS This was a retrospective review of 349 children with LQTS (mean age at diagnosis, 8.0 ± 5.7 years; mean corrected QT interval, 469 ± 51 ms; long QT syndrome type 1 [LQT1] in 46%, LQT2 in 31%, and LQT3 in 9%) evaluated from 2000 to 2013. A subset analysis was performed on patients referred for cardiac transplantation. RESULTS Only 3 patients (0.9%; all LQT3; 2 female) underwent cardiac transplantation at ages 4, 11, and 17 years. Overall, 90 of 349 (26%) were symptomatic (exhibited LQTS-associated cardiac events) before LQTS diagnosis, including those who ultimately underwent transplant. Age at sentinel event was associated with transplantation (3 of 26 [12%] with an event at <1 year of life were transplanted vs 0 of 64 with an event after age 1; P = .02). Genotype was also a risk factor (3 of 32 patients with LQT3 were transplanted [9.4%] vs 0 of 270 patients with LQT1 or LQT2; P = .001). Before transplant, all patients had recurrent ventricular fibrillation-terminating shocks despite combination drug therapy and bilateral sympathetic denervation. All transplanted patients are alive at follow-up. CONCLUSION Cardiac transplantation is seldom necessary for the management of LQTS. However, patients with LQT3 and in utero/neonatal expressivity are at higher risk of treatment failure and refractory ventricular arrhythmias with standard therapy, and cardiac transplantation should be considered for this malignant subset of LQTS.

Artefactual atrial flutter due to interference from a portable media device.

Portable media devices are widely used by todays youth. When used in hospitals, these devices can produce artefactual arrhythmias on telemetry.

Development of paediatric electrophysiology standards for Florida Children’s Medical Services

The Florida Childrens 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.

Catecholaminergic polymorphic ventricular tachycardia in a 3-year-old with occult myocarditis.

BRYANT, R.M., et al.: Catecholaminergic Polymorphic Ventricular Tachycardia in a 3‐Year‐Old with Occult Myocarditis. Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare clinical entity in children. Occult myocarditis has not been previously implicated as an etiologic agent. A 3‐year‐old female presents with a presumed breath‐holding spell and is found to have ventricular fibrillation requiring DC cardioversion. An invasive electrophysiological study was performed demonstrating the absence of inducible ventricular arrhythmias. Low dose epinephrine confirmed the presence CPVT. Right ventricular endomyocardial biopsies sent for polymerase chain reaction (PCR) analysis demonstrated the presence of adenoviral DNA. The authors hypothesize that occult myocarditis may be the inciting agent for CPVT in children.