11.2.1 Functional valve anatomy

Video: Front view of the mitral valve from the LA in three-dimensional reconstruction; the anterior leaflet is larger than the posterior leaflet; the commissure is C-shaped.

• A fibrous ring whose appearance, seen from the RA, resembles an inverted letter "D", the straight part of which is anterior, at the level of the fibrous trigone (area in telediastole: 5-6 cm²). The posterior part is thinner (see Figure 11.1B). In three dimensions, the mitral annulus has a saddle shape with the highest points anterior (aortic valve) and posterior; the lowest points are opposite the commissures. The normal AP diameter is 26-32 mm; the total height is approximately 10 mm (Figure 11.3) [16]. In telediastole, atrial contraction causes the annulus to narrow. In systole, the annulus undergoes 3 movements: its saddle shape increases, its circumference decreases by 25% and it slides approximately 1 cm towards the apex ("descent" of the mitral annulus) [11,18]. In the 4-cavity TEE view (0°), the annulus is sectioned in its lower part and the coaptation point appears in the plane of the annulus, whereas in the long-axis view (120°), the annulus is sectioned in its upper part and the coaptation point is located 5-7 mm below the plane of the annulus [6,14]. These concepts are important for the definition of mitral prolapse, which must be determined in the long-axis view (120-140°). Annular non-planarity is measured by the ratio of the height H (distance between the highest and lowest points, 8-10 mm) to the intercommissural distance (ICD, 30-35 mm), which is usually 0.2 [14]. Non-planarity is also assessed by the angle between the anterior and posterior points based on the intercommissural line; its normal value is > 130° [12]. These measurements are made on TEE using 3D reconstruction; some programmes calculate them automatically from geometric analysis of the annulus (Figure 11.4). As the LV dilates, the mitral annulus becomes more rounded and circular; it loses its saddle shape and flattens; the valve loses its seal in systole and the stress on the leaflets increases [5]. Dilatation occurs mainly at the expense of the posterior leaflet.
• Two leaflets; the posterior leaflet is arciform and divided into 3 anatomically well differentiated festoons (P1 anterior, P2 middle and P3 posterior); its insertion represents 2/3 of the circumference of the annulus. The anterior leaflet is more homogeneous and square in shape; its division into 3 parts A1, A2 and A3 does not correspond to distinct anatomical entities. Despite their different shapes, the two leaflets have an equivalent surface area. The length of the leaflets (distance from the base to the end of A2 or P2) is 22-23 mm for the anterior leaflet and 12-13 mm for the posterior leaflet.

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  Figure 11.2: Overview of the mitral apparatus. A: The mitral valve with its ring, chords, papillary muscles and ventricular wall. B: The anterior leaflet is "square", whereas the posterior leaflet is crescent-shaped; the pillars are perpendicular to the commissures; on occlusion, intraventricular systolic pressure presses the free edges of the two leaflets together along the zona rugosa; the height of coaptation is 0.6-1.0 cm. The length of the leaflets (green arrow) is 22-23 mm for the anterior leaflet and 12-13 mm for the posterior leaflet [4]. C: Intraventricular view of the subvalvular apparatus anchored to the pillars; this structure resembles the pillars and vaults of a cathedral (D: Sagrada Familia, Antoni Gaudi, Barcelona) because they have the same function: to support pressure. AA: anterior ring (fibrous trigone). AL: anterior leaflet. AC: Anterior commissure. PC: posterior commissure. PL: posterior leaflet. APM: anterior papillary muscle. PPM: posterior papillary muscle.  

• 25-30 cords inserted on the ventricular face of the leaflets; 1^st order cords are attached to the distal end and 2^nd order cords to the body of the leaflets; 3^rd order cords are attached near the base and maintain the geometry of the ventricle; cords are on average 1.5 cm long.

•  Two papillary muscles, one antero-lateral and the other postero-medial, located vertically above the commissures; the bundle of cords implanted on each pillar is distributed over both layers, either anteriorly (antero-lateral pillar ALP) or posteriorly (postero-medial pillar PMP). The ALP is vascularised by two coronary networks (IVA and CX), whereas the PMP is only vascularised by the RC. The PMP is often bifid.

• The wall of the LV on which each abutment is implanted; contraction of this wall is essential to ensure mitral occlusion; in the event of akinesia or dilation, the radial shortening defect maintains excessive traction on the corresponding chords and prevents the leaflets from reaching their coaptation point (see Figure 11.53). 

   

  Figure 11.3: Mitral annulus configuration. A: The septal insertion of the mitral valve is more proximal than that of the tricuspid valve, which is more apical; the offset is 1 cm (green). B: Saddle shape of the mitral annulus, with the highest points anterior (aortic valve) and posterior. C: In the 4-cavity view, the annulus is sectioned at its lowest points; the coaptation point of the mitral valve (white arrow) appears in the plane of the annulus. D: In the long-axis view, the annulus is sectioned at its highest points; the coaptation point of the mitral valve appears below the plane of the annulus. This difference between the two views is important in the definition of mitral prolapse [1].

   

  Figure 11.4: Saddle shape of the mitral annulus in three-dimensional reconstruction. A: The highest points are anterior (aortic annulus) and posterior and define the anteroposterior diameter (APD); the lowest points are opposite the valve commissures and define the second valve diameter. The height of the annulus (H) is approximately 10 mm; the intercommissural distance (ICD) runs from one commissure to the other. The angle of elevation (green) is based on the intercommissural line and defines the opening between the two highest points. B: Compared to diastole (top), the saddle shape becomes more pronounced in systole (bottom). C and D: 3D parametric echo reconstruction images (Q-Lab™ programme, Philips) of the mitral and aortic annuli in two pathological situations. C: Restriction of leaflet trajectory due to ventricular dilatation; the blue colouring indicates the area below the plane of the annulus. D: Prolapse of both leaflets in Barlow's disease, with determination of the mitral angle between the planes of the two valves. A: Anterior. P: Posterior.

In diastole, the mitral valve has an open area of 4-6 cm². Its gradient is ≤ 4 mmHg and may increase if systolic volume is greatly increased (mitral regurgitation). In systole, the mitral valve is closed by two opposing forces (Figure 11.5).

• Occluding force: intraventricular pressure (100-150 mmHg) forces the free edges of the two leaflets together along the zona rugosa; the height of this coaptation surface is 0.6-1.0 cm and represents 20-25% of the total leaflet length.
• Tethering force: Contraction of the ventricular wall and papillary muscles tensions the chords, holding the valve in its coaptation plane and preventing it from tilting into the LA.

If the mitral leaflets are occluded edge-to-edge, the valve cannot withstand the intraventricular pressure; it loses its seal and becomes inadequate. The normal dimensions of the mitral valve are given in Table 11.1 [13,17].

The orthogonal planes for the mitral valve on TEE are different from the orthogonal planes of the heart. These are the horizontal 4-cavity 0° plane and the sagittal 2-cavity 90° plane. However, the mitral valve rotates about 60° in the frontal plane relative to the body (Figures 11.6). Its orthogonal planes are therefore the 40-60° bi-commissural plane, which cuts it through the two commissures, and the 120-150° long-axis plane, which cuts it through the greatest length of the leaflets (A2 and P2); this plane includes the long-axis view of the left ventricle and the aortic valve; it is approximately perpendicular to the previous plane (Figure 11.7). To these two planes is added the short axis 0-20° transgastric view of the mitral valve, but this view is not always feasible.

 Figure 11.5: LV contraction. A: The increase in intraventricular pressure during systole forces the two mitral leaflets together along their free edges (purple arrows); contraction of the wall and papillary muscles (APM: anterior papillary muscle, PPM: posterior papillary muscle) tightens the chords and maintains the mitral valve in its closed plane (green arrows). The balance of these two forces forms the internal skeleton of the ventricle, which allows blood to be ejected into the LV outflow tract (LVOT) without the ventricle twisting on itself. The contraction starts at the apex and ends in the plenum. B: If the course of the posterior wall and the PPM is too long or if the ventricle is too small in systole (catecholaminergic overstimulation, hypovolaemia, concentric hypertrophy), the posterior wall moves anteriorly (green arrow); the coaptation point of the mitral valve is displaced anteriorly towards the aorta and approaches the LVOT; the tip of the posterior leaflet is in contact with the body of the anterior leaflet. The anterior leaflet is then pushed towards the LVOT as intraventricular pressure increases during systole (blue arrow). White line: mitral valve angle.

Figure 11.6: TEE cross sections of the mitral valve. The orthogonal cross-sectional planes of the body (4-cavity 0° and 2-cavity 90°, in white) do not correspond to the orientation of the mitral valve. The mitral valve is off-axis by 60°, so its orthogonal planes (in blue) are the bi-commissural plane at 40-60° and the long-axis plane at 120-150°, which is perpendicular to it and intersects the chase chamber and the aortic valve. The left atrial appendage (LAA) lies opposite the anterior mitral commissure. The third orthogonal plane is the 0° transgastric short axis view.

 Figure 11.7: Transesophageal echocardiographic views of the mitral valve. These are orthogonal views of the valve. A: 120° long-axis view of the LV with measurement of the length of the anterior leaflet at A2. B: 60° bi-commissural view. C: 0° transgastric short axis view. OT: Outflow tract. APM: anterior papillary muscle. PPM: Posterior papillary muscle. C1: Anterior commissure. C2: posterior commissure. The diameter of the mitral annulus is measured at 120-140° (A) and 60° (B) [1].

 Aortic valve

The aortic valve is part of the dynamic assembly that forms the root of the aorta. This assembly consists of several components (Figures 11.8) [1,19].

• A crown-shaped fibrous aortic structure with 3 vertical branches arising from the cusp commissures. The junction between the musculature of the LV outflow tract and the fibrous tissue of the aorta is incorrectly referred to as the aortic 'ring', although there is no separate anatomical structure at this level.
• Three semilunar cusps defined by their body, their free edge and their U-shaped base on the aortic wall opposite each sinus of Valsalva; the base measures 1.5 times the free edge. The lower insertion of the cusps is on the basal ring, which is anatomically located in the LV outflow tract (LVOT), below the junction between the aorta and the LV. The cusps are attached to the sinotubular junction.
• Three sinuses of Valsalva, which are bulges in the aortic root opposite the cusps; the right coronary sinus arises from the right sinus (the most anterior); the common trunk arises from the left sinus; the non-coronary sinus is the most posterior.
• Sinotubular junction between the sinuses of Valsalva and the ascending aorta, where the commissures of the valve remain.

The aortic valve lies anterior to the mitral valve, oriented so that the non-coronary (NC) leaflet is posterior, opposite the interatrial septum; the right coronary (RC) cusp is the most anterior (Figure 11.9). The height of each leaflet is 13-15 mm, but their surface is slightly asymmetrical: the NC leaflet is slightly larger than the right and left coronary leaflets. The central part of the free edges shows a fibrous reinforcement corresponding to their coaptation point (Arantius nodules); on the ventricular face of the cusps there is fibrous degeneration (Lambl excrescences).

Video: Short-axis view of the aortic valve (40° mid-oesophageal view) with its three cusps; the non-coronary cusp is at 10 o'clock, opposite the interatrial septum; the right coronary cusp is at 6 o'clock and the left coronary cusp is at 2 o'clock.