The points where the leaflet attachments run parallel - distally upstream towards the ascending aorta - are called the commissures.
The three bulges of the aortic wall are named the sinuses of Valsalva , after the Italian anatomist Antonio Valsalva. Two of the three sinuses host the origin of the coronary arteries and the sinuses are termed accordingly the left, right and non-coronary sinus. They are limited proximally by the attachments of the valve leaflets and distally by the sinotubular junction. At their base, ventricular musculature is partly incorporated.
The sinus wall itself is predominantly made up of aortic wall, although it is thinner than the native aorta 5 , 24 , The precise function of the sinuses of Valsalva is unclear.
There is evidence that the vortices created in the sinuses lead to stress reduction on the aortic leaflets and support coronary flow 4 , 5 , In valve sparing aortic valve surgery, maintenance or recreation of the sinuses has been shown to effectively recreate the vortices in the sinuses and may be beneficial in terms of normal leaflet movement and valve durability 5 , 24 - 26 Figure 2.
However, aortic root reimplantation without recreation of the aortic sinuses has not been shown to have deleterious effects on valve durability despite abnormal leaflet motion In general, there is a need for aortic root replacement material that imitates the compliant characteristics of the normal aortic root.
This would allow for an ideal, and low stress, movement of the leaflets and could be a future area of interest and research not only for prosthetic material design but also for tissue engineering.
Under each commissure lies one of the three interleaflet triangles. Although histologically they consist of thinned aortic wall, hemodynamically they are extensions of the ventricular outflow tract and reach the level of the sinotubular junction in the area of the commissures. The triangle between the right- and non-coronary sinuses faces the right atrium.
It is in direct continuity with the membranous septum proximally which contains the His bundle. This area is of special importance during aortic valve procedures, as injury here can lead to temporary or permanent conduction abnormalities, which may require the implantation of a permanent pacemaker. The origins of the coronaries show great variability.
A common single ostium or multiple ostia in the right and left anterior interventricular and circumflex branches of the anterior aortic sinus have also been reported. The right coronary sinus had multiple openings. The extra openings were minute and varied in number from one to three. These openings are of the first branch of the right coronary artery, the infundibular branch. In such cases, one of the extra ostia may be that of the SA nodal artery. Schlesinger et al.
Standring et al. In a majority of the cases, the positions of the ostia were below the sinutubular ridge. Valodaver et al. Turner and Navratnam found that 62 of the 74 main coronary ostia lay either at or immediately below the sinutubular ridge. The observations from this study are similar to the observations by Sahni and Jit They reported higher origins in the range of 1. The discrepancy in the findings described above might be due to overlooking the arched pattern of the sinutubular ridge.
It is known that during normal function, the cusps do not flatten against the sinus walls, even at maximum systolic pressure. Few such cases have been reported in the literature. In the majority of cases in the present study, the positioning of the ostia was above the margin of the cusp and below the sinutubular ridge.
This observation suggests that the positioning of the ostium within the sinus, rather than at or above the ridge, is functionally advantageous. Support for this assumption comes from the fact that the thickness of the wall of the aortic sinus at mid-level is half of the thickness of the aortic wall and one quarter of the thickness of the sinutubular ridge. Further studies are required to determine whether positioning of the ostia at or above the ridge or below the level of the cusps is disadvantageous to coronary filling in any way.
It was observed that the right coronary ostium tended to deviate more often towards Commissure I. Turner and Navratnam documented similar observations. The left coronary artery is positioned near its origin in such a way that it lies posterior to the pulmonary trunk and then follows a course that is anterior and to the left.
Therefore, its ostial position remains either central or moves toward Commissure III, if the pulmonary trunk is relatively anterior. Circumferential deviation does not seem to be very functionally significant. However, knowledge of the frequency of circumferential deviation and also of measurements of cusp height and ostial height from the bottom of the sinus will be of help to radiologists in interpreting images of the coronary origins and to clinicians during procedures like angiography and angioplasty.
Wolloscheck et al. Of the hearts studied, we found two cases of an absent left main coronary artery i. In a large angiographic series, Topaz et al. They also suggested that recognition of this coronary anomaly is necessary to ensure accurate angiographic interpretation and is important for patients undergoing cardiac surgery for selectively perfusing these separate vessels during cardiopulmonary bypass.
Slit-like ostia were seen in a number of cases. There have been reported cases of sudden death in young individuals where the coronary ostia were found to be slit-like at autopsy. The present study describes the normal and variant anatomy of the ostia of the coronary arteries in an unsuspected population.
It provides a basis for understanding the normal variants, for determining the incidence of anomalies, and for evaluating the value of screening for such anomalies. No openings were observed in the pulmonary sinuses or the right posterior aortic sinus.
The number of openings in the aortic sinuses varied from 2 - 5 in the present series; multiple ostia were mostly seen in the right sinus. On occasion, normal variants, such as multiple ostia, vertical or circumferential shift in position, and slit-like ostia, may confuse interpretation of the images and may pose a difficulty during procedures, such as angiography, angioplasty, and coronary artery bypass grafting. Arrows indicate the circumferential deviation of the ostia towards the commissures.
National Center for Biotechnology Information , U. Journal List Clinics Sao Paulo v. Clinics Sao Paulo. Subhash D. Joshi , I Sharda S. Sharda S. Author information Article notes Copyright and License information Disclaimer. Email: moc. Received Sep 25; Accepted Oct This article has been cited by other articles in PMC. Open in a separate window. Figure 1a. Figure 2. Figure 3. Figure 5.
Table 2 Positions of the coronary ostia with respect to the sinutubular ridge and the cusps of the aortic valve. Table 3 The heights of the cusps and the coronary ostia were measured from the bottom of the sinus. Height of the cusp from bottom of the sinus Height of the ostia from bottom of the sinus Range Average Range Average Right 8—15 mm Figure 6. Table 4 Positions of the coronary ostia with reference to the commissures.
Figure 1b. Clinicians, especially surgeons, frequently speak of the aortic valve having an annulus or ring, as if there is a band-like circle of fibrous accretions.
Anatomically, this is far from the case. McAlpine 2 in again emphasized the lack of rings in all four cardiac valves. In this work, the word is applied only to the fibrous attachments of aortic and pulmonary leaflets which, in reality, constitute only a segment, not of a circle, but of an ellipse. A search for a reasonable term has met with failure. The term annulus, used to designate four fibrous structures to which the four valves of the heart are attached, is, in my opinion, ill-founded—no such structures are to be found.
In reviewing the aortic root, Berdajs et al. Clearly, the aortic root is a complex structure that requires analysis part by part but always remembering that all the parts contribute to form one functional unit that is commonly referred to as the aortic valve. The spaces between the luminal surface of the three bulges on the aortic root and their respective valvar leaflets are known as the aortic sinuses of Valsalva. Davies considered the wall of the aortic root the aortic sleeve, distinguishing it from the aortic wall on account of its histological composition.
The superior border of the sinuses is the sinutubular junction also known as the supra-aortic ridge Figures 1 C and 2. On the outside, the sinutubular junction is where the tubular portion of the aorta joins onto the sinusal portion.
Inside, there is usually a slightly raised ridge of thickened aortic wall. But, the sinutubular junction is not perfectly circular.
It takes on the contour of the three sinuses, giving it a mildly trefoil or scalloped outline Figure 1 A. Silver and Roberts studied formalin-fixed hearts from adult patients with normally functioning aortic valves and found that the luminal area of the aorta at the sinutubular junction increased with age and with heart weight where increased heart weight was attributed to systemic hypertension.
The right sinus is the largest as is its height, with the left sinus being the smallest on both counts. When left ventricular pressure exceeds that in the aortic root, the valvar leaflets are pushed apart and fall back into their respective sinuses, allowing unimpeded ejection of blood.
The orifices of the coronary arteries are commonly found close to the level of the sinutubular junction Figure 3 A. A The ventricular surface of the aortic leaflet has a nodule dotted line. Note the height of the leaflet is less than the height of the sinus. The right coronary orifice is sited just inferior to the sinutubular junction. B This section through a right coronary aortic sinus shows the musculature in the depth of the sinus elastic van Gieson stain.
C This is the heart shown in Figure 1 C. Following removal of the aortic leaflets, three crescentic ridges mark the hingelines. The broken line indicates the level of the ventriculo-arterial junction. Two of the three interleaflet fibrous triangles o are shown. The irregular shape marks the site of the atrioventricular conduction bundle and left bundle branch. D and E are superior and right views of the aortic root following removal of the arterial walls of the sinuses.
They display the interleaflet fibrous triangles and hingelines of the leaflets forming a coronet arrangement. Each of the three leaflets of the normal aortic valve has a free margin and a margin where it is attached in semilunar fashion to the aortic root.
The maximal height of each leaflet is considerably less than that of its sinus on account of its scoop-shaped free margin Figure 3 A and B. When the valve opens, the leaflets fall back into their sinuses without the potential of occluding any coronary orifice. The semilunar hingelines of adjacent leaflets meet at the level of the sinutubular junction, forming the commissures. The body of the leaflets are pliable and thin in the young, although its thickness is not uniform.
Each leaflet has a somewhat crimpled surface facing the aorta and a smoother surface facing the ventricle. The leaflet is slightly thicker towards its free margin. On its ventricular surface, is the zone of apposition, known as the lunule, occupying the full width along the free margin and spanning approximately one-third of the depth of the leaflet. This is where the leaflet meets the adjacent leaflets during valvar closure. Fenestrations in the lunules are common, especially in the elderly, but the valve remains competent because they are above the closure line.
Larger fenestrations that extend beyond the zones of apposition, however, can lead to significant valvar regurgitation. With age, the leaflets become thicker and stiffer. Sclerosis, dystrophic calcification, or commissural fusion can result in a stenotic valve. But, as noted by Roberts in , the three leaflets are not perfectly equal in dimensions. On histology, each leaflet comprises of a fibrous core covered by subendothelial fibroelastic layers termed the arterialis on the aortic surface and the ventricularis on the ventricular surface.
The latter is thickest along the closing edges of the leaflet. The fibrous core has two components: the fibrosa and the spongiosa, bordered by the arterialis and the ventricularis, respectively. The fibrosa contains mainly collagen fibres with some elastin. The larger collagen bundles are aligned circumferentially, parallel to the free margin, adding to the undulations on the arterialis aspect.
Radially aligned collagen fibres are found near to the hingeline. The collagen fibres are mainly type I, providing strength to the leaflet. The spongiosa comprises of loose connective tissue rich in proteoglycans and allows shearing between the adjacent layers.
The ventricularis is thinner than the fibrosa and contains more elastin and less organized collagen fibres. At the lunule and the free margin of each leaflet, the ventricularis becomes thicker, especially at the nodule of Arantius where it is a mass of elastic tissue.
It has been demonstrated in the pig valve that the ventricularis contains a considerable amount of sheet elastin, whereas the elastin in the fibrosa is arranged like tubular meshwork that extended circumferentially across the leaflet. The core of the leaflet is continuous with the fibrous wall of the aortic sleeve at the hingelines where the fibrous tissue is thickened.
When the leaflets are detached from the wall, the semilunar hingelines appear like raised ridges Figure 3 C. It is where ventricular myocardium terminates and gives way to the wall of the aortic sleeve.
Here, precise location of the junction is not possible and we can only extrapolate by completing the circle around the outflow tract, and making the assumption that there is a sharp line between myocardium and sleeve Figure 3 C. Nevertheless, the semilunar hingelines of the valvar leaflets create an intricate arrangement at this junction. The nadirs of the hingelines are locates below the ventriculo-arterial junction. Thus, where the hingelines cross muscle, myocardial segments are included into the aortic sinuses Figure 3 B.
The extent of myocardial inclusion varies from heart to heart. The right coronary sinus and the anterior part of the left coronary sinus are involved. The remaining part of the left coronary sinus and the whole of the non-coronary sinus do not contain myocardium.
In human, myocardium is present in the non-coronary and posterior half of the left-coronary sinus only when there is persistence of the left ventriculo-infundibular fold inner heart curvature but this seldom happens.
Usually, the fold disappears completely resulting in fibrous continuity between aortic and mitral valves. The area of valvar continuity is thickened at both ends to form the right and left fibrous trigones; the right trigone contributing to the central fibrous body of the heart see next section.
The anatomic ventriculo-arterial junction, however, does not coincide with the functional junction, again owing to the configuration of the semilunar hingelines. First, the ventricular parts within the aortic sinuses become incorporated, functionally, into the aorta.
Second, the parts of the wall of the aortic sleeve that are in between adjacent leaflets, lie above the anatomic ventriculo-arterial junction but become, haemodynamically, a part of the ventricle when the valve is closed. These triangular-shaped portions deserve special consideration see below Figure 3 C. The semilunar attachments of the leaflets across the anatomic ventriculo-arterial junction and into the aortic sleeve leave three pieces of wall in between the arcs.
These are the interleaflet fibrous triangles also described as interannular trigones or fibrous trigones, intervalvaular trigone that project above the ventricular mass like three prongs of a coronet Figure 3 D and E , in potential communication with extracardiac space. McAlpine 2 has pointed to these areas as potential sites of aneurysmal formation.
The triangles are thinner and less collagenous than the hingelines or the sinusal walls. The triangle between the left and right coronary sinuses lies immediately behind the right ventricular outlet. The triangle between the left-coronary and non-coronary leaflets is along the area of aortic-mitral fibrous continuity but its upper part abuts on the transverse pericardial sinus.
The latter is the landmark for the site of the His bundle of the cardiac conduction system. Having penetrated the central fibrous body, the atrioventricular conduction bundle passes between the membranous septum and the crest of the muscular ventricular septum to bifurcate into right and left bundle branches. Thus, the interleaflet triangle between the right- and non-coronary leaflets is a good guide to the atrioventricular conduction bundle and the proximal portion of the left bundle branch.
The latter, covered with a fibrous sheath, is often visible in the subendocardium of the outflow tract in heart specimens. Considering the aortic root as one functional unit, it is a three-dimensional structure adjoining distally to the aorta and proximally to the ventricle, and all parts have to work in harmony. When there is dysfunction it is unlikely to involve only a single element, apart from, for example, isolated perforation of the leaflet.
Using 25 perfusion fixed preparations of human aortic roots, Berdajs et al. Using only 10 specimens and without pressure fixation, Kunzelman et al. In the living, the shape of the aortic root changes through the cardiac cycle. Thubrikar et al. During systole the sinutubular junction increases initially as aortic pressure increases and decreases later as aortic pressure drops, and the base decreases so the root adopts a cylindrical shape.
In terms of number of leaflets, the aortic valve can have 1—4 leaflets of variable sizes. Functional abnormality may be considered in terms of aortic stenosis and aortic regurgitation.
In some cases, the valve is both stenotic and regurgitant when the orifice becomes more or less like a fixed aperture.
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