Development of the pharyngeal arch system related to the pulmonary and bronchial vessels in the avian embryo. With a concept on systemic-pulmonary collateral artery formation

TAPVR: Molecular Pathways and Animal Models

The venous pole of the heart where the pulmonary veins will develop encompasses the sinus venosus and the atrium. In the fourth week of development, the sinus venosus consists of a left and a right part receiving blood from the common cardinal vein, the omphalomesenteric and umbilical veins. Asymmetrical expansion of the common atrium corresponds with a rightward shift of the connection of the sinus to the atrium. The right-sided part of the sinus venosus including its tributing cardinal veins enlarges to form the right superior and inferior vena cava that will incorporate into the right atrium. The left-sided part in human development largely obliterates and remodels to form the coronary sinus in adults. In approximately the same time window (4th-fifth weeks), a splanchnic vascular plexus surrounds the developing lung buds (putative lungs) with a twofold connection. Of note, during early developmental stages, the primary route of drainage from the pulmonary plexus is toward the systemic veins and not to the heart. After lumenization of the so-called mid-pharyngeal endothelial strand (MPES), the first anlage of the pulmonary vein, the common pulmonary vein can be observed in the dorsal mesocardium, and the primary route of drainage will gradually change toward a cardiac drainage. The splanchnic pulmonary venous connections with the systemic cardinal veins will gradually disappear during normal development. In case of absence or atresia of the MPES, the pulmonary-to-systemic connections will persist, clinically resulting in total anomalous pulmonary venous return (TAPVR). This chapter describes the developmental processes and molecular pathways underlying anomalous pulmonary venous connections.

Large isolated major aortopulmonary collateral artery causing dilated left ventricle

Isolated major aortopulmonary collateral artery (MAPCA), in the absence of evidence of structural heart disease, is a very rare observation. This anomaly usually appears in preterm newborns. In the majority of babies, isolated MAPCAs cause no symptoms and regress spontaneously after birth and their conservative management is usually sufficient. We report a case of an asymptomatic full-term 5-month-old infant presenting with heart murmur as the only sign during clinical evaluation. Echocardiography revealed a dilated left ventricle, with no pulmonary hypertension. Computed tomography angiogram showed a large MAPCA arising from the descending thoracic aorta and supplying blood to the left lower lobe. The condition was managed successfully by percutaneous obliteration with Amplatzer vascular plugs. Isolated MAPCA is usually a benign anomaly, presenting no clinical finding and requiring no specific treatment. However, in a small minority of infants, this congenital disorder may progress, with detrimental impacts on cardiac structure before clinical symptoms appear. Early intervention may be required to prevent irreversible sequelae.

Ductus arteriosus: more than just the patent ductus arteriosus

The ductus arteriosus is important to fetal circulation. Failure to close at birth is a common event. In this educational pictorial essay, we illustrate the association of the ductus arteriosus with a variety of congenital cardiac, vascular and pulmonary lesions. These lesions can impact the systemic circulation, the pulmonary circulation or the airway and include coarctation of the aorta, ductal origin of the pulmonary artery and vascular rings.

The mechanical and morphological properties of systemic and pulmonary arteries differ in the earth boa, a snake without ventricular pressure separation

The walls of the mammalian aorta and pulmonary artery are characterized by diverging morphologies and mechanical properties, which has been correlated with high systemic and low pulmonary blood pressures, as a result of intraventricular pressure separation. However, the relation between intraventricular pressure separation and diverging aortic and pulmonary artery wall morphologies and mechanical characteristics is not understood. The snake cardiovascular system poses a unique model for the study of this question, since representatives both with and without intraventricular pressure separation exist. In this study we perform uniaxial tensile testing on vessel samples taken from the aortas and pulmonary arteries of the earth boa, Acrantophis madagascariensis, a species without intraventricular pressure separation. We then compare these morphological and mechanical characteristics with samples from the ball python, Python regius, and the yellow anaconda, Eunectes notaeus, species with and without intraventricular pressure separation, respectively. Our data suggest that although the aortas and pulmonary arteries of A. madagascariensis respond similarly to the same intramural blood pressures, they diverge in morphology, and that this attribute extends to E. notaeus. In contrast, P. regius aortas and pulmonary arteries diverge both morphologically and in terms of their mechanical properties. Our data indicate that intraventricular pressure separation cannot fully explain diverging aortic and pulmonary artery morphologies. Following the Law of Laplace, we propose that pulmonary arteries of small luminal diameter represent a mechanism to protect the fragile pulmonary vasculature by reducing the blood volume that passes through, to which genetic factors may contribute more strongly than physiological parameters.

Staged correction of pulmonary atresia, ventricular septal defect, and collateral arteries

Objectives

Pulmonary atresia (PA) with ventricular septal defect (VSD) and systemic‐pulmonary collateral arteries (SPCAs) presents with variable anatomy with regard to the pulmonary vasculature, requiring personalized surgical treatment. A protocol consisting of staged unifocalization and correction was employed.

Methods

Since 1989, 39 consecutive patients were included (median age at first operation 13 months). In selected cases, a central aorto‐pulmonary shunt was performed as the first procedure. Unifocalization procedures were performed through a lateral thoracotomy. Correction consisted of shunt takedown, VSD closure, and interposition of an allograft between the right ventricle and the reconstructed pulmonary artery. Echocardiographic data were obtained postoperatively and at interval follow‐up.

Results

In 39 patients 66 unifocalization procedures were performed. Early mortality was 5%. Seven patients were considered not suitable for correction, of which four have since died. One patient is awaiting further correction. A correction was performed successfully in 28 patients. Operative mortality was 3% and late mortality was 11%. Median follow‐up after the correction was 19 years. Eleven patients required homograft replacement. Freedom from conduit replacement was 88%, 73%, and 60% at 5, 10, and 15 years respectively. Right ventricular function was reasonable or good in 75% of patients. All but one patient were in NYHA Class I or II.

Conclusions

After complete unifocalization 30/37 patients (81%) were considered correctable. The staged approach of PA, VSD, and SPCAs results in adequate correction and good functional capacity. RV function after correction remains reasonable or good in the majority of patients.

Early development of the pulmonary vascular system: An anatomical and histochemical reinvestigation of the pulmonary venous return development in mice

Pulmonary venous return development establishes the fetal circulation and is critical for the formation of pulmonary circulation independent of systemic circulation at birth. Anomalous returns lead to inappropriate drainage of blood flow, sometimes resulting in neonatal cyanosis and cardiac failure. While many classical studies have discussed the anatomical features of the pulmonary venous system development, the cellular dynamics of the endothelia based on the molecular marker expression remain unknown. In the present study, we examined the expression of several endothelial markers during early pulmonary vascular system development of murine embryos. We show that Endomucin and CD31 are expressed early in endothelial cells of the splanchnic plexus, which is the precursor of the pulmonary vascular system. Three-dimensional analyses of the expression patterns revealed the spatiotemporal modification of the venous returns to systemic venous systems or sinoatrial canal during the formation of the pulmonary plexus. We herein report the results of spatiotemporal analyses of the early pulmonary venous system development with histochemistry as well as a delineation of the anatomical features of the tentative drainage pathways.

Fate of the Arterial Origin of Major Aortopulmonary Collateral Arteries After Unifocalization

BACKGROUND

During unifocalization procedures for pulmonary atresia with ventricular septal defect and major aortopulmonary collateral arteries, collateral arteries are either ligated or detached. Not much is known of the fate of the remaining arterial origins in the long term. Available computed tomography (CT) or magnetic resonance (MR) imaging of the intrathoracic arteries was examined to investigate possible abnormalities at the former position of the collateral arteries as well as ascending aortic diameters.

METHODS

From 1989 to 2018, we performed 66 unifocalization procedures in 39 patients. One hundred and twenty-nine collateral arteries were ligated or detached. In 52% (15) of the surviving patients (with a total of 55 ligated or detached collaterals), sufficient imaging of the thoracic aorta from CT (11) and/or MR (9) was available for evaluation.

RESULTS

The median interval between unifocalization procedure and imaging was 15 years (interquartile range [IQR]: 9-19 years). In 93% (14) of the scanned patients, 18 blunt ends were detected at the location of a former collateral artery. No aneurysm formation of the descending aorta was observed. The median diameter of the ascending aorta was 35 mm (IQR: 31-40 mm). During follow-up, no aortic dissection or rupture occurred.

CONCLUSIONS

Aortic imaging late after unifocalization showed abnormalities in 93% of the scanned patients. Abnormalities consisted mostly of blunt ends of the former collateral artery. We recommend to include routine imaging of the aorta during late follow-up to detect eventual future abnormalities and monitor aortic diameters. Ascending aortic diameters showed slight dilatation with no clinical implications so far.

Pulmonary ductal coarctation and left pulmonary artery interruption; pathology and role of neural crest and second heart field during development

Objectives

In congenital heart malformations with pulmonary stenosis to atresia an abnormal lateral ductus arteriosus to left pulmonary artery connection can lead to a localised narrowing (pulmonary ductal coarctation) or even interruption We investigated embryonic remodelling and pathogenesis of this area.

Material and methods

Normal development was studied in WntCre reporter mice (E10.0–12.5) for neural crest cells and Nkx2.5 immunostaining for second heart field cells. Data were compared to stage matched human embryos and a VEGF120/120 mutant mouse strain developing pulmonary atresia.

Results

Normal mouse and human embryos showed that the mid-pharyngeal endothelial plexus, connected side-ways to the 6^th pharyngeal arch artery. The ventral segment formed the proximal pulmonary artery. The dorsal segment (future DA) was solely surrounded by neural crest cells. The ventral segment had a dual outer lining with neural crest and second heart field cells, while the distal pulmonary artery was covered by none of these cells. The asymmetric contribution of second heart field to the future pulmonary trunk on the left side of the aortic sac (so-called pulmonary push) was evident. The ventral segment became incorporated into the pulmonary trunk leading to a separate connection of the left and right pulmonary arteries. The VEGF120/120 embryos showed a stunted pulmonary push and a variety of vascular anomalies.

Summary

Side-way connection of the DA to the left pulmonary artery is a congenital anomaly. The primary problem is a stunted development of the pulmonary push leading to pulmonary stenosis/atresia and a subsequent lack of proper incorporation of the ventral segment into the aortic sac. Clinically, the aberrant smooth muscle tissue of the ductus arteriosus should be addressed to prohibit development of severe pulmonary ductal coarctation or even interruption of the left pulmonary artery.

Unilateral interruption of pulmonary artery with pulmonary hypertension: a case for heart lung transplantation?

Unilateral interruption of pulmonary artery is a rare congenital anomaly which is usually associated with other congenital heart disease. Even more rarely it may occur in isolation. Most of the cases are incidentally detected in adulthood. Some cases develop pulmonary hypertension for yet unknown reasons; such cases usually present in infancy with right heart failure. Surgical correction in such cases is associated with adverse outcomes. Heart lung transplantation should be considered in such patients. We report a 3-year-old boy with interruption of right pulmonary artery with severe pulmonary hypertension and right heart failure who was considered for heart lung transplantation.

A literature review of systemic to pulmonary collaterals in preterm infants to emphasise their existence and clinical importance

AIM

Cardiorespiratory physiology plays an important role in neonatal care with increasing utility of point-of-care ultrasound. This review is to bring to light the importance of systemic to pulmonary collaterals (SPCs) in the preterm population without congenital heart disease (CHD) and provide a useful diagnostic tool to the neonatologist performing a cardiac ultrasound.

METHODS

Medline, PubMed, EMBASE and the Internet were searched up to November 2017 for articles in English which included SPCs in preterm infants without CHD. This comprised title, abstract and full-text screening of relevant data.

RESULTS

A total of 10 studies which included case reports, retrospective observational studies and one small prospective cohort study were identified and analysed in detail. The studies had varying focus such as variable incidence, clinical presentation, association with chronic lung disease, pathophysiology and clinical importance of SPCs. SPCs were overall thought to be prevalent, underdiagnosed and of clinical significance in preterm infants.

CONCLUSION

Systemic to pulmonary collaterals are a potential left-to-right shunt in preterm infants and may contribute to worsening chronic lung disease (CLD) or heart failure. They should be carefully looked for when performing bedside cardiac ultrasound as the findings can mimic those seen in patent ductus arteriosus (PDA).

Impact of near-infrared angiography on the quality of anatomical resection during video-assisted thoracic surgery segmentectomy

Background

The aim of the present study was to assess the impact of near-infrared angiography in guiding intraoperatively sublobar anatomical resection by video-assisted thoracic surgery (VATS).

Methods

We retrospectively analyzed data from 67 patients who underwent segmentectomy by VATS from November 2014 to November 2017 at the University Hospitals of Geneva, Switzerland. The need to modify arterial or parenchymal resection based on intraoperative near-infrared imaging was considered the primary study outcome.

Results

A total of 67 patients (28 men, 39 women, mean age 66±10 years) underwent anatomical pulmonary segmentectomy by VATS. Histological analysis revealed a primary lung tumor in 59 patients. The mean ± standard deviation (SD) operation time was 154±51 minutes. Identification of the intersegmental plane (ISP) with near-infrared angiography was achieved in 88% of patients and led to modification of the resection during segmentectomy in 7 patients (10%), avoiding inappropriate resection; 2 patients had distant tumor recurrences (3%).

Conclusions

Near-infrared angiography during VATS segmentectomy is effective for identifying ISPs, with respect to the oncological margins, as well as for correcting the anatomical resection.

A case of unusual configuration of the right bronchial arteries combined with cryptogenic severe bilateral hypertrophy

Bronchial arteries commonly originate from thoracic aorta between T5 and T6. Ectopic origins from aortic arch, supraortic trunks and their branches, coronary arteries, and even abdominal aorta have been described in the literature. In some circumstances, such as pulmonary artery malformations, chronic embolism, or inflammatory diseases of the lung, the bronchial arteries become hypertrophied and eventually could be the only supply of pulmonary circulation. Here, we describe a case of an elderly man who presented an unusual pattern of bronchial arteries of the right lung combined with severe bilateral hypertrophy of bronchial vessels. In the right side, one bronchial artery originated from the descendent aorta and anastomosed with a branch descending from the thyrocervical trunk, which, in turn, received in its path an anastomosis from the superior intercostal artery. The right lung also received a second bronchial artery that originated from the internal thoracic artery. This arterial configuration could be explained by the persistence of precostal longitudinal anastomoses during the embrionary development. Left bronchial arteries presented an orthotopic origin from the descending aorta. Arteries of both sides were very hypertrophic and tortuous resembling major aortopulmonary collateral arteries described in patients with pulmonary atresia. Hypertrophy was more pronounced in the right lung with some segments presenting a lumen diameter of 10 mm. No cardiac or vascular malformations that could explain the hypertrophy of bronchial arteries were observed. In contrast, both lungs showed clear signs of chronic inflammation and fibrosis that could be the cause of bronchial artery hypertrophy.

Endothelium in the pharyngeal arches 3, 4 and 6 is derived from the second heart field

Oxygenated blood from the heart is directed into the systemic circulation through the aortic arch arteries (AAAs). The AAAs arise by remodeling of three symmetrical pairs of pharyngeal arch arteries (PAAs), which connect the heart with the paired dorsal aortae at mid-gestation. Aberrant PAA formation results in defects frequently observed in patients with lethal congenital heart disease. How the PAAs form in mammals is not understood. The work presented in this manuscript shows that the second heart field (SHF) is the major source of progenitors giving rise to the endothelium of the pharyngeal arches 3 - 6, while the endothelium in the pharyngeal arches 1 and 2 is derived from a different source. During the formation of the PAAs 3 - 6, endothelial progenitors in the SHF extend cellular processes toward the pharyngeal endoderm, migrate from the SHF and assemble into a uniform vascular plexus. This plexus then undergoes remodeling, whereby plexus endothelial cells coalesce into a large PAA in each pharyngeal arch. Taken together, our studies establish a platform for investigating cellular and molecular mechanisms regulating PAA formation and alterations that lead to disease.

The Effects of Hemodynamic Alterations on Lung Volumes in Fetuses with Tetralogy of Fallot: An MRI Study

This study assessed whether the presence of tetralogy of Fallot (TOF) affects fetal lung development and whether these fetuses are at risk of pulmonary hypoplasia (PH). Furthermore, we investigated whether the degree of the concomitant pulmonary valve (PV) stenosis or a stenosis in the branch pulmonary arteries correlates with the fetal lung volume. Lung volumetry was performed in 16 fetuses with TOF who underwent MRI between gestational weeks 21 and 35 and in 22 controls. Fetal biometric data and the diameters of the PVs were evaluated by ultrasound. PV and branch pulmonary artery diameters were standardized (z-scores), and fetal lung volume/fetal body weight (FLV/FBW) ratios (ml/g) were calculated. The mean FLV/FBW ratio (0.031 ± 0.009 ml/g) in the TOF group was statistically significantly lower than in the control group (0.041 ± 0.009 ml/g; P = 0.003). None of the fetuses with TOF met the criterion for PH. FLV did not correlate with the degree of PV stenosis, but rather with the presence of a significant stenosis in at least one branch pulmonary artery. The presence of TOF moderately affects fetal lung growth, which is apparently not dependent on the degree of the PV stenosis. However, only an additional stenosis in at least one branch pulmonary artery was associated with a small FLV, but not with PH. Thus, reduced pulmonary blood flow may be offset by additional factors, such as the ability to establish a sufficient collateral system and to alter structural vascular size and, thus, pulmonary vascular resistance.

Heterochrony and early left-right asymmetry in the development of the cardiorespiratory system of snakes

Snake lungs show a remarkable diversity of organ asymmetries. The right lung is always fully developed, while the left lung is either absent, vestigial, or well-developed (but smaller than the right). A 'tracheal lung' is present in some taxa. These asymmetries are reflected in the pulmonary arteries. Lung asymmetry is known to appear at early stages of development in Thamnophis radix and Natrix natrix. Unfortunately, there is no developmental data on snakes with a well-developed or absent left lung. We examine the adult and developmental morphology of the lung and pulmonary arteries in the snakes Python curtus breitensteini, Pantherophis guttata guttata, Elaphe obsoleta spiloides, Calloselasma rhodostoma and Causus rhombeatus using gross dissection, MicroCT scanning and 3D reconstruction. We find that the right and tracheal lung develop similarly in these species. By contrast, the left lung either: (1) fails to develop; (2) elongates more slowly and aborts early without (2a) or with (2b) subsequent development of faveoli; (3) or develops normally. A right pulmonary artery always develops, but the left develops only if the left lung develops. No pulmonary artery develops in relation to the tracheal lung. We conclude that heterochrony in lung bud development contributes to lung asymmetry in several snake taxa. Secondly, the development of the pulmonary arteries is asymmetric at early stages, possibly because the splanchnic plexus fails to develop when the left lung is reduced. Finally, some changes in the topography of the pulmonary arteries are consequent on ontogenetic displacement of the heart down the body. Our findings show that the left-right asymmetry in the cardiorespiratory system of snakes is expressed early in development and may become phenotypically expressed through heterochronic shifts in growth, and changes in axial relations of organs and vessels. We propose a step-wise model for reduction of the left lung during snake evolution.

Development of major aorto-pulmonary collateral arteries in vegf120/120 isoform mouse embryos with tetralogy of fallot

The degree of right ventricular outflow tract obstruction, pulmonary stenosis (PS) and the development of major aorto-pulmonary collateral arteries (MAPCAs) in patients with tetralogy of Fallot (TOF) is related to clinical outcome. Vegf120/120 mutant mouse embryos develop TOF with various degrees of PS, comparable to humans. We aimed to study the ontogeny of the development of MAPCAs in this mouse model. The development of the right ventricular outflow tract, pulmonary arteries, and ductus arteriosus (DA) and formation of MAPCAs were studied in both wild type as well as Vegf120/120 mice from embryonic day 10.5 until day 19.5. Of the 49 Vegf120/120 embryos, 35 embryos (71%) had ventral displacement of the outflow tract and a subaortic ventricular septal defect. A time-related development in severity of PS to pulmonary atresia (PA) was observed. From embryonic day 12.5, hypoplasia of the DA was seen in 13 (37%) and absent DA in 12 (37%) of these embryos. The 3 (6%) embryos with PA and absent DA developed MAPCAs, after day 15.5. In all, the MAPCAs arose from both subclavian arteries, running posterior in the thoracic cavity, along the vagal nerve. The MAPCAs connected the pulmonary arteries at the site of the hilus. A time-related development of PS to PA can lead, in combination with absent DA, to the development of MAPCAs later in embryonic life as an alternative route for pulmonary perfusion in this mouse model. This finding contributes to a better understanding of the consecutive morphological changes in the development toward MAPCAs in humans.

Growth of diminutive central pulmonary arteries after right ventricle to pulmonary artery homograft implantation

BACKGROUND

The management of tetralogy of Fallot, pulmonary atresia, and major aortopulmonary collateral arteries is controversial because of the wide variability of pulmonary artery (PA) and major aortopulmonary collateral arteries morphology. Several different staged strategies have been used to promote growth of diminutive PA branches. We have preferred a right ventricular (RV)-PA homograft for symmetrical growth of the central PA branches. In this study we evaluated the success of this strategy.

METHODS

Between 2006 and 2012, 23 patients with pulmonary atresia and diminutive PAs underwent RV-PA homograft implantation. Median age was 2 months (range, 4 days to 18 months), and median body weight was 5.1 kg (range, 1.7 to 8.5 kg). The type of homograft was aortic in 8, pulmonary in 6, and femoral vein in 9. The mean diameter of the homograft was 10.5 mm (range, 6 to 16 mm). All procedures were performed on cardiopulmonary bypass. The PA diameter was measured at the time of the operation and subsequent catheterization.

RESULTS

The median size of the branch PA was 2.1 mm. In the 18 patients who had serial assessment of PA size, the right PA increased by 307% ± 184%, the left PA increased by 283% ± 139%, and the Nakata index increased from 28.8 ± 20.1 mm(2)/m(2) to 253 ± 96 mm(2)/m(2) during a median period of 347 days (range, 44 to 1,520 days). The PA growth ratio (PA growth in mm/mo) was similar between the right PA (0.42 ± 0.46 mm/mo) and the left PA (0.43 ± 0.47 mm/mo). There was no acute conduit failure. Seventeen patients required 28 percutaneous interventions for embolization of an aortopulmonary collateral or stenosis of the conduit or PA. There were no hospital deaths. Three patients died late after other procedures during a mean follow-up of 44.7 months. Twenty patients (87%) have undergone complete repair to date.

CONCLUSIONS

RV-PA homograft implantation can be performed in neonates and infants with minimal risk of acute occlusion. The RV-PA homograft promotes rapid and balanced growth of central pulmonary arteries leading to complete repair in most patients.

Unilateral absence of pulmonary artery: pathophysiology, symptoms, diagnosis and current treatment

Unilateral absence of pulmonary artery (UAPA) is a rare malformation that can present as an isolated lesion or may be associated with other congenital heart defects. UAPA is often associated with other congenital cardiovascular anomalies, such as tetralogy of Fallot, atrial septal defect, coarctation of aorta, right aortic arch, truncus arteriosus and pulmonary atresia. Diagnosis of UAPA is very difficult and is based on taking a complete medical history, physical examination and imaging examinations. Clinical symptoms include exercise intolerance, haemoptysis and recurrent respiratory infections. Adult patients with UAPA are often asymptomatic. There is no consensus regarding the treatment for UAPA. The therapeutic approach should be based on symptoms of the patient, pulmonary artery anatomy and associated aortopulmonary collaterals. Treatment options for these patients include partial or total pneumonectomy, closure of selected collateral arteries not solely responsible for pulmonary blood flow or a primary versus staged pulmonary artery anastomosis. This review summarizes pathophysiology, symptomatology and current diagnosis and treatment of this disease.

Expression of the BMP receptor Alk3 in the second heart field is essential for development of the dorsal mesenchymal protrusion and atrioventricular septation

RATIONALE

The dorsal mesenchymal protrusion (DMP) is a prong of mesenchyme derived from the second heart field (SHF) located at the venous pole of the developing heart. Recent studies have shown that perturbation of its development is associated with the pathogenesis of atrioventricular (AV) septal defect. Although the importance of the DMP to AV septation is now established, the molecular and cellular mechanisms underlying its development are far from fully understood. Prior studies have demonstrated that bone morphogenetic protein (BMP) signaling is essential for proper formation of the AV endocardial cushions and the cardiac outflow tract. A role for BMP signaling in regulation of DMP development remained to be elucidated.

OBJECTIVE

To determine the role of BMP signaling in DMP development.

METHODS AND RESULTS

Conditional deletion of the BMP receptor Alk3 from venous pole SHF cells leads to impaired formation of the DMP and a completely penetrant phenotype of ostium primum defect, a hallmark feature of AV septal defects. Analysis of mutants revealed decreased proliferative index of SHF cells and, consequently, reduced number of SHF cells at the cardiac venous pole. In contrast, volume and expression of markers associated with proliferation and active BMP/transforming growth factor β signaling were not significantly altered in the AV cushions of SHF-Alk3 mutants.

CONCLUSIONS

BMP signaling is required for expansion of the SHF-derived DMP progenitor population at the cardiac venous pole. Perturbation of Alk3-mediated BMP signaling from the SHF results in impaired development of the DMP and ostium primum defects.

The 22q11 deletion: DiGeorge and velocardiofacial syndromes and the role of TBX1

Hemizygous deletion of 22q11 affects approximately 1:4000 live births and may give rise to many different malformations but classically results in a constellation of phenotypes that receive a diagnosis of DiGeorge syndrome or velocardiofacial syndrome. Particularly affected are the heart and great vessels, the endocrine glands of the neck, the face, the soft palate, and cognitive development. Although up to 50 genes may be deleted, it is haploinsufficiency of the transcription factor TBX1 that is thought to make the greatest contribution to the disorder. Mouse embryos are exquisitely sensitive to varying levels of Tbx1 mRNA, and Tbx1 is required in all three germ layers of the embryonic pharyngeal region for normal development. TBX1 controls cell proliferation and affects cellular differentiation in a cell autonomous fashion, but it also directs non-cell autonomous effects, most notably in the signaling between pharyngeal surface ectoderm and the rostral neural crest. TBX1 interacts with several signaling pathways, including fibroblast growth factor, retinoic acid, CTNNB1 (formerly known as β-catenin), and bone morphogenetic protein (BMP), and may regulate pathways by both DNA-binding and non-binding activity. In addition to the structural abnormalities seen in 22q11 deletion syndrome (DS) and Tbx1 mutant mouse models, patients reaching adolescence and adulthood have a predisposition to psychiatric illness. Whether this has a developmental basis and, if so, which genes are involved is an ongoing strand of research. Thus, knowledge of the genetic and developmental mechanisms underlying 22q11DS has the potential to inform about common disease as well as developmental defect.

Development of the pulmonary vein and the systemic venous sinus: an interactive 3D overview

Knowledge of the normal formation of the heart is crucial for the understanding of cardiac pathologies and congenital malformations. The understanding of early cardiac development, however, is complicated because it is inseparably associated with other developmental processes such as embryonic folding, formation of the coelomic cavity, and vascular development. Because of this, it is necessary to integrate morphological and experimental analyses. Morphological insights, however, are limited by the difficulty in communication of complex 3D-processes. Most controversies, in consequence, result from differences in interpretation, rather than observation. An example of such a continuing debate is the development of the pulmonary vein and the systemic venous sinus, or “sinus venosus”. To facilitate understanding, we present a 3D study of the developing venous pole in the chicken embryo, showing our results in a novel interactive fashion, which permits the reader to form an independent opinion. We clarify how the pulmonary vein separates from a greater vascular plexus within the splanchnic mesoderm. The systemic venous sinus, in contrast, develops at the junction between the splanchnic and somatic mesoderm. We discuss our model with respect to normal formation of the heart, congenital cardiac malformations, and the phylogeny of the venous tributaries.

Development of the venous pole of the heart in the frog Xenopus laevis: a morphological study with special focus on the development of the venoatrial connections

The heart of lung-breathing vertebrates normally shows an asymmetric arrangement of its venoatrial connections along the left-right (L-R) body axis. The systemic venous tributaries empty into the right atrium while the pulmonary venous tributaries empty into the left atrium. The ways by which this asymmetry evolves from the originally symmetrically arranged embryonic venous heart pole are poorly defined. Here we document the development of the venous heart pole in Xenopus laevis (stages 40-46). We show that, prior to the appearance of the mouth of the common pulmonary vein (MCPV), the systemic venous tributaries empty into a bilaterally symmetric chamber (sinus venosus) that is demarcated from the developing atriums by a circular ridge of tissue (sinu-atrial ridge). A solitary MCPV appears during stage 41. From the time point of its first appearance onwards, the MCPV lies cranial to the sinu-atrial ridge and to the left of the developing interatrial septum and body midline. L-R lineage analysis shows that the interatrial septum and MCPV both derive from the left body half. The CPV, therefore, opens from the beginning into the future left atrium. The definitive venoatrial connections are established by the formation of a septal complex that divides the lumen of the venous heart pole into systemic and pulmonary venous flow pathways. This complex arises from the anlage of the interatrial septum and the left half of the sinu-atrial ridge.

Unifocalization of major aortopulmonary collateral arteries in pulmonary atresia with ventricular septal defect is essential to achieve excellent outcomes irrespective of native pulmonary artery morphology

OBJECTIVE

Pulmonary atresia with ventricular septal defect and major aortopulmonary collateral arteries is a complex lesion with a high rate of natural attrition. We evaluated the outcomes of our strategy of unifocalization in the management of these patients.

METHODS

From 1989 to 2008, 216 patients entered a pathway aiming for complete repair by unifocalizing major aortopulmonary arteries to a right ventricle-pulmonary artery conduit with ventricular septal defect closure. Where ventricular septation was not possible, definitive repair was considered to include pulmonary artery reconstruction and a right ventricle-pulmonary artery conduit or systemic shunt. Native pulmonary artery morphology was classified into confluent intrapericardial (n = 139), confluent intrapulmonary (n = 51), and nonconfluent intrapulmonary (n = 26).

RESULTS

A total of 203 patients (85%) had definitive repair at a median age of 2.0 years. There was no statistically significant difference in survival after complete repair among the 3 morphologic pulmonary artery groups (P = .18). A total of 132 patients (56%) had complete repair with ventricular septal defect closure, as a single procedure in 111 patients and a staged procedure in 21 patients. Focalization of major aortopulmonary collateral arteries with proven long-term patency with the right ventricle was associated with a survival benefit compared with 14 patients in whom unifocalization was not possible and who had only systemic shunts. Overall survival was 89% at 3 years after definitive repair. During follow-up, 190 patients required 196 catheter reinterventions and 60 surgical reinterventions.

CONCLUSION

By using a strategy of unifocalization, intrapericardial pulmonary artery reconstruction, and right ventricle-pulmonary artery conduit, excellent long-term survival can be achieved in this group of patients even in the absence of native intrapericardial pulmonary arteries.

Loss of unc45a precipitates arteriovenous shunting in the aortic arches

Aortic arch malformations are common congenital disorders that are frequently of unknown etiology. To gain insight into the factors that guide branchial aortic arch development, we examined the process by which these vessels assemble in wild type zebrafish embryos and in kurzschluss(tr12) (kus(tr12)) mutants. In wild type embryos, each branchial aortic arch first appears as an island of angioblasts in the lateral pharyngeal mesoderm, then elaborates by angiogenesis to connect to the lateral dorsal aorta and ventral aorta. In kus(tr12) mutants, angioblast formation and initial sprouting are normal, but aortic arches 5 and 6 fail to form a lumenized connection to the lateral dorsal aorta. Blood enters these blind-ending vessels from the ventral aorta, distending the arteries and precipitating fusion with an adjacent vein. This arteriovenous malformation (AVM), which shunts nearly all blood directly back to the heart, is not exclusively genetically programmed, as its formation correlates with blood flow and aortic arch enlargement. By positional cloning, we have identified a nonsense mutation in unc45a in kus(tr12) mutants. Our results are the first to ascribe a role for Unc45a, a putative myosin chaperone, in vertebrate development, and identify a novel mechanism by which an AVM can form.

Clinical investigation of systemic-pulmonary collateral arteries

Systemic-pulmonary collateral arteries are known to develop in children with congenital heart disease, chronic pulmonary infection, and prematurity. At present, these abnormal connections between the systemic and the pulmonary systems are thought to develop from the vascular plexus, which normally gives rise to the pulmonary and bronchial vasculature. The objective of this study was to review our patients with systemic-pulmonary collateral arteries and evaluate possible risk factors. The records of patients with systemic-pulmonary collateral arteries seen at our hospital over a 4-year period were retrospectively reviewed. They were grouped into one of the following five categories: premature, heart disease, pulmonary disease, healthy, and others. Age, gender, weight, and the results of echocardiography were recorded, as was the condition on follow-up. We reviewed the records of 284 patients: 130 premature, 13 heart disease, 30 pulmonary disease, 92 healthy, and 19 others. Over the same period, 3314 healthy 1-month-old infants had undergone echocardiography for health screening. Among the 92 healthy children with systemic-pulmonary collateral arteries, 52 were diagnosed at the health-screening exam. Therefore, we estimate the incidence of unsuspected systemic-pulmonary collateral arteries in healthy 1-month-old infants to be 1.57% (52/3314). We conclude that systemic-pulmonary collateral arteries may be present normally after birth and then gradually disappear. However, if there are certain predisposing factors, they may persist in order to augment pulmonary flow.

Microvascular endowment in the developing chicken embryo lung

In the current study, the contribution of the major angiogenic mechanisms, sprouting and intussusception, to vascular development in the avian lung has been demonstrated. Sprouting guides the emerging vessels to form the primordial vascular plexus, which successively surrounds and encloses the parabronchi. Intussusceptive angiogenesis has an upsurge from embryonic day 15 (E15) and contributes to the remarkably rapid expansion of the capillary plexus. Increased blood flow stimulates formation of pillars (the archetype of intussusception) in rows, their subsequent fusion and concomitant delineation of slender, solitary vascular entities from the disorganized meshwork, thus crafting the organ-specific angioarchitecture. Morphometric investigations revealed that sprouting is preponderant in the early period of development with a peak at E15 but is subsequently supplanted by intussusceptive angiogenesis by the time of hatching. Quantitative RT-PCR revealed that moderate levels of basic FGF (bFGF) and VEGF-A were maintained during the sprouting phase while PDGF-B remained minimal. All three factors were elevated during the intussusceptive phase. Immunohistoreactivity for VEGF was mainly in the epithelial cells, whereas bFGF was confined to the stromal compartment. Temporospatial interplay between sprouting and intussusceptive angiogenesis fabricates a unique vascular angioarchitecture that contributes to the establishment of a highly efficient gas exchange system characteristic of the avian lung.

Major aorto-pulmonary collateral arteries (MAPCAs)--Bronchial fistula presenting as tracheotomy bleed

Tracheal hemorrhage is a common occurrence in pediatric patients with long-term tracheotomies. The majority of these events are related to self-limited etiologies, such as granulation tissue or suction trauma. Tracheo-arterial fistula, however, represents a frequently fatal form of tracheal hemorrhage that may initially be difficult to distinguish from other causes. Previous reports have described the pathophysiology, presentation and management of tracheo-arterial fistula involving the innominate artery. We describe a case of a 21-month-old male with a history of significant congenital cardiac malformations and chronic tracheotomy tube dependence who presented with intermittent, brisk bleeding from the tracheotomy tube. He was ultimately diagnosed with and treated for an arterio-bronchial fistula from a major aorto-pulmonary collateral artery. We review the etiology and management of this disorder.

Apoptosis as an instrument in cardiovascular development

Cell death as a phenomenon in embryonic development was first described over 100 years ago. Approximately 30 years ago the process was named apoptosis, and its involvement is now recognized in many life processes, in virtually every animal species, and from fertilization to the death of an organism. In cardiovascular development, it coincides with major developmental processes in specific time windows. Both intrinsic (controlled by mitochondrial activity) and extrinsic (starting with death receptors) apoptotic pathways co-regulate developmental mechanisms. During cardiac development, many cell populations are recruited to the heart, where they differentiate into cardiomyocytes, fibroblasts, smooth muscle cells, endocardial and endothelial cells lining the inner surfaces, and epicardial cells lining the outer contours. In particular, neural crest-derived cell populations, which migrate to specific locations in the heart, are prone to apoptosis. During the complex geometric changes that occur in the primary heart tube and connected vessel segments, proper interaction of the respective cell populations guarantees the ensuing steps of differentiation. Growth factors, including endothelin, VEGF, and TGF-beta, as well as other factors, such as FasL, play dominant roles in these phases. Transgenic and knockout studies have provided strong evidence for aberrant patterns of apoptosis resulting in congenital malformations and syndromic malformations, including septation anomalies, interrupted aortic arch segments, coronary anomalies, and DiGeorge syndrome. Embryonic remodeling of the arterial system, including the coronary arteries, is accompanied by apoptosis patterns, the disruption of which results in severe malformations. It is interesting to note that hemodynamic factors, such as flow-driven shear stress, regulate the expression of genes that are important for signaling molecules such as endothelin and NO-synthase. In general, high shear stress protects against apoptosis, thus preventing the onset of disease processes in the fully-grown vasculature, and regulating the remodeling of the vascular system in the embryo.

Vasculogenesis drives pulmonary vascular growth in the developing chick embryo

Formation of the pulmonary vasculature has been described as occurring by outgrowth of existing vessels (angiogenesis), de novo formation of new vessels (vasculogenesis), or a combination of both processes. Uncertainty about the contribution of angiogenesis and vasculogenesis to pulmonary vascular formation is partly due to methodologic approaches. Evidence in favor of angiogenesis stems from studies that used vascular-filling methods. Such methods identify only directly continuous lumina. Evidence for vasculogenesis has been provided by the use of molecular markers of blood vessel endothelium. Use of both methods has not been combined in the same species, however. We hypothesized, based on published evidence from quail and mouse, that chick pulmonary vascular formation occurs by vasculogenesis. To test that hypothesis, we used vascular filling, serial section, and immunohistochemical methods to analyze the developing lungs of chick embryos from Hamburger and Hamilton stages 20 to 43. Vascular filling suggested that the lumen of the pulmonary arteries sprouted from the sixth pharyngeal arch arteries. However, serial sections and immunohistochemical localization of fetal liver kinase-1 protein, the receptor for vascular endothelial growth factor, showed that the pulmonary arterial tree formed from endothelial cell precursors and coalescence of isolated blood vessels in the mediastinal splanchnic mesenchyme centrally to the developing lung tissue distally. Pulmonary veins grew from the left atrium to the developing lungs. Pulmonary blood vessel formation occurred continuously throughout the embryonic period studied. Our results show that vasculogenesis is the main process by which the pulmonary vasculature forms in the developing chick embryo.

Lung vascular development: implications for the pathogenesis of bronchopulmonary dysplasia

Past studies have primarily focused on how altered lung vascular growth and development contribute to pulmonary hypertension. Recently, basic studies of vascular growth have led to novel insights into mechanisms underlying development of the normal pulmonary circulation and the essential relationship of vascular growth to lung alveolar development. These observations have led to new concepts underlying the pathobiology of developmental lung disease, especially the inhibition of lung growth that characterizes bronchopulmonary dysplasia (BPD). We speculate that understanding basic mechanisms that regulate and determine vascular growth will lead to new clinical strategies to improve the long-term outcome of premature babies with BPD.

3D reconstruction of the vessels that enter the right atrium of the mouse heart at Theiler Stage 20

Computer-generated 3D reconstructions of a serially sectioned mouse embryo at Theiler Stage (TS) 20 (E 12-12.5 d.p.c.) were studied. This study investigated the vessels that enter the right atrium of the heart and the drainage of the ductus venosus. It was principally undertaken to allow a comparison to be made between the situation in the mouse and at a comparable stage of human development. Later stages of prenatal development were also studied in the mouse by the analysis of serially sectioned embryos at TS 21-26. As no left brachiocephalic vein forms in the mouse, unlike the situation in the human, the left (cranial) superior vena cava drains via the left common cardinal vein, later to become the coronary sinus, into the floor of the right atrium. It was also noted that unlike the situation in the human, at no stage during the prenatal period does the ductus venosus enter the right atrium. Even shortly before birth, it enters the intra-hepatic part of the inferior vena cava at a considerable distance caudal to the right atrium. This study indicates that the haemodynamics of the prenatal cardiac circulation in the mouse differs significantly from that in the human.

Basics of cardiac development for the understanding of congenital heart malformations

Cardiovascular development has become a crucial element of transgene technology in that many transgenic and knockout mice unexpectedly present with a cardiac phenotype, which often turns out to be embryolethal. This demonstrates that formation of the heart and the connecting vessels is essential for the functioning vertebrate organism. The embryonic mesoderm is the source of both the cardiogenic plate, giving rise to the future myocardium as well as the endocardium that will line the system on the inner side. Genetic cascades are unravelled that direct dextral looping and subsequent secondary looping and wedging of the outflow tract of the primitive heart tube. This tube consists of a number of transitional zones and intervening primitive cardiac chambers. After septation and valve formation, the mature two atria and two ventricles still contain elements of the primitive chambers as well as transitional zones. An essential additional element is the contribution of extracardiac cell populations like neural crest cells and epicardium-derived cells. Whereas the neural crest cell is of specific importance for outflow tract septation and formation of the pharyngeal arch arteries, the epicardium-derived cells are essential for proper maturation of the myocardium and coronary vascular formation. Inductive signals, sometimes linked to apoptosis, of the extracardiac cells are thought to be instructive for differentiation of the conduction system. In summary, cardiovascular development is a complex interplay of many cell-cell and cell-matrix interactions. Study of both (transgenic) animal models and human pathology is unravelling the mechanisms underlying congenital cardiac anomalies.

Pulmonary atresia, ventricular septal defect, and multiple aorta pulmonary collateral arteries

Pulmonary atresia with ventricular septal defect and major aorta pulmonary collaterals arteries is a rare and complex congenital cardiac defect. There is considerable variability in the anatomy, morphology, and geometry of the native pulmonary arteries and the collateral vessels. While the ultimate goal of therapy is a biventricular correction with complete unifocalization, establishment of right ventricular to pulmonary arterial continuity, and closure of all intracardiac defects, achieving this endpoint can be frustrating and difficult. A carefully considered approach for each individual patient is required. Patients with appropriate anatomy may undergo a definitive single-stage unifocalization and biventricular correction in early infancy. Patients with less favorable anatomy will require a more eclectic approach. While our knowledge of the genetics of this defect is rudimentary, further advances in genetic understanding and technology hold tremendous promise for the development of future therapies.

Development of pharyngeal arch arteries in early mouse embryo

The formation and transformation of the pharyngeal arch arteries in the mouse embryo, from 8.5 to 13 days of gestation (DG), was observed using scanning electron microscopy of vascular casts and graphic reconstruction of 1-microm serial epoxy-resin sections. Late in 8.5-9DG (12 somites), the paired ventral aortae were connected to the dorsal aortae via a loop anterior to the foregut which we call the 'primitive aortic arch', as in the chick embryo. The primitive aortic arch extended cranio-caudally to be transformed into the primitive internal carotid artery, which in turn gave rise to the primitive maxillary artery and the arteries supplying the brain. The second pharyngeal arch artery (PAA) appeared late in 9-9.5DG (16-17 somites), and the ventral aorta bent dorsolaterally to form the first PAA anterior to the first pharyngeal pouch by early in 9.5-10DG (21-23 somites). The third PAA appeared early in 9.5-10DG (21-23 somites), the fourth late in 9.5-10DG (27-29 somites), and the sixth at 10DG (31-34 somites). By 10.5DG (35-39 somites), the first and second PAAs had been transformed into other arteries, and the third, fourth and sixth PAAs had developed well, though the PAA system still exhibited bilateral symmetry. By 13DG, the right sixth PAA had disappeared, and the remaining PAAs formed an aortic-arch system that was almost of the adult type.

Systemic-to-pulmonary blood supply in Tetralogy of Fallot with pulmonary atresia

Tetralogy of Fallot with pulmonary atresia is one of the most challenging congenital cardiac malformations, for the morphologist, cardiologist and surgeon alike. Much of the difficulty in this lesion concerns the nature and development of pulmonary arterial supply, and the manner in which complete segmental supply to the lungs can be successfully restored or maintained. In this review, we discuss the anatomy and nomenclature of the lesion, emphasising the variability that can occur in pulmonary arterial anatomy, particularly in the presence of systemic-to-pulmonary collateral arteries. We speculate on the likely embryologic origins of these connections. Then by means of anatomic-clinical correlations, we emphasise the diagnostic approach to delineating the origin and extent of the pulmonary vasculature.