Amy L. Juraszek

Morphogenesis of the right ventricle requires myocardial expression of Gata4

Mutations in developmental regulatory genes have been found to be responsible for some cases of congenital heart defects. One such regulatory gene is Gata4, a zinc finger transcription factor. In order to circumvent the early embryonic lethality of Gata4-null embryos and to investigate the role of myocardial Gata4 expression in cardiac development, we used Cre/loxP technology to conditionally delete Gata4 in the myocardium of mice at an early and a late time point in cardiac morphogenesis. Early deletion of Gata4 by Nkx2-5Cre resulted in hearts with striking myocardial thinning, absence of mesenchymal cells within the endocardial cushions, and selective hypoplasia of the RV. RV hypoplasia was associated with downregulation of Hand2, a transcription factor previously shown to regulate formation of the RV. Cardiomyocyte proliferation was reduced, with a greater degree of reduction in the RV than in the LV. Late deletion of Gata4 by Cre recombinase driven by the alpha myosin heavy chain promoter did not selectively affect RV development or generation of endocardial cushion mesenchyme but did result in marked myocardial thinning with decreased cardiomyocyte proliferation, as well as double-outlet RV. Our results demonstrate a general role of myocardial Gata4 in regulating cardiomyocyte proliferation and a specific, stage-dependent role in regulating the morphogenesis of the RV and the atrioventricular canal.

A GATA-6 gene heart-region-specific enhancer provides a novel means to mark and probe a discrete component of the mouse cardiac conduction system.

The transcriptional programs that specify the distinct components of the cardiac conduction system are poorly understood, in part due to a paucity of definitive molecular markers. In the present study we show that a cGATA-6 gene enhancer can be used to selectively express transgenes in the atrioventricular (AV) conduction system as it becomes manifest in the developing multichambered mouse heart. Furthermore, our analysis of staged cGATA-6/lacZ embryos revealed that the activity of this heart-region-specific enhancer can be traced back essentially to the outset of the cardiogenic program. We provide evidence that this enhancer reads medial/lateral and anterior/posterior positional information before the heart tube forms and we show that the activity of this enhancer becomes restricted at the heart looping stage to AV myocardial cells that induce endocardial cushion formation. We infer that a deeply-rooted heart-region-specific transcriptional program serves to coordinate AV valve placement and AV conduction system formation. Lastly, we show that cGATA-6/Cre mice can be used to delete floxed genes in the respective subsets of specialized heart cells.

Physical Models Aiding in Complex Congenital Heart Surgery

PURPOSE Our aim was to improve spatial imagination of complex congenital cardiac abnormalities for subsequent surgical intervention. DESCRIPTION Magnetic resonance imaging data of a patient with complex congenital heart malformations was post-processed with software developed at our institution. The resulting virtual surface data sets were printed out three-dimensionally by rapid prototyping techniques. EVALUATION We present the first patient operated on with intraoperative use of physical models representing the intracardiac volumes (RepliCast) or muscle and vessel walls (RepliCardio). The courses of the coronary arteries were visible on the RepliCast, whereas the RepliCardio showed intracardiac views a surgeon could never obtain intraoperatively in the relaxed heart. Other than on virtual reconstructions presented on computer screens, physical models vastly improve the spatial imagination and give precise information regarding localization and actual size of abnormal structures. The self-explanatory utility of these models shortened preparation and expedited orientation on the open heart. CONCLUSIONS The additional spatial information provided by RepliCast and RepliCardio models may enable even high-risk correction procedures in patients with complex congenital heart disease.

Autophagy is essential for cardiac morphogenesis during vertebrate development

Genetic analyses indicate that autophagy, an evolutionarily conserved lysosomal degradation pathway, is essential for eukaryotic differentiation and development. However, little is known about whether autophagy contributes to morphogenesis during embryogenesis. To address this question, we examined the role of autophagy in the early development of zebrafish, a model organism for studying vertebrate tissue and organ morphogenesis. Using zebrafish that transgenically express the fluorescent autophagy reporter protein, GFP-LC3, we found that autophagy is active in multiple tissues, including the heart, during the embryonic period. Inhibition of autophagy by morpholino knockdown of essential autophagy genes (including atg5, atg7, and becn1) resulted in defects in morphogenesis, increased numbers of dead cells, abnormal heart structure, and reduced organismal survival. Further analyses of cardiac development in autophagy-deficient zebrafish revealed defects in cardiac looping, abnormal chamber morphology, aberrant valve development, and ectopic expression of critical transcription factors including foxn4, tbx5, and tbx2. Consistent with these results, Atg5-deficient mice displayed abnormal Tbx2 expression and defects in valve development and chamber septation. Thus, autophagy plays an essential, conserved role in cardiac morphogenesis during vertebrate development.

Double Outlet Right Ventricle: Aetiologies and Associations

Background: Double outlet right ventricle (DORV), a clinically significant congenital heart defect, occurs in 1–3% of individuals with congenital heart defects. In contrast to other major congenital heart defects, there are no systematic or comprehensive data regarding associations, aetiologies, and pathogenesis of DORV. We analysed reported cases in the medical literature to address these issues. Methods: We queried the PubMed database using key words “double outlet right ventricle” and “DORV” for case reports, epidemiologic analyses and animal studies with this cardiac anomaly. The anatomic subtype of DORV was classified according to criteria of Van Praagh. Results: Chromosomal abnormalities were present in 61 of the 149 cases of DORV. Trisomies 13 and 18, and del 22q11 were the most commonly associated cytogenetic lesions; different anatomic subtypes of DORV were noted in trisomies 13 and 18 versus del 22q11. DORV was reported in many uncommon or rare non-chromosomal syndromes. Mutations and non-synonymous sequence variants in the CFC1 and CSX genes were the most commonly reported monogenic loci associated with DORV in humans; numerous genes are reported in murine models of DORV. Animal studies implicate maternal diabetes and prenatal exposure to ethanol, retinoids, theophylline, and valproate in DORV teratogenesis. Conclusions: The large number of genes associated with DORV in both humans and animal models and the different anatomic subtypes seen in specific aetiologies indicate the likelihood of several distinct pathogenetic mechanisms for DORV, including impairment of neural crest derivative migration and impairment of normal cardiac situs and looping.

Aortic Stenosis and Severe Mitral Regurgitation in the Fetus Resulting in Giant Left Atrium and Hydrops Pathophysiology, Outcomes, and Preliminary Experience With Pre-Natal Cardiac Intervention

OBJECTIVES The objective of this article is to review anatomic, physiologic, and clinical features of fetuses and neonates with severe mitral regurgitation (MR) in conjunction with aortic stenosis (AS) and left ventricular (LV) and left atrial (LA) dilation and to present preliminary results of pre-natal intervention for this condition. BACKGROUND Severe fetal valvar AS with an abnormal mitral valve (MV) and MR can lead to left heart dilation, with consequent compression of the right ventricle (RV); hydrops and low cardiac output are often associated. METHODS This is a retrospective review of fetuses diagnosed with AS, severe MR, and LA dilation (2002 to 2009) and neonates with the same combination of abnormalities (1988 to 2009). RESULTS Fourteen fetuses and 7 neonates were investigated. Eleven fetuses had severe hydrops; all had polyhydramnios and a structurally abnormal MV, abnormal MV inflow pattern, restrictive/intact atrial septum, retrograde flow in the transverse aortic arch, and compression of the right heart. The mean indexed RV output was 326 ± 160 ml/kg/min, lower than the normal average fetal combined ventricular output of 550 ± 150 ml/kg/min. Ten fetuses underwent pre-natal cardiac intervention: aortic valvuloplasty (n = 8) and/or atrial septal dilation/stenting (n = 5). Seven of these, and 11 overall, were live born. Nine patients died (median age 6 days), and 2 patients are currently alive. All 7 patients diagnosed in the neonatal period died (median age 1 day). CONCLUSIONS Aortic stenosis associated with significant MR in the fetus can cause severe LA and LV enlargement, leading to low cardiac output and hydrops. Despite the potential advantages of early pre-natal diagnosis and both fetal and neonatal interventions, this rare complex of anomalies carries a poor prognosis.

Atrial remodeling after the Fontan operation.

The hemodynamics after Fontan surgery are notable for hypertension and dilation of the right atrium (RA). The effect of this stress on atrial cytoarchitecture has not been systematically studied and might be relevant to arrhythmias and their treatment. Morphologic and histopathologic analyses were performed on tissue from the RA and left atrium (LA) from autopsy specimens of Fontan hearts (n = 47). The findings were compared to those from control samples from young patients with normal atrial hemodynamics (n = 15). Most Fontan specimens were from young patients who died after a relatively short duration of Fontan physiology. The tissues were analyzed for wall thickness, fibrosis content, and fibrosis pattern. The mean wall thickness for the RA (3.0 +/- 1.0 mm) and LA (2.3 +/- 0.6 mm) in the Fontan hearts was significantly greater than that in the control hearts (RA, 1.8 +/- 0.4 mm; LA, 1.8 +/- 0.5 mm; p <0.001 and p = 0.024, respectively). The predictors for thickening of the RA included (1) older age at Fontan surgery, (2) older age at death, and (3) longer duration of Fontan circulation. The Fontan hearts and control hearts exhibited nearly identical fibrosis patterns in the RA and LA. Neither wall thickness nor fibrosis varied with the underlying heart defect or style of Fontan connection. In conclusion, atrial remodeling after Fontan surgery for univentricular heart physiology involves increased wall thickness in both the RA and LA. Interstitial fibrosis was also observed in the Fontan atria; however, because a similar pattern was present in the control tissue, this likely represented normal fibroelastic atrial structure, rather than a specific response to Fontan hemodynamics. The degree of wall thickening observed in the Fontan atria was not so excessive as to preclude transmural lesions during catheter or surgical ablation of reentrant arrhythmias.

Cardiac Risk After Craniopharyngioma Therapy

Although long-term survival after craniopharyngioma treatment is excellent in childhood and early adulthood, sudden deaths in two craniopharyngioma survivors with cardiac findings suggest a need to determine whether treated patients exhibit potential substrates for sudden cardiac death. We present a retrospective review of two index patients with cardiac mortality. This motivated a prospective cardiac screening of 12 survivors that identified nearly a third with significant QTc prolongation. QTc-prolonging medication and stimulants should be used with caution in this population, and routine electrocardiogram screening may identify those at highest risk.

Isolated Left-sided Scimitar Vein Connecting All Left Pulmonary Veins to the Right Inferior Vena Cava

When the common pulmonary vein fails to develop, the embryonic connections of the pulmonary veins to one or more of the systemic veins almost always persist. Anomalous pulmonary venous connections to the inferior vena cava (IVC) are typically characterized by hypoplasia of the involved pulmonary veins and pulmonary artery, as well as abnormal parenchyma of the involved lung. Such cases have been described as “scimitar syndrome.” We report the case of a young female patient in whom all the left pulmonary veins converged into a common vessel that drained into the IVC but who had a normal left pulmonary artery and left lung. Surgical intervention was successful, and our patient is still alive.

Mortality in hypoplastic left heart syndrome: Review of 216 autopsy cases of aortic atresia with attention to coronary artery disease

OBJECTIVES Aortic atresia (AA) in hypoplastic left heart syndrome (HLHS) has been associated with increased mortality in several prior studies. We reviewed our autopsy series to explore the relationship of coronary abnormalities to anatomic subsets of HLHS with AA. METHODS We retrospectively reviewed all pathology specimens with AA/MS (mitral stenosis) and AA/MA (mitral atresia) in the Cardiac Registry of Childrens Hospital Boston between 1955 and 2009 including autopsy reports, operative notes, and imaging studies. Formalin-fixed hearts were examined, and cases found to have macroscopic coronary artery abnormalities were sectioned at mid-left ventricular level in the transverse plane and at mid-right ventricular level in the longitudinal plane for histologic analysis of coronary arteries using tissue sections stained with hematoxylin and eosin. RESULTS A total of 216 autopsy cases were identified with AA/MS (134) and AA/MA (82). Coronary anomalies were found in 49 cases, left ventricle-coronary fistula in 39, all in AA/MS, and 10 other coronary abnormalities, all in AA/MA. Histologic study confirmed fistulas only in the AA/MS group with no evidence of fistulas in the AA/MA group. CONCLUSIONS The occurrence of left ventricle-coronary fistulas appears limited to the AA/MS group, and coronary fistula specimens were disproportionately more prevalent in postoperative specimens. Further clinical studies are required to validate this finding and to identify subgroups that carry a higher mortality risk.