Advances in Treatments for Aortic Valve and Root Diseases

This book describes the different aspects of aortic valve and root diseases including comprehensive discussion of the state-of-the-art diagnostic imaging options, disease risk stratification, selection of candidates for valve repair or percutaneous intervention, and most recent therapeutic options. The growing prevalence of valvular heart disease represents a major challenge in terms of short- and long-term management and surveillance. Aortic valve diseases, including aortic stenosis and regurgitation, are among the most frequent of these, while the number of cases of aortic root disease is also on the rise. Aortic valve disease treatment options include valve surgery, valve repair, minimally invasive valve surgery, and percutaneous approaches and all are covered in this volume.

Advances in Treatments for Aortic Valve and Root Diseases is a highly illustrated, case oriented reference aimed at cardiology fellows in training, while also helpful to surgeons, cardiologists, imagers, interventionalists, as well as other clinicians and students involved in the diagnosis and treatment of aortic valve and root diseases.

• Language: English
• Publisher: Springer
• Release date: Apr 3, 2018
• ISBN: 9783319664835

Book preview

Part IAnatomy

© Springer International Publishing AG, part of Springer Nature 2018

Khalil Fattouch, Patrizio Lancellotti, Mani A. Vannan and Giuseppe Speziale (eds.)Advances in Treatments for Aortic Valve and Root Diseaseshttps://doi.org/10.1007/978-3-319-66483-5_1

1. The Clinical Anatomy of the Aortic Root

Robert H. Anderson¹, ²  , Diane E. Spicer³, ⁴ and Shumpei Mori⁵

(1)

Institute of Genetic Medicine, Newcastle University, Newcastle-upon-Tyne, UK

(2)

60 Earlsfield Road, London, SW18 3DN, UK

(3)

Department of Pediatric Cardiology, University of Florida, Gainesville, FL, USA

(4)

Johns Hopkins All Children’s Heart Institute, St Petersburg, FL, USA

(5)

Division of Cardiovascular Medicine, Department of Internal Medicine, Kobe University Graduate School of Medicine, Kobe, Japan

Robert H. Anderson

Email: [e-mail]

Keywords

ValveSinusSinutubular junctionAnnulusLeaflet

1.1 Introduction

The definitive outflow tracts in the postnatal hearts possess three components. These are the intrapericardial arterial trunks, the arterial roots, and the subvalvar ventricular outflow tracts. The distal boundary of the aortic root with the intrapericardial component of the ascending aorta is clearly marked by the sinutubular junction. The proximal boundary, in contrast, has no direct anatomic substrate. It is represented by the virtual plane that can be created by joining together the basal attachments of the moving components of the root. As we will see, the virtual nature of this entrance to the root creates problems in defining the so-called valvar annulus. This is the more so, since many surgeons consider the semilunar hinges of the moving components to represent the annulus [1]. This is but one of the issues with nomenclature which plague the search for consensus when describing the components of the aortic root. As was emphasised by the study group of German cardiac surgeons, the current situation can be considered as a modern-day tower of Babel [1]. In this chapter, as we describe the anatomical feature of the root, we also seek to provide solutions to the terminological problems. We emphasise the importance, if we are to achive maximal clinical traction, of describing the components in attitudinally appropriate fashion [2]. With this in mind, we show how the availability of datasets obtained using computed tomography now permits the heart to be viewed with as much, or even more, accuracy during life as when the organ is held in one’s hands in the autopsy room [3]. To start, we explain the reasons underscoring our choice of the terms used to describe the components of the root. Thereafter, we describe its central position within the heart. We then concentrate on those anatomical features that are of particular interest to the diagnostician, the surgeon, and the catheter interventionist.

1.2 Naming the Components of the Root

The words we use to describe the parts of the aortic root are equally applicable to the pulmonary root. They can, by and large, also be used to describe the components of the atrioventricular valves. This comparison serves also to emphasise some of the current difficulties. Thus, there are some who seek to differentiate the moving components of the atrioventricular valves as the leaflets, but to describe the moving parts of the arterial valves as the cusps. There are multiple reasons why this approach is less than satisfactory. In the first place, the right-sided atrioventricular valve is universally called the tricuspid valve , showing that, at some time previously, the moving parts of this valve, and the mitral valve, with its alternative title of the bicuspid valve, were also considered to be cusps. This likely reflects the similarity to the surfaces of the molar and premolar teeth to the surfaces of the closed valves when viewed from their atrial aspect. The closed surfaces of the arterial valves also present a similar appearance when viewed from their ventricular aspect (Fig. 1.1a). It is very unusual nowadays, however, for the arterial valves to be assessed from this aspect. The surgeon tends to view the valves from the arterial aspect. For morphologists, they are typically viewed, and interrogated, in opened fashion (Fig. 1.1b). Assessment from the opened viewpoint then emphasises the inadequacy of using the word cusp to describe the moving components. When defined literally, a cusp is a point or elevation, or the crossing point of two curves. As is seen in Fig. 1.1b, the hinges of the curved moving components cross at the sinutubular junction. If defined literally, therefore, this crossing point should be recognised as the cusp. Instead, these distal attachments of the moving components at the sinutubular junction are universally described as the valvar commissures (Fig. 1.1b).

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Fig. 1.1

The images show the problems with the use of cusp to describe the moving parts of the aortic root. If defined literally, a cusp is a point or elevation, or the crossing point of two curves. When seen in closed position (Panel a), there is a resemblance between the ventricular margins of the moving parts and the surface of a molar or premolar tooth, these surfaces also described as cusps. When seen in the open position, however, (Panel b), there is no resemblance of the moving parts to the surfaces of the teeth. Instead, the crossing points of their semilunar hinges become evident at the sinutubular junction (white ovals on broad dashed black line). These points, however, are traditionally described as the valvar commissures (see Fig. 1.2). Note the area of fibrous continuity between the moving components of the aortic and mitral valves, shown as a black dotted line in panel a, and the virtual nature of the entrance to the root shown as the black dotted line in Panel b. Note also the fibrous triangles separating the ventricular aspects of the semilunar moving components (black arrows in panel b). The authors retain their intellectual copyright in the images from which these figures were prepared

This usage then creates still further problems in terms of naming, since for anatomists a commissure is the line of union of adjacent structures, as seen in the lips or the eyelids. If defined in anatomical fashion, therefore, it would be the zones of apposition of the moving components between their peripheral attachments at the sinutubular junction and the centroid of the valvar orifice which would be called the commissures (Fig. 1.2). It is most unlikely that clinicians will ever desist from naming the peripheral attachments as the commissures, so we follow this conventional usage in this chapter. It is necessary, however, also to recognise the importance of the zones of apposition between the moving components. It is the snug closure along these areas (Fig. 1.2) that ensures valvar competence. That leaves us with the problem of how properly to describe the moving components themselves. We prefer to name these parts as the leaflets, thus avoiding the need to use cusp. We have a further reason underscording this approach. This is because cusp is also seemingly used by some investigators, particularly electrophysiologists [4], to describe the pockets of the aortic root which support the leaflets in semilunar fashion. The components of the root that support the leaflets are the sinuses of Valsalva. They should not be labelled as cusps.

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Fig. 1.2

The images show the arterial aspect of the closed aortic valve as seen in an anatomical specimen (Panel a) and a fish-eye view of a reconstructed computed tomographic dataset obtained from a patient undergoing analysis of coronary arterial disease. The stars show the peripheral attachments of the semilunar hinges of the moving components of the root at the sinutubular junction. These are known traditionally as the commissures. When defined anatomically, however, a commissure is the zone of apposition between two adjacent parts, as shown by the white arrows. Since it is unlikely that commissure will be used to describe anything other than the peripheral attachments of the hingelines, we will describe the junctional areas as the zones of apposition. As is seen from both panels, these fit snugly together when the valve is competent. The authors retain their intellectual copyright in the images from which these figures were prepared

The anatomy of the sinuses of Valsalva , furthermore, is itself complicated. This is because the semilunar hinges of the leaflets supported by the two sinuses that give rise to the coronary arteries (Fig. 1.3a) extend beyond the anatomic junction of the arterial sinusal walls with the supporting ventricular structures. This means that, in these two sinuses, which are adjacent to the pulmonary trunk, there are small crescents of myocardium incorporated at their base, with the myocardial support being greater in the right coronary than the left coronary sinus (Fig. 1.3b). There is no myocardium, however, incorporated at the base of the third aortic sinus, which is opposite to the pulmonary trunk (Fig. 1.3a). The leaflet of the aortic valve supported by this sinus is in fibrous continuity with the aortic, or anterior, leaflet of the mitral valve. In most instances, this sinus is called the non-coronary sinus. This is usually an appropriate designation. Very rarely, however, a coronary artery can take its origin from this sinus [5]. In such circumstances, it makes no sense to name the sinus as being non-coronary. We prefer, therefore, to identify the sinus as being non-adjacent (Fig. 1.3a).

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Fig. 1.3

The images show the optimal convention for naming the sinuses of the aortic root. The two sinuses adjacent to the pulmonary root give rise to the coronary arteries. The root is viewed from the arterial aspect in the specimen shown in panel a. The third sinus, which does not usually give rise to a coronary artery, is not adjacent to the pulmonary root. It can, however, on rare occasions give rise to a coronary artery. We prefer, therefore, to describe the sinus as being non-adjacent. The image obtained by virtual dissection of a computed tomographic dataset obtained from a patient undergoing analysis for coronary arterial disease (Panel b), orientated to match the image shown in panel a, reveals the presence of the small crescents of myocardium incorporated at the base of the two sinuses which give rise to the coronary arteries (white double headed dotted arrows). The authors retain their intellectual copyright in the images from which these figures were prepared

When we assess the aortic root in opened fashion (Fig. 1.1b), we then recognise further components of the root which, until relatively recently, have received scant attention from clinicians. These are the interleaflet triangles [6]. Part of the subvalvar component of the root, and hence part of the left ventricular cavity, they are distal to the virtual basal plane created by joining together the proximal attachments of the semilunar leaflets. They separate, furthermore, the cavity of the left ventricle from either the pericardial space, or the tissue plane between the aortic root and the subpulmonary infundibulum. We will describe, in a subsequent section, the relationships of these triangles in detail, since in many ways an appreciation of their location is the key to understanding the overall valvar anatomy [6]. As can be seen from Fig. 1.1b, nonetheless, the triangles occupy the spaces within the root located on the ventricular aspects of the semilunar hinges of the leaflets. It is these semilunar hinges, therefore, which mark the haemodynamic ventriculo-arterial junction. They separate the parts of the root which, during catheterisation procedures, register aortic as opposed to left ventricular pressures. These haemodynamic ventriculo-arterial junctions, however, are markedly different from the anatomic junctions between the proximal extent of the arterial walls of the valvar sinuses and the supporting ventricular structures [7]. As already explained, it is because the semilunar hinges cross this anatomic ventriculo-aortic junction that the crescents of myocardium are incorporated at the bases of the two sinuses giving rise to the coronary arteries (Fig. 1.3b). And, as also explained, the virtual basal plane marking the entrance of the root is constructed by joining together the proximal attachments of the leaflets.

It is the virtual nature of this plane that creates the perhaps biggest persisting problem in reaching consensus on naming the components of the root, namely the nature of the so-called annulus. In the sense that the boundaries of the virtual plane created by joining together the nadirs of the semilunar hingelines form a little ring, there is justification in taking the basal ring to represent the valvar annulus. This is the approach taken by clinicians when measuring the dimensions of the root. In contrast, many, but not all, surgeons consider the semilunar hinges of the leaflets to represent the valvar annulus [1]. When reconstructed, however, these hingelines take the form of a coronet rather than a little ring (Fig. 1.4). The semilunar hingelines also extend through the full length of the root, with the dimensions of their diameters varying according to whether measured at the level of the virtual basal plane, the mid-sinusal level, or at the sinutubular junction (Fig. 1.5). For better or worse, furthermore, it is the diameter of the virtual basal plane that is measured by echocardiographers and angiographers when accounting for the valvar annulus. This, therefore, is the plane that should probably now be taken as the clinical annulus [8], although it must be remembered that many surgeons will still describe the valvar coronet as the surgical annulus [9]. A case can be made, therefore, for distinguishing between the surgical and the echocardiographic annuluses [10].

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Fig. 1.4

The image is prepared by reconstructing the hingelines of the attachments of the valvar leaflets as seen in a computed tomographic dataset obtained from a patient undergoing investigation for coronary arterial disease. It shows that, although the hinges of the atrioventricular valves are attached in relatively annular fashion, the hinges of the arterial valves produce a coronet arrangement when viewed in three dimensions. The authors retain their intellectual copyright in the image from which this figure was prepared

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Fig. 1.5

The image in Panel a shows a section taken through a computed tomographic dataset obtained from an individual undergoing assessment for suspected coronary arterial disease. The section is cut through the nadirs of the right coronary and the non-adjacent aortic valvar sinuses. It shows how the dimensions of the root vary in terms of its distal, middle, and proximal boundaries, with the proximal border formed by joining together the attachments of the hinges of the valvar leaflets (See also Figs. 1.6 and 1.7). The solid and dotted double-headed red arrows show the so-called effective and geometric heights of the valvar leaflets. Note that the line of closure of the leaflets is no more than half way up the height of the arterial root. This is confirmed by the reconstructed images shown in Panel b. The central point of coaptation of the closed leaflets is appreciably proximal to their peripheral attachment at the sinutubular junction. The authors retain their intellectual copyright in the images from which these figures were prepared

Acceptance that the virtual basal plane represents the echocardiographic annulus, nonetheless, is not without its own problems. This is because, when measured at mid-sinusal level, or at the sinutubular junction, the aortic root is more-or-less circular, and there is little difference in the dimensions of its diameters (Compare Figs. 1.6 and 1.7). This is not the case when assessing the shape of the virtual basal plane. Rather than being circular, it is decidedly ovoid. Hence, there are potentially significant differences when assessing the root in terms of measurements taken from the nadirs of the valvar leaflets as opposed to planes that bisect the root (Fig. 1.8). Because of these potential problems, it is more sensible nowadays to measure the area of the entrance to the root using three-dimensional techniques (Fig. 1.5), rather than seeking to use a solitary measurement to represent the valvar annulus (Fig. 1.8). It is then also necessary to recognise that, when the valvar leaflets are in their closed position (Fig. 1.2), the central point of coaptation is no more than halfway up the length of the root (Fig. 1.5). This is the area recognised by surgeons as the effective height of the leaflets, to be distinguished from their geometric height, which is achieved when the leaflets are lying in their open position within the valvar sinuses [11].

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Fig. 1.6

The images show the potential problems in measuring the dimensions of the aortic root at the level of the basal ring (Panel b) as opposed to mid-sinusal level (Panel a). The cross-sections are taken from the computed tomographic dataset used to create Fig. 1.5. When measuring at mid-sinusal level, the bisected diameter is shorter than the distance measured from sinus to sinus. At the level of the virtual basal ring, because of the ovoid shape of the basal component of the root, the measurements taken from sinus to sinus (red and blue double headed arrows) themselves vary, and also vary relative to the section that bisects the root (yellow double headed arrow). The sections indicated by the red and yellow arrows are shown in Fig. 1.7. The authors retain their intellectual copyright in the images from which these figures were prepared

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Fig. 1.7

The images show two sections taken through the computed tomographic dataset used to produce Figs. 1.5 and 1.6. Panel a shows a parasternal long axis cut taken through the nadirs of the right coronary and non-adjacent aortic valvar sinuses. It is contrasted, in panel b, with a cut taken from the nadir of the right coronary sinus to the zone of apposition between the left coronary and non-adjacent aortic valvar leaflets, this plane bisecting the aortic root. The cut from nadir-to-nadir underestimates the diameter of the root by one-eighth. The authors retain their intellectual copyright in the images from which these figures were prepared

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Fig. 1.8

The panels illustrate the potential problems in providing accurate measurements of the virtual basal plane, which is the echocardiographic annulus, when assessing the dimensions from nadir to nadir of the valvar leaflets, rather than taking a measurement that bisects the aortic root. The upper left hand panel shows the arrangement as seen from the ventricular base, whereas the lower left panel shows a virtual dissection as viewed from the atrial aspect. The red and yellow arrows show dimensions comparable to those shown in Figs. 1.6 and 1.7. The authors retain their intellectual copyright in the images from which these figures were prepared

1.3 Attitudinal Anatomy of the Root

Another of the problems that continue to plague a full understanding of the anatomy of the aortic root is the ongoing penchant of anatomists and cardiologists to describe the heart in so-called Valentine location, as if removed from the body and positioned on its apex, rather than as it lies in the body. There is no excuse now for continuing to use this approach to naming components of the heart. Not only does it break the cardinal rule of human anatomy, namely that all structures within the body should be named using the so-called anatomical position, with the subject standing upright and facing the observer, but the anatomy itself is now increasingly demonstrated in the clinical setting using three-dimensional techniques which show the heart in its bodily location. The most egregious example of the use of the Valentine approach is the naming of the coronary artery that is inferior and interventricular as being posterior and descending (Fig. 1.9) [12]. Less obvious is the naming of the aortic valvar sinuses. If designated as being right coronary, left coronary, and non-adjacent, the constraints of the Valentine approach are removed, since these terms themselves do not depend on the relationships between the sinuses and the bodily coordinates. The right coronary sinus, however, is located anteriorly relative to the two other sinuses when the heart is normally located, with the non-adjacent and left coronary sinuses being positioned side-by-side, with the non-adjacent sinus to the right (Fig. 1.9).

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Fig. 1.9

The aortic valvar sinuses have been reconstructed from a computed tomographic dataset prepared from an individual undergoing assessment for suspected coronary arterial disease. They are shown as seen from the front. The right coronary aortic sinus, shown in yellow, is positioned in front of the non-adjacent, and left coronary sinuses, shown in green and red, respectively. Note that the so-called posterior descending artery, which in this individual arises from the circumflex artery, is interventricular and located inferiorly. The authors retain their intellectual copyright in the image from which this figure was prepared

1.4 Location of the Aortic Root Within the Heart

Assessment of the cardiac base from the atrial aspect shows how the aortic root forms its centrepiece (Fig. 1.10). Viewing the cardiac silhouette from the front confirms the central location of the root, positioned as it is at the junction of the left ventricular outflow tract and the intrapericardial component of the ascending aorta (Fig. 1.11). The current ability to separate the components of the heart by interrogation of computed tomographic datasets confirms that the so-called right chambers of the heart are, in reality, located anteriorly relative to their presumed left-sided counterparts. The aortic root is wedged between the anteriorly positioned infundibulum of the right ventricle and the anterior attachment of the atrial septum (Fig. 1.10). Unlike the right ventricle, which possesses a completely muscular outflow tract, the infundibulum, which lifts the leaflets of the pulmonary valve away from the cardiac base, the outflow tract of the left ventricle is relatively short, and has no discrete anterior boundary. Its posterior boundary is formed by the extensive area of fibrous continuity between the leaflets of the aortic and mitral valves. It is the attachments of this so-called aortic-mitral curtain which anchor the aortic and mitral valves to the roof of the left ventricle (Figs. 1.12 and 1.13). When the left ventricle is opened, it is easier to recognise the thickenings of both ends of the aortic-mitral curtain. These areas are the so-called right and left fibrous trigones. As shown in Figs. 1.12 and 1.13, it is the attachment of the trigones to the summits of the ventricular walls which anchors the combined valvar unit within the base of the left ventricle. The right fibrous trigone itself is then usually in fibrous continuity with the membranous part of the ventricular septum. The septal component then forms the right wall of the proximal part of the aortic root and the right-sided cardiac chambers (Fig. 1.12). The conjoined structure formed centrally within the cardiac base from the right trigone and the membranous septum is also the strongest part of the insulating plane between the atrial and ventricular chambers. It is the so-called central fibrous body (Fig. 1.14). The membranous septum itself is also continuous distally with the fibrous tissue that fills the gap found on the ventricular aspect of the right aortic and non-adjacent valvar sinuses as the hinge lines of the leaflets supported by these sinuses come together at the sinutubular junction. Such areas of fibrous tissue are also found on the ventricular aspect of the junctional zones between the other valvar sinuses. It is an appreciation of the locations and the relationships of these areas of fibrous tissue separating the distal attachments of the valvar sinuses, the so-called interleaflet fibrous triangles [6], that underscores the overall understanding of the anatomy of the aortic root.

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Fig. 1.10

The heart has been dissected by removing the larger part of the atrial myocardium, along with the arterial trunks. It is viewed from the atrial aspect, showing the central location of the aortic root within the cardiac base. The authors retain their intellectual copyright in the image from which this figure was prepared

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Fig. 1.11

The images are prepared using a computed tomographic dataset obtained from an individual undergoing assessment for suspected coronary arterial disease. The images in panel a shows the extent of the pericardial cavity, which is separating the intra-and extrapericardial components of the ascending aorta. The dataset has been coloured so as to show the subvalvar component of the left ventricle. In panel b, the components of the so-called right heart have been added. As can be seen, in reality the right heart chambers are anterior to their supposedly left counterparts, with the aortic root wedged between the infundibulum of the right ventricle and the posteriorly located left atrium. The authors retain their intellectual copyright in the images from which these figures were prepared

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Fig. 1.12

The heart has been sectioned across the short axis of the ventricular mass, and is viewed from the ventricular apex. The image shows the attachments of the aortic mitral curtain (dotted black line) through the right and left fibrous trigones (black open triangles) to the roof of the left ventricle. Note that there is an inferior extension from the subvalvar outflow tract that interposes between the inferior part of the muscular ventricular septum and the leaflets of the mitral valve. In consequence, the leaflets of the mitral valve are hinged from the ventricular septum only towards the crux of the heart (white star with red borders). The space between the septum and the valvar leaflets (red arrow) is known as the postero-inferior diverticulum of the outflow tract (See Fig. 1.13). The authors retain their intellectual copyright in the image from which this figure was prepared

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Fig. 1.13

The images are prepared by virtual dissection of a computed tomographic dataset obtained from an individual undergoing assessment for suspected coronary arterial disease. They are cuts through the cardiac base, viewed from the ventricular apex, and replicate the image prepared from a specimen as shown in Fig. 1.12. Panel a shows how the aortic root is positioned between the atrial chambers posteriorly and the infundibulum of the right ventricle anteriorly. The cut is taken apical to the roof of the left ventricle, which is formed by fibrous continuity between the leaflets of the aortic and mitral valves. Panel b is prepared by angling the section plane so as to show that the postero-inferior extension of the left ventricular outflow tract, which interposes between the mitral valvar orifice and the inferior part of the muscular ventricular septum. The authors retain their intellectual copyright in the images from which these figures were prepared

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Fig. 1.14

The aortic root has been opened through a cut across the left coronary aortic sinus, and is viewed from the front. The aortic-mitral curtain, formed from fibrous continuity between the aortic leaflet of the mitral valve, the non-adjacent leaflet of the aortic valve, and part of the left coronary aortic valvar leaflet, forms the roof of the left ventricle. The ends of the area of fibrous countinuity (dashed black line) are thickened to form the right and left fibrous trigones (black open triangles). The right trigone is continuous in the medial wall of the aortic root with the membranous component of the ventricular septum (red triangle), which in turn is continuous with the fibrous interleaflet triangle interposed between the right coronary and the non-adjacent aortic valvar sinuses (green triangle). Note the continuity of the interleaflet triangle between the non-adjacent and the left coronary aortic sinuses (yellow triangle) with the aortic-mitral continuity. Note also the shorter interleaflet triangle (blue triangle) between the two coronary aortic sinuses. It is only the two leaflets supported by the sinuses giving rise to the coronary arteries that also have attachment to the left ventricular muscular walls (blue and yellow dashed double headed arrows). The authors retain their intellectual copyright in the image from which this figure was prepared

It is the basal continuation of the membranous part of the ventricular septum that constitutes the largest of the triangles. As already shown and discussed, the membranous septum itself separates the medial wall of the aortic root from the right-sided heart chambers (Fig. 1.12). It is the attachment of the hinge of the septal leaflet of the tricuspid valve to its right side that separates the septum into its atrioventricular and interventricular components. Viewing the area from the right side in a virtual dissection shows how the attachment of the inner heart curvature, known as the ventriculo-infundibular fold, separates the membranous septum from the apex of the interleaflet triangle. The two components of the membranous septum, separated from each other by the hinge of the septal leaflet of the tricuspid valve, are obviously inside the heart. The interleaflet triangle, in contrast, separates the most distal part of the left ventricular outflow tract, within the aortic root, from the right side of the transverse pericardial sinus. The right coronary artery runs through this space as it extends from its sinusal origin to reach the right atrioventricular groove (Fig. 1.15). This relationship to the rightward margin of the transverse sinus is well demonstrated by removing the interleaftet triangle in the autopsied heart, and again viewing the specimen from the right side. The dissection in the autopsied heart (Fig. 1.16a) confirms the location of the triangle of Koch as shown by the virtual dissection, and again shows the landmarks that permit prediction of the course of the atrioventricular conduction axis, a feature of great surgical significance. Sectioning a virtual dataset then shows the relationships between the fibrous triangle and membranous septum to the extracardiac and intracardiac spaces, respectively (Fig. 1.16b).

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Fig. 1.15

The virtual dissection is prepared from a computed tomographic dataset obtained from an individual undergoing assessment for suspected coronary arterial disease. It shows the boundary between the right coronary and the non-adjacent aortic valvar sinuses as viewed from the right side. Note how the ventriculo-infundibular (Vent-inf.) fold separates the interleaflet triangle, which is outside the heart, from the membranous septum. It is the septal leaflet of the tricuspid valve that divides the membranous septum (MS) into its atrioventricular and interventricular components, with the hinge line continuing inferiorly to form the anterior boundary of the triangle of Koch, which is shown by the white dotted lines. The white star with red borders show the location of the atrioventricular node at the apex of Koch’s triangle, with the red dotted line showing the site of the atrioventricular conduction axis, with the right bundle branch emerging in the right ventricle beneath the origin of the medial papillary muscle (PM). The authors retain their intellectual copyright in the image from which this figure was prepared

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Fig. 1.16

The dissection shown in Panel a is made by removing the interleaflet triangle that separates the right coronary and non-adjacent aortic valvar sinuses, along with the portion of the ventriculo-infundibular fold adjacent to the atrioventricular junction so as to reveal the interventricular component of the membranous septum. The heart is then viewed from the right side. The dotted black lines show the location of the triangle of Koch, with site of the atrioventricular node marked by the white star with red borders (compare with Fig. 1.15). The red dotted line shows the course of the atrioventricular conduction axis, with the right bundle branch tracking towards the medial papillary muscle (PM). The section in panel b is a long axis section through the interleaflet triangle (double headed red arrow) and the membranous septum (double headed yellow arrow). Note that the fibrous interleaflet triangle separated the distal extent of the aortic root from the transverse pericardial sinus. The authors retain their intellectual copyright in the images from which these figures were prepared

The triangle that fills the space on the ventricular aspects of the two aortic valvar sinuses that support the coronary arteries is the smallest of the three triangles. It separates the distal extent of the aortic root from the tissue plane that, in turn, is located between the anterior aspect of the root and the free-standing muscular subpulmonary infundibulum (Fig. 1.17). The third triangle, filling the space between the ventricular aspects of the left coronary and non-adjacent aortic sinuses, is continuous apically with the extensive area of fibrous continuity which forms the aortic-mitral curtain (Fig. 1.13). This triangle again separates the distal extent of the aortic root from the transverse sinus of the pericardial cavity. Due to its more posterior location, however, this triangle is related to the middle component of the transverse pericardial sinus. It is the anterior interatrial groove that forms the posterior boundary of the pericardial sinus in this location, with the atrial septum and the oval fossa directly behind the atrial walls (Fig. 1.18). Bachmann’s bundle, made up of the aggregated cardiomyocytes that preferentially conduct the cardiac impulse from the sinus node to the left atrium, extends through these atrial walls.

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Fig. 1.17

The dissection shown in Panel a is made by first removing the pulmonary valve and its supporting free-standing infundibular sleeve from the base of the heart, and then removing the fibrous interleaflet triangle interposed between the right and left coronary aortic valvar sinuses. Note the location of the first septal perforating artery. The image in panel b comes from a computerised tomographic dataset, and shows the relationship between the anterior wall of the aortic root in the area of the interleaflet triangle and the subpulmonary infundibulum. The authors retain their intellectual copyright in the images from which these figures were prepared

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Fig. 1.18

The dissection in Panel a is made by removing the fibrous interleaflet triangle interposed between the non-adjacent and left coronary aortic valvar sinuses, and photographing the aortic root from behind. Bachmann’s bundle runs through the anterior interatrial fold. Panel b shows how the interleaflet triangle (double headed red arrow) separates the distal extent of the aortic root from the transverse pericardial sinus. The section is viewed from the right side. The authors retain their intellectual copyright in the images from which these figures were prepared

The location of the triangles can be appreciated by taking histological sections through the aortic root at mid-sinusal level (Fig. 1.19a) and at the level of the membranous septum virtual basal plane (Fig. 1.19b). The overall relationship of the root is then better demonstrated by interrogation of datasets prepared during life using multidetector computed tomography. A section from such a dataset taken through the cardiac base shows the root sandwiched between the atrial chambers and the infundibulum of the right ventricle (Fig. 1.20a). By combining the information obtained with sectioning the different levels of the root (Fig. 1.19), we can then construct a cartoon showing the location of the sinuses as seen attitudinally, emphasising the location of the support provided by the underlying venticular components, with only a small part of the basal circumference being muscular, the larger parts being fibrous (Fig. 1.20b—compare with Fig. 1.19).

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Fig. 1.19

The sections are taken through a human aortic root sectioned in its short axis. Panel a is at mid-sinusal level, and shows the interleaflet triangles separating the ventricular aspect of the root from extracardiac tissues. The black arrow with green borders shows the basal part of the triangle continuous with the membranous septum, as revealed by panel b, which is taken closer to the ventricular apex. This panel shows how the hinge of the septal leaflet of the tricuspid valve separates the membranous septum into its atrioventricular (dotted double headed black arrow) and interventricular (solid double headed black arrow) components. The black arrow with blue borders shows the triangle separating the root from the subpulmonary infunbibulum, while the black arrow with yellow borders shows how the triangle between the non-adjacent and left coronary aortic sinuses is continuous apically with the aortic-mitral curtain. The images are created using original material prepared by Professor Nigel Brown, St George’s Medical University, and are reproduced with his kind permission. Professor Brown retains his intellectual copyright in the images from which the figures were prepared

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Fig. 1.20

The image obtained by sectioning the computed tomographic dataset (Panel a), viewed from the ventricular apex in attitudinally appropriate fashion, shows the central location of the root, with the atrial chambers posterior and the infundibulum of the right ventricle to the front. The cartoon shown in Panel b then combines the information regarding the relationships of the different parts of the root. The black arrows with coloured borders show the locations of the three interleaflet fibrous triangles (Compare with Fig. 1.19). The authors retain their intellectual copyright in the images from which these figures were prepared

1.5 Surgical Anatomy of the Aortic Root

As shown in Fig. 1.4, reconstruction of the semilunar hinges of the aortic valvar leaflets produces a coronet-like configuration. It is the remnants of these attachment of the leaflets within the root, when the leaflets themselves have been removed during replacement of the aortic valve, that surgeons use to anchor the sutures used to secure the placement of valvar prostheses (Fig. 1.21). It is, presumably, for this reason that many surgeons continue to describe these lines of attachment as the valvar annulus. There is, however, no specific anatomic structure forming the alleged annulus over and above the attachment of the leaflets to the supporting structures. The semilunar lines of attachment mark the haemodynamic ventriculo-arterial junction, but they cross the anatomic ventriculo-arterial junction. It is the extent of the overall attachments of the leaflets, furthermore, which defines the extent of the root. As described in the previous section, the interleaflet triangles separate the tips of the valvar hinges as they come together at the sinutubular junction. The locations of these spaces between the sinuses can then be used as sites of incision to enlarge the congenitally narrowed root. Thus, it is incisions made through the interleaflet triangle that separates the non-coronary and the left coronary aortic sinuses, continuing proximally into the aortic-mitral curtain, which provides the substrate for the Nicks-Manougian approach to enlargement of the root [13]. Incisions through the interleaflet triangle separating the right and left coronary aortic sinuses, continuing anteriorly into the subpulmonary infundibulum, underscore the Rastan-Konno approach. It is not possible, however, to enlarge the root through the triangle between the right coronary and the non-adjacent aortic sinuses. This is because the membranous septum forms the base of this triangle, and the atrioventricular conduction axis penetrates through the atrioventricular component of the septum. This anatomy itself, of course, is of major surgical significance. It is now also of major concern to interventional cardiologists, since bundle branch block is a well-recognised complication of transcutaneous insertion of aortic valvar prostheses [14]. So as to appreciate the adjacency of the conduction axis to the valvar structure, we cannot do better than consult the original cartoon prepared by Tawara [15] when he first described the location of the conduction axis (Fig. 1.22). As can be seen from his reconstruction, the fan formed by the fascicles of the left bundle branch descends onto the smooth left ventricular septal surface just beneath the nadir of the hinge of the right coronary aortic leaflet. It is this relationship that provided the necessary information for the interventional cardiologist so as to avoid iatrogenic disturbances of rhythm [14]. For the cardiac surgeon, providing that sutures are placed within the remaining semilunar hinges of the valvar leaflet during valvar replacements, there should be no danger of damaging the components of the atrioventricular conduction axis.

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Fig. 1.21

The dissection is made by opening the aortic root through the left coronary aortic sinus, and removing the leaflets of the aortic valve. This reveals the semilunar valvar hinges, described by many cardiac surgeons as the valvar annulus. Note that the nadirs of the hinges of the leaflets guarding the sinuses giving rise to the coronary arteries extend proximally beyond the anatomic ventriculo-arterial junction so that crescents of myocardium are incorporated within the bases of the sinuses (white star and white arrow with red borders). The red dotted line shows the proximal extent of the atrioventricular conduction axis and the left bundle branch (see also Fig. 1.22). The authors retain their intellectual copyright in the image from which this figure was prepared

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Fig. 1.22

The image is modified from the original reconstruction prepared by Tawara [15] to show the location of the left bundle branch

Conclusion

The aortic root is the central part of both the heart and the left ventricular outflow tract. It is delimited by the semilunar lines of attachment of the valvar leaflets. These leaflets are suspended predominantly from the aortic valvar sinuses of Valsalva. The most proximal attachments of the two leaflets supported by the sinuses which give rise to the coronary arteries, however, cross the anatomic ventriculo-arterial junction. This means that small crescents of myocardium are incorporated as the bases of both these sinuses. Three-dimensional reconstruction of the overall arrangement of the valvar hinges produces a coronet-like configuration. It is the hinges that are described by some cardiac surgeons as the valvar annulus. Clinical diagnosticians, in contrast, tend to describe the diameter of the virtual plane constructed by joining together the nadirs of attachment of the leaflets as the annulus. There is no anatomic structure corresponding to this plane. The dimensions of the root, furthermore vary markedly not only according to the depth measurements are taken within the root, but also depending on whether they are taken from the nadirs of adjacent leaflets or by bisecting the root. These various discrepancies emphasise the importance of distinguishing between the surgical and clinical annuluses. They also indicate that appropriate measurement should take into account the full extent and configuration of the root.

References

1.

Sievers HH, Hemmer G, Beyersdorf F, Moritz M, Moosdorf R, Lichtenberg A, et al. The everyday used nomenclature of the aortic root