MULTIMEDIA MANUAL OF
doi:10.1093/mmcts/mmu024 published online 11 December 2014.
MMCTS
CARDIO-THORACIC SURGERY
Exercises in anatomy: tetralogy of Fallot Robert H. Andersona*, Anne Sarwarkb, Diane E. Spicerc,d and Carl L. Backerb Institute of Genetic Medicine, Newcastle University, Newcastle-upon-Tyne, UK Division of Pediatric Cardiac Surgery, Lurie Children’s Hospital, Chicago, IL, USA c Division of Pediatric Cardiology, University of Florida, Gainesville, FL, USA d Children’s Heart Institute of Florida, All Children’s Hospital, St Petersburg, FL, USA a
b
* Corresponding author. 60 Earlsfield Road, London SW18 3DN, UK. Tel: +44-20-88704368; e-mail: [email protected] (R.H. Anderson). Received 23 October 2014; accepted 3 November 2014.
Abstract It is axiomatic that those performing surgery on the congenitally malformed heart require a thorough knowledge of the lesions they will be called upon to correct. The necessary anatomical knowledge is becoming increasingly difficult to obtain at first hand, since relatively few centres now hold archives of specimens obtained in an appropriately legal fashion from the patients unfortunately dying in previous years. One centre with such an archive is Ann and Robert H. Lurie Children’s Hospital in Chicago, known previously as Chicago Memorial Children’s Hospital. The archive was established by Farouk S. Idriss, and was subsequently enhanced and consolidated by his son, Rachid. It is now under the care of Carl L. Backer, the current chief of paediatric cardiothoracic surgery at Lurie Children’s. With the support of Carl, the archive has been triaged and catalogued by Diane E. Spicer and Robert H. Anderson. It has now been used to create a series of video presentations, illustrating the salient features of surgical anatomy of selected entities, with the videoclips being edited and prepared for publication by Anne Sarwark. This video contains the fruits of the first of these exercises in anatomy, and is devoted to tetralogy of Fallot. We begin the exercise by making comparisons between the normal heart and the arrangement seen in typical tetralogy. We emphasize the need to recognize the ‘building blocks’ of the normal outflow tracts, and show how they come apart in tetralogy. We then show the variations to be found in the specific morphology of the borders of the hole between the ventricles, with the crest of the apical ventricular septum being overridden by the orifice of the aortic valve such that the latter structure has a biventricular connection. We emphasize that it is the squeeze between the deviated muscular outlet septum and septoparietal trabeculations that is the essential phenotypic feature of the lesion. We then proceed to demonstrate the further variation to be found in the length of the outlet septum, which in extreme cases can be fibrous and hypoplastic rather than muscular. We also show how the ventriculo-arterial connection can vary from being concordant to becoming double outlet from the right ventricle. We conclude by emphasizing that the anatomy of tetralogy can also be recognized when the subpulmonary outflow tract is atretic rather than stenotic. Keywords: Education • Ventricular septal defect • Subpulmonary obstruction • Aortic overriding • Eisenmenger defect
INTRODUCTION This video presentation is the first that we have prepared using specimens from the Farouk S. Idriss Cardiac Registry at the Ann & Robert H. Lurie Children’s Hospital of Chicago, hereto known as Lurie Children’s. The archive was assembled initially by Dr Idriss, who was the chief paediatric cardiovascular thoracic surgeon at Children’s Memorial Hospital, now Lurie Children’s, for the period from 1967 until 1989. The archive was then curated by Rachid Idriss, the son of Farouk, and has been carefully conserved and expanded over the years under the supervision of Constantine Mavroudis, who succeeded Dr Idriss as the chief of paediatric cardiovascular thoracic surgery. Dr Mavroudis was himself succeeded in 2008 by Carl Backer. It was thanks to the support provided by Dr Backer that we have been able to refine the archive, which subsequent to its expansion contained over 2500 cardiac specimens. Over the preceding 5 years, we have selected the best examples of the various lesions, cataloguing them in an individual fashion so that they can now be retained for future purposes of education
and research. On the basis of this analysis, we have selected the best of these retained hearts to produce a series of video presentations. This video has been edited by Anne Sarwark, Medical Editor for the Division of Cardiovascular-thoracic Surgery at Lurie Children’s. The initial set of videoclips is devoted to the anatomical features of the variants of tetralogy of Fallot, comparing the abnormal arrangement of the right ventricular outflow tract with the situation observed in the normal heart.
The anatomy of tetralogy of Fallot As explained in our introduction, we begin our review by examining the normal heart, specifically the relationship of the muscular components making up the outflow tract of the right ventricle [1, 2], which separate one from the other in the setting of tetralogy of Fallot (Video 1) [3]. Our video shows how opening the right ventricle reveals the tricuspid valve, along with the pulmonary valve, the latter supported by the complete submuscular pulmonary
© The Author 2014. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
Video 1: Introduction.
infundibulum. A key feature of the right ventricular anatomy is the location of the muscular strap that reinforces the septal surface of the ventricle, known as the septomarginal trabeculation, or the septal band. When traced towards the ventricular base, it is seen to divide into two limbs [1]. The cephalad limb extends towards the left sinus of the pulmonary trunk, while the caudal limb comes back towards the area of the membranous septum, where it gives rise to the medial papillary muscle. Inserting between the limbs is the supraventricular crest. In the subsequent clips, we will show how the crest itself has two components. In the normal heart, however, we see only the muscular fold that interposes between the hinges of the tricuspid and pulmonary valves. Dissection of a normal heart, as depicted in Video 2, makes it possible to identify the components of the normal supraventricular crest. The dissection was made by cutting away the parietal wall of the right ventricle, and removing the right coronary aortic sinus to reveal the leaflet that guards that sinus. The pulmonary trunk is also dissected to reveal its left sinus. We then demonstrate how the limbs of the septal band clasp the supraventricular crest. Tracing the septal trabeculation towards the apex shows how it gives rise to a free-standing septoparietal trabeculation, the moderator band, which gives rise to the anterior papillary muscle. A further series of septoparietal trabeculations, of major importance in the setting of tetralogy, can then be seen extending from the septomarginal trabeculations to the anterior wall of the right ventricle. The cut across the supraventricular crest itself shows that its larger part is made up of the inner heart curvature, which is the musculature between the hinges of the leaflets of the tricuspid and pulmonary valves, also known as the ventriculo-infundibular fold [1]. The most distal extent of the outflow musculature becomes a free-standing sleeve of infundibular musculature. This lifts the leaflets of the pulmonary valve away from the base of the heart, making it possible to remove the pulmonary valve for use in the Ross procedure [2]. In this regard, the dissection emphasizes the location of the first septal perforating artery. Attention to the insertion of the crest between the limbs of the septomarginal trabeculation shows how, if a knife was inserted at this point, a track could be made into the subaortic outflow tract. In the normally constructed heart, however, there is no way of knowing where the fold stops, and the septal musculature begins. In the normal heart, therefore, it is best simply to recognize the entirety of the muscular fold as the supraventricular crest, and to appreciate that it inserts between the limbs of the septomarginal trabeculation or
2
Video 2: Components of the normal supraventricular crest.
Video 3: The essence of tetralogy.
septal band. As we will show, when we examine the examples of tetralogy, we see how these myocardial building blocks of the outflow tract come apart, permitting recognition in their own right. In the next clip (Video 3), we demonstrate the essence of classical tetralogy of Fallot [3]. The heart is seen from right side, having opened the right ventricle through a cut along its inferior wall. At the site in the normal heart that is occupied by the supraventricular crest, we now see the extensive hole between the ventricles. The four features that constitute the classical tetralogy are readily evident. The first is the hole between the ventricles, with its rightward borders forming the ventricular septal defect [4]. The second feature is the overriding leaflets of the aortic valve, producing biventricular connection of the aortic root [5]. The third feature is narrowing of the subpulmonary outflow tract, which is produced by a squeeze between the deviated outlet, or conal septum and the parietal wall of the right ventricle. The fourth feature is the hypertrophy of the ventricular walls, which is the haemodynamic consequence of the anatomical components of the tetralogy. Of the four features, one can be chosen as the phenotypic feature, namely the squeeze between the deviated outlet septum and the anterior ventricular wall, specifically the septoparietal trabeculations [6]. As we will show subsequently, the dimensions of the outlet septum can vary quite markedly. The ventriculo-infundibular fold is recognized as the structure that separates the leaflets of the
3
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
aortic and tricuspid valves. The muscular outlet septum, recognized because it separates the outflow tracts, has a body, made more stenotic in the demonstrated heart by the presence upon it of a fibrous ridge. It then has septal and parietal attachments. It used to be thought that mere anterocephalad deviation of the muscular outlet septum was sufficient to produce the subpulmonary obstruction. This, however, is not the case, since as we show in Video 4, the outlet septum can be deviated just as much in the Eisenmenger ventricular septal defect without there being subpulmonary obstruction [7]. The heart with the Eisenmenger defect is shown in a comparable fashion with the heart with tetralogy seen in Video 3. As in tetralogy, the ventricular septal defect opens into the right ventricle between the limbs of the septomarginal trabeculation. Also as in tetralogy, there is overriding of the leaflets of the aortic valve. In the Eisenmenger defect, however, the subpulmonary outflow tract is unobstructed. This means that something else is needed to produce the characteristic morphology of tetralogy of Fallot. As we show in Video 5, this is the squeeze between the deviated outlet septum and the septoparietal trabeculations. The heart chosen to reveal the phenotypic features of tetralogy (Video 5) was prepared by cutting away the entire parietal wall of the right ventricle. This reveals the squeeze produced between the outlet septum, deviated in an anterocephalad fashion relative to the limbs of the septoparietal trabeculation, and the hypertro-
Video 4: The Eisenmenger ventricular septal defect.
Video 5: The pathognomonic features of tetralogy.
phied septoparietal trabeculations that form the parietal wall of the right ventricular outflow tract. In the chosen heart, the squeeze is exacerbated by fibrous tissues, which sequestrate the subpulmonary area as a discrete infundibular chamber. Video 6 then uses the same heart as shown in Video 5 to emphasize how the building blocks of the outflow tracts have come apart in the setting of tetralogy. The overriding aorta opens to the right ventricle between the limbs of the septomarginal trabeculation. The septomarginal trabeculation itself, also known as the septal band, extends towards the apex of the right ventricle. Attention is directed to the series of septoparietal trabeculations arising from its anterior border, along with the anterior papillary muscle of the tricuspid valve. It is the squeeze between the more distal of these septoparietal trabeculations and the deviated outlet septum that produces the phenotypic feature of the lesion. The muscular outlet septum, which separates the subaortic and subpulmonary outlets, is exclusively a right ventricular structure in tetralogy. It is the presence of offsetting of the hinges of the arterial valves that reveals the extent of the free-standing subpulmonary infundibular sleeve. The ventriculo-infundibular fold is recognized as interposing between the leaflets of the aortic and tricuspid valves. In this heart, the fold stops short of the posterocaudal limb of the septomarginal trabeculation, revealing the fibrous continuity between the leaflets of the aortic and tricuspid valve. It is this feature that makes the ventricular septal defect perimembranous [3]. As we show in the next clips, however, not all examples of tetralogy have such perimembranous defects. In Video 7A, we have returned to the initial heart demonstrated so as to emphasize the arrangement seen most frequently, namely a perimembranous defect. As is shown, the hole described as the ventricular septal defect is not the same as the geometric interventricular communication [4]. The latter locus is the cranial continuation of the long axis of the muscular ventricular septum. Because of the overriding of the aortic root, this locus transects the leaflets of the aortic valve [5]. It is the margins of the hole between the ventricles as seen from the right ventricular aspect that constitutes the ventricular septal defect, in other words the curved area representing the putative locus of ventricular septation. In most examples of tetralogy, as was seen in Video 6, the ventriculo-infundibular fold stops short of the caudal limb of the septal band. This means that there is fibrous continuity between the leaflets of the aortic and tricuspid valves. In the heart shown, the fibrous area is reinforced in its most posteroinferior quadrant
Video 6: Recognizing the muscle bundles.
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
by the remnant of the interventricular component of the membranous septum [8]. It is these features that make the defect perimembranous. This knowledge is important, since it permits inferences to be made regarding the location of the atrioventricular conduction axis [9]. As is shown, the atrioventricular node is at the apex of the triangle of Koch. The right bundle branch surfaces beneath the medial papillary muscle. Taking a line from the apex of the triangle of Koch to the medial papillary muscle, therefore, shows the location of the conduction axis. Viewing the heart from the left ventricular aspect confirms that fibrous tissue is forming the posteroinferior margin of the defect, specifically the small membranous flap in this particular heart. The conduction axis penetrates through the atrioventricular component of the membranous septum. Usually, there is a small margin between the bundle and the crest of the septum. Sometimes, however, the bundle branches on the crest of the ventricular septum, so it is wise, when approaching from the right side, to place sutures some way away from the free edge of the septum [9]. When the defect is perimembranous, nonetheless, the bundle is always at risk in its posteroinferior margin. In Video 7B, we show an example of tetralogy with a muscular posteroinferior rim. The heart is prepared to replicate the subcostal equivalent of the echocardiographic section. Again, the squeeze is seen between the deviated muscular outlet septum and the hypertrophied septoparietal trabeculations, exacerbated by fibrous excretions at the mouth of the subpulmonary infundibulum. The posteroinferior muscular rim of the septal defect is the consequence of fusion between the ventriculo-infundibular fold and the posterocaudal limb of the septomarginal trabeculation. Because the entirety of the posteroinferior margin of the defect is myocardial, the defect is muscular rather than perimembranous. Viewing the heart from the left ventricular aspect shows how the muscular rim protects the conduction axis. In the heart shown, the muscular posteroinferior rim is relatively thin, so that the surgeon would probably continue to place stitches along the right ventricular aspect so as to be sure of avoiding damage to the conduction axis. In other hearts nonetheless, the muscle bar can be substantial. Stitches can then be placed within the muscular rim without fear of damaging the axis. In Video 7C, we show a further variation in the borders of the ventricular septal defect. In Video 7A and B, we showed the features that distinguished perimembranous from muscular defects, namely fibrous continuity or discontinuity between the leaflets of the aortic and tricuspid valves. The heart shown in Video 7C is neither perimembranous nor muscular. It is doubly committed and juxta-arterial. This is because its cranial border is formed by fibrous tissue joining the leaflets of the aortic and pulmonary valves, often reinforced by a hypoplastic outlet septum that is fibrous rather than muscular. The feature is due to the failure of formation of a muscular subpulmonary infundibulum. In the heart shown, the posteroinferior margin of the defect is itself muscular, thus providing protection of the conduction axis. Viewing the heart from its left ventricular aspect shows the integrity of the membranous septum, with the muscle bar separating the conduction axis from the edge of the defect. As shown in the other heart seen in this clip, nonetheless, such doubly committed and juxtaarterial defects can also extend to become perimembranous. The conduction axis is then at risk posteroinferiorly. Earlier in our exercise, we referred to the variation in the dimensions of the muscular outlet septum. In Video 8, we returned to one of the hearts shown previously to emphasize this point. In the heart shown, the outlet septum is extensive and thick so that the
4
Video 7: Variations in the margins of the VSD: (A) Perimembranous defect.
Video 7: Variations in the margins of the VSD: (B) Muscular posteroinferior rim.
Video 7: Variations in the margins of the VSD: (C) Doubly committed defect.
subpulmonary infundibulum has significant length. The major obstruction is at the mouth of the infundibulum, but additional obstruction can be found at valvar level, often in the setting of a valve with two leaflets. We then make comparisons with a heart sectioned to replicate the subcostal oblique echocardiographic section [10]. The ventricular septal defect is perimembranous, so the infer-
5
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
Video 8: Variations in the size of the outlet septum.
Video 9: Variations in the ventriculo-arterial connection: (A) Concordant connections.
Video 10: Tetralogy with pulmonary atresia.
In Video 9, we show further variation among hearts having the pathognomonic feature of tetralogy of Fallot. This involves the precise ventriculo-arterial connections. In most examples, as shown in Video 9A, two-third of the circumference of the aorta is attached within the morphologically left ventricle, meaning that the ventriculo-arterial connections are concordant. In Video 9B, we see another heart with the pathognomonic feature of tetralogy. In this heart, almost the entirety of the aortic root is supported within the right ventricle. Despite the pathognomonic features of tetralogy, therefore, the heart also has the unequivocal ventriculo-arterial connection of double outlet from the right ventricle. The presence of fibrous continuity between the leaflets of the aortic valve and the atrioventricular valves does not disguise the fact that there is double outlet right ventricle [5]. Hence, tetralogy can co-exist with double outlet connection. The latter feature is no more than the end of the spectrum of variability in commitment of the aorta to the ventricular mass. In the final video of our presentation (Video 10), we show the extreme of obstruction of the subpulmonary outflow tract, namely tetralogy with pulmonary atresia [11]. This is but one of the associated malformations that can co-exist with tetralogy. In the heart demonstrated, the pulmonary trunk narrows as it approaches the ventricular base, with no direct communication between the cavity of the right ventricle and the cavity of the pulmonary trunk. The pulmonary arteries are confluent, and they are fed by a patent arterial duct. In other situations, the pulmonary arteries are fed by systemic-to-pulmonary collateral arteries [11], but an entirely separate video will be needed to show the features of this combination. Suffice it to say that tetralogy can co-exist with varied associated malformations, of which pulmonary atresia is but one. Conflict of interest: none declared.
Video 9: Variations in the ventriculo-arterial connection: (B) Double outlet from the right ventricle.
ence can be drawn that the conduction axis will be at risk beneath the membranous flap. In this heart, however, the muscular outlet septum is hypoplastic so that the subpulmonary infundibulum is relatively short. As shown in the next heart, a spectrum can then be recognized that culminates in hearts with fibrous outlet septums.
REFERENCES [1] Anderson RH, Becker AE, Van Mierop LHS. What should we call the ‘crista’? Br Heart J 1977;39:856–9. [2] Merrick AF, Yacoub MH, Ho SY, Anderson RH. Anatomy of the muscular subpulmonary infundibulum with regard to the Ross procedure. Ann Thorac Surg 2000;69:556–61. [3] Anderson RH, Allwork SP, Ho SY, Lenox CC, Zuberbuhler JR. Surgical anatomy of tetralogy of Fallot. J Thorac Cardiovasc Surg 1981;81:887–96.
6
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
[4] Anderson RH, Spicer DE, Giroud J, Mohun TJ. Tetralogy of Fallot: nosological, morphological, and morphogenetic considerations. Cardiol Young 2013;23:857–65. [5] Anderson RH, Spicer DE, Henry GW, Rigsby C, Hlavacek AM, Mohun TJ. What is aortic overriding? Cardiol Young 2014;1:1–14. [6] Anderson RH, Weinberg PM. The clinical anatomy of tetralogy of Fallot. Cardiol Young 2005;15(Suppl. 1):38–47. [7] Fukuda T, Suzuki T, Ito T. Clinical and morphologic features of perimembranous ventricular septal defect with overriding of the aorta – the so-called Eisenmenger ventricular septal defect. A study making comparisons with tetralogy of Fallot and perimembranous ventricular defect without aortic overriding. Cardiol Young 2000;103:43–352.
[8] Suzuki A, Ho SY, Anderson RH, Deanfield JE. Further morphologic studies on tetralogy of Fallot, with particular emphasis on the prevalence and structure of the membranous flap. J Thorac Cardiovasc Surg 1990;99: 528–35. [9] Anderson RH, Monro JL, Ho SY, Smith A, Deverall PB. Les voies de conduction auriculo-ventriculaires dans la tétralogie de Fallot. Coeur 1977;8:793–807. [10] Gatzoulis MA, Soukias ND, Ho SY, Josen M, Anderson RH. Echocardiographicmorphologic correlations in tetralogy of Fallot. Eur Heart J 1999; 20:221–31. [11] Anderson RH, Devine WA, del Nido P. The surgical anatomy of tetralogy of Fallot with pulmonary atresia rather than pulmonary stenosis. J Card Surg 1991;6:41–59.
doi:10.1093/mmcts/mmu024 published online 11 December 2014.
MMCTS
CARDIO-THORACIC SURGERY
Exercises in anatomy: tetralogy of Fallot Robert H. Andersona*, Anne Sarwarkb, Diane E. Spicerc,d and Carl L. Backerb Institute of Genetic Medicine, Newcastle University, Newcastle-upon-Tyne, UK Division of Pediatric Cardiac Surgery, Lurie Children’s Hospital, Chicago, IL, USA c Division of Pediatric Cardiology, University of Florida, Gainesville, FL, USA d Children’s Heart Institute of Florida, All Children’s Hospital, St Petersburg, FL, USA a
b
* Corresponding author. 60 Earlsfield Road, London SW18 3DN, UK. Tel: +44-20-88704368; e-mail: [email protected] (R.H. Anderson). Received 23 October 2014; accepted 3 November 2014.
Abstract It is axiomatic that those performing surgery on the congenitally malformed heart require a thorough knowledge of the lesions they will be called upon to correct. The necessary anatomical knowledge is becoming increasingly difficult to obtain at first hand, since relatively few centres now hold archives of specimens obtained in an appropriately legal fashion from the patients unfortunately dying in previous years. One centre with such an archive is Ann and Robert H. Lurie Children’s Hospital in Chicago, known previously as Chicago Memorial Children’s Hospital. The archive was established by Farouk S. Idriss, and was subsequently enhanced and consolidated by his son, Rachid. It is now under the care of Carl L. Backer, the current chief of paediatric cardiothoracic surgery at Lurie Children’s. With the support of Carl, the archive has been triaged and catalogued by Diane E. Spicer and Robert H. Anderson. It has now been used to create a series of video presentations, illustrating the salient features of surgical anatomy of selected entities, with the videoclips being edited and prepared for publication by Anne Sarwark. This video contains the fruits of the first of these exercises in anatomy, and is devoted to tetralogy of Fallot. We begin the exercise by making comparisons between the normal heart and the arrangement seen in typical tetralogy. We emphasize the need to recognize the ‘building blocks’ of the normal outflow tracts, and show how they come apart in tetralogy. We then show the variations to be found in the specific morphology of the borders of the hole between the ventricles, with the crest of the apical ventricular septum being overridden by the orifice of the aortic valve such that the latter structure has a biventricular connection. We emphasize that it is the squeeze between the deviated muscular outlet septum and septoparietal trabeculations that is the essential phenotypic feature of the lesion. We then proceed to demonstrate the further variation to be found in the length of the outlet septum, which in extreme cases can be fibrous and hypoplastic rather than muscular. We also show how the ventriculo-arterial connection can vary from being concordant to becoming double outlet from the right ventricle. We conclude by emphasizing that the anatomy of tetralogy can also be recognized when the subpulmonary outflow tract is atretic rather than stenotic. Keywords: Education • Ventricular septal defect • Subpulmonary obstruction • Aortic overriding • Eisenmenger defect
INTRODUCTION This video presentation is the first that we have prepared using specimens from the Farouk S. Idriss Cardiac Registry at the Ann & Robert H. Lurie Children’s Hospital of Chicago, hereto known as Lurie Children’s. The archive was assembled initially by Dr Idriss, who was the chief paediatric cardiovascular thoracic surgeon at Children’s Memorial Hospital, now Lurie Children’s, for the period from 1967 until 1989. The archive was then curated by Rachid Idriss, the son of Farouk, and has been carefully conserved and expanded over the years under the supervision of Constantine Mavroudis, who succeeded Dr Idriss as the chief of paediatric cardiovascular thoracic surgery. Dr Mavroudis was himself succeeded in 2008 by Carl Backer. It was thanks to the support provided by Dr Backer that we have been able to refine the archive, which subsequent to its expansion contained over 2500 cardiac specimens. Over the preceding 5 years, we have selected the best examples of the various lesions, cataloguing them in an individual fashion so that they can now be retained for future purposes of education
and research. On the basis of this analysis, we have selected the best of these retained hearts to produce a series of video presentations. This video has been edited by Anne Sarwark, Medical Editor for the Division of Cardiovascular-thoracic Surgery at Lurie Children’s. The initial set of videoclips is devoted to the anatomical features of the variants of tetralogy of Fallot, comparing the abnormal arrangement of the right ventricular outflow tract with the situation observed in the normal heart.
The anatomy of tetralogy of Fallot As explained in our introduction, we begin our review by examining the normal heart, specifically the relationship of the muscular components making up the outflow tract of the right ventricle [1, 2], which separate one from the other in the setting of tetralogy of Fallot (Video 1) [3]. Our video shows how opening the right ventricle reveals the tricuspid valve, along with the pulmonary valve, the latter supported by the complete submuscular pulmonary
© The Author 2014. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
Video 1: Introduction.
infundibulum. A key feature of the right ventricular anatomy is the location of the muscular strap that reinforces the septal surface of the ventricle, known as the septomarginal trabeculation, or the septal band. When traced towards the ventricular base, it is seen to divide into two limbs [1]. The cephalad limb extends towards the left sinus of the pulmonary trunk, while the caudal limb comes back towards the area of the membranous septum, where it gives rise to the medial papillary muscle. Inserting between the limbs is the supraventricular crest. In the subsequent clips, we will show how the crest itself has two components. In the normal heart, however, we see only the muscular fold that interposes between the hinges of the tricuspid and pulmonary valves. Dissection of a normal heart, as depicted in Video 2, makes it possible to identify the components of the normal supraventricular crest. The dissection was made by cutting away the parietal wall of the right ventricle, and removing the right coronary aortic sinus to reveal the leaflet that guards that sinus. The pulmonary trunk is also dissected to reveal its left sinus. We then demonstrate how the limbs of the septal band clasp the supraventricular crest. Tracing the septal trabeculation towards the apex shows how it gives rise to a free-standing septoparietal trabeculation, the moderator band, which gives rise to the anterior papillary muscle. A further series of septoparietal trabeculations, of major importance in the setting of tetralogy, can then be seen extending from the septomarginal trabeculations to the anterior wall of the right ventricle. The cut across the supraventricular crest itself shows that its larger part is made up of the inner heart curvature, which is the musculature between the hinges of the leaflets of the tricuspid and pulmonary valves, also known as the ventriculo-infundibular fold [1]. The most distal extent of the outflow musculature becomes a free-standing sleeve of infundibular musculature. This lifts the leaflets of the pulmonary valve away from the base of the heart, making it possible to remove the pulmonary valve for use in the Ross procedure [2]. In this regard, the dissection emphasizes the location of the first septal perforating artery. Attention to the insertion of the crest between the limbs of the septomarginal trabeculation shows how, if a knife was inserted at this point, a track could be made into the subaortic outflow tract. In the normally constructed heart, however, there is no way of knowing where the fold stops, and the septal musculature begins. In the normal heart, therefore, it is best simply to recognize the entirety of the muscular fold as the supraventricular crest, and to appreciate that it inserts between the limbs of the septomarginal trabeculation or
2
Video 2: Components of the normal supraventricular crest.
Video 3: The essence of tetralogy.
septal band. As we will show, when we examine the examples of tetralogy, we see how these myocardial building blocks of the outflow tract come apart, permitting recognition in their own right. In the next clip (Video 3), we demonstrate the essence of classical tetralogy of Fallot [3]. The heart is seen from right side, having opened the right ventricle through a cut along its inferior wall. At the site in the normal heart that is occupied by the supraventricular crest, we now see the extensive hole between the ventricles. The four features that constitute the classical tetralogy are readily evident. The first is the hole between the ventricles, with its rightward borders forming the ventricular septal defect [4]. The second feature is the overriding leaflets of the aortic valve, producing biventricular connection of the aortic root [5]. The third feature is narrowing of the subpulmonary outflow tract, which is produced by a squeeze between the deviated outlet, or conal septum and the parietal wall of the right ventricle. The fourth feature is the hypertrophy of the ventricular walls, which is the haemodynamic consequence of the anatomical components of the tetralogy. Of the four features, one can be chosen as the phenotypic feature, namely the squeeze between the deviated outlet septum and the anterior ventricular wall, specifically the septoparietal trabeculations [6]. As we will show subsequently, the dimensions of the outlet septum can vary quite markedly. The ventriculo-infundibular fold is recognized as the structure that separates the leaflets of the
3
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
aortic and tricuspid valves. The muscular outlet septum, recognized because it separates the outflow tracts, has a body, made more stenotic in the demonstrated heart by the presence upon it of a fibrous ridge. It then has septal and parietal attachments. It used to be thought that mere anterocephalad deviation of the muscular outlet septum was sufficient to produce the subpulmonary obstruction. This, however, is not the case, since as we show in Video 4, the outlet septum can be deviated just as much in the Eisenmenger ventricular septal defect without there being subpulmonary obstruction [7]. The heart with the Eisenmenger defect is shown in a comparable fashion with the heart with tetralogy seen in Video 3. As in tetralogy, the ventricular septal defect opens into the right ventricle between the limbs of the septomarginal trabeculation. Also as in tetralogy, there is overriding of the leaflets of the aortic valve. In the Eisenmenger defect, however, the subpulmonary outflow tract is unobstructed. This means that something else is needed to produce the characteristic morphology of tetralogy of Fallot. As we show in Video 5, this is the squeeze between the deviated outlet septum and the septoparietal trabeculations. The heart chosen to reveal the phenotypic features of tetralogy (Video 5) was prepared by cutting away the entire parietal wall of the right ventricle. This reveals the squeeze produced between the outlet septum, deviated in an anterocephalad fashion relative to the limbs of the septoparietal trabeculation, and the hypertro-
Video 4: The Eisenmenger ventricular septal defect.
Video 5: The pathognomonic features of tetralogy.
phied septoparietal trabeculations that form the parietal wall of the right ventricular outflow tract. In the chosen heart, the squeeze is exacerbated by fibrous tissues, which sequestrate the subpulmonary area as a discrete infundibular chamber. Video 6 then uses the same heart as shown in Video 5 to emphasize how the building blocks of the outflow tracts have come apart in the setting of tetralogy. The overriding aorta opens to the right ventricle between the limbs of the septomarginal trabeculation. The septomarginal trabeculation itself, also known as the septal band, extends towards the apex of the right ventricle. Attention is directed to the series of septoparietal trabeculations arising from its anterior border, along with the anterior papillary muscle of the tricuspid valve. It is the squeeze between the more distal of these septoparietal trabeculations and the deviated outlet septum that produces the phenotypic feature of the lesion. The muscular outlet septum, which separates the subaortic and subpulmonary outlets, is exclusively a right ventricular structure in tetralogy. It is the presence of offsetting of the hinges of the arterial valves that reveals the extent of the free-standing subpulmonary infundibular sleeve. The ventriculo-infundibular fold is recognized as interposing between the leaflets of the aortic and tricuspid valves. In this heart, the fold stops short of the posterocaudal limb of the septomarginal trabeculation, revealing the fibrous continuity between the leaflets of the aortic and tricuspid valve. It is this feature that makes the ventricular septal defect perimembranous [3]. As we show in the next clips, however, not all examples of tetralogy have such perimembranous defects. In Video 7A, we have returned to the initial heart demonstrated so as to emphasize the arrangement seen most frequently, namely a perimembranous defect. As is shown, the hole described as the ventricular septal defect is not the same as the geometric interventricular communication [4]. The latter locus is the cranial continuation of the long axis of the muscular ventricular septum. Because of the overriding of the aortic root, this locus transects the leaflets of the aortic valve [5]. It is the margins of the hole between the ventricles as seen from the right ventricular aspect that constitutes the ventricular septal defect, in other words the curved area representing the putative locus of ventricular septation. In most examples of tetralogy, as was seen in Video 6, the ventriculo-infundibular fold stops short of the caudal limb of the septal band. This means that there is fibrous continuity between the leaflets of the aortic and tricuspid valves. In the heart shown, the fibrous area is reinforced in its most posteroinferior quadrant
Video 6: Recognizing the muscle bundles.
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
by the remnant of the interventricular component of the membranous septum [8]. It is these features that make the defect perimembranous. This knowledge is important, since it permits inferences to be made regarding the location of the atrioventricular conduction axis [9]. As is shown, the atrioventricular node is at the apex of the triangle of Koch. The right bundle branch surfaces beneath the medial papillary muscle. Taking a line from the apex of the triangle of Koch to the medial papillary muscle, therefore, shows the location of the conduction axis. Viewing the heart from the left ventricular aspect confirms that fibrous tissue is forming the posteroinferior margin of the defect, specifically the small membranous flap in this particular heart. The conduction axis penetrates through the atrioventricular component of the membranous septum. Usually, there is a small margin between the bundle and the crest of the septum. Sometimes, however, the bundle branches on the crest of the ventricular septum, so it is wise, when approaching from the right side, to place sutures some way away from the free edge of the septum [9]. When the defect is perimembranous, nonetheless, the bundle is always at risk in its posteroinferior margin. In Video 7B, we show an example of tetralogy with a muscular posteroinferior rim. The heart is prepared to replicate the subcostal equivalent of the echocardiographic section. Again, the squeeze is seen between the deviated muscular outlet septum and the hypertrophied septoparietal trabeculations, exacerbated by fibrous excretions at the mouth of the subpulmonary infundibulum. The posteroinferior muscular rim of the septal defect is the consequence of fusion between the ventriculo-infundibular fold and the posterocaudal limb of the septomarginal trabeculation. Because the entirety of the posteroinferior margin of the defect is myocardial, the defect is muscular rather than perimembranous. Viewing the heart from the left ventricular aspect shows how the muscular rim protects the conduction axis. In the heart shown, the muscular posteroinferior rim is relatively thin, so that the surgeon would probably continue to place stitches along the right ventricular aspect so as to be sure of avoiding damage to the conduction axis. In other hearts nonetheless, the muscle bar can be substantial. Stitches can then be placed within the muscular rim without fear of damaging the axis. In Video 7C, we show a further variation in the borders of the ventricular septal defect. In Video 7A and B, we showed the features that distinguished perimembranous from muscular defects, namely fibrous continuity or discontinuity between the leaflets of the aortic and tricuspid valves. The heart shown in Video 7C is neither perimembranous nor muscular. It is doubly committed and juxta-arterial. This is because its cranial border is formed by fibrous tissue joining the leaflets of the aortic and pulmonary valves, often reinforced by a hypoplastic outlet septum that is fibrous rather than muscular. The feature is due to the failure of formation of a muscular subpulmonary infundibulum. In the heart shown, the posteroinferior margin of the defect is itself muscular, thus providing protection of the conduction axis. Viewing the heart from its left ventricular aspect shows the integrity of the membranous septum, with the muscle bar separating the conduction axis from the edge of the defect. As shown in the other heart seen in this clip, nonetheless, such doubly committed and juxtaarterial defects can also extend to become perimembranous. The conduction axis is then at risk posteroinferiorly. Earlier in our exercise, we referred to the variation in the dimensions of the muscular outlet septum. In Video 8, we returned to one of the hearts shown previously to emphasize this point. In the heart shown, the outlet septum is extensive and thick so that the
4
Video 7: Variations in the margins of the VSD: (A) Perimembranous defect.
Video 7: Variations in the margins of the VSD: (B) Muscular posteroinferior rim.
Video 7: Variations in the margins of the VSD: (C) Doubly committed defect.
subpulmonary infundibulum has significant length. The major obstruction is at the mouth of the infundibulum, but additional obstruction can be found at valvar level, often in the setting of a valve with two leaflets. We then make comparisons with a heart sectioned to replicate the subcostal oblique echocardiographic section [10]. The ventricular septal defect is perimembranous, so the infer-
5
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
Video 8: Variations in the size of the outlet septum.
Video 9: Variations in the ventriculo-arterial connection: (A) Concordant connections.
Video 10: Tetralogy with pulmonary atresia.
In Video 9, we show further variation among hearts having the pathognomonic feature of tetralogy of Fallot. This involves the precise ventriculo-arterial connections. In most examples, as shown in Video 9A, two-third of the circumference of the aorta is attached within the morphologically left ventricle, meaning that the ventriculo-arterial connections are concordant. In Video 9B, we see another heart with the pathognomonic feature of tetralogy. In this heart, almost the entirety of the aortic root is supported within the right ventricle. Despite the pathognomonic features of tetralogy, therefore, the heart also has the unequivocal ventriculo-arterial connection of double outlet from the right ventricle. The presence of fibrous continuity between the leaflets of the aortic valve and the atrioventricular valves does not disguise the fact that there is double outlet right ventricle [5]. Hence, tetralogy can co-exist with double outlet connection. The latter feature is no more than the end of the spectrum of variability in commitment of the aorta to the ventricular mass. In the final video of our presentation (Video 10), we show the extreme of obstruction of the subpulmonary outflow tract, namely tetralogy with pulmonary atresia [11]. This is but one of the associated malformations that can co-exist with tetralogy. In the heart demonstrated, the pulmonary trunk narrows as it approaches the ventricular base, with no direct communication between the cavity of the right ventricle and the cavity of the pulmonary trunk. The pulmonary arteries are confluent, and they are fed by a patent arterial duct. In other situations, the pulmonary arteries are fed by systemic-to-pulmonary collateral arteries [11], but an entirely separate video will be needed to show the features of this combination. Suffice it to say that tetralogy can co-exist with varied associated malformations, of which pulmonary atresia is but one. Conflict of interest: none declared.
Video 9: Variations in the ventriculo-arterial connection: (B) Double outlet from the right ventricle.
ence can be drawn that the conduction axis will be at risk beneath the membranous flap. In this heart, however, the muscular outlet septum is hypoplastic so that the subpulmonary infundibulum is relatively short. As shown in the next heart, a spectrum can then be recognized that culminates in hearts with fibrous outlet septums.
REFERENCES [1] Anderson RH, Becker AE, Van Mierop LHS. What should we call the ‘crista’? Br Heart J 1977;39:856–9. [2] Merrick AF, Yacoub MH, Ho SY, Anderson RH. Anatomy of the muscular subpulmonary infundibulum with regard to the Ross procedure. Ann Thorac Surg 2000;69:556–61. [3] Anderson RH, Allwork SP, Ho SY, Lenox CC, Zuberbuhler JR. Surgical anatomy of tetralogy of Fallot. J Thorac Cardiovasc Surg 1981;81:887–96.
6
R.H. Anderson et al. / Multimedia Manual of Cardio-Thoracic Surgery
[4] Anderson RH, Spicer DE, Giroud J, Mohun TJ. Tetralogy of Fallot: nosological, morphological, and morphogenetic considerations. Cardiol Young 2013;23:857–65. [5] Anderson RH, Spicer DE, Henry GW, Rigsby C, Hlavacek AM, Mohun TJ. What is aortic overriding? Cardiol Young 2014;1:1–14. [6] Anderson RH, Weinberg PM. The clinical anatomy of tetralogy of Fallot. Cardiol Young 2005;15(Suppl. 1):38–47. [7] Fukuda T, Suzuki T, Ito T. Clinical and morphologic features of perimembranous ventricular septal defect with overriding of the aorta – the so-called Eisenmenger ventricular septal defect. A study making comparisons with tetralogy of Fallot and perimembranous ventricular defect without aortic overriding. Cardiol Young 2000;103:43–352.
[8] Suzuki A, Ho SY, Anderson RH, Deanfield JE. Further morphologic studies on tetralogy of Fallot, with particular emphasis on the prevalence and structure of the membranous flap. J Thorac Cardiovasc Surg 1990;99: 528–35. [9] Anderson RH, Monro JL, Ho SY, Smith A, Deverall PB. Les voies de conduction auriculo-ventriculaires dans la tétralogie de Fallot. Coeur 1977;8:793–807. [10] Gatzoulis MA, Soukias ND, Ho SY, Josen M, Anderson RH. Echocardiographicmorphologic correlations in tetralogy of Fallot. Eur Heart J 1999; 20:221–31. [11] Anderson RH, Devine WA, del Nido P. The surgical anatomy of tetralogy of Fallot with pulmonary atresia rather than pulmonary stenosis. J Card Surg 1991;6:41–59.
