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Those using the mouse for the purposes of electrophysiological research presume that the morphology of the conduction axis is comparable with the human arrangement. As yet, however, to the best of our knowledge, no direct comparison has been made between the species. By comparing our extensive histological findings in the human heart with comparable serially-sectioned datasets prepared from adult murine hearts, we aimed to provide this information. When comparing the gross anatomy, we used three-dimensional datasets of neonatal mice hearts prepared using episcopic microscopy. The overall cardiac architecture is comparable, although the mouse has a persistent left superior caval vein draining via the coronary sinus. An inferior pyramidal space and an infero-septal recess are both present in the murine heart, although they are not as well developed as in the human heart. The overall arrangement of the conduction axis is similarly comparable, albeit with subtle differences reflecting the incomplete wedging of the subaortic outflow tract in the murine heart. Most significantly, the findings in both species reveal the presence of extensive superior septal pathways, which perhaps explain the finding of base-to-apex activation of the ventricular mass known to occur in the murine heart.

The heart and aortic arch arteries in amniotes form a double circulation, taking oxygenated blood from the heart to the body and deoxygenated blood to the lungs. These major vessels are formed in embryonic development from a series of paired and symmetrical arteries that undergo a complex remodelling process to form the asymmetric arch arteries in the adult. These embryonic arteries form in the pharyngeal arches, which are symmetrical bulges on the lateral surface of the head. The pharyngeal arches, and their associated arteries, are found in all classes of vertebrates, but the number varies, typically with the number of arches reducing through evolution. For example, jawed vertebrates have six pairs of pharyngeal arch arteries but amniotes, a clade of tetrapod vertebrates, have five pairs. This had led to the unusual numbering system attributed to each of the pharyngeal arch arteries in amniotes (1, 2, 3, 4, and 6). We, therefore, propose that these instead be given names to reflect the vessel: mandibular (1st), hyoid (2nd), carotid (3rd), aortic (4th) and pulmonary (most caudal). Aberrant arch artery formation or remodelling leads to life-threatening congenital cardiovascular malformations, such as interruption of the aortic arch, cervical origin of arteries, and vascular rings. We discuss why an alleged fifth arch artery has erroneously been used to interpret congenital cardiac lesions, which are better explained as abnormal collateral channels, or remodelling of the aortic sac.

Although first described in the final decade of the 19th century, the axis responsible for atrioventricular conduction has long been the source of multiple controversies. Some of these continue to reverberate. When first described by His, for example, many doubted the existence of the bundle we now name in his honour, while Kent suggested that multiple pathways crossed the atrioventricular junctions in the normal heart. It was Tawara who clarified the situation, although many of his key definitions have not universally been accepted. In key studies in the third decade of the 20th century, Mahaim then suggested the presence of ubiquitous connections that provided “paraspecific” pathways for atrioventricular conduction. In this review, we show the validity of these original investigations, based on our own experience with a large number of datasets from human hearts prepared by serial histological sectioning. Using our own reconstructions, we show how the atrioventricular conduction axis can be placed back within the heart. We emphasise that newly emerging techniques will be key in providing the resolution to map cellular detail to the gross evidence provided by the serial sections.

Hikspoors et al. generate a pictorial account of human embryonic heart development between 3.5 and 8 weeks. This resource provides detailed, interactive 3D anatomical models and quantifies the developmental milestones of key structures in cardiac function.

This case describes the first example of a double-barreled aorta in the setting of a common arterial trunk. Our use of annotated and segmented 3-dimensional models greatly enhanced our ability to elucidate the complex anatomy. (Level of Difficulty: Advanced.)

The major vessels in mammals that take blood away from the heart and deliver it to the arms and the head take their origin from the aortic arch and are derived from the arteries formed within the embryonic pharyngeal arches. These pharyngeal arch arteries, initially symmetrical, form in a cranial to caudal sequence within the pharyngeal mesenchyme. They then undergo a complex process of remodeling to produce the asymmetrical brachiocephalic arteries as seen in the adult. A complex interaction between the tissues of the pharyngeal arches and the genes they express is required to ensure that arterial formation and remodeling is able to proceed normally. If this process is disrupted, life-threatening congenital cardiovascular malformations can occur, such as interruption of the aortic arch, isolation of individual arteries, or so-called vascular rings. Here, using state-of-the-art imaging techniques, we describe the morphogenesis of the arteries in humans and mice and the cardiovascular defects in the Tbx1 mutant mouse model. We provide details of the process of remodeling, clarifying also the morphogenesis of the external carotid artery and the so-called “migration” of the left subclavian artery.

As yet, there is no agreed definition for the so-called “hypoplastic left heart syndrome”. Even its origin remains contentious. Noonan and Nadas, who as far as we can establish first grouped together patients as belonging to a “syndrome” in 1958, suggested that Lev had named the entity. Lev, however, when writing in 1952, had described “hypoplasia of the aortic outflow tract complex”. In his initial description, as with Noonan and Nadas, he included cases with ventricular septal defects. In a subsequent account, he suggested that only those with an intact ventricular septum be included within the syndrome. There is much to commend this later approach. When assessed on the basis of the integrity of the ventricular septum, the hearts to be included can be interpreted as showing an acquired disease of fetal life. Recognition of this fact is important to those seeking to establish the genetic background of left ventricular hypoplasia. Flow is also of importance, with septal integrity then influencing its effect on the structure of the hypoplastic ventricle. In our review, we summarise the evidence supporting the notion that an intact ventricular septum should now be part of the definition of the hypoplastic left heart syndrome.

Background: Anatomical considerations suggest the supraventricular crest (SC) is important for right ventricular free-wall to septum (RV FW-S) inward motion and may importantly influence overall right ventricular (RV) function. The influence of approximation of the FW-S on overall RV function, and implicitly the importance of the SC, may be judged from patients with repaired tetralogy of Fallot (rToF), where the components of this muscular bridge are separated. Methods: RV functional parameters were determined from magnetic resonance imaging (CMR) and related to RV FW-S approximation in 106 rToF patients, compared to CMR parameters in 30 normal subjects and with echocardiography in another 39 normal subjects. Results: In normal subjects, the SC shortened 41 ± 5% during systole and basal FW-S distance shortened significantly more than mid-ventricular FW-S distance (47 ± 17% vs. 23 ± 12%; p

Abstract Background The three-dimensional rearrangement of the right ventricular (RV) myocardium during cardiac deformation is unknown. Previous in-vivo studies have shown that myocardial left ventricular (LV) deformation is driven by rearrangement of aggregations of cardiomyocytes that can be characterised by changes in the so-called E3-angle. Ex-vivo imaging offers superior spatial resolution compared with in-vivo measurements, and can thus provide novel insight into the deformation of the myocardial microstructure in both ventricles. This study sought to describe the dynamic changes of the orientations of the cardiomyocytes in both ventricles brought upon by cardiac contraction, with particular interest in the thin-walled RV, which has not previously been described in terms of its micro-architecture. Methods The hearts of 14 healthy 20 kg swine were excised and preserved in either a relaxed state or a contracted state. Myocardial architecture was assessed and compared between the two contractional states by quantification of the helical, transmural and E3-angles of the cardiomyocytes using high-resolution diffusion tensor imaging. Results The differences between the two states of contraction were most pronounced in the endocardium where the E3-angle decreased from 78.6° to 24.8° in the LV and from 82.6° to 68.6° in the RV. No significant change in neither the helical nor the transmural angle was found in the cardiomyocytes of the RV. In the endocardium of the LV, however, the helical angle increased from 35.4° to 47.8° and the transmural angle increased from 3.1° to 10.4°. Conclusion The entire myocardium rearranges through the cardiac cycle with the change in the orientation of the aggregations of cardiomyocytes being the predominant mediator of myocardial wall thickening. Interestingly, differences also exist between the RV and LV, which helps in the explanation of the different physiological capabilities of the ventricles.

Abstract Background Discussions continue as to whether ventricular septal defects are best categorized according to their right ventricular geography or their borders. This is especially true when considering the perimembranous defect. Our aim, therefore, was to establish the phenotypic feature of the perimembranous defect, and to establish the ease of distinguishing its geographical variants. Methods and results We assessed unrepaired isolated perimembranous ventricular defects from six historic archives, subcategorizing them using the ICD-11 coding system. We identified 365 defects, of which 94 (26%) were deemed to open centrally, 168 (46%) to open to the outlet, and 84 (23%) to the inlet of the right ventricle, with 19 (5%) being confluent. In all hearts, the unifying phenotypic feature was fibrous continuity between the leaflets of the mitral and tricuspid valves. This was often directly between the valves, but in all instances incorporated continuity through the atrioventricular portion of the membranous septum. In contrast, we observed fibrous continuity between the leaflets of the tricuspid and aortic valves in only 298 (82%) of the specimens. When found, discontinuity most commonly was seen in the outlet and central defects. There were no discrepancies between evaluators in distinguishing the borders, but there was occasional disagreement in determining the right ventricular geography of the defect. Conclusions The unifying feature of perimembranous defects, rather than being aortic-to-tricuspid valvar fibrous continuity, is fibrous continuity between the leaflets of the atrioventricular valves. While right ventricular geography is important in classification, it is the borders which are more objectively defined.

There are still confusing descriptions of how congenitally malformed hearts should be categorised, even in their simplest forms. Despite repeated attempts toward a unified and simplified analysis, morphologists and clinicians continue to use different nomenclatures. This variability has a profound impact not only on how we communicate with patients but also on how the healthcare professionals produce clinical reports, research papers and educational and training materials, not to mention the impact on other levels such as managerial, administrative, coding, financial and media communications. Moreover, there are influences on how we actually treat patients based on a different understanding of nomenclature. This paper aims to explain a method of analysing the cardiac segments and their connections based on the current understanding of structural development.

Persistence of the left superior caval vein is the most commonly reported thoracic venous anomaly. The vein usually drains into the right atrium through the coronary sinus, reflecting its developmental origin. We describe an unusual variant, in which the vein drained directly into the right atrium.

Abstract Background Chronic pulmonary regurgitation often leads to myocardial dysfunction and heart failure. It is not fully known why secondary hypertrophy cannot fully protect against the increase in wall stress brought about by the increased end-diastolic volume in ventricular dilation. It has been assumed that mural architecture is not deranged in this situation, but we hypothesised that there might be a change in the pattern of orientation of the aggregations of cardiomyocytes, which would contribute to contractile impairment. Methods We created pulmonary valvular regurgitation by open chest, surgical suturing of its leaflets in seven piglets, performing sham operations in seven control animals. Using cardiovascular magnetic resonance imaging after 12 weeks of recovery, we demonstrated significantly increased right ventricular volumes in the test group. After sacrifice, diffusion tensor imaging of their hearts permitted measurement of the orientation of the cardiomyocytes. Results The helical angles in the right ventricle approached a more circumferential orientation in the setting of right ventricular RV dilation (p = 0.007), with an increased proportion of surface-parallel cardiomyocytes. In contrast, this proportion decreased in the left ventricle. Also in the left ventricle a higher proportion of E3 angles with a value around zero was found, and conversely a lower proportion of angles was found with a numerical higher value. In the dilated right ventricle the proportion of E3 angles around −90° is increased, while the proportion around 90° is decreased. Conclusion Contrary to traditional views, there is a change in the orientation of both the left ventricular and right ventricular cardiomyocytes subsequent to right ventricular dilation. This will change their direction of contraction and hinder the achievement of normalisation of cardiomyocytic strain, affecting overall contractility. We suggest that the aetiology of the cardiac failure induced by right vetricular dilation may be partly explained by morphological changes in the myocardium itself.

Abstract Cardiac arrhythmias and conduction disturbances are accompanied by structural remodelling of the specialised cardiomyocytes known collectively as the cardiac conduction system. Here, using contrast enhanced micro-computed tomography, we present, in attitudinally appropriate fashion, the first 3-dimensional representations of the cardiac conduction system within the intact human heart. We show that cardiomyocyte orientation can be extracted from these datasets at spatial resolutions approaching the single cell. These data show that commonly accepted anatomical representations are oversimplified. We have incorporated the high-resolution anatomical data into mathematical simulations of cardiac electrical depolarisation. The data presented should have multidisciplinary impact. Since the rate of depolarisation is dictated by cardiac microstructure, and the precise orientation of the cardiomyocytes, our data should improve the fidelity of mathematical models. By showing the precise 3-dimensional relationships between the cardiac conduction system and surrounding structures, we provide new insights relevant to valvar replacement surgery and ablation therapies. We also offer a practical method for investigation of remodelling in disease, and thus, virtual pathology and archiving. Such data presented as 3D images or 3D printed models, will inform discussions between medical teams and their patients, and aid the education of medical and surgical trainees.

Fetal trabecular muscles in the heart undergo a poorly described morphogenetic process that results into a solidified compact myocardium after birth. Tian et al. show that cardiomyocytes in the fetal compact layer also contribute to this process, forming a hybrid myocardial zone that is composed of cells derived from both trabecular and compact layers.

The left pulmonary artery arising from the ascending aorta is an infrequent finding. It may be found isolated or with intracardiac anomalies. We present a new case of the left pulmonary artery arising from the ascending aorta and pool these findings with those of previously reported cases. Associated cardiac, extracardiac, and syndromic findings are discussed along with the implications of these in the evaluation and management of this condition.

Background: The vestibular atrial septal defect is an interatrial communication located in the antero-inferior portion of the atrial septum. Reflecting either inadequate muscularization of the vestibular spine and mesenchymal cap during development, or excessive apoptosis within the developing antero-inferior septal component, the vestibular defect represents an infrequently recognized true deficiency of the atrial septum. We reviewed necropsy specimens from three separate archives to establish the frequency of such vestibular defects and their associated cardiac findings, providing additional analysis from developing mouse hearts to illustrate their potential morphogenesis. Materials and methods: We analyzed the hearts in the Farouk S. Idriss Cardiac Registry at Ann and Robert H. Lurie Children’s Hospital in Chicago, IL, the Van Mierop Archive at the University of Florida in Gainesville, Florida, and the archive at Johns Hopkins All Children’s Heart Institute in St. Petersburg, Florida, identifying all those exhibiting a vestibular atrial septal defect, along with the associated intracardiac malformations. We then assessed potential mechanisms for the existence of such defects, based on the assessment of 450 datasets of developing mouse hearts prepared using the technique of episcopic microscopy. Results: We analyzed a total of 2100 specimens. Of these, 68 (3%) were found to have a vestibular atrial septal defect. Comparable defects were identified in 10 developing mouse embryos sacrificed at embryonic data 15.5, by which stage the antero-inferior component of the atrial septum is usually normally formed. Conclusion: The vestibular defect is a true septal defect located in the muscular antero-inferior rim of the oval fossa. Our retrospective review of autopsied hearts suggests that the defect may be more common than previously thought. Increased awareness of the location of the defect should optimize its future clinical identification. We suggest that the defect exists because of failure, during embryonic development, of union of the components that bind the leading edge of the primary atrial septum to the atrioventricular junctions, either because of inadequate muscularisation or excessive apoptosis.

Aorto-ventricular tunnel is an extremely rare congenital heart defect, consisting of failure of attachment of an aortic leaflet along the semilunar hinge. In all published reports the leaflet involved was either the right coronary leaflet, most frequently, or the left coronary leaflet, in most of the cases opening toward the left ventricle, with only one-eighth of the reported cases communicating with the right ventricle. Treatment of the aorto-ventricular tunnel has been anecdotally reported by interventional closure with a device and more frequently with surgical approach, either as an isolated malformation or as associated lesions. To the best of our knowledge, the presence of an aorto-ventricular tunnel of the non-adjacent aortic leaflet in transposition of the great arteries has never been reported. We have observed an aorto-ventricular tunnel involving the non-adjacent leaflet of the aortic root, which after arterial switch became the pulmonary root. The patient presented 18 years after the arterial switch with progressive dilatation of the right ventricle due to severe degree of pulmonary valve regurgitation, confirmed by echocardiography and cardiac MRI. Indication for surgery was given with the plan for a pulmonary valve implantation. Because of the intra-operative finding of disconnection of the anterior leaflet of the pulmonary valve (former aortic valve) along the semilunar hinge, the surgical plan was modified and the anterior leaflet was attached to the valve annulus, with subsequent plasty in correspondence with the right and left commissurae to reduce the size of the dilated annulus to normal diameter. The post-operative course was uneventful, with extubation after few hours and discharge 4 days after surgery, with echocardiography showing trivial degree of pulmonary valve regurgitation. The patient remains in good conditions 6 months after surgery.

There is considerable confusion as to how best describe the components of the arterial valves. It is hardly surprising, therefore, that similar uncertainties apply to concepts for their development. In this review, we describe the anatomy of the arterial valves as seen in the postnatal heart. We suggest that their working components are best described as leaflets, housed in supporting arterial sinuses. The roots surrounding the leaflets, which are hinged in semilunar fashion, can then be defined as extending from a virtual ring at their base to the sinutubular junction. We also discuss the problems related to definition of the valvar “annulus”. Understanding the development of the arterial roots, which are formed in the central part of the embryonic outflow tract, is facilitated by considering the outflow tract itself as possessing three components, as opposed to the traditional “conus” and “truncus”. These three parts can be described as being distal, intermediate, and proximal. The distal part is separated to form the intrapericardial arterial trunks, while the proximal part becomes the ventricular outflow tracts. It is the intermediate component that houses the developing arterial valves, and their supporting valvar sinuses. The distal parts of the cushions that separate the outflow tract into aortic and pulmonary components, along with the intercalated cushions, excavate to form the leaflets. The walls of the sinuses are formed by growth of non-myocardial tissues from the heart-forming area. We then show how these features can be used to interpret the anatomy and development of congenitally malformed arterial valves.

It is now established that the entity often described as an “aortopulmonary septal complex„ is better considered as an “outflow tract septal complex„. This change is crucial for appropriate understanding of not only malformations of the outflow tract, but also ventricular septal defects. Thus, the embryonic outflow tract, as it develops, is separated into its two components by fusion of a protrusion from the dorsal wall of the aortic sac with the distal end of the outflow cushions. The key point with regard to morphogenesis is that, with ongoing development, these structures lose their septal integrity, although they can still be identified as septal structures when the ventricular septum itself is deficient. In the normal postnatal heart, however, the aortic and pulmonary components have their own walls throughout the length of the outflow tracts. All of this is of clinical significance, since some current concepts of categorisation of the ventricular septal defects are based on the existence in the normal heart of a “conal septum„, along with a “septum of the atrioventricular canal„. In this review, we show how analysis of postnatal hearts reveals the definitive ventricular septum to possess only muscular and fibrous components in the absence of either discrete outflow or inlet components. We also show that this information regarding development, in turn, is of major significance in determining whether categorisation of ventricular septal defects is best approached, in the first instance, on the basis of the borders of the defects or the fashion in which they open to the right ventricle.

Hypoplastic left heart syndrome occurs in up to 3% of all infants born with congenital heart disease and is a leading cause of death in this population. Although there is strong evidence for a genetic component, a specific genetic cause is only known in a small subset of patients, consistent with a multifactorial etiology for the syndrome. There is controversy surrounding the mechanisms underlying the syndrome, which is likely due, in part, to the phenotypic variability of the disease. The most commonly held view is that the “decreased„ growth of the left ventricle is due to a decreased flow during a critical period of ventricular development. Research has also been hindered by what has been, up until now, a lack of genetically engineered animal models that faithfully reproduce the human disease. There is a growing body of evidence, nonetheless, indicating that the hypoplasia of the left ventricle is due to a primary defect in ventricular development. In this review, we discuss the evidence demonstrating that, at least for a subset of cases, the chamber hypoplasia is the consequence of hyperplasia of the contained cardiomyocytes. In this regard, hypoplastic left heart syndrome could be viewed as a neonatal form of cardiomyopathy. We also discuss the role of the endocardium in the development of the ventricular hypoplasia, which may provide a mechanistic basis for how impaired flow to the developing ventricle leads to the anatomical changes seen in the syndrome.

So-called heterotaxy or isomerism is characterized by abnormal lateralization and malformations of the bodily organs. The mechanism is unclear, although there is growing evidence that ciliary dyskinesia is involved. We reviewed genetic findings from patients with isomerism to determine if affected genes were known to be associated with isomerism and ciliary dyskinesia and determine associations between genotype and clinical findings. We identified patients with isomerism cared for over a 16- year period. Characteristics were compared between those with and without identified mutations. A total of 83 patients with isomerism were identified. Of those who had genotyping, 14/27 had mutations identified, most frequently involving the CFC1 and NODAL genes. Specific mutations were associated with clinical findings, with NODAL mutations often portending need for increased clinical support. Genes associated with isomerism and/or ciliary dyskinesia were identified in the cohort. Specific gene mutations may help predict clinical course.

In his recent review for the Journal of Cardiovascular Development and Disease, Cirillo offers a concept for “cardiac memory” based on the notion that the ventricular cone can be unwrapped to show a myocardial band extending from the pulmonary to the aortic root. The concept of the myocardial band was itself developed by Torrent Guasp, and has subsequently been championed by Buckberg. Neither Torrent Guasp, when formulating his initial concept, nor Buckberg in his subsequent endorsements, have validated the results of dissection using histological or other techniques that would reveal the boundaries of the alleged band. In contrast, there is a wealth of evidence showing that such boundaries do not exist and that the cardiomyocytes are packed together within the walls of the ventricular cone in the form of a three-dimensional mesh. The evidence demonstrating the manner of packing of the cardiomyocytes within the ventricular walls was summarised in another recent review published in the journal. It is disappointing that Cirillo chose to ignore the wealth of evidence disproving the concept on which he bases his entire review. Only by recognising the existence of this evidence can we truly understand ventricular function correctly, as envisaged by Cirillo.

It is now well over 100 years since Sunao Tawara clarified the location of the axis of the specialised myocardium responsible for producing coordinated ventricular activation. Prior to that stellar publication, controversies had raged as to how many bundles crossed the place of the atrioventricular insulation as found in mammalian hearts, as well as the very existence of the bundle initially described by Wilhelm His Junior. It is, perhaps surprising that controversies continue, despite the multiple investigations that have taken place since the publication of Tawara’s monograph. For example, we are still unsure as to the precise substrates for the so-called slow and fast pathways into the atrioventricular node. Much has been done, nonetheless, to characterise the molecular make-up of the specialised pathways, and to clarify their mechanisms of development. Of this work itself, a significant part has emanated from the laboratory coordinated for a quarter of a century by Antoon FM Moorman. In this review, which joins the others in recognising the value of his contributions and collaborations, we review our current understanding of the anatomy, development, and evolution of the atrioventricular conduction axis.

The precise nature of packing together of the cardiomyocytes within the ventricular walls has still to be determined. The spiraling nature of the chains of interconnected cardiomyocytes has long been recognized. As long ago as the end of the nineteenth century, Pettigrew had emphasized that the ventricular cone was not arranged on the basis of skeletal muscle. Despite this guidance, subsequent anatomists described entities such as “bulbo-spiral muscles”, with this notion of subunits culminating in the suggestion that the ventricular cone could be unwrapped so as to produce a “ventricular myocardial band”. Others, in contrast, had suggested that the ventricular walls were arranged on the basis of “sheets”, or more recently “sheetlets”, with investigators seeking to establishing the angulation of these entities using techniques such as magnetic resonance imaging. Our own investigations, in contrast, have shown that the cardiomyocytes are aggregated together within the supporting fibrous matrix so as to produce a three-dimensional myocardial mesh. In this review, we summarize the previous accounts, and provide the anatomical evidence we have thus far accumulated to support the model of the myocardial mesh. We show how these anatomic findings underscore the concept of the myocardial mesh functioning in antagonistic fashion. They lend evidence to support the notion that the ventricular myocardium works as a muscular hydrostat.

Pediatric cardiologists treating patients with severe congenital cardiac defects define “visceral heterotaxy” on the basis of isomerism of the atrial appendages. The isomeric features represent an obvious manifestation of disruption of left-right asymmetry during embryonic development. Thus, there are two subsets of individuals within the overall syndrome, with features of either right or left isomerism. Within the heart, it is only the atrial appendages that are truly isomeric. The remainder of the cardiac components shows variable morphology, as does the arrangement of the remaining body organs. Order is provided in this potentially chaotic arrangement simply by describing the specific features of each of the systems. These features as defined by clinicians, however, seem less well recognized by those investigating the developmental origins of the disruption of symmetry. Developmental biologists place much greater emphasis on ventricular looping. Although the direction of the loop can certainly be interpreted as representing an example of asymmetry, it is not comparable to the isomeric features that underscore the clinical syndromes. This is because, thus far, there is no evidence of ventricular isomerism, with the ventricles distinguished one from the other on the basis of their disparate anatomical features. In similar fashion, some consider transposition to represent abnormal lateralization, but again, clinical diagnosis depends on recognition of the lateralized features. In this review, therefore, we discuss the key questions that currently underscore the mismatch in the approaches to “lateralization” as taken by clinicians and developmental biologists.

In the review, now published as part of the special issue devoted to the development of the conduction tissues, de Vries and his colleagues discuss the potential role of the so-called “dead-end tract” as a substrate for arrhythmogenesis [1].[...]

The recent identification of a second mesodermal region as a source of cardiomyocytes has challenged the views on the formation of the heart. This second source of cardiomyocytes is localized centrally on the embryonic disc relative to the remainder of the classic cardiac crescent, a region also called the pharyngeal mesoderm. In this review, we discuss the concept of the primary and secondary cardiogenic fields in the context of folding of the embryo, and the subsequent temporal events involved in formation of the heart. We suggest that, during evolution, the heart developed initially only with the components required for a systemic circulation, namely a sinus venosus, a common atrium, a ‘left’ ventricle and an arterial cone, the latter being the myocardial outflow tract as seen in the heart of primitive fishes. These components developed in their entirety from the classic cardiac crescent. Only later in the course of evolution did the appearance of novel signalling pathways permit the central part of the cardiac crescent, and possibly the contiguous pharyngeal mesoderm, to develop into the cardiac components required for the pulmonary circulation. These latter components comprise the right ventricle, and that part of the left atrium that derives from the mediastinal myocardium, namely the dorsal atrial wall and the atrial septum. It is these elements which are now recognized as developing from the second field of pharyngeal mesoderm. We suggest that, rather than representing development from separate fields, the cardiac components required for both the systemic and pulmonary circulations are derived by patterning from a single cardiac field, albeit with temporal delay in the process of formation. [ABSTRACT FROM AUTHOR]

In this review, we summarise the ongoing debate surrounding the anatomy of the atrioventricular conduction axis and its relevance to pacing. We highlight previous disagreements and emphasise the importance of understanding the anatomical location of the axis. We give credit and support to the initial descriptions by His and Tawara, in particular their attention to the relationship of the atrioventricular conduction axis with the membranous septum. We express our disagreements with recent diagrams that incorrectly, in our opinion, depict the left bundle and right bundle branches. We offer our own latest understanding of the location and relationships of the atrioventricular conduction axis, including details of its development, and differences between human and animal hearts. We also emphasise the importance of understanding the relationship between the inferior pyramidal space and the inferoseptal recess so as appropriately to place the axis within the heart. We conclude by emphasising the need to consider the heart in the context of the body, describing its component parts by using attitudinally appropriate nomenclature.

Background: Atrioventricular (AV) conduction ablation has been achieved by targeting the area of penetration of the conduction axis as defined by recording a His bundle potential. Ablation of the His bundle may reduce the possibility of a robust junctional escape rhythm. It was hypothesised that specific AV nodal ablation is feasible and safe. Methods: The anatomical position of the AV node in relation to the site of penetration of the conduction axis was identified as described in dissections and histological sections of human hearts. Radiofrequency (RF) ablation was accomplished based on the anatomical criteria. Results: Specific anatomical ablation of the AV node was attempted in 72 patients. Successful AV nodal ablation was accomplished in 63 patients (87.5%), following 60 minutes (IQR 50–70 minutes) of procedure time, 3.4 minutes (IQR 2.4–5.5 minutes) of fluoroscopy time, and delivery of 4 (IQR 3–6) RF lesions. Αn escape rhythm was present in 45 patients (71%), and the QRS complex was similar to that before ablation in all 45 patients. Atropine was administered in six patients after the 10-min waiting period and did not result in restoration of conduction. In nine patients, AV conduction could not be interrupted, and AV block was achieved with ablation of the His after delivery of 12 (IQR 8–15) RF lesions. No cases of sudden death were encountered, and all patients had persistent AV block during a median 10.5 months (IQR 5–14 months) of follow-up. Conclusion: Anatomical ablation of the AV node is feasible and safe, and results in an escape rhythm similar to that before ablation.

The name Ivan Mahaim is well-known to electrophysiologists. However, alternative anatomical substrates can produce the abnormal rhythms initially interpreted on the basis of the pathways he first described. These facts have prompted suggestions that Mahaim should be deprived of his eponym. It is agreed that specificity is required when describing the pathways that produce the disordered cardiac conduction, and that the identified pathways should now be described in an attitudinally appropriate fashion. The authors remain to be convinced that understanding will be enhanced simply by discarding the term ‘Mahaim physiology’ from the lexicon. It is fascinating to look back at the history of accessory atrioventricular junctional conduction pathways outside the normal accessory atrioventricular conduction system, and their possible role in rhythm disturbances. It took both the anatomist and the clinical arrhythmologist quite some time to understand the complex anatomical architecture and the ensuing electrophysiological properties. Over the years, the name Mahaim was often mentioned in those discussions, although these pathways were not the ones that produced the eponym. The reason for this review, therefore, is to present relevant information about the person and what followed thereafter.

Uniatrial but biventricular atrioventricular connection is a rare congenital cardiac abnormality where the left atria-ventricular connection is absent and the right atrio-ventricular connection straddles the crest of the muscular ventricular septum. This anomaly has been referred to as double outlet right atrium and the atrio-ventricular valve as a common atrioventricular valve in the past.In the absence of a primary atrial septal defect, the atrio-ventricular junction is not a common junction and the valve cannot hence be described as a common trio-ventricular valve. We demonstrate this paradox by an illustrative case and contrast this with two other cases where a common atrio-ventricular valve was predominantly committed to the right atrium.

The pulmonary dominant variant of the common arterial trunk has always been reported to be associated with aortic coarctation, or interruption of the aortic arch, along with a duct-dependent systemic circulation. This mandates a complex surgical repair with attendant high surgical mortality. We report a 23-day-old baby with a pulmonary dominant trunk with mild aortic hypoplasia but with an arch free of coarctation or interruption, who underwent successful surgical repair. In the preoperative evaluation of a common arterial trunk, pulmonary dominance may not necessarily denote an adverse risk factor when the aorta is only mildly hypoplastic.

Background: Pulmonary stenosis in patients with common arterial trunk protects the pulmonary vasculature. In our recently published prospective study of common arterial trunk, some patients with sinusal origin of the pulmonary arterial segment had pulmonary stenosis induced by systolic excursion of a truncal valvar leaflet. We aimed to determine the detailed morphologic characteristics of this unusual finding. Methods and Results: All 70 patients underwent echocardiography and computed tomographic angiography as per predefined study protocol. In selected cases, we also performed cardiac catheterization. Among 27 patients with aortic dominance, we found sinusal origin of the pulmonary arterial segment. In 5 of these patients, pulmonary stenosis was induced by systolic excursion of a truncal valvar leaflet. In all these patients, the truncal valve was trisinusate, albeit with asymmetric sinuses. The pulmonary arterial segment arose from the largest left sinus with its relatively large leaflet obstructing the pulmonary orifice during systole. In the remaining 22 patients, without pulmonary stenosis but with sinusal origin of pulmonary arterial segment, the truncal valve was quadrisinusate in 7, bisinusate in 2, and trisinusate in 13. None of the patients with quadrisinusate and bisinusate truncal valves had pulmonary stenosis. Among the 13 patients with trisinusate valves, the sinuses of the truncal valve were symmetrical in 6, while in 7, the pulmonary orifice originated from a smaller asymmetric sinus. Conclusion: Pulmonary stenosis, produced by a relatively large leaflet of an asymmetric truncal sinus, may prevent early development of pulmonary vascular disease. Timely recognition of this unusual mechanism of pulmonary stenosis is important for optimal management.

Bicuspidity of both the semilunar valves is rarely reported. We report the first ever case of bilateral bicuspid semilunar valves in a case of transposition.

Computed tomography has an established role in the evaluation of a variety of cardiac disorders, including congenital heart diseases. The current generation of high-speed scanners produces volumetric data at low doses of radiation. The interpretation of cardiac anatomy, however, is generally limited to multiplanar assessment of two-dimensional images. The volume rendering technique provides an excellent three-dimensional demonstration of external morphology but offers little information about the intracardiac anatomy. The alternative approach of virtual cardiac dissection, which is a modification of volume rendering, on the other hand, provides crucial insights regarding the intracardiac anatomy. At present, virtual cardiac dissection requires expensive software packages. These software packages are not available in all countries, thus limiting its use in routine clinical care. We present here the details of a newly developed technique that permits virtual cardiac dissection using a personal computer and open-source software. Our technique involves no additional cost and can be achieved in the comfort of the office or operating room of the cardiologist, radiologist, or cardiac surgeon. This enhanced three-dimensional visualization of intracardiac anatomy will surely improve the understanding of the morphological details of both normal and malformed hearts. In addition, by permitting assessment in projections with which modern-day cardiologists and cardiac surgeons are conversant, it is likely to improve clinical decision-making. We illustrate here its potential utility in the morphologic assessment of the atrial septum and its deficiencies, along with malformations of the ventricular outflow tracts, including common arterial trunk.