MMCTS
(February 19, 2007). doi:10.1510/mmcts.2006.002527
Copyright © 2007 European Association for Cardio-thoracic Surgery
Critical Overview
The surgical anatomy of the aortic root
Robert H. Anderson*
Cardiac Unit, Institute of Child Health, University College, 30 Guilford Street, London WC1N 1EH, UK
* Corresponding author: * Tel.: +44-171-9052295; fax: +44-171-9052324 E-mail: r.anderson{at}ich.ucl.ac.uk
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Summary
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There is still no consensus on the best way to describe the anatomy of the aortic root. Different surgeons use the term ‘annulus’ to describe different parts of the components of the aortic valve. There is also lack of agreement within the surgical literature with regard to the nature of the ventriculo-aortic junction. In this review, I describe the components of the aortic valve, and its supporting ventricular structures, as seen by the anatomist. The essence of the valvar complex is the semilunar attachments of the valvar leaflets. These extend from their basal attachments within the left ventricle to their distal attachments at the sinutubular junction. The extent of the leaflets defines the length of the root. Within this length, the semilunar lines of attachments of the leaflets cross the anatomic ventriculo-aortic junction, the latter being the circular line marking the transition from ventricular to arterial walls. The posterior part of this line is made up of fibrous continuity between the leaflets of the aortic and mitral valves. Because the semilunar lines of attachment cross this anatomic junction, crescents of ventricular wall are incorporated at the base of each arterial valvar sinus, whilst triangles of arterial wall are incorporated between the zones of apposition of the valvar leaflets as they extend to become attached at the sinutubular junction. The overall, three-dimensional arrangement of the leaflets takes the form of a crown. It is questionable whether this crown is best described as an ‘annulus’, just as it is questionable whether the leaflets should be described as ‘cusps’, or only the peripheral parts of the zones of apposition between the leaflets as the ‘commissures’. Only time, and usage, will answer these questions.
Key Words: Leaflets • Commissures • Annulus • Aortic valve
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Introduction
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It is axiomatic that surgeons operating on the aortic root, if they are to perform at maximal efficiency, need fully to understand the structure of the components of the aortic valve. Equally, they need to be able to relate the valve to the surrounding cardiac structures. The latter aspect is the more important since, with the aortic root forming the centrepiece of the heart (Photo 1), its components are related to all the other chambers of the heart.
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Photo 1 This section through the heart, replicating the parasternal long axis echocardiographic cut, shows how the aortic root is the centrepiece of the heart. The root extends from the basal attachments of the valvar leaflets within the ventricle (yellow arrows) to the sinutubular junction (red dotted line). The compass shows the orientation relative to the remaining thoracic organs.
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Despite the obvious need for such information, it remains the fact that there is still no consensus as how best to describe the component parts of the root [1]. In particular, the enigmatic ‘annulus’ is defined and described in markedly different fashions [2, 3]. Indeed, in a recent contribution to the Multimedia Manual [4], the ‘annulus’ is not mentioned until the discussion. The structure thus described, whatever it is, is then introduced without any anatomic definition. In this review, I will describe the arrangement of the aortic root as seen by the anatomist, albeit with some illustrations orientated to match the views obtained by the surgeon. My emphasis will be on the semilunar attachments of the aortic valvar leaflets, and their relationships to the aorta and its ventricular support [5,6,7]. In their own contribution to the Manual, Lausberg and Schäfers [4] rightly emphasise the importance of the aorto-ventricular junction. They fail, however, to tell the reader whether they refer to the junction between the left ventricular structures and the aortic valvar sinuses, this representing the anatomic junction, or the semilunar lines of attachment of the arterial valvar leaflets, this locus representing the haemodynamic ventriculo-arterial junction. As I have shown previously [5], it is recognition of the distinction between these two junctions that is the key to understanding.
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What is the aortic root?
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The aortic root, representing the outflow tract from the left ventricle, provides the supporting structures for the leaflets of the aortic valve, and forms the bridge between the left ventricle and the ascending aorta. The root itself, surrounding and supporting the leaflets, has length in that it extends from the basal attachments of the leaflets within the left ventricle to the sinutubular junction (Photo 2). The discrete anatomic ventriculo-aortic junction is a circular locus within this root, formed where the supporting ventricular structures give way to the fibro-elastic walls of the aortic valvar sinuses. This discrete ring, however, is markedly discordant with the morphology of the attachment of the leaflets of the aortic valve. Indeed, it is crossed at several points by the hingelines of the valvar leaflets. These lines, semilunar in structure, extend throughout the root, running from their basal attachments within the left ventricle to their distal attachments at the sinutubular junction (Photo 3). The root as thus defined, therefore, is a cylinder, its walls being made up of the aortic valvar sinuses along with the interdigitating intersinusal fibrous triangles, and with two small crescents of ventricular muscle incorporated at its proximal end (Schematic 1).
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Photo 2 This close-up of the section illustrated in Photo 1 shows the extent of the aortic root, and reveals the semilunar attachments of the valvar leaflets supported by the right coronary and non-coronary aortic valvar sinuses. The red dotted line again shows the sinutubular junction, which is the distal extent of the root, whilst the red arrow shows the basal attachment of the right coronary aortic valvar leaflet, marking the proximal extent of the root. As shown by the yellow arrow, the anatomic ventriculo-aortic junction is in the middle part of the root, and is crossed by the hinge-lines of the valvar leaflets (see Photo 3).
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Photo 3 The aortic root has been opened from behind and spread apart, so that the full width of the cylinder can be seen. The aortic valvar leaflets have then been removed, revealing the semilunar nature of their attachments. The purple dotted line shows the anatomic ventriculo-aortic junction, which is the union between the ventricular musculature and the aortic wall at the bases of the left and right coronary aortic valvar sinuses (#1, #2), but between the aortic wall and fibrous continuity with the mitral valve at the base of the non-coronary sinus (#3). Note how the semilunar attachments incorporate muscle at the base of the coronary aortic sinuses, but fibrous tissue within the ventricle as the hingelines extend distally to reach the sinutubular junction (red dashed triangle).
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Schematic 1 The cartoon shows a bisected aortic root, and illustrates how the semilunar attachment of the valvar leaflets incorporates aortic wall in the intersinusal triangles, and ventricular tissues at the base of each of the coronary aortic sinuses.
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It is the semilunar attachments of the leaflets within the valvar sinuses that form the haemodynamic junction between the left ventricle and the aorta. All structures on the distal side of these attachments are subject to arterial pressures, whereas all parts proximal to the attachments are subjected to ventricular pressures. In functional terms, all three sinuses of the root, and their contained leaflets, are identical. Anatomically, however, it is necessary to distinguish between the three components. This is best achieved by noting that two of the valvar sinuses give rise to the coronary arteries (Photo 4). These can be nominated as the right and left coronary aortic sinuses. These two sinuses, for their greater part, are made up of the aortic wall. But, because the semilunar attachments of the leaflets cross the anatomic ventriculo-aortic junction, a crescent of ventricular musculature is incorporated at the base of each of these two sinuses (Photo 3, Schematic 1). The third sinus does not give rise to a coronary artery, and hence, can be designated as the non-coronary aortic sinus. There is no muscular crescent at the base of this sinus, since this sinus has exclusively fibrous walls, the basal part beneath the anatomic ventriculo-aortic junction being part of the important continuity between the leaflets of the aortic and mitral valves that is a feature of the outflow tract of the left ventricle (Photo 5).
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Photo 4 The heart has been dissected by removing the atrial chambers and the arterial trunks, and is photographed from above, looking down on the atrioventricular and ventriculo-arterial junctions. It is orientated as it may be seen by the surgeon. The dissection shows how two of the aortic valvar sinuses (#1, #2) give rise to coronary arteries, and can be nominated as the left and right coronary aortic sinuses, respectively. The third sinus (#3) does not give rise to a coronary artery, and hence, is the non-coronary aortic sinus. Note again that the aortic valve forms the cardiac centrepiece.
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Photo 5 The aortic root has been opened from the front, and the leaflets of the aortic valve removed. The dissection shows how the interleaflet triangle between the non-coronary and left coronary aortic sinuses (purple dashed line) is part of the area of fibrous continuity with the aortic leaflet of the mitral valve. The red dotted line marks the anatomic ventriculo-aortic junction.
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The areas between the basal attachments of the aortic sinuses within the ventricle itself, which extend distally to the level of the sinutubular junction, are triangular extensions of the left ventricular outflow tract. They are thinned fibrous areas of the aortic wall. Removing these triangular extensions puts the most distal parts of the left ventricle in direct communication either with the pericardial space or, in the case of the triangle between the two coronary aortic valvar sinuses, with the fibroadipose plane of tissue between the back of the subpulmonary infundibulum and the front of the aorta (Photos 6– 8). As shown in Photo 5, the triangle between the left coronary and the non-coronary aortic valvar sinuses is part of the extensive curtain of aortic-to-mitral valvar fibrous continuity. This triangle, when removed, creates a window to the transverse pericardial sinus, the latter being the space between the back of the aortic root and the anterior atrial walls (Photo 6).
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Photo 6 The heart is viewed from the right and behind, having pulled apart the aorta and the anterior atrial walls to show the transverse pericardial sinus. The interleaflet triangle between the non- and right coronary aortic sinuses has also been removed, showing how it communicates with the transverse sinus.
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Photo 7 The heart has been opened through the right atrium and ventricle, and is viewed from the right side. The fibrous triangle between the non-coronary and right coronary aortic sinuses has been removed, showing how it abuts on the area of the membranous septum, but extends distally so as to be in potential communication with the pericardial cavity above the supraventricular crest of the right ventricle (yellow asterisks).
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Photo 8 This dissection has been made first by removing the free-standing subpulmonary infundibulum, and then by removing the triangle between the two coronary aortic sinuses. As can be seen, the tip of the triangle ‘points’ to the tissue plane between the back of the infundibulum and the aortic root.
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The triangle between the non-coronary and the right coronary aortic valvar sinuses is directly continuous with the membranous part of the ventricular septum. The basal part of this fibrous wall is crossed on its right side by the hinge of the tricuspid valve, dividing the membranous septum itself into atrioventricular and interventricular components. The apical part of the triangle extends to the sinutubular junction. Removal of this part creates a window between the left ventricular outflow tract and the right side of the transverse pericardial sinus, opening externally above the attachment of the supraventricular crest of the right ventricle (Photo 7).
The third triangle, which separates the two coronary aortic valvar sinuses, is the least extensive of the three. To show the location of this triangle, it is first necessary to remove the free-standing muscular subpulmonary infundibulum. Once this has been done, then it can be seen that removal of the triangle itself creates a window between the subaortic outflow tract and the plane of tissue which separates the aortic root from the infundibulum (Photo 8).
The semilunar attachment of the valvar leaflets, therefore, divides the aortic root into supravalvar and subvalvar components. The supravalvar components, the aortic sinuses, are primarily aortic in structure, but contain structures of ventricular origin at their base. The supporting subvalvar parts are primarily ventricular, but extend as thin-walled fibrous triangles to the level of the sinutubular junction. The sinutubular junction itself forms the discrete distal boundary of the root. The valvar leaflets are attached peripherally at this level, and hence, the junction is an integral part of the valvar mechanism. Any significant dilation at the level of the sinutubular junction will produce valvar incompetence. It is moot, therefore, whether stenosis at this level should be labelled as ‘supraaortic’, since the sinutubular junction is just as crucial a component of the overall valvar mechanism as are the leaflets and their supporting sinuses [8]. Anatomically, the sinutubular junction is no more than the distal extent of the overall valvar complex.
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Is there a valvar annulus?
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The answer to this question, the major ongoing conundrum for the cardiac surgeon, depends very much on the structure nominated to represent the ‘annulus’. If we take refuge in the dictionary, and seek etymological origins, then we find that an annulus is no more than a little ring. In this regard, it is certainly the case that the entirety of the aortic root can be removed from the heart, and can be slipped on the finger in the form of a ring. As far as I am aware, however, no surgeon defines the entirety of the root as the aortic valvar annulus. Most surgeons seem to nominate the remnants of the removed valvar leaflets as their annulus [3, 9]. As I have described, however, by virtue of their semilunar position, these structures are supported in crown-like fashion when viewed in the three-dimensional context of the overall aortic root (Schematic 2). Other surgeons, in contrast, define the virtual basal ring constructed by joining together the most proximal parts of each leaflet as the ‘annulus’ [2]. It is certainly this diameter that is typically analysed by the echocardiographer when providing measurements of the diameter of the purported structure (Schematic 3).
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Schematic 2 The cartoon shows an idealised aortic root. The attachments of the valvar leaflets, shown in red, extend through the entire length of the root, from the sinutubular junction, in blue, to the virtual basal ring, shown in green, and produced by joining together the basal attachments of the leaflets. The crown-like attachments of the leaflets cross the anatomic ventriculo-aortic junction, shown in yellow.
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Schematic 3 The cartoon shows how measurement of the basal ring provides information relating only to the entrance of the aortic root. To provide full details, measurements should be taken also of the diameter of the sinutubular junction, and at mid-sinusal level. None of these measurements take account of the diameter at the anatomic ventriculo-aortic junction.
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In view of these ongoing discrepancies, it is my own belief that the aortic root would be best understood if divorced from the concept of the ‘annulus’. This is unlikely to happen. We need to understand, therefore, that the aortic root itself is cylindrical, with the valvar leaflets supported within the root in crown-like, rather than circular, fashion (Schematic 2). We should also take note that there can be marked differences in diameter of its component parts, not only in the normal patient, but particularly in the setting of disease [10, 11].
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The relationships of the aortic root
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When viewed in attitudinally correct orientation [12, 13], the aortic root is positioned to the right and posterior relative to the subpulmonary infundibulum (Photo 9).
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Photo 9 The cavities of the heart have been cast in blue for the right side, and red for the left side. As can be seen, when positioned in attitudinally appropriate fashion, the aortic root is posterior and to the right of the pulmonary valve.
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The subpulmonary infundibulum itself is a complete muscular funnel, supporting in uniform fashion the leaflets of the pulmonary valve. The leaflets of the aortic valve, in contrast, are attached only in part to the muscular walls of the left ventricle, since so as to fit the orifices of both aortic and mitral valves within the circular profile of the left ventricle, there is no muscle between them in the ventricular roof. The aortic root, furthermore, is wedged between the orifices of the two atrioventricular valves (Photo 4). As already discussed, the root is related to all four cardiac chambers. These relationships can be well recognised in the clinical situation. The proximity of the root to the anterior interatrial groove is now appreciated by those who have inserted devices via catheters to close defects of the oval fossa, only to find the arms of the devices eroding into the aorta. The relationship to the subpulmonary infundibulum is well demonstrated by the spread of bacterial infection from the valve, or by aneurysmal dilation of the right coronary aortic sinus of Valsalva. The most important surgical relationship, nonetheless, is probably to the atrioventricular node and the penetrating atrioventricular bundle. The node, located in the wall of the right atrium at the apex of the triangle of Koch, is relatively distant from the root. As the conduction axis penetrates through the central fibrous body, however, it is positioned at the base of the interleaflet triangle between the non- and right coronary aortic sinuses (Photo 9). Having penetrated through the fibrous plane providing atrioventricular insulation, the bundle then branches on the crest of the muscular ventricular septum, the left bundle branch fanning out on the smooth left ventricular side, whilst the cord-like right bundle branch penetrates back through the muscular septum, emerging on the septal surface in the environs of the medial papillary muscle. In this position, therefore, the muscular axis responsible for atrioventricular conduction should be relatively distant from most surgical manoeuvres carried out to replace or repair the aortic valve and its supporting structures (Schematic 4).
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Schematic 4 The cartoon shows the location of the atrioventricular conduction axis as it would be seen by the surgeon looking down through the aortic root.
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Clinical implications
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There are several inferences from the complex interplay of ventricular and arterial structures which make up the aortic root that are important in the clinical context. I have already emphasised that, when seen in long axis section, the diameter of the root varies markedly through its short length. The root is much wider at the midpoint of the sinuses than at either the sinutubular junction or at the basal attachment of the leaflets, whilst the basal diameter can be up to one-fifth wider than the outlet at the sinutubular junction [10, 11]. This becomes of significance when considering measurements of the ‘annulus’. As already discussed, as I understand the situation, most surgeons consider the crown-like hinges of the leaflets to represent this structure, and these extend through all three levels of the root. Proper values can only be provided when measurements are made at the bottom of the valvar attachments, at the widest point of the sinuses, and also at the sinutubular junction (Schematic 3). When considering this feature in the context of cardiac surgery, it is obviously necessary to remove the native valvar leaflets along their semilunar attachments during the process of valvar replacement. Some prostheses then used for the purposes of replacement have a truly circular sewing ring. Should the stitches used for securing this ring be placed within the semilunar remnants of the removed valvar leaflets, then there will be some distortion when the valve is ‘seated’, albeit that this does not usually compromise its subsequent function. When autopsied hearts are examined subsequent to valvar replacement, the circular sewing ring is usually found to be located at the anatomic ventriculo-arterial junction [6]. It is an appreciation of the normal discrepancy between this junction and the haemodynamic junction which is the key to understanding the clinical anatomy of the aortic root. Whether it is appropriate to describe the semilunar attachments as the valvar ‘annulus’ then depends very much on philosophies concerning communication and the usage of words.
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Words and how we use them
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For better or worse, it is now an inescapable fact that American English has become the ‘lingua franca’ of the scientific world. It is surprising, therefore, that in the field of cardiac surgery we employ so many words in a fashion that is foreign to their vernacular use. Consider the word ‘cusp’. If we consult any dictionary, we find that this means a point, or an elevation. This is how the word is used appropriately in anatomy to describe the surfaces of the molar teeth. Is it appropriate, however, to use this word to describe the components of the skirts of tissue that guard the atrioventricular and ventriculo-arterial junctions? In my opinion, these structures, serving the same function at both junctions, are best described as leaflets. Then consider the current use of ‘commissure’. When defined literally, this is the zone of apposition between adjacent anatomic structures, and is used in this fashion to describe the junctions of bones in the skull, or the lines of opening and closing of the eyes and mouth. When used in the setting of the cardiac valves, therefore, the ‘commissure’ should account for the entirety of the zones of apposition between the valvar leaflets. Currently, we use the word to describe only the peripheral ends of these zones of apposition. What, then, of the ‘annulus’? As already discussed, this is no more than a little ring. Is the crown-like configuration of the semilunar valves and their supporting sinuses best described as an annulus? Only time will tell.
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Acknowledgements
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Many of the illustrations used for this review are modified from those appearing in ‘Surgical Anatomy of the Heart’, published by Cambridge University Press. We thank the co-authors of this book, Drs Benson Wilcox and Andrew Cook, for permission to modify the images for the purposes of our current work.
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Footnotes
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 The author has chosen to retain the copyright on this work. 
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References
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- Antunes MJ. The aortic valve: an everlasting mystery to surgeons. Eur J Cardiothorac Surg 2005;28:855–856.[Free Full Text]
- Thubrikar MJ, Labrosse MR, Zehr KJ, Robicsek F, Gong GG, Fowler BL. Aortic root dilatation may alter the dimensions of the valve leaflets. Eur J Cardiothorac Surg 2005;28:850–855.[Abstract/Free Full Text]
- Pretre R, Kadner A, Dave H, Bettex D, Genoni M. Tricuspidisation of the aortic valve with creation of a crown-like annulus is able to restore a normal valve function in bicuspid aortic valves. Eur J Cardiothorac Surg 2006;29:1001–1006.[Abstract/Free Full Text]
- Lausberg HF, Schafers H-J. Valve sparing aortic replacement – root remodeling. Multimed Man Cardiothorac Surg doi:10.1510/mmcts.2006.001982.[Abstract/Free Full Text]
- Anderson RH. Editorial note: The anatomy of arterial valvar stenosis. Int J Cardiol 1990;26:355–360.
- Sutton JP III, Ho SY, Anderson RH. The forgotten interleaflet triangles: a review of the surgical anatomy of the aortic valve. Ann Thorac Surg 1995;59:419–427.[Abstract/Free Full Text]
- Anderson RH. Clinical anatomy of the aortic root. Heart 2000;84:670–673.[Free Full Text]
- Stamm C, Li J, Ho SY, Redington AN, Anderson RH. The aortic root in supravalvular aortic stenosis: the potential surgical relevance of morphologic findings. J Thorac Cardiovasc Surg 1997;114:16–24.[Abstract/Free Full Text]
- Yacoub MH, Kilner PJ, Birks EJ, Misfeld M. The aortic outflow and root: a tale of dynamism and crosstalk. Ann Thorac Surg 1999;68: S37–43.[CrossRef][Medline]
- Reid K. The anatomy of the sinus of Valsalva. Thorax 1970;25:79–85.[Medline]
- Kunzelman KS, Grande J, David TE, Cochran RP, Verrier ED. Aortic root and valve relationships: impact on surgical repair. J Thorac Cardiovasc Surg 1994;107:162–170.[Abstract/Free Full Text]
- McAlpine WA. Heart and coronary arteries. An anatomical atlas for clinical diagnosis, radiological investigation, and surgical treatment. Berlin: Springer-Verlag 1995.
- Cook AC, Anderson RH. Editorial. Attitudinally correct nomenclature. Heart 2002;87:503–506.[Free Full Text]
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Summary
Introduction
