Complete transposition of the great arteries: types and morphogenesis of ventriculoarterial discordance

Pathogenesis and Surgical Treatment of Dextro-Transposition of the Great Arteries (D-TGA): Part II

Dextro-transposition of the great arteries (D-TGA) is the second most common cyanotic heart disease, accounting for 5-7% of all congenital heart defects (CHDs). It is characterized by ventriculoarterial (VA) connection discordance, atrioventricular (AV) concordance, and a parallel relationship with D-TGA. As a result, the pulmonary and systemic circulations are separated [the morphological right ventricle (RV) is connected to the aorta and the morphological left ventricle (LV) is connected to the pulmonary artery]. This anomaly is included in the group of developmental disorders of embryonic heart conotruncal irregularities, and their pathogenesis is multifactorial. The anomaly's development is influenced by genetic, epigenetic, and environmental factors. It can occur either as an isolated anomaly, or in association with other cardiac defects. The typical concomitant cardiac anomalies that may occur in patients with D-TGA include ventriculoseptal defects, patent ductus arteriosus, left ventricular outflow tract obstruction (LVOTO), mitral and tricuspid valve abnormalities, and coronary artery variations. Correction of the defect during infancy is the preferred treatment for D-TGA. Balloon atrial septostomy (BAS) is necessary prior to the operation. The recommended surgical correction methods include arterial switch operation (ASO) and atrial switch operation (AtrSR), as well as the Rastelli and Nikaidoh procedures. The most common postoperative complications include coronary artery stenosis, neoaortic root dilation, neoaortic insufficiency and neopulmonic stenosis, right ventricular (RV) outflow tract obstruction (RVOTO), left ventricular (LV) dysfunction, arrhythmias, and heart failure. Early diagnosis and treatment of D-TGA is paramount to the prognosis of the patient. Improved surgical techniques have made it possible for patients with D-TGA to survive into adulthood.

Conotruncal Heart Defects: A Narrative Review of Molecular Genetics, Genomics Research and Innovation

Congenital heart defects (CHDs) are most prevalent cardiac defects that occur at birth, leading to significant neonatal mortality and morbidity, especially in the developing nations. Among the CHDs, conotruncal heart defects (CTDs) are particularly noteworthy, comprising a significant portion of congenital cardiac anomalies. While advances in imaging and surgical techniques have improved the diagnosis, prognosis, and management of CTDs, their molecular genetics and genomic substrates remain incompletely understood. This expert review covers the recent advances from January 2016 onward and examines the complexities surrounding the genetic etiologies, prevalence, embryology, diagnosis, and clinical management of CTDs. We also emphasize the known copy number variants and single nucleotide variants associated with CTDs, along with the current planetary health research efforts aimed at CTDs in large cohort studies. In all, this comprehensive narrative review of molecular genetics and genomics research and innovation on CTDs draws from and highlights selected works from around the world and offers new ideas for advances in CTD diagnosis, precision medicine interventions, and accurate assessment of prognosis and recurrence risks.

Human Genetics of d-Transposition of Great Arteries

Although several genes underlying occurrence of transposition of the great arteries have been found in the mouse, human genetics of the most frequent cyanotic congenital heart defect diagnosed in neonates is still largely unknown. Development of the outflow tract is a complex process which involves the major genes of cardiac development, acting on myocardial cells from the anterior second heart field, and on mesenchymal cells from endocardial cushions. These genes, coding for transcription factors, interact with each other, and their differential expression conditions the severity of the phenotype. A precise description of the anatomic phenotypes is mandatory to achieve a better comprehension of the complex mechanisms responsible for transposition of the great arteries.

Lodewyk H.S. van Mierop (March 31, 1927-October 17, 2021): a true giant

We honour a great man and a true giant. Lodewyk H.S. van Mierop (March 31, 1927 - October 17, 2021), known as Bob, was not only a Paediatric Cardiologist but also a dedicated Scientist. He made many significant and ground-breaking contributions to the fields of cardiac anatomy and embryology. He was devoted as a teacher, spending many hours with medical students, Residents, and Fellows, all of whom appreciated his regularly scheduled educational sessions. Those of us who were fortunate to know and spend time with him will always remember his great mind, his willingness to share his knowledge, and his ability to encourage spirited and fruitful discussions. His life was most productive, and he will long be remembered by many through his awesome and exemplary scientific contributions.His legacy continues to influence the current and future generations of surgeons and all providers of paediatric and congenital cardiac care through the invaluable archive he established at University of Florida in Gainesville: The University of Florida van Mierop Heart Archive. Undoubtedly, with these extraordinary contributions to the fields of cardiac anatomy and embryology, which were way ahead of his time, Professor van Mierop was a true giant in Paediatric Cardiology. The invaluable archive he established at University of Florida in Gainesville, The University of Florida van Mierop Heart Archive, has been instrumental in teaching medical students, Residents, Medical Fellows, and Surgical Fellows. Only a handful of similar archives exist across the globe, and these archives are the true legacy of giants such as Dr. van Mierop. We have an important obligation to leave no stone unturned to continue to preserve these archives for the future generations of surgeons, physicians, all providers of paediatric and congenital cardiac care, and, most importantly, our patients.

Commissural Malalignment as a predictor of coronary artery abnormalities in patients with transposition of great arteries

Background

In patients with transposition of the great arteries (TGA), commissural malalignment (CM) between semilunar valves may be associated with abnormal coronary (CA) pattern. We intend to assess the degree of CM with incidence of unusual CA anatomy.

Methods

We proposed a ratio to measure the distance of both ends of the anterior facing sinuses of the pulmonary valve from the facing commissure of the aortic valve. We labeled it as D1 and D2 distance. A ratio (C ratio) of the smaller distance (either D1 or D2 whichever is shorter) over the sum of both D1 and D2 was taken (D1 or D2 whichever is shorter / D1 + D2). We related this ratio with the incidence of the unusual CA anatomy in D-TGA patients.

Results

We had a total of 158 patients. We defined the point beyond which the C-Ratio becomes significantly associated with abnormal coronary artery pattern, this represents the median effective level (EL50). The EL50 of the C-Ratio was found to be equal to 31% (0.31). The prediction revealed that the CA pattern would most probably be usual when there is a minor commissural malalignment (C-Ratio less than the EL50) and most probably be unusual when there is a major malalignment (C-Ratio is greater than the EL50). The sensitivity was 71% and the specificity 88% (p-value < 0.0001).

Conclusions

The C-Ratio helps to categorize the degree of CM as minor (less than 0.31) or major (more than 0.31). A higher C-Ratio predicts a higher incidence of unusual CA pattern.

Fetal and postnatal echocardiographic imaging of transposition of the great arteries with the aortic valve posterior to the pulmonary valve

Transposition of the great arteries (TGA) with a posterior aorta is an uncommon but historically important variant of TGA. In this arrangement, the aorta is posterior to the pulmonary valve, maintains fibrous continuity with the mitral valve, and arises from the right ventricle. We present a case of fetal echocardiography demonstrating TGA with a posterior aorta. Postnatal transthoracic echocardiography and intra-operative assessment confirm the anatomy. To the best of our knowledge, this is the first published case of this anatomic lesion by fetal echocardiography.

Some Isolated Cardiac Malformations Can Be Related to Laterality Defects

Human beings are characterized by a left–right asymmetric arrangement of their internal organs, and the heart is the first organ to break symmetry in the developing embryo. Aberrations in normal left–right axis determination during embryogenesis lead to a wide spectrum of abnormal internal laterality phenotypes, including situs inversus and heterotaxy. In more than 90% of instances, the latter condition is accompanied by complex and severe cardiovascular malformations. Atrioventricular canal defect and transposition of the great arteries—which are particularly frequent in the setting of heterotaxy—are commonly found in situs solitus with or without genetic syndromes. Here, we review current data on morphogenesis of the heart in human beings and animal models, familial recurrence, and upstream genetic pathways of left–right determination in order to highlight how some isolated congenital heart diseases, very common in heterotaxy, even in the setting of situs solitus, may actually be considered in the pathogenetic field of laterality defects.

Pdgfrα functions in endothelial-derived cells to regulate neural crest cells and the development of the great arteries

Originating as a single vessel emerging from the embryonic heart, the truncus arteriosus must septate and remodel into the aorta and pulmonary artery to support postnatal life. Defective remodeling or septation leads to abnormalities collectively known as conotruncal defects, which are associated with significant mortality and morbidity. Multiple populations of cells must interact to coordinate outflow tract remodeling, and the cardiac neural crest has emerged as particularly important during this process. Abnormalities in the cardiac neural crest have been implicated in the pathogenesis of multiple conotruncal defects, including persistent truncus arteriosus, double outlet right ventricle and tetralogy of Fallot. However, the role of the neural crest in the pathogenesis of another conotruncal abnormality, transposition of the great arteries, is less well understood. In this report, we demonstrate an unexpected role of Pdgfra in endothelial cells and their derivatives during outflow tract development. Loss of Pdgfra in endothelium and endothelial-derived cells results in double outlet right ventricle and transposition of the great arteries. Our data suggest that loss of Pdgfra in endothelial-derived mesenchyme in the outflow tract endocardial cushions leads to a secondary defect in neural crest migration during development.

Summary: Loss of Pdgfrα in endothelial-derived mesenchyme results in defective neural crest behavior and is associated with conotruncal defects including, surprisingly, transposition of the great arteries.

Cardiac Embryology and Molecular Mechanisms of Congenital Heart Disease: A Primer for Anesthesiologists

Congenital heart disease is diagnosed in 0.4% to 5% of live births and presents unique challenges to the pediatric anesthesiologist. Furthermore, advances in surgical management have led to improved survival of those patients, and many adult anesthesiologists now frequently take care of adolescents and adults who have previously undergone surgery to correct or palliate congenital heart lesions. Knowledge of abnormal heart development on the molecular and genetic level extends and improves the anesthesiologist's understanding of congenital heart disease. In this article, we aim to review current knowledge pertaining to genetic alterations and their cellular effects that are involved in the formation of congenital heart defects. Given that congenital heart disease can currently only occasionally be traced to a single genetic mutation, we highlight some of the difficulties that researchers face when trying to identify specific steps in the pathogenetic development of heart lesions.

The Spectrum of Congenital Heart Disease with Transposition of the Great Arteries from the Cardiac Registry of the University of Padua

Transposition of the great arteries (TGA) is a cardiac condition in which the arterial trunks arise from the inappropriate ventricle: the aorta from the right ventricle and the pulmonary trunk from the left ventricle [discordant ventriculo-arterial (VA) connection]. In complete TGA, the discordant VA connection is associated with situs solitus or inversus and concordant atrioventricular (AV) connection. The hemodynamic consequence of these combined connections is that systemic and pulmonary circulations function in "parallel" rather than in "series". The presence of situs solitus or inversus associated with both AV and VA discordant connections characterizes a different anatomical complex known as "corrected TGA." In these hearts, the double discordance at AV and VA levels permits a normal sequence of the blood flow from the right atrium to the pulmonary artery and from the left atrium to the aorta. The systemic and pulmonary circulation in these hearts functions regularly in series, and the blood sequence is "physiologically corrected." Thus, the term transposition, either complete or corrected, identifies two precise, different anatomical complexes, both characterized by VA discordance. However, among congenital heart disease (CHD), there are other anatomical complexes with discordant VA connection in the setting of isomeric atrial situs (right or left) or of univentricular AV connections (double inlet or absent connections). In these latter conditions, the term "transposition" is still necessary to stress that the great arteries are "transposed" in relation to the ventricular septum (aorta from the right ventricle and pulmonary trunk from the left ventricle) but certainly does not figure out the anatomical complexes named complete or corrected transposition. We reviewed the hearts with discordant VA connection of our Anatomical Collection, consisting of 1,640 specimens with CHD, with the aim to discuss the anatomy and the frequency of the anatomical variants of TGA and to clarify terminology and classification. The knowledge of the precise anatomy of these malformation are really important for clinical diagnosis and surgical planning.

Transposition of great arteries: new insights into the pathogenesis

Transposition of great arteries (TGA) is one of the most common and severe congenital heart diseases (CHD). It is also one of the most mysterious CHD because it has no precedent in phylogenetic and ontogenetic development, it does not represent an alternative physiological model of blood circulation and its etiology and morphogenesis are still largely unknown. However, recent epidemiologic, experimental, and genetic data suggest new insights into the pathogenesis. TGA is very rarely associated with the most frequent genetic syndromes, such as Turner, Noonan, Williams or Marfan syndromes, and in Down syndrome, it is virtually absent. The only genetic syndrome with a strong relation with TGA is Heterotaxy. In lateralization defects TGA is frequently associated with asplenia syndrome. Moreover, TGA is rather frequent in cases of isolated dextrocardia with situs solitus, showing link with defect of visceral situs. Nowadays, the most reliable method to induce TGA consists in treating pregnant mice with retinoic acid or with retinoic acid inhibitors. Following such treatment not only cases of TGA with d-ventricular loop have been registered, but also some cases of congenitally corrected transposition of great arteries (CCTGA). In another experiment, the embryos of mice treated with retinoic acid in day 6.5 presented Heterotaxy, suggesting a relationship among these morphologically different CHD. In humans, some families, beside TGA cases, present first-degree relatives with CCTGA. This data suggest that monogenic inheritance with a variable phenotypic expression could explain the familial aggregation of TGA and CCTGA. In some of these families we previously found multiple mutations in laterality genes including Nodal and ZIC3, confirming a pathogenetic relation between TGA and Heterotaxy. These overall data suggest to include TGA in the pathogenetic group of laterality defects instead of conotruncal abnormalities due to ectomesenchymal tissue migration.

Double outlet right ventricle versus aortic dextroposition: morphologically distinct defects

This study concerns the morphological differentiation between double outlet right ventricle (DORV) and aortic dextroposition (AD) defects, namely tetralogy of Fallot and Eisenmenger anomaly. Indeed, despite the similar condition in terms of sequential ventriculo-arterial connections, DORV and AD are two distinct morphological entities. It is proposed that the borderline between these two groups of malformations is represented by the specific insertion of the infundibular septum into the left anterior cranial division of the septomarginal trabeculation (or septal band) occurring in ADs and lacking in DORV. Furthermore, the spiraliform versus straight parallel arrangement of the great arteries in the two groups of anomalies is emphasized as an additional and distinctive morphological feature. Emphasis is also given to the association of straight parallel great arteries conotruncal malformations, DORV and transposition of the great arteries, with the asplenia type of heterotaxy laterality defects. Within this context, the absence of subaortic ventricular septal defect and concomitantly of spiraliform great arteries in the asplenia group of heterotaxy anomalies, as detected by this study, further substantiates our belief of not mixing collectively the ADs with the DORV in clinico-pathological diagnosis.

'Big-eyed frog' sign on spatiotemporal image correlation (STIC) in the antenatal diagnosis of transposition of the great arteries

OBJECTIVE

To determine the value of simultaneous visualization of the cross-sectional view of both atrioventricular (AV) valves, the pulmonary artery and the aorta (en-face view of the AV valves and great vessels) in the identification of fetuses with transposition of the great arteries (TGA).

METHODS

This was a retrospective analysis of volume datasets obtained with the spatiotemporal image correlation (STIC) technique from 56 fetuses with and 30 fetuses without congenital heart defects. Volume datasets were reviewed offline to compare the en-face view of the AV valves and great vessels between fetuses with normal echocardiography and those with TGA.

RESULTS

The en-face view of both AV valves and great vessels in fetuses with TGA displayed the main pulmonary artery situated side-by-side with the aorta ('big-eyed frog' sign). In contrast, fetuses with normal hearts did not have this characteristic sonographic sign. This novel sonographic sign also helped to identify additional cases of TGA in 17 fetuses with complex heart defects.

CONCLUSION

The big-eyed frog sign may prove helpful in the prenatal diagnosis of TGA.

Cyanotic congenital heart disease with increased pulmonary blood flow

Pediatricians daily encounter children with systemic cyanosis. The numerous reasons for cyanosis in neonates and infants include pulmonary, hematologic, toxic, and cardiac causes. Congenital heart defects may cause cyanosis. Often, an obvious cardiac reason for cyanosis is decreased PBF; however, several congenital heart defects cause systemic cyanosis with increased PBF, such as TGA, truncus arteriosus, and TAPVR. Because neonates are discharged from the hospital soon after birth, this magnifies the importance of each physical examination. Pediatricians need to remain alert for children who have symptoms of increased PBF with or without cyanosis. With advances in the diagnosis and treatment of patients with CHD, corrective procedures can be performed at many ages.

Anatomic spectrum of abnormal ventriculoarterial connections: surgical implications

To clarify the salient anatomic features of surgical significance, we investigated 33 specimens representing the spectrum of abnormal ventriculoarterial connections. In those with tetralogy of Fallot or double-outlet right ventricle with subaortic ventricular septal defect, the muscular outlet septum separating the subarterial outflow tracts was always inserted into (or in front of) the anterior limb of the septomarginal trabeculation (septal band). In those having double-outlet right ventricle with doubly committed ventricular septal defect, the outlet septum was lacking. When the ventricular septal defect was in subpulmonary position, with either double-outlet or discordant ventriculoarterial connections, the outlet septum was attached to the posterior limb of the septomarginal trabeculation. The outlet septum was deviated into the subpulmonary outlet in hearts with discordant ventriculoarterial connections and pulmonary stenosis. It is the interrelations between the septomarginal trabeculation, the outlet septum, and the ventriculoinfundibular fold that hold the key to the understanding of surgical anatomy and determine the optimal choice of procedure for definitive biventricular repair.

Coronary arteries in transposition of the great arteries

The topic of coronary arteries in transposition of the great arteries (TGA) is complex and confusing despite having been the subject of several recently published reports. One hundred thirty-three autopsy specimens of uncomplicated TGA were studied, with special attention to methodologic issues in anatomic description and classification. Uncomplicated TGA was defined as congenital anomaly involving origin of the aorta from the right ventricle and of the pulmonary artery from the left ventricle. Three types of transposition were recognized ("anterior aorta," "side-by-side," and "posterior aorta") depending on the aortopulmonary relations, which were intrinsically defined by the relation of the valvular orifices of the great arteries with respect to the atrioventricular orifices. The frequency of distribution of individual coronary patterns differs substantially in the first 2 types of TGA. As in normal hearts, coronary arteries in TGA tend to originate from the facing sinuses (adjacent to the pulmonary valve); in TGA, however, variations in further distal anatomy are much more frequent. It is suggested that individual coronary patterns be described in terms of number of ostia, exact ostial location within or outside the aortic sinuses, and proximal course and distribution. The use of strict, simplified classifications of coronary patterns is discouraging because of the relevance of each individual anatomic parameter to clinical aims. Because of the aortopulmonary switch repair for TGA, this study emphasizes the surgical implications of the different coronary features.

Spectrum of heart malformations in mice with situs solitus, situs inversus, and associated visceral heterotaxy

BACKGROUND

We present a study of the heart malformations found in a collection of mouse fetuses of the iv/iv strain between days 16.5 and 18.5 of gestation.

METHODS AND RESULTS

One hundred hearts were serially sectioned and studied by segmental analysis with a light microscope. Forty additional hearts were analyzed with a scanning microscope. Forty percent of the hearts were found to be malformed. The most frequently occurring heart malformations were persistence of the sinus venosus (9%), common atrium (17%), common atrioventricular canal (24%), double-outlet right ventricle (12%), Fallot's tetralogy (8%), and transposition of the great arteries (5%). These malformations do not usually occur in isolation but rather appear in the formation of complex cardiopathies. The most severe and frequent is the combination of persistence of sinus venosus, common atrium, common atrioventricular canal, and double-outlet right ventricle; this is the "bulboventricular heart." The morphology of each lesion, as well as the degree of association, is similar to that found in human hearts with complex cardiopathies. Some of these cardiopathies appear to be directly related to formation of the cardiac loop. The iv/iv mouse appears to constitute an excellent model with which to study the etiology and pathogenesis of complex heart defects in humans. These hearts show a high phenotypic variability in the presentation of heart lesions. From a genetic viewpoint, there is a basic defect--the bulboventricular heart--which can be considered congenital. The other malformations can be considered formes frustes of the defect type.

CONCLUSIONS

The iv gene is a developmental gene that affects basic developmental mechanisms. In this regard, heart lesions may not be the primary result of the abnormal gene activity but rather are secondary to defective interactions during cardiac development.

Morphogenetic considerations on congenital malformations of the outflow tract. Part 2: Complete transposition of the great arteries and double outlet right ventricle

On the basis of our recent embryologic work concerning the separation process of the outflow tract, our study of the morphology of specimens from the Leiden Collection of malformed hearts, and in conjunction with our review of the literature, we have reconsidered the morphogenesis of complete transposition and double outlet right ventricle. In complete transposition, a mirror-image arrangement of the columns of the aorto-pulmonary septum could explain the discordant ventriculo-arterial connexion and might thus play a role in its development. Dedicating a cardinal role to the aorto-pulmonary septum in the morphogenesis of complete transposition does not, however, seem justified. Double outlet right ventricle is not an embryologic entity. From the stance of the embryologist, we prefer to consider double outlet right ventricle in terms of a feature that may occur in specimens related to hearts with either a concordant ventriculo-arterial connexion (such as tetralogy of Fallot, or the so-called Eisenmenger ventricular septal defect), or a discordant ventriculo-arterial connexion (complete transposition).

Morphologic aspects of complete transposition

SummaryComplete transposition is a morphologic entity which exists by virtue of a concordant atrioventricular connection co-existing with a discordant connection at the ventriculoarterial level. If diagnosed in this manner, all variants can be described simply and unambiguously in terms of associated malformations along with variations in relationships and infundibular morphology.