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The aortic valve separates the left ventricular outflow from the ascending aorta and it is one of the two semilunar valves of the heart (i.e. aortic and pulmonary valve, named after their three crescent-shaped cusps). The role of semilunar valves is to prevent the backflow of blood into the ventricles during diastole, when the intraventricular pressure becomes lower than the pressure in the aorta or pulmonary artery.
The aortic root is a three-dimensional structure adjoining to the aorta and the left ventricle, with several components acting as a functional unit to ensure the valve competence: aortic valve, aortic annulus, Valsalva sinuses and sino-tubular junction (Figure 1).
- Aortic valve has three cusps of very similar size with rapid and unrestricted systolic opening: right coronary, left coronary (named in correspondence with the Valsalva sinuses that give rise to the two main coronary arteries) and non-coronary. Aortic cusps have a semilunar attachment to the aortic root and a free margin where they have an increased thickness and a central nodule (of Arantius). The insertions of adjacent cusps meet at the level of the sinutubular junction, forming the commissures. The total area of the cusps exceeds with 40% the area of the aortic root, therefore the aortic valve cusps normally have an apposition surface, with a 2-3 mm long overlap. Congenital anatomical variants of aortic valve morphology are: bicuspid (most common - 2%), quadricuspid and unicuspid valve.
- Aortic annulus consists of the three semilunar arcs (oriented upwards) formed by the basal attachments of the cusps, therefore having a 3D “crown-like” configuration (Figure 1).  Yet, tomographic imaging methods (including 2D echocardiography) consider the aortic annulus as a flat ring projected between the most basal insertion of the cusps. The aortic annulus has an elliptical shape, with the larger diameter in a transversal orientation. One third (in correspondence with left and non-coronary cusps) is in continuity with the anterior leaflet of the mitral valve (fibrous continuity or mitral-aortic curtain).
- Valsalva sinuses commonly refer to the three outpouchings of the aortic root, while anatomically they represent the space between these buldges and their respective cusps.
- Sino-tubular junction represents the distal boundary of the aortic root, separating it from the tubular part of the ascending aorta. During diastole, the sinutubular junction moves inwards and the base moves outwards commissures, changing the cylindrical shape to a more conical shape.
Echocardiographic examination of normal aortic valve anatomy
The anatomy of the aortic valve can be noninvasively assessed by transthoracic echocardiography. Transthoracic imaging usually is adequate, although transesophageal echocardiography may be helpful when image quality is suboptimal.
The echocardiographic windows which allow the morphologic assessment of the aortic valve are:
- parasternal (long-and short-axis views) - commonly used
- apical (5-chamber and long-axis views)
- subcostal (5-chamber and short-axis views)
In parasternal long-axis view, the normal aortic valve demonstrates the excursion of valve leaflets in a parallelogram-shaped ("box") pattern, with a central closure line in diastole. The same amount of systolic separation is maintained during most of systole. An eccentric closure line (anteriorly or posteriorly) with normal systolic separation may suggest a bicuspid aortic valve. Leaflets may show fine systolic fluttering in healthy individuals (Media: M-mode image of normal aortic valve.jpg).
2D echocardiography in the parasternal long-axis view demonstrates linear thin lines, parallel and close to the walls of the aortic root in sistole. In this view, the right cusp lies anteriorly and either non-coronary or left coronary leaflets may be seen posteriorly (Figure 2). The origin of right coronary artery from the right Valsalva sinus may be also visualized in this view. Normal aortic valve cusp coaptation occurs approximately at a level corresponding to the middle of the sinuses of Valsalva, i.e. halfway between the ventriculo-aortic junction and the sinotubular junction (Media: Aortic cusps.jpg).
This view is commonly used for measurements of the left ventricular outflow tract/aortic annulus and of the aortic root diameters (Media: Aortic root diameters.jpg) at various levels, by taking advantage of the superior axial image resolution. 2D measurements are preferable to M-mode, since there is a systematic underestimation of the measurements with the latter. The antero-posterior diameter of the aortic annulus is measured between the hinge points of the aortic valve cusps (inner edge - inner edge) during mid-systole, when the annulus reaches its largest size. The medio-lateral diameter of the aortic annulus can be measured only by 3D echocardiography.  Normally, the aortic root diameter at the level of Valsalva sinuses is the largest, followed by the sinotubular junction and the aortic annulus.
In short-axis view, the aortic valve is visualized en face as seen from the left ventricle. The three cusps open symmetrically and form a circular or triangular orifice during systole; during diastole, they appear as an „Y” sign with equal space between the 3 commissures (sometimes referred to as an inverted Mercedes-Benz sign) (Figure 3). The short-axis perspective is most helpful to determine the number of cusps and to assess the integrity of cusps and commissures, as well as to document the normal origin of coronary arteries from their respective sinuses (particularly in children). The discrimination between a bicuspid and a tricuspid aortic valve is most reliably done during sistole, since a raphe between 2 fused cusps of a bicuspid valve is indistinguishable from a normal commissure of a tricuspid valve when the valve is closed during diastole.
Apical (Media: Apical views of aortic valve.jpg) or subcostal (Media: Subcostal views of aortic valve.jpg) views are used less frequently in adults to assess aortic valve morphology, especially when the parasternal window is inadequate.
When 2D echocardiography is inconclusive or the parasternal window is inadequate, 3D echocardiography allows to obtain short-axis views of the aortic valve also from unconventional approaches (apical or subcostal, provided that there is an optimal acoustic window). The aortic valve can be seen en face not only from the left ventricle, but also from the aortic root or any desired unconventional orientation. The perspective from the aortic root may be more suited to assess valve morphology and cusp number, since the commissures are oriented upwards (Figure 4). In addition, 3D echocardiography enables the en face visualization of left ventricular outflow tract/aortic annulus.
When a definite diagnosis cannot be made by transthoracic approach or a more detailed assessment is required (surgical or procedural planning, suspected infective endocarditis etc), the aortic valve morphology can be comprehensively assessed by combining long- and short-axis transoesophageal views. The orientation of the cusps and commissures is characteristically different from the transthoracic approach, as the transducer is located posteriorly with respect to the aortic valve (Media: Transoesophageal view of aortic valve.jpg). Two-dimensional transoesophageal echocardiography is the standard recommended method when more precise measurements of aortic annulus are needed. Three-dimensional echocardiography can provide a more comprehensive and accurate quantitation of aortic root morphology (both maximal and minimal annular diameters, annular area and circumference, cusp length, annular-coronary ostia distances etc)(Figure 5), which is crucial for planning therapeutic interventions (i.e. TAVI).
- ↑ 1.0 1.1 1.2 Ho SY. Structure and anatomy of the aortic root. Eur J Echocardiogr 2009;10:i3-10
- ↑ Anderson RH. The surgical anatomy of the aortic root. Multimed Man Cardiothorac Surg 2007;doi:10.1510/mmcts.2006.002527
- ↑ 3.0 3.1 Evangelista A, Flachskampf FA, Erbel R et al. Echocardiography in aortic diseases: EAE recommendations for clinical practice. Eur J Echocardiogr 2010;11:645-58
- ↑ Baumgartner H, Hung J, Bermejo J et al. Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice. Eur J Echocardiogr 2009;10:1-25
- ↑ 5.0 5.1 Muraru D, Badano LP, Vannan M, Iliceto S. Assessment of aortic valve complex by three-dimensional echocardiography: a framework for its effective application in clinical practice. Eur Heart J Cardiovasc Imaging 2012;13:541-55
- Oh JK, Seward JB, Tajik AJ. The Echo Manual. Third ed. Lippincott Williams & Wilkins, 2006
- Anderson RH. Clinical anatomy of the aortic root. Heart 2000;84:670-3.
- Piazza N, de Jaegere P, Schultz C, Becker AE, Serruys PW, Anderson RH. Anatomy of the aortic valvar complex and its implications for transcatheter implantation of the aortic valve. Circ Cardiovasc Interv 2008;1:74-81.