Andrew D. Cole

Mutations in Cardiac T-Box Factor Gene TBX20 Are Associated with Diverse Cardiac Pathologies, Including Defects of Septation and Valvulogenesis and Cardiomyopathy

The T-box family transcription factor gene TBX20 acts in a conserved regulatory network, guiding heart formation and patterning in diverse species. Mouse Tbx20 is expressed in cardiac progenitor cells, differentiating cardiomyocytes, and developing valvular tissue, and its deletion or RNA interference-mediated knockdown is catastrophic for heart development. TBX20 interacts physically, functionally, and genetically with other cardiac transcription factors, including NKX2-5, GATA4, and TBX5, mutations of which cause congenital heart disease (CHD). Here, we report nonsense (Q195X) and missense (I152M) germline mutations within the T-box DNA-binding domain of human TBX20 that were associated with a family history of CHD and a complex spectrum of developmental anomalies, including defects in septation, chamber growth, and valvulogenesis. Biophysical characterization of wild-type and mutant proteins indicated how the missense mutation disrupts the structure and function of the TBX20 T-box. Dilated cardiomyopathy was a feature of the TBX20 mutant phenotype in humans and mice, suggesting that mutations in developmental transcription factors can provide a sensitized template for adult-onset heart disease. Our findings are the first to link TBX20 mutations to human pathology. They provide insights into how mutation of different genes in an interactive regulatory circuit lead to diverse clinical phenotypes, with implications for diagnosis, genetic screening, and patient follow-up.

Three-dimensional quantitative echocardiographic assessment of ventricular volume in healthy human fetuses and in fetuses with congenital heart disease.

The purpose of this study was to evaluate the feasibility of three‐dimensional freehand echocardiographic assessment of ventricular volumetry in healthy fetuses and in fetuses with congenital heart disease. The study was approved by the hospital institutional review board. After echocardiographic examination by conventional ultrasonographic equipment interfaced with a magnetic tracking system, three‐dimensional cardiac data were collected prospectively in 57 fetuses. Ventricular volumes were determined from three‐dimensional data sets, and 22 fetuses with congenital heart disease were compared with 29 healthy fetuses. A multiple regression analysis of covariance was performed to assess between‐group differences. Gated three‐dimensional volume data sets enabled assessment of ventricular volumes in 51 of the 57 fetuses. Both fetuses with and without congenital heart disease had exponential increases in cardiac volumes during gestation. In fetuses with congenital heart disease and a marked inequality of ventricular size but no heart failure, the combined end‐diastolic and stroke volumes of both ventricles were found to be significantly reduced compared with controls with no disease and fetuses with other types of congenital heart disease. Three‐dimensional imaging can provide estimates of ventricular volume changes in fetal hearts with abnormal ventricular morphology that cannot easily be performed by two‐dimensional echocardiography, and it may provide insight into evolving congenital heart disease.

Levosimendan for low cardiac output: a pediatric experience.

This was a retrospective observational study in a pediatric intensive care unit, in which 19 patients received levosimendan. There were no adverse events attributable to levosimendan and no instances where the clinical condition worsened after administration. Arterial lactate levels decreased significantly following levosimendan administration during cardiopulmonary bypass for anticipated low cardiac output. In those with established low cardiac output, trends toward improved hemodynamics were seen, with heart rate reduction, an increase in mean blood pressure, a reduction in arterial lactate, and reduced conventional inotrope use. Levosimendan was safely used in a small number of pediatric patients with established low cardiac output state who demonstrated improved hemodynamics and tissue perfusion, with a tendency to reduced conventional inotrope usage, and this warrants its evaluation as an inotrope in the pediatric population.

GATA4 mutations in 357 unrelated patients with congenital heart malformation.

Congenital heart disease (CHD) represents one of the most common birth defects, but the genetic causes remain largely unknown. Mutations in GATA4, encoding a zinc finger transcription factor with a pivotal role in heart development, have been associated with CHD in several familial cases and a small subset of sporadic patients. To estimate the pathogenetic role of GATA4 in CHD, we screened for mutations in 357 unrelated patients with different congenital heart malformations. In addition to nine synonymous changes, we identified two known (A411V and D425N) and two novel putative mutations (G69D and P163R) in five patients with atrial or ventricular septal defects that were not seen in control subjects. The four mutations did not show altered GATA4 transcriptional activity in synergy with the transcription factors NKX2-5 and TBX20. Our data expand the spectrum of mutations associated with cardiac septal defects but do not support GATA4 mutations as a common cause of CHD.

Somatic mutations in NKX2–5, GATA4, and HAND1 are not a common cause of tetralogy of Fallot or hypoplastic left heart

The majority of congenital heart disease (CHD) occurs as a sporadic finding, with a minority of cases associated with a known genetic abnormality. Combinations of genetic and environmental factors are implicated, with the recent and intriguing hypothesis that an apparently high rate of somatic mutations might explain some sporadic CHD. We used samples of right ventricular myocardium from patients undergoing surgical repair of tetralogy of Fallot (TOF) and hypoplastic left heart (HLH) to examine the incidence of somatic mutation in cardiac tissue. TOF is a common form of cyanotic CHD, occurring in 3.3 per 10,000 live births. HLH is a rare defect in which the left side of the heart is severely under‐developed. Both are severe malformations whose genetic etiology is largely unknown. We carried out direct sequence analysis of the NKX2–5 and GATA4 genes from fresh frozen cardiac tissues and matched blood samples of nine TOF patients. Analysis of NKX2–5, GATA4, and HAND1 was performed from cardiac tissue of 24 HLH patients and three matched blood samples. No somatic or germline mutations were identified in the TOF or HLH patients. Although limited by sample size, our study suggests that somatic mutations in NKX2–5 and GATA4 are not a common cause of isolated TOF or HLH.

Myocardial ischemia is more important than the effects of cardiopulmonary bypass on myocardial water handling and postoperative dysfunction: A pediatric animal model

OBJECTIVES Low cardiac output state is the principal cause of morbidity after surgical intervention for congenital heart disease. Myocardial ischemia-reperfusion injury, apoptosis, capillary leak syndrome, and myocardial edema are associated factors. We established a clinically relevant model to examine relationships between myocardial ischemia, edema, and cardiac dysfunction and to assess the role of the water transport proteins aquaporins. METHODS Sixteen lambs were studied. Seven were control animals not undergoing cardiopulmonary bypass, and 9 underwent bypass. Six had 90 minutes of aortic crossclamping with blood cardioplegia and moderate hypothermia. The remaining 3 underwent cardiopulmonary bypass without aortic crossclamping. Hemodynamic and biochemical data were recorded, and myocardial edema, apoptotic markers, and aquaporin expression were determined after death. RESULTS The group undergoing cardiopulmonary bypass with aortic crossclamping had a low cardiac output state, with early postoperative tachycardia, hypotension, increased serum lactate levels, and impaired tissue oxygen delivery (P < .05) compared with the group undergoing cardiopulmonary bypass without aortic crossclamping. The lambs undergoing cardiopulmonary bypass with aortic crossclamping had increased myocardial water (P < .05) compared with those not undergoing cardiopulmonary bypass and a 2-fold increase in aquaporin 1 mRNA expression (P < .05) compared with those not undergoing cardiopulmonary bypass and those undergoing cardiopulmonary bypass without aortic crossclamping. CONCLUSIONS A temporal association between hemodynamic dysfunction, myocardial edema, and increased aquaporin 1 expression was demonstrated. Cardiopulmonary bypass without ischemia was associated with minimal edema, negligible myocardial dysfunction, and static aquaporin expression. Ischemic reperfusion injury is the main cause of myocardial edema and myocardial dysfunction, but a causal relationship between edema and dysfunction remains to be proved.

Fetal and post‐natal diagnosis of major congenital heart disease: Implications for medical and psychological care in the current era

Aim:  The fetal or post‐natal diagnosis of major congenital cardiac abnormality has important medical and psychological consequences.

Five-year Analysis of Operative Mortality and Neonatal Outcomes in Congenital Heart Disease

BACKGROUND We sought to compare overall mortality with neonatal outcomes over a five year period to define risk factors for mortality and service development priorities. METHODS A retrospective cohort study of surgical outcomes following repair or palliation of structural congenital heart defects January 2005-2010. We defined mortality according to contemporary international guidelines and classified surgical procedures using the Risk Adjustment in Congenital Heart Surgery (RACHS-1) score. The effect of age and weight at operation on mortality and annual variation in case-complexity and surgeon case-mix were assessed. Subgroup analysis was performed in patients who were ≤30 days at operation (neonates). RESULTS Overall mortality within 30 days of operation or prior to hospital discharge was 1.3 and 1.9%, respectively. Mortality was higher in neonates (6.8%) and low birth weight infants (≤2.5kg) (12.1%). Mortality was similar in bypass versus non-bypass procedures (odds ratio 0.74, p=0.425). Annual mortality rates were consistent despite a marked increase in case-complexity. Neonates overall required longer periods of intensive care support and were more likely to suffer serious complications compared to older children. Age, weight and RACHS-1 score were independent risk factors for mortality on multivariate analysis. In neonates undergoing bypass procedures, only RACHS-1 score was a significant risk factor. CONCLUSIONS This study provides an accurate and contemporary audit of mortality risk associated with congenital heart surgery. Outcomes compare favourably to international benchmarks but highlight the risks of morbidity and mortality associated with neonatal cardiac surgery.

Use of sildenafil and nitric oxide in the management of hypoxemia owing to pulmonary arteriovenous fistulas after total cavopulmonary connection

Use of sildenafil and nitric oxide in the management of hypoxemia owing to pulmonary arteriovenous fistulas after total cavopulmonary connection Sameer Bhate, MCh DNB(CVTS), Michael Rossiter-Thornton, BMedSc(Hons), Stephen G. Cooper, MB, ChB, FRACP, Jonathan Gillis, PhD, FRACP, Andrew D. Cole, BAppSci(Hons), Gary S. Sholler, MBBS, FRACP, Richard B. Chard, BDS, MBBS, FRACS, and David S. Winlaw, MD, FRACS, Sydney, Australia

Myocardial membrane injury in pediatric cardiac surgery: An animal model

OBJECTIVE Reduced myocardial performance invariably follows pediatric cardiac surgery and is manifested by a low cardiac output state in its severest form. The role of myocardial membrane proteins in this setting is unknown. Dystrophin and dysferlin are involved in membrane integrity, whereas aquaporins selectively transport water. These proteins were examined in a model of pediatric cardiac surgery, together with a trial of poloxamer 188, which may reduce membrane injury. METHODS Eight lambs were randomized to saline with or without poloxamer 188. Lambs underwent 2 hours of cardiopulmonary bypass and aortic crossclamping. After a further 9 hours of monitoring, the hearts were assessed for water content, capillary leak, and protein expression. RESULTS Dystrophin expression was unaffected by ischemia/reperfusion, but dysferlin expression was reduced. Aquaporin 1 protein increased after ischemia/reperfusion. Poloxamer 188 administration was associated with supranormal levels of dystrophin, preservation of dysferlin expression, and normalization of aquaporin 1 expression. Poloxamer 188 was associated with less capillary leak, maintained colloid osmotic pressure, and less hemodilution. Poloxamer 188 was associated with an improved hemodynamic profile (higher blood pressure, higher venous saturation, and lower lactate), although the heart rate tended to be higher. CONCLUSIONS Changes in protein expression within the myocardial membrane were found in a clinically relevant model of pediatric cardiac surgery. Indicators of reduced performance, such as lower blood pressure and lower oxygen delivery, were lessened in association with the administration of the membrane protecting poloxamer 188. Poloxamer 188 was also associated with potentially beneficial changes in membrane protein expression, reduced capillary leakage, and less hemodilution.