Echocardiographic features and outcomes of fetuses with isolated restrictive foramen ovale or redundant foramen ovale flap using atrial septum excursion index.

PURPOSE: This study was designed to investigate the application value of the atrial septum excursion index (ASEI) in fetuses with isolated restrictive foramen ovale (RFO) or redundant foramen ovale flap (RFOF) and the outcomes of these fetuses. METHODS: This was a retrospective study. Healthy pregnant women who were examined by antenatal fetal echocardiography from January 1, 2019 to December 31, 2021, at Sir Run Run Shaw Hospital were enrolled. One hundred seventy-seven (177) fetuses were categorized into three groups by diagnosis: (1) RFOF (n = 33), (2) RFO (n = 21), and (3) normal (n = 123). Fetal echocardiographic features and postnatal outcomes were collected. RESULTS: The median ASEIs were 0.50 (range, 0.41-0.65) in the control group, 0.76 (range, 0.67-0.88) in the RFOF group and 0.31 (range, 0.14-0.35) in the RFO group, and the differences were significant (p < 0.001). The ratios of right atrium/left atrium, right ventricle/left ventricle, and pulmonary artery diameter to aorta diameter (PA/AO) and the pulmonary annulus Z-scores were greater in fetuses with RFOF and RFO than in the controls (p < 0.05). Twenty-seven of 33 fetuses (87.9%) with RFOF and 19 of 21 fetuses (90.5%) with RFO had good outcomes after birth. CONCLUSION: The ASEI may be a new tool for quantitatively assessing the mobility of foramen ovale flaps in fetuses with isolated RFOF or RFO.

Nr2f1a balances atrial chamber and atrioventricular canal size via BMP signaling-independent and -dependent mechanisms.

Determination of appropriate chamber size is critical for normal vertebrate heart development. Although Nr2f transcription factors promote atrial maintenance and differentiation, how they determine atrial size remains unclear. Here, we demonstrate that zebrafish Nr2f1a is expressed in differentiating atrial cardiomyocytes. Zebrafish nr2f1a mutants have smaller atria due to a specific reduction in atrial cardiomyocyte (AC) number, suggesting it has similar requirements to Nr2f2 in mammals. Furthermore, the smaller atria in nr2f1a mutants are derived from distinct mechanisms that perturb AC differentiation at the chamber poles. At the venous pole, Nr2f1a enhances the rate of AC differentiation. Nr2f1a also establishes the atrial-atrioventricular canal (AVC) border through promoting the differentiation of mature ACs. Without Nr2f1a, AVC markers are expanded into the atrium, resulting in enlarged endocardial cushions (ECs). Inhibition of Bmp signaling can restore EC development, but not AC number, suggesting that Nr2f1a concomitantly coordinates atrial and AVC size through both Bmp-dependent and independent mechanisms. These findings provide insight into conserved functions of Nr2f proteins and the etiology of atrioventricular septal defects (AVSDs) associated with NR2F2 mutations in humans.

Development of the atrial septum in relation to postnatal anatomy and interatrial communications.

The atrial septum is probe patent in some 30% of the population, and is prone to have overt defects. Atrial septation is the coming together of several myocardial structures and mesenchymal tissues of intracardiac and extracardiac origin that must change identity to myocardium. We propose that the propensity for malformation of the atrial septum reflects this complicated morphogenesis. The morphogenesis of the atrial septum initiates from a ridge of mesenchyme, only a few hundred micrometres long, in the roof of the undivided atrial cavity. By growth of the myocardial primary septum, the mesenchymal ridge will be approximated to, and ultimately fuse, with the mesenchyme of the atrioventricular cushions. This fusion also takes in the so-called vestibular spine, and serves to close the primary atrial foramen. Interatrial communication is maintained by the development of perforations in the myocardial septum that will coalesce to produce the secondary foramen. Late in gestation, an infolding of the right atrial roof, previously identified as the secondary septum, will come to form the roof of the secondary foramen. Muscularisation of the mesenchymal ridge and vestibular spine serves to reinforce the attachment of the primary muscular septum to the atrioventricular insulating plane, with the muscularised components, and the cranial infolding, then producing the rims of the oval fossa as seen in the postnatal heart. We show that other lesions that produce the potential for interatrial shunting are outside the confines of the atrial septum, and hence are best considered as interatrial communications, rather than 'atrial septal defects'.

Comparative transcriptome analysis of atrial septal defect identifies dysregulated genes during heart septum morphogenesis.

Congenital heart disease (CHD) is one of most common birth defects, causing fetal loss and death in newborn all over the world. Atrial and ventricular septal defects were the most common CHD subtypes in most districts. During the past decades, several genes were identified to control atrial septum formation, and mutations of these genes can cause cardiac septation defects. However, the pathogenic mechanism of ASD on transcriptional levels has not been well elucidated yet. Herein, we performed comparative transcriptome analysis between normal and atrial septal defect (ASD) patients by Illumina RNA sequencing (RNA-seq). Advanced bioinformatic analyses were employed to identify dysregulated genes in ASD. The results indicated that cardiac specific transcriptional factors (GATA4 and NKX2-5), extracellular signal molecules (VEGFA and BMP10) and cardiac sarcomeric proteins (MYL2, MYL3, MYH7, TNNT1 and TNNT3) were downregulated in ASD which may affect heart atrial septum formation, cardiomyocyte proliferation and cardiac muscle development. Importantly, cell cycle was dominant pathway among downregulated genes, and decreased expression of the proteins included in cell cycle may disturb cardiomyocyte growth and differentiation during atrial septum formation. Our study provided evidences of understanding pathogenic mechanism of ASD and resource for validation of CHD genomic studies.

Atrial and ventricular septal changes in ethanol vapour exposed chick embryos.

OBJECTIVE: To study the effects of ethanol vapour exposure on development of atrial and ventricular septa of chick embryo. METHODS: The experimental study was conducted at the College of Physicians and Surgeons, Islamabad, from 2006 to 2007. The experimental and control groups were further divided into three subgroups based on the day of sacrifice. The experimental group was exposed to ethanol vapours produced in a specially-designed vapour chamber and then compared with age-matched controls. RESULTS: There were 90 eggs in each of the two groups. The development of inter-ventricular septum completed at day 7 of development in chick embryo. Ethanol vapour exposure produced a small discontinuity at day 10 of development in a chick embryo which may be labelled as ventricular septal defect since ventricular development is completed by day 7. Interatrial septum formed till day 7 with small perforations which persisted till hatching. CONCLUSIONS: Ethanol vapour exposure may lead to ventricular septal defect.

Fetal critical aortic stenosis with natural improvement of hydrops fetalis due to spontaneous relief of severe restrictive atrial communication.

We describe a rare case of fetal critical aortic stenosis with spontaneous relief of severe restrictive atrial communication, resulting in complete resolution of hydrops fetalis in utero. Fetal ultrasonography showed hydrops fetalis caused by critical aortic stenosis with a severely restrictive foramen ovale and severe mitral regurgitation at 23 weeks of gestation. Hydrops fetalis, however, spontaneously resolved, showing an obvious increase of flow through the foramen ovale and pulmonary vein at 26 weeks of gestation. The neonate required balloon dilation of the aortic valve and balloon atrioseptostomy immediately after birth and also received bilateral pulmonary artery banding and arterial duct stenting 1 week later. The patient was in good condition after conversion to biventricular circulation via Ross procedure at 8 months old. The present case suggests that atrioseptostomy as a fetal intervention may improve outcome in even a hydropic condition.

Clarifying the morphology of the ostium primum defect.

The 'ostium primum' defect is still frequently considered to be the consequence of deficient atrial septation, although the key feature is a common atrioventricular junction. The bridging leaflets of the common atrioventricular valve, which are joined to each other, are depressed distal to the atrioventricular junction, and fused to the crest of the muscular ventricular septum, which is bowed in the concave direction towards the ventricular apex. As a result, shunting across the defect occurs between the atrial chambers. These observations suggest that the basic deficiency in the 'ostium primum' defect is best understood as a product of defective atrioventricular septation, rather than an atrial septal defect. We have now encountered four examples of 'ostium primum' defects in mouse embryos that support this view. These were identified from a large number of mouse embryo hearts collected from a normal, outbred mouse colony and analysed by episcopic microscopy as part of an ongoing study of normal mouse cardiac development. The abnormal hearts were identified from embryos collected at embryonic days 15.5, 16.5 and 18.5 (two cases). We have analysed the features of the abnormal hearts, and compared the findings with those obtained in the large number of normally developed embryos. Our data show that the key feature of normal atrioventricular septation is the ventral growth through the right pulmonary ridge of a protrusion from the dorsal pharyngeal mesenchyme, confirming previous findings. This protrusion, known as the vestibular spine, or the dorsal mesenchymal protrusion, reinforces the closure of the primary atrial foramen, and muscularises along with the mesenchymal cap of the primary atrial septum to form the ventro-caudal buttress of the oval foramen, identified by some as the 'canal septum'. Detailed analysis of the four abnormal hearts suggests that in each case there has been failure of growth of the vestibular spine, with the result that the common atrioventricular junction found earlier during normal development now persists during cardiac development. Failure of separation of the common junction also accounts for the trifoliate arrangement of the left atrioventricular valve in the abnormal hearts. Analysis of the episcopic datasets also permits recognition of the location of the atrioventricular conduction axis. Comparison of the location of this tract in the normal and abnormal hearts shows that there is no separate formation of a ventricular component of the 'canal septum' as part of normal development. We conclude that it is abnormal formation of the primary atrial septum that is the cause of so-called 'secundum' atrial septal defects, whereas it is the failure to produce a second contribution to atrial septation (via growth of the vestibular spine) that results in the 'ostium primum' defect.

Rac1 signaling is critical to cardiomyocyte polarity and embryonic heart development.

BACKGROUND: Defects in cardiac septation are the most common form of congenital heart disease, but the mechanisms underlying these defects are still poorly understood. The small GTPase Rac1 is implicated in planar cell polarity of epithelial cells in Drosophila; however, its role in mammalian cardiomyocyte polarity is not clear. We tested the hypothesis that Rac1 signaling in the second heart field regulates cardiomyocyte polarity, chamber septation, and right ventricle development during embryonic heart development. METHODS AND RESULTS: Mice with second heart field-specific deficiency of Rac1 (Rac1(SHF)) exhibited ventricular and atrial septal defects, a thinner right ventricle myocardium, and a bifid cardiac apex. Fate-mapping analysis showed that second heart field contribution to the interventricular septum and right ventricle was deficient in Rac1(SHF) hearts. Notably, cardiomyocytes had a spherical shape with disrupted F-actin filaments in Rac1(SHF) compared with elongated and well-aligned cardiomyocytes in littermate controls. Expression of Scrib, a core protein in planar cell polarity, was lost in Rac1(SHF) hearts with decreased expression of WAVE and Arp2/3, leading to decreased migratory ability. In addition, Rac1-deficient neonatal cardiomyocytes displayed defects in cell projections, lamellipodia formation, and cell elongation. Furthermore, apoptosis was increased and the expression of Gata4, Tbx5, Nkx2.5, and Hand2 transcription factors was decreased in the Rac1(SHF) right ventricle myocardium. CONCLUSIONS: Deficiency of Rac1 in the second heart field impairs elongation and cytoskeleton organization of cardiomyocytes and results in congenital septal defects, thin right ventricle myocardium, and a bifid cardiac apex. Our study suggests that Rac1 signaling is critical to cardiomyocyte polarity and embryonic heart development.

Technical challenges of atrial septal stent placement in fetuses with hypoplastic left heart syndrome and intact atrial septum.

OBJECTIVES: The objective of this study was to describe our single-institution experience with prenatal atrial septal stent placement for fetuses with hypoplastic left heart syndrome and an intact atrial septum (HLHS/IAS). BACKGROUND: Infants born with HLHS/IAS are at high risk for neonatal death, despite maximal postnatal therapy. Prenatal atrial septoplasty by static balloon dilation has been effective in decompressing the left atrium (LA) in utero, but several factors have limited the size of septal defects. We attempted to overcome the limitations of balloon septoplasty using transcatheter atrial septal stents. METHODS: All records from our institution of fetuses with HLHS/IAS that underwent prenatal atrial septal stent placement were reviewed, including operative notes and echocardiograms. RESULTS: Nine fetuses between 24 and 31 weeks gestation with HLHS/IAS underwent attempted fetal atrial septal stent placement. A stent was deployed across the atrial septum in five fetuses, with four fetuses demonstrating flow across the stent at the time of intervention. In four cases, stent placement failed due to malposition or embolization, but in three of the four cases, atrial balloon septoplasty at the same in-utero procedure successfully and acutely decompressed the LA. There were no maternal complications. There was one fetal demise. The remaining eight fetuses survived to delivery, but four died in the neonatal period (two of which had been stented). CONCLUSIONS: Ultrasound-guided atrial septal stent placement is feasible in some fetuses with HLHS/IAS. Visualization of the septum and catheter tip is critical to technical success. Additional experience is necessary to determine the clinical impact of this intervention. © 2013 Wiley Periodicals, Inc.

The pathogenesis of atrial and atrioventricular septal defects with special emphasis on the role of the dorsal mesenchymal protrusion.

Partitioning of the four-chambered heart requires the proper formation, interaction and fusion of several mesenchymal tissues derived from different precursor populations that together form the atrioventricular mesenchymal complex. This includes the major endocardial cushions and the mesenchymal cap of the septum primum, which are of endocardial origin, and the dorsal mesenchymal protrusion (DMP), which is derived from the Second Heart Field. Failure of these structures to develop and/or fully mature results in atrial septal defects (ASDs) and atrioventricular septal defects (AVSD). AVSDs are congenital malformations in which the atria are permitted to communicate due to defective septation between the inferior margin of the septum primum and the atrial surface of the common atrioventricular valve. The clinical presentation of AVSDs is variable and depends on both the size and/or type of defect; less severe defects may be asymptomatic while the most severe defect, if untreated, results in infantile heart failure. For many years, maldevelopment of the endocardial cushions was thought to be the sole etiology of AVSDs. More recent work, however, has demonstrated that perturbation of DMP development also results in AVSD. Here, we discuss in detail the formation of the DMP, its contribution to cardiac septation and describe the morphological features as well as potential etiologies of ASDs and AVSDs.

Regulatory variation in a TBX5 enhancer leads to isolated congenital heart disease.

Recent studies have identified the genetic underpinnings of a growing number of diseases through targeted exome sequencing. However, this strategy ignores the large component of the genome that does not code for proteins, but is nonetheless biologically functional. To address the possible involvement of regulatory variation in congenital heart diseases (CHDs), we searched for regulatory mutations impacting the activity of TBX5, a dosage-dependent transcription factor with well-defined roles in the heart and limb development that has been associated with the Holt-Oram syndrome (heart-hand syndrome), a condition that affects 1/100 000 newborns. Using a combination of genomics, bioinformatics and mouse genetic engineering, we scanned ∼700 kb of the TBX5 locus in search of cis-regulatory elements. We uncovered three enhancers that collectively recapitulate the endogenous expression pattern of TBX5 in the developing heart. We re-sequenced these enhancer elements in a cohort of non-syndromic patients with isolated atrial and/or ventricular septal defects, the predominant cardiac defects of the Holt-Oram syndrome, and identified a patient with a homozygous mutation in an enhancer ∼90 kb downstream of TBX5. Notably, we demonstrate that this single-base-pair mutation abrogates the ability of the enhancer to drive expression within the heart in vivo using both mouse and zebrafish transgenic models. Given the population-wide frequency of this variant, we estimate that 1/100 000 individuals would be homozygous for this variant, highlighting that a significant number of CHD associated with TBX5 dysfunction might arise from non-coding mutations in TBX5 heart enhancers, effectively decoupling the heart and hand phenotypes of the Holt-Oram syndrome.

Cor triloculare biventriculare with left superior vena cava.

Cor triloculare biventriculare is a rare congenital malformation of the heart in which there is a complete absence of the atrial septum. It is usually associated with other anomalies like complete atrioventricular canal defect, polysplenic syndrome, isolated dextrocardia, Ellis-van Creveld syndrome, or persistent left superior vena cava. We report a case of a stillborn male foetus of 35 weeks gestation with common atrium, complete atrioventricular canal defect, and persistent left superior vena cava. The possible embryological basis and clinical implication of this variation are discussed.

Hypoplastic left heart syndrome with restrictive atrial septum and advanced heart block documented with a novel fetal electrocardiographic monitor.

Hypoplastic left ventricle with congenital heart block has been reported previously in a fetus with concurrent left atrial isomerism and levo-transposition of the great arteries. We present the unusual case of an infant diagnosed in utero with hypoplastic left heart syndrome, a restrictive atrial septum and advanced heart block but with D-looping of the ventricles and no atrial isomerism. In addition, fetal heart rhythm was documented with the assistance of a new fetal electrocardiographic monitor.

Ablation of Nkx2-5 at mid-embryonic stage results in premature lethality and cardiac malformation.

AIMS: Human congenital heart disease linked to mutations in the homeobox transcription factor, NKX2-5, is characterized by cardiac anomalies, including atrial and ventricular septal defects as well as conduction and occasional defects in contractility. In the mouse, homozygous germline deletion of Nkx2-5 gene results in death around E10.5. It is, however, not established whether Nkx2-5 is necessary for cardiac development beyond this embryonic stage. Because human NKX2-5 mutations are related to septum secundum type atrial septal defects (ASD), we hypothesized that Nkx2-5 deficiency during the processes of septum secundum formation may cause cardiac anomalies; thus, we analysed mice with tamoxifen-inducible Nkx2-5 ablation beginning at E12.5 when the septum secundum starts to develop. METHODS AND RESULTS: Using tamoxifen-inducible Nkx2-5 gene-targeted mice, this study demonstrates that Nkx2-5 ablation beginning at E12.5 results in embryonic death by E17.5. Analysis of mutant embryos at E16.5 shows arrhythmias, contraction defects, and cardiac malformations, including ASD. Quantitative measurements using serial section histology and three-dimensional reconstruction demonstrate growth retardation of the septum secundum and enlarged foramen ovale in Nkx2-5-ablated embryos. Functional cardiac defects may be attributed to abnormal expression of transcripts critical for conduction and contraction, including cardiac voltage-gated Na(+) channel pore-forming α-subunit (Na(v)1.5-α), gap junction protein connexin40, cardiac myosin light chain kinase, and sarcolipin within 4 days after tamoxifen injection. CONCLUSION: Nkx2-5 is necessary for survival after the mid-embryonic stage for cardiac function and formation by regulating the expression of its downstream target genes.

Down's syndrome-like cardiac developmental defects in embryos of the transchromosomic Tc1 mouse.

AIMS: Cardiac malformations are prevalent in trisomies of human chromosome 21 [Down's syndrome (DS)], affecting normal chamber separation in the developing heart. Efforts to understand the aetiology of these defects have been severely hampered by the absence of an accurate mouse model. Such models have proved challenging to establish because synteny with human chromosome Hsa21 is distributed across three mouse chromosomes. None of those engineered so far accurately models the full range of DS cardiac phenotypes, in particular the profound disruptions resulting from atrioventricular septal defects (AVSDs). Here, we present analysis of the cardiac malformations exhibited by embryos of the transchromosomic mouse line Tc(Hsa21)1TybEmcf (Tc1) which contains more than 90% of chromosome Hsa21 in addition to the normal diploid mouse genome. METHODS AND RESULTS: Using high-resolution episcopic microscopy and three-dimensional (3D) modelling, we show that Tc1 embryos exhibit many of the cardiac defects found in DS, including balanced AVSD with single and separate valvar orifices, membranous and muscular ventricular septal defects along with outflow tract and valve leaflet abnormalities. Frequencies of cardiac malformations (ranging from 38 to 55%) are dependent on strain background. In contrast, no comparable cardiac defects were detected in embryos of the more limited mouse trisomy model, Dp(16Cbr1-ORF9)1Rhr (Ts1Rhr), indicating that trisomy of the region syntenic to the Down's syndrome critical region, including the candidate genes DSCAM and DYRK1A, is insufficient to yield DS cardiac abnormalities. CONCLUSION: The Tc1 mouse line provides a suitable model for studying the underlying genetic causes of the DS AVSD cardiac phenotype.