Cardiovascular defects associated with abnormalities in midline development in the Loop-tail mouse mutant

Loop-tail (Lp) is a naturally occurring mouse mutant that develops severe neural tube defects. In this study, we describe complex cardiovascular defects in Lp homozygotes, which include double-outlet right ventricle, with obligatory perimembranous ventricular septal defects, and double-sided aortic arch, with associated abnormalities in the aortic arch arteries. Outflow tract and aortic arch defects are often related to abnormalities in the cardiac neural crest, but using molecular and anatomic markers, we show that neural crest migration is normal in Lp/Lp embryos. On the other hand, the heart fails to loop normally in Lp/Lp embryos, in association with incomplete axial rotation and reduced cervical flexion. As a consequence, the ventricular loop is shifted posteromedially relative to its position in wild-type embryos. This suggests that the observed cardiac alignment defects in the Lp mutant may be secondary to failure of neural tube closure and incomplete axial rotation. Double-sided aortic arch is a rare finding among mouse models. In humans, it is usually an isolated malformation, only rarely occurring in combination with other cardiac defects. We suggest that the double-sided arch arises as a primary defect in the Lp mutant, unrelated to the alignment defects, perhaps reflecting a role for the (as-yet-unknown) Lp gene in maintenance/regression of the aortic arch system.

Misexpression of noggin leads to septal defects in the outflow tract of the chick heart

BMP-2 and BMP-4 are known to be involved in the early events which specify the cardiac lineage. Their later patterns of expression in the developing mouse and chick heart, in the myocardium overlying the atrioventricular canal (AV) and outflow tract (OFT) cushions, also suggest that they may play a role in valvoseptal development. In this study, we have used a recombinant retrovirus expressing noggin to inhibit the function of BMP-2/4 in the developing chick heart. This procedure resulted in abnormal development of the OFT and the ventricular septum. A spectrum of abnormalities was seen ranging from common arterial trunk to double outlet right ventricle. In hearts infected with noggin virus, where the neural crest cells have been labelled, the results show that BMP-2/4 function is required for the migration of neural crest cells into the developing OFT to form the aortopulmonary septum. Prior to septation, misexpression of noggin also leads to a decrease in the number of proliferating mesenchymal cells within the proximal cushions of the outflow tract. These results suggest that BMP-2/4 function may mediate several key events during cardiac development.

Anatomic-electrophysiological correlations concerning the pathways for atrioventricular conduction

The remarkable success of radiofrequency ablation in recent decades in curing atrioventricular nodal reentrant tachycardias has intensified efforts to provide a solid theoretical basis for understanding the mechanisms of atrioventricular transmission. These efforts, which were made by both anatomists and electrophysiologists, frequently resulted in seemingly controversial observations. Quantitatively and qualitatively, our understanding of the mysteries of propagation through the inhomogeneous and extremely complex atrioventricular conduction axis is much deeper than it was at the beginning of the past century. We must go back to the initial sources, nonetheless, in an attempt to provide a common ground for evaluating the morphological and electrophysiological principles of junctional arrhythmias. In this review, we provide an account of the initial descriptions, which still provide an appropriate foundation for interpreting recent electrophysiological findings.

The anatomy of the septal perforating arteries in normal and congenitally malformed hearts

BACKGROUND

Many cardiac operations involve incisions and sutures on or near the ventricular septum. These jeopardize the septal perforating arteries. Our aim was to provide guidelines for the surgeon to predict the site of these vessels.

METHODS AND RESULTS

We dissected 50 hearts. In 16 of these we also conducted histologic examination of the area of the septum containing the atrioventricular node, the penetrating bundle (of His), and the branching atrioventricular bundle to elucidate the source of the vascular supply to these structures. The major perforating septal arteries arise from the superior interventricular artery or, in hearts with a rudimentary right ventricle, from the superior delimiting artery. The first is usually the largest. The location of this artery can be predicted relative to the position of the medial papillary muscle. In abnormal hearts, holes within the ventricular septum in the presence of a well-developed muscular outlet septum were found to deviate the path of the septal perforating arteries in a predictable manner. The triangular area bordered by the margin of the ventricular septal defect, the muscular outlet septum, and the medial papillary muscle is free of major perforating arteries. The histologic studies showed that the conduction tissues at the base of the ventricles tend to receive their blood supply from arteries arising from the inferior interventricular artery, except in double-inlet left ventricle, in which the arterial supply is from the right-sided delimiting artery.

CONCLUSION

The location of the first superior septal perforating artery is predictable in many cases. Its course leaves a triangular area on the muscular ventricular septum that is free of major arteries.

Development of the myocardium of the atrioventricular canal and the vestibular spine in the human heart

To establish the morphogenetic mechanisms underlying formation and separation of the atrioventricular connections, we studied the remodeling of the myocardium of the atrioventricular canal and the extracardiac mesenchymal tissue of the vestibular spine in human embryonic hearts from 4.5 to 10 weeks of development. Septation of the atrioventricular junction is brought about by downgrowth of the primary atrial septum, fusion of the endocardial cushions, and forward expansion of the vestibular spine between atrial septum and cushions. The vestibular spine subsequently myocardializes to form the ventral rim of the oval fossa. The connection of the atrioventricular canal with the atria expands evenly. In contrast, the expression patterns of creatine kinase M and GlN2, markers for the atrioventricular and interventricular junctions, respectively, show that the junction of the canal with the right ventricle forms by local growth in the inner curvature of the heart. Growth of the caudal portion of the muscular ventricular septum to make contact with the inferior endocardial cushion occurs only after the canal has expanded rightward. The atrioventricular node develops from that part of the canal myocardium that retains its continuity with the ventricular myocardium.

Long-term results of relief of subaortic stenosis in univentricular atrioventricular connection with discordant ventriculoarterial connections

BACKGROUND

We set out to examine the long-term results of relief of subaortic stenosis by enlargement of ventricular septal defect in patients with univentricular atrioventricular connection to a dominant left ventricle and discordant ventriculoarterial connections.

METHODS

Twenty-four patients underwent enlargement of ventricular septal defect between 1985 and 1998 at a median age of 3.2 years (range, 3 weeks to 14 years). Ten patients were younger than 1 year of age. Eighteen had undergone previous banding of the pulmonary trunk, 9 of whom also required repair of coarctation of the aorta. The median subaortic gradient before enlargement was 46 mm Hg. Twenty-three patients had a patch to enlarge the rudimentary right ventricle.

RESULTS

Five patients (21%) died in the early postoperative period. The overall survival at 1 and 3 years was 73%, and at 5 and 10 years was 68% and 60%, respectively. Complete heart block requiring insertion of a pacemaker occurred in 2 patients (8%). A Fontan operation was performed in 10 patients, 5 underwent a bidirectional Glenn procedure, and 2 required cardiac transplantation. Follow-up was complete in all survivors at a median time of 6.7 years (range, 8 months to 13 years). From the earlier part of the series, 3 patients experienced aortic insufficiency and 2 had recurrent obstruction. Factors adversely affecting survival were age younger than 1 year at operation and presence of obstruction within the aortic arch.

CONCLUSIONS

Our experience shows that, in patients with univentricular atrioventricular connection to a dominant left ventricle and subaortic stenosis, enlargement of the ventricular septal defect provides satisfactory relief of obstruction except in those younger than 1 year of age, and those who have associated obstruction in the aortic arch.

Topographic anatomy of the inferior pyramidal space: relevance to radiofrequency catheter ablation

INTRODUCTION

Radiofrequency catheter ablation carried out in the vicinity of the triangle of Koch risks damaging not only the AV conduction tissues but also their arterial supply. The aim of this study was to examine the relationship of the AV nodal artery to the inferior pyramidal space, the triangle of Koch, and the right atrial endocardial surface.

METHODS AND RESULTS

We studied 41 heart specimens, 24 by gross dissections and 17 by histologic sections. The proximity of the AV nodal artery to the surface landmarks of the triangle of Koch was variable, but it was notable that in 75% of specimens the artery passed close to the endocardial surface of the right atrium and within 0.5 to 5 mm of the mouth of the coronary sinus. In all specimens, the mean distance of the artery to the endocardial surface was 3.5 +/- 1.5 mm at the base of Koch's triangle. The location of the compact AV node and its inferior extensions varied within the landmarks of the triangle. At the mid-level of Koch's triangle, the compact node was medially situated in 82% of specimens, but it was closer to the hinge of the tricuspid valve in the remaining 18% of specimens. In 12% of specimens, the inferior parts of the node extended to the level of the mouth of the coronary sinus.

CONCLUSION

The nodal artery runs close to the orifice of the coronary sinus, the endocardial surface of the right atrium, the middle cardiac vein, and the specialized conduction tissues in most hearts. The nodal artery and/or the AV conduction tissues can be at risk of damage when ablative procedures are carried out at the base of the triangle of Koch.

Double orifice right atrioventricular valve in atrioventricular septal defect: morphology and extension of the concept of fusion of leaflets

A rare observation of a double orifice right atrioventricular valve in a partial form of atrioventricular septal defect is reported. The concept of leaflet fusion along part of their anticipated zones of apposition is used to explain the formation of this anomaly. We show that this concept can account for the different morphologic presentations of atrioventricular septal defect.

Transthoracic three-dimensional echocardiography for the assessment of straddling tricuspid or mitral valves

BACKGROUND

The advent of 3D echocardiography has provided a technique which, potentially, could afford significant additional information over conventional cross-sectional echocardiography in the assessment of patients with straddling atrioventricular valves prior to surgical correction.

METHODS

Eight patients, aged from 1 month to 9.2 years, were examined with 3D echocardiography. All but three had discordant ventriculoarterial connections or double outlet right ventricle. Data suitable for reconstruction was acquired with transthoracic scanning. Right and left ventricular volumes were calculated in the 3D dataset.

RESULTS

3D echocardiography proved capable of defining the exact degree of straddling by imaging the proportion of tension apparatus attached to either side of the ventricular septum. It was able also to display the atrioventricular junction "en face", thus permitting identification of the precise site of insertion of the muscular ventricular septum relative to the atrioventricular junction. This made it possible first, to calculate the degree of valvar override, and second, to predict the location of the penetrating atrioventricular bundle. End-diastolic volume of the right ventricle in those with straddling tricuspid valves was 73 (61-83)% of normal, and, of the left ventricle in those with mitral valvar straddling 71 (40-97)% of normal.

CONCLUSIONS

3D echocardiography can aid in planning the optimal surgical procedure in patients with straddling or overrriding atrioventricular valves, as it provides diagnostic information superior to standard cross-sectional techniques. It also allows for exact measurement of the volumes of the respective ventricles.

Twisted atrioventricular connections in double inlet right ventricle: evaluation by magnetic resonance imaging

Twisted atrioventricular connections occur almost exclusively in the hearts with biventricular atrioventricular connections. Only one example of double inlet left ventricle has been illustrated in which the axes of the two atrioventricular valves crossed each other. We describe herein three patients, and one autopsied specimen, with double inlet right ventricle in which magnetic resonance imaging clearly demonstrated twisted atrioventricular connections.

A multifilamented electrode in the middle cardiac vein reduces energy requirements for defibrillation in the pig

OBJECTIVE

To compare the defibrillation efficacy of a novel lead system placed in the middle cardiac vein with a conventional non-thoracotomy lead system.

METHODS

In eight pigs (weighing 35-71 kg), an electrode was advanced transvenously to the right ventricular apex (RV), with the proximal electrode in the superior caval vein (SCV). Middle cardiac vein (MCV) angiography was used to delineate the anatomy before a three electrode system (length 2 x 25 mm + 1 x 50 mm) was positioned in the vein. An active housing (AH) electrode was implanted in the left pectoral region. Ventricular fibrillation was induced and biphasic shocks were delivered by an external defibrillator. The defibrillation threshold was measured and the electrode configurations randomised to: RV-->AH, RV+MCV-->AH, MCV-->AH, and RV-->SCV+AH.

RESULTS

For these configurations, mean (SD) defibrillation thresholds were 27.3 (9.6) J, 11.9 (2.9) J, 15.2 (4.3) J, and 21.8 (9.3) J, respectively. Both electrode configurations incorporating the MCV had defibrillation thresholds that were significantly less than those observed with the RV-->AH (p < 0.001) and RV-->SCV+AH (p < 0.05) configurations. Necropsy dissection showed that the MCV drained into the coronary sinus at a location close to its orifice (mean distance = 2.7 (2.2) mm). The MCV bifurcated into two main branches that drained the right and left ventricles, the left branch being the dominant vessel in the majority (6/7) of cases.

CONCLUSIONS

Placement of specialised defibrillation electrodes within the middle cardiac vein provides more effective defibrillation than a conventional tight ventricular lead.

Anatomy of the human atrioventricular junctions revisited

There have been suggestions made recently that our understanding of the atrioventricular junctions of the heart is less than adequate, with claims for several new findings concerning the arrangement of the ordinary working myocardium and the specialised pathways for atrioventricular conduction. In reality, these claims are grossly exaggerated. The structure and architecture of the pathways for conduction between the atrial and ventricular myocardium are exactly as described by Tawara nearly 100 years ago. The recent claims stem from a failure to assess histological findings in the light of criterions established by Monckeberg and Aschoff following a similar controversy in 1910. The atrioventricular junctions are the areas where the atrial myocardium inserts into, and is separated from, the base of the ventricular mass, apart from at the site of penetration of the specialised axis for atrioventricular conduction. There are two such junctions in the normal heart, surrounding the orifices of the mitral and tricuspid valves. The true septal area between the junctions is of very limited extent, being formed by the membranous septum. Posterior and inferior to this septal area, the atrial myocardium overlies the crest of the ventricular septum, with the atrial component being demarcated by the landmarks of the triangle of Koch. The adjacent structures, and in particular the so-called inferior pyramidal space, were accurately described by McAlpine (Heart and Coronary Arteries, 1975). Thus, again there is no need for revision of our understanding. The key to unravelling much of the alleged controversy is the recognition that, as indicated by Tawara, the atrioventricular node becomes the atrioventricular bundle at the point where the overall axis for conduction penetrates into the central fibrous body. There are also marked differences in arrangement, also described by Tawara, between the disposition of the conduction axis in man as compared to the dog.

The anatomy of interatrial communications--what does the interventionist need to know?

Increasingly, the interventional cardiologist is seeking to close interatrial communications by inserting devices by means of catheterisation. So as to optimise these procedures, it is advantageous to have a firm grasp of the anatomy of the normal atrial septal structures, this then providing the basis to understand the morphology of the holes which can exist between the chambers, not all of which are true septal defects. A true septal structure can be removed without exiting from the cavities of the heart. It is the flap valve of the oval fossa, along with the anterior rim of the fossa, which fulfill this criterion. The remainder of the extensive rim of the normal fossa is no more than an infolding between the walls of the right and left atria and their venous tributaries, and has different dimensions at various points around the circumference. The so-called muscular atrioventricular "septum" is a sandwich incorporating a layer of epicardial fibro-adipose tissue. True defects of the atrial septum, therefore, exist because of deficiency, perforation, or absence of the flap valve. Most of these defects will prove suitable for interventional closure, but potential caveats include multiple defects, aneurysm of the flap valve, or adjacency of the fossa to the venous orifices. The other interatrial communications, namely the sinus venosus, coronary sinus, and "ostium primum" defects are outside the confines of the oval fossa. Recognition of this feature is the key to their diagnosis, and their differentiation from true atrial septal defects. Of these defects, only the coronary sinus defect is likely to be suitable for device closure, and then only in the very rare circumstances when it is seen in isolation.

Ventricular septal defects: morphology of the doubly committed juxtaarterial and muscular variants

In our previous review of the phenotypic features of ventricular septal defects, we concentrated on the perimembranous variant, showing how its distinguishing feature, as viewed from the right ventricle, was fibrous continuity in its postero-inferior rim between the leaflets of the aortic and tricuspid valves. In this second review, we focus on the morphology of those defects which have exclusively muscular rims when viewed from their right side, and the variant with the phenotypic feature of fibrous continuity between the leaflets of the two arterial valves. As with the defects described as being perimembranous, once they have been characterised, it is the position of the defect relative to the components of the morphologically right ventricle that is the primary determinant of the options and strategies for treatment. Therefore, clarification of the morphology is the key to establishing the related risks for each particular defect.

Atrial development in the human heart: an immunohistochemical study with emphasis on the role of mesenchymal tissues

The development of the atrial chambers in the human heart was investigated immunohistochemically using a set of previously described antibodies. This set included the monoclonal antibody 249-9G9, which enabled us to discriminate the endocardial cushion-derived mesenchymal tissues from those derived from extracardiac splanchnic mesoderm, and a monoclonal antibody recognizing the B isoform of creatine kinase, which allowed us to distinguish the right atrial myocardium from the left. The expression patterns obtained with these antibodies, combined with additional histological information derived from the serial sections, permitted us to describe in detail the morphogenetic events involved in the development of the primary atrial septum (septum primum) and the pulmonary vein in human embryos from Carnegie stage 14 onward. The level of expression of creatine kinase B (CK-B) was found to be consistently higher in the left atrial myocardium than in the right, with a sharp boundary between high and low expression located between the primary septum and the left venous valve indicating that the primary septum is part of the left atrial gene-expression domain. This expression pattern of CK-B is reminiscent of that of the homeobox gene Pitx2, which has recently been shown to be important for atrial septation in the mouse. This study also demonstrates a poorly appreciated role of the dorsal mesocardium in cardiac development. From the earliest stage investigated onward, the mesenchyme of the dorsal mesocardium protrudes into the dorsal wall of the primary atrial segment. This dorsal mesenchymal protrusion is continuous with a mesenchymal cap on the leading edge of the primary atrial septum. Neither the mesenchymal tissues of the dorsal protrusion nor the mesenchymal cap on the edge of the primary septum expressed the endocardial tissue antigen recognized by 249-9G9 at any of the stages investigated. The developing pulmonary vein uses the dorsal mesocardium as a conduit to reach the primary atrial segment. Initially, the pulmonary pit, which will becomes the portal of entry for the pulmonary vein, is located along the midline, flanked by two myocardial ridges. As development progresses, tissue remodeling results in the incorporation of the portal of entry of the pulmonary vein in left atrial myocardium, which is recognized because of its high level of creatine. Closure of the primary atrial foramen by the primary atrial septum occurs as a consequence of the fusion of these mesenchymal structures.

Cross-sectional imaging of a cadaveric human heart

The precise relationship of the components of the heart can be difficult to understand. With recent developments in cardiac ultrasound and other imaging modalities, most professionals need to be familiar with cross-sectional cardiac anatomy. We have created a teaching technique based on a normal human heart removed at autopsy. It was scanned using a computed tomography scanner and the images examined in different planes. The images were annotated and used in a computer-based teaching program to convey the details of cardiac anatomy. Images corresponding to planes typically used in echocardiography were also examined. The resulting images were of high resolution and illustrated many subtle structures rarely seen in conventional studies of cardiac anatomy. This system has benefits to both clinicians and anatomists.

Anatomic conundrum in a case of complete transposition of the aorta and pulmonary trunk

An unusual cord-like structure was found on postmortem examination of the heart of a 30-year-old woman who had complete transposition of the great arteries. This extended from the posterior aspect of the right side of the base of the aorta to the posterior wall of the distal part of the arch immediately proximal to the insertion of the arterial ligament. The nature and origin of this is discussed.

The nature of the superior sinus venosus defect

The location, and morphology, of the superior sinus venosus interatrial communication remains contentious. As part of a clinical study, we examined anatomic specimens and echocardiograms so as to clarify the arrangement of the normal atrial septal structures, and compared them with the arrangement found in the superior sinus venosus defect. The pathognomonic diagnostic criterion in the abnormal hearts was overriding of the intact muscular rim of the oval fossa by the mouth of the superior caval vein. This muscular rim is, in reality, a tube of myocardium which encloses a core of extracardiac adipose tissue. Understanding of this anatomic conundrum clarifies the understanding of the structures of both the normal atrial septum and sinus venosus defects.

Developmental patterning of the myocardium

The heart in higher vertebrates develops from a simple tube into a complex organ with four chambers specialized for efficient pumping at pressure. During this period, there is a concomitant change in the level of myocardial organization. One important event is the emergence of trabeculations in the luminal layers of the ventricles, a feature which enables the myocardium to increase its mass in the absence of any discrete coronary circulation. In subsequent development, this trabecular layer becomes solidified in its deeper part, thus increasing the compact component of the ventricular myocardium. The remaining layer adjacent to the ventricular lumen retains its trabeculations, with patterns which are both ventricle- and species-specific. During ontogenesis, the compact layer is initially only a few cells thick, but gradually develops a multilayered spiral architecture. A similar process can be charted in the atrial myocardium, where the luminal trabeculations become the pectinate muscles. Their extent then provides the best guide for distinguishing intrinsically the morphologically right from the left atrium. We review the variations of these processes during the development of the human heart and hearts from commonly used laboratory species (chick, mouse, and rat). Comparison with hearts from lower vertebrates is also provided. Despite some variations, such as the final pattern of papillary or pectinate muscles, the hearts observe the same biomechanical rules, and thus share many common points. The functional importance of myocardial organization is demonstrated by lethality of mouse mutants with perturbed myocardial architecture. We conclude that experimental studies uncovering the rules of myocardial assembly are relevant for the full understanding of development of the human heart.

Relationship in the chick of the developing pulmonary vein to the embryonic systemic venous sinus

Previous studies have shown that the relationship of the systemic venous sinus (sinus venosus) to the developing pulmonary vein are very similar in mice, rats, and man, with the pulmonary vein gaining access to the heart through a persisting segment of the dorsal mesocardium. It has been suggested that this process differs in avian development, with the pulmonary vein being connected to the systemic venous sinus with subsequent transfer to the left atrium. Here we have investigated the anatomical sequence of events in the chick, using serial histological sections and microdissection followed by scanning electron microscopy. We examined a temporal series of chick embryos, ranging from Hamburger and Hamilton stage 15 to stage 30. Although there are some differences in detail, the development of the pulmonary venous connections in the chick was found to be directly comparable to that already described in eutherian mammals. In both mammals and the chick, the dorsal mesocardial connection, which connects the primitive atrium to the posterior thoracic wall, forms a fixed point through which the pulmonary vein gains access to the atrial compartment of the heart, only varying if the connection itself is anomalous. The tributaries of the systemic venous sinus and the primary atrial septal structures develop around the dorsal connection.

The atrioventricular junctions in Ebstein malformation

OBJECTIVE

To review the anatomical structure of the right atrioventricular junction, including the specialised atrioventricular conduction system, in hearts with Ebstein's malformation, to identify potential substrates for the abnormalities in conduction.

METHODS

Five heart specimens representing the morphological spectrum of Ebstein malformation were examined grossly and histologically.

RESULTS

On the endocardial surface, the atrioventricular junction was marked by a faint line in two hearts, and by a small ridge in the other three. Analysis of the right parietal junction in four hearts revealed only two accessory muscular atrioventricular connections. A plane of fibrofatty tissue separated atrial from ventricular myocardium in the right parietal junction in all hearts. The compact atrioventricular node was closer to the coronary sinus than usual. Accessory nodoventricular connections were present in four hearts, while accessory fasciculo-ventricular connections were found in one. The right bundle branch was hypoplastic or absent in four hearts.

CONCLUSIONS

In this small series, the parietal atrioventricular junction was better developed than previously thought. Structural abnormalities of the atrioventricular conduction system, however, were present. These may account for some of the conduction abnormalities frequently observed with the Ebstein malformation.

Late ventricular structure after partial left ventriculectomy

Nine months after partial ventriculectomy, a 53-year-old man died of progressive heart failure. His heart was examined to determine the alignment of the muscle fibers around the ventricular scar, which was 11 cm long, 1.3 cm thick and 4 cm wide. The scar reached 2 to 12 mm beyond the surgical suture line. The fibers in the middle and subendocardial layers were malaligned, resulting in convergence, compression and regional necrosis.

Developmental patterning of the myocardium

The heart in higher vertebrates develops from a simple tube into a complex organ with four chambers specialized for efficient pumping at pressure. During this period, there is a concomitant change in the level of myocardial organization. One important event is the emergence of trabeculations in the luminal layers of the ventricles, a feature which enables the myocardium to increase its mass in the absence of any discrete coronary circulation. In subsequent development, this trabecular layer becomes solidified in its deeper part, thus increasing the compact component of the ventricular myocardium. The remaining layer adjacent to the ventricular lumen retains its trabeculations, with patterns which are both ventricle- and species-specific. During ontogenesis, the compact layer is initially only a few cells thick, but gradually develops a multilayered spiral architecture. A similar process can be charted in the atrial myocardium, where the luminal trabeculations become the pectinate muscles. Their extent then provides the best guide for distinguishing intrinsically the morphologically right from the left atrium. We review the variations of these processes during the development of the human heart and hearts from commonly used laboratory species (chick, mouse, and rat). Comparison with hearts from lower vertebrates is also provided. Despite some variations, such as the final pattern of papillary or pectinate muscles, the hearts observe the same biomechanical rules, and thus share many common points. The functional importance of myocardial organization is demonstrated by lethality of mouse mutants with perturbed myocardial architecture. We conclude that experimental studies uncovering the rules of myocardial assembly are relevant for the full understanding of development of the human heart.

Congenitally malformed hearts from a population of children undergoing cardiac transplantation: comments on sequential segmental analysis and dissection

Our aim is to examine the types of cardiac malformations found in a population of children undergoing cardiac transplantation, and to discuss a method for examining cardiac explants based on intrinsic morphology. We describe in detail the congenital malformations found in 65 cardiac explants acquired from a population of children over a period of 15 years. The specimens were examined and diagnosed using the method of sequential segmental analysis. The most prevalent type of cardiac malformation was severe obstruction of the left heart (29. 2%), followed by double-outlet right ventricle (15.4%), complete transposition (13.8%), hearts with left-hand ventricular topology (10.8%), ventricular septal defect(s) (9.2%), tricuspid valvar agenesis (4.6%), and tetralogy of Fallot (4.6%). These abnormalities accounted for 87.6% of the specimens studied. We also cataloged the extracardiac malformations found at autopsy in those patients who died despite the transplantation. Extracardiac malformations were identified in 10 of the 19 patients who came to autopsy. Three had heterotaxy syndrome with isomerism of the atrial appendages, one with right and two with left isomerism. Other anomalies included tracheoesophageal fistula, pulmonary sequestration, extrahepatic biliary atresia, duodenal atresia, choanal atresia, and vascular malformations.Our study shows that even the most complicated cardiac malformations can readily be diagnosed in an explanted heart using the segmental approach based on observed morphology.

Coronary arterial origins in transposition of the great arteries: factors that affect outcome. A morphological and clinical study

OBJECTIVE

Transfer of the coronary arteries is crucial during the arterial switch operation for transposition, but little attention has been paid to the position of their orifices relative to the valvar sinuses. The objective of this study was to determine the factors which are important for effective transfer and to determine potential surgical significance.

DESIGN

Morphological and clinical study.

SETTING

Two national centres for neonatal cardiac surgery.

PATIENTS

277 patients with transposition of the great arteries. One group comprised 88 necropsy specimens (ages ranging from 17 weeks of fetal life to 17 years old), and the other comprised 189 children undergoing surgery. The coronary artery orifices were inspected relative to the depth of the aortic sinuses (vertical origin), relative to the commissures between the valvar leaflets (radial origin), and their angle of exit from the aortic wall (angle of origin). The data were compared with the surgical results.

RESULTS

In the necropsy specimens, the vertical origin of the arteries was at, or above, the sinutubular junction in 20%, the radial origin was paracommissural in 3%, and the angle of origin was not orthogonal in 7%. Those with high take off and paracommissural origin were all intramural. In the clinical cases, those children with high take off, paracommissural origin or tangential origin had an increased risk at surgery.

CONCLUSIONS

In 20% of hearts, high take off, paracommissural orifice, or tangential origin of coronary arteries is found. This may be recognised preoperatively by echocardiography and may cause technical difficulty in transfer during the arterial switch procedure.

Anatomy of the muscular subpulmonary infundibulum with regard to the Ross procedure

BACKGROUND

To clarify the precise anatomical relationship of the muscular subpulmonary infundibulum.

METHODS

Eleven hearts were dissected, and microscopic sections taken through the arterial trunks of a 37-week-old fetus and of a neonate. The anatomy was also investigated during operative Ross procedures.

RESULTS

The sinotubular junctions of the pulmonary and aortic roots cross obliquely. The leaflets of the pulmonary valve are lifted away from the ventricular septum by the free-standing subpulmonary infundibulum, whereas the aortic valve is deeply wedged between the atrioventricular junctions. The muscular infundibulum spirals around the aortic root, being longest below the right-facing aortic sinus and shortest below the left. The first septal perforating artery pierces the septum below the shortest part of the infundibulum, sometimes within a millimeter of the pulmonary valvar hinge, but a muscular sleeve lifts the pulmonary leaflets from the septal musculature.

CONCLUSIONS

The pulmonary valvar leaflets are supported entirely by free-standing musculature, having no direct relationship with the ventricular septum. This makes possible the Ross procedure.

How constant anatomically is the tendon of Todaro as a marker for the triangle of Koch?

INTRODUCTION

Although well recognized by anatomists as a border of the triangle of Koch demarcating the location of the AV node, the tendon of Todaro is not visible in the operating room or in the catheterization laboratory. Instead, clinicians use as surrogate a projected line between the eustachian valve and the central fibrous body. The constancy of the tendon of Todaro within this border remains to be determined.

MATERIALS AND RESULTS

We reexamined serial histologic sections from 25 adults and 50 infants and gross dissections in four normal hearts. The tendon of Todaro was identified in all cases and traced to the central fibrous body in all but one case. It tended to be thicker in the hearts of infants cases (0.2 to 0.8 mm vs 0.1 to 0.6 mm). The tendon and the hinge-line of the septal leaflet of the tricuspid valve were consistent as landmarks for location of the compact AV node in all the cases studied by histology. Gross dissections traced the tendon to the free edge of the eustachian valve.

CONCLUSION

The tendon of Todaro is present in hearts obtained from both adults and infants. It, or its surrogate, is a reliable border for the triangle of Koch and serves as a landmark to location of the atrial components of the AV conduction axis.

Adolescents' use of tobacco, health locus of control, and self-monitoring

This study examined the association of the traits, health locus of control, and self-monitoring with adolescents' tobacco uptake. Participants were 112 rural adolescents (12 to 19 years old, M = 15.3). Of that sample, 33% used tobacco. Tobacco users were found to score lower on the dimension of Internality and higher on the dimension of Chance, as compared with nonusers of tobacco, indicating a more external Health Locus of Control. In addition, tobacco users were lower self-monitors than were nonusers. These results suggest that adolescents who use tobacco feel less in control of their lives in relation to nonusers, believe that chance plays a larger role in their health, and believe they may be unable to monitor and adapt their communication to achieve positive outcomes.

Categorisation of ventricular septal defects: review of the perimembranous morphology

The Association for European Paediatric Cardiology, the Society of Thoracic Surgeons, and the European Association for Cardiothoracic Surgery, have recently published detailed hierarchical listings for the description of ventricular septal defects. This review details the anatomic basis for the European codes, illustrating the phenotypic features of the various holes that can be described as perimembranous ventricular septal defects.

Common arterial trunk associated with double aortic arch

The combination of common arterial trunk associated with double aortic arch is very rare. We are aware of only four cases ever reported in English literature. We add two cases of this entity and comment on the morphological aspects, the clinical impact of the combined lesions, and their diagnostic and therapeutic implications.

Transthoracic 3-dimensional echocardiography in the assessment of subaortic stenosis due to a restrictive ventricular septal defect in double inlet left ventricle with discordant ventriculoarterial connections

To evaluate the accuracy and clinical utility of three-dimensional echocardiography in the assessment of the size and shape of the ventricular septal defect in double inlet left ventricle.

METHODS

We validated the technique in an autopsy study, and then performed a clinical investigation. Six autopsied hearts were immersed in a waterbath and examined with 3-dimensional echocardiography. We identified the cross-section within the dataset which optimally displayed the ventricular septal defect "en face", and compared its smallest and largest diameters, as well as its area. The ventricular septal defect was then filled with a silicone sealant and a section prepared for direct measurement. In patients, we measured the diameters and area of the ventricular septal defect in endsystole nad computed the aortic valvar area in endsystole from the cross-section showing the aortic valve "en face". Ten patients with double inlet left ventricle, aged between 2 and 15 years, were studied using rotational or parallel scanning. All patients had undergone banding of the pulmonary trunk at a mean age of 7 (3-36) days, usually at the time of repair of the coarctation. Two patients had undergone surgical enlargement of the ventricular septal defect prior to echocardiographic examination.

RESULTS

The correlation between the areas of the ventricular septal defect in the specimens measured directly and by 3-dimensional echocardiography was r=0.98, with limits of agreement between -0.1-0.08 cm2. In the patients, the area of the defect was measured as 3.9+/-2 cm2, whereas the aortic valvar area was 2.6+/-0.9 cm2. The ratio between the areas was 1.5 (0.5-2.3). Three patients with areas of the ventricular septal defect smaller than those of the aortic valve had resting Doppler gradients between double inlet left ventricle and the aorta of 16, 20 and 30 mm Hgs, respectively.

CONCLUSIONS

3-dimensional echocardiography provides accurate assessment of the area of the ventricular septal defect in double inlet left ventricle, and is helpful in identifying patients with subaortic stenosis caused by restrictive defects.

Anatomy of the left atrium: implications for radiofrequency ablation of atrial fibrillation

INTRODUCTION

The feasibility of treating atrial fibrillation with radiofrequency ablation has revived interest in the structure of the left atrium, a chamber that has been neglected in many textbooks of anatomy.

METHODS AND RESULTS

We reviewed the gross structure of the left atrium by examining the septum, the appendage, and insertions of the pulmonary veins in normal hearts. The limited extent of the true septal component is relevant to procedures using the transseptal approach. On gross examination, the musculature of the atrial wall is composed of overlapping bundles of aligned fibers that, in the majority of hearts, are arranged in characteristic patterns with only minor individual variations. Muscular sleeves extend into the walls of the pulmonary veins to varying distances. The longest sleeves are in the left upper veins. Bachmann's bundle anteriorly, and other smaller bundles superiorly and posteriorly, bridge the septal raphe to blend with musculature of the right atrium. Tongues of left atrial musculature from the posterior wall also extend into the wall of the coronary sinus.

CONCLUSION

The left atrium is more complex than usually conceived. Understanding its structure, and the arrangement of its musculature, will help in improving strategies for linear lesions when attempting to compartmentalize the chamber, or when placing focal lesions for ablating ectopic sources.

Localisation and quantitation of autonomic innervation in the porcine heart II: endocardium, myocardium and epicardium

The immunological problems of pig hearts supporting life in human recipients have potentially been solved by transgenic technology. Nevertheless, other problems still remain. Autonomic innervation is important for the control of cardiac dynamics and there is evidence suggesting that some neurons remain intact after transplantation. Previous studies in the human heart have established regional differences in both general autonomic innervation and in its component neural subpopulations. Such studies are lacking in the pig heart. Quantitative immunohistochemical and histochemical techniques were used to demonstrate the pattern of innervation in pig hearts (Sus scrofa). Gradients of immunoreactivity for the general neural marker protein gene product 9.5 were observed both within and between the endocardial, myocardial and epicardial plexuses throughout the 4 cardiac chambers. An extensive ganglionated plexus was observed in the epicardial tissues and, to a lesser extent, in the myocardial tissues. The predominant neural subpopulation displayed acetylcholinesterase activity, throughout the endocardium, myocardium and epicardium. These nerves showed a right to left gradient in density in the endocardial plexus, which was not observed in either the myocardial or epicardial plexuses. A large proportion of nerves in the ganglionated plexus of the atrial epicardial tissues displayed AChE activity, together with their cell bodies. Tyrosine hydroxylase (TH)-immunoreactive nerves were the next most prominent subpopulation throughout the heart. TH-immunoreactive cell bodies were observed in the atrial ganglionated plexuses. Endocardial TH- and NPY-immunoreactive nerves also displayed a right to left gradient in density, whereas in the epicardial tissues they showed a ventricular to atrial gradient. Calcitonin gene-related peptide (CGRP)-immunoreactive nerves were the most abundant peptide-containing subpopulation after those possessing NPY immunoreactivity. They were most abundant in the epicardial tissues of the ventricles. Several important differences were observed between the innervation of the pig heart compared with the human heart. These differences may have implications for the function of donor transgenic pig hearts within human recipients.

Localisation and quantitation of autonomic innervation in the porcine heart I: conduction system

This study was prompted by the prospect of transgenic pigs providing donor hearts for transplantation in human recipients. Autonomic innervation is important for the control of cardiac dynamics, especially in the conduction system. Our objective was to assess the relative distribution of autonomic nerves in the pig heart, focusing initially on the conduction system but addressing also the myocardium, endocardium and epicardium (see Crick et al. 1999). Quantitative immunohistochemical and histochemical techniques were adopted. All regions of the conduction system possessed a significantly higher relative density of the total neural population immunoreactive for the general neuronal marker protein gene product 9.5 (PGP 9.5) than did the adjacent myocardium. A similar density of PGP 9.5-immunoreactive innervation was observed between the sinus node, the transitional region of the atrioventricular node, and the penetrating atrioventricular bundle. A differential pattern of PGP 9.5-immunoreactive innervation was present within the atrioventricular node and between the components of the ventricular conduction tissues, the latter being formed by an intricate network of Purkinje fibres. Numerous ganglion cell bodies were present in the peripheral regions of the sinus node, in the tissues of the atrioventricular groove, and even in the interstices of the compact atrioventricular node. Acetylcholinesterase (AChE)-containing nerves were the dominant subpopulation observed, representing 60-70% of the total pattern of innervation in the nodal tissues and penetrating atrioventricular bundle. Tyrosine hydroxylase (TH)-immunoreactive nerves were the next most abundant neural subpopulation, representing 37% of the total pattern of innervation in the compact atrioventricular node compared with 25% in the transitional nodal region. A minor population of ganglion cell bodies within the atrioventricular nodal region displayed TH immunoreactivity. The dominant peptidergic nerve supply possessed immunoreactivity for neuropeptide Y (NPY), which displayed a similar pattern of distribution to that of TH-immunoreactive nerve fibres. Calcitonin gene-related peptide (CGRP)-immunoreactive nerves represented 8-9% of the total innervation of the nodal tissues and penetrating atrioventricular bundle, increasing to 14-19% in the bundle branches. Somatostatin-immunoreactive nerve fibres were relatively sparse (4-13% of total innervation) and were most abundant in the nodes, especially the compact atrioventricular node. The total pattern of innervation of the porcine conduction system was relatively homogeneous. A substantial proportion of nerve fibres innervating the nodal tissues could be traced to intracardiac ganglia indicative of an extensive intrinsic supply. The innervation of the atrioventricular node and ventricular conduction tissues was similar to that observed in the bovine heart, but markedly different to that of the human heart. It is important that we are aware of these findings in view of the future use of transgenic pig hearts in human xenotransplantation.

Management of ventricular septal defect: a survey of practice in the United Kingdom

BACKGROUND

A survey of pediatric cardiac surgeons was performed to establish current opinions in the United Kingdom concerning closure of ventricular septal defect.

METHODS

Questionnaires were sent to 14 pediatric cardiac centers in 1995 (16 surgeons, 100% response), and again in 1997 (20 surgeons, 100% response).

RESULTS

Results are presented for 1997, with findings from 1995 shown in parentheses. Eleven (6) surgeons used bypass exclusively, 9 (10) sometimes used circulatory arrest. Operative techniques were similar, although the material used for the patch varied. Multiple defects were approached via the transatrial route by 18 (15), right ventriculotomy by 11 (7) and left ventriculotomy by 7 (6). The juxta-arterial defect was approached via the transpulmonary route by 16 (13), a combination by 9 (11), transatrial by 10 (6), and transventricular by 9 (5). The most common indications for pulmonary arterial banding were "Swiss cheese" defect for 13 (13), and functionally single ventricle for 5 (6). Ventricular septal defect associated with coarctation was repaired in two stages by 13 (10), a single stage by 5 (3), or either by 1 (3).

CONCLUSIONS

Pediatric cardiac surgeons in the United Kingdom demonstrate a uniform, evidence-based approach to the management of ventricular septal defect.