The aortic valve is one component of the aortic root, which connects the left ventricular outflow tract to the ascending aorta. The function of the aortic root is to guide the unidirectional flow of large volumes of blood with minimal resistance while maintaining laminar flow. Another function is to optimize coronary blood flow. These functions require complex dynamic interactions between different anatomical components that may be affected by pathological processes.
THE AORTIC ROOT
The aortic root is deeply anchored within the base of the heart between the pulmonary root anteriorly and the mitral and tricuspid valves posteriorly ( Fig. 20-1 ). The junction between the atrioventricular valves and the aortic root is occupied by the fibrous skeleton of the heart including the two fibrous trigones.
The aortic root is delineated by the sino-tubular junction distally and the left ventricular outflow tract proximally ( Fig. 20-2 ). It consists of three different components: the sinuses of Valsalva, the annulus, and the leaflets. The anatomy of these components is described sequentially as the surgeon visualizes them following a transverse aortotomy above the sino-tubular junction ( Fig. 20-3 ).
The sino-tubular junction is a small ridge of transverse collagen and elastic bundles overriding the sinuses of Valsalva and the commissures ( Fig. 20-4 ). The ratio between the circumference of the sino-tubular junction and the circumference of the annulus varies according to patient weight. In younger patients, this ratio is approximately 0.9. In older patients, the sino-tubular junction tends to dilate, resulting in this ratio becoming ≥1.
The sinuses of Valsalva look like bulges of aortic tissue extending from the sino-tubular junction to the aortic annulus. The aortic wall thickness at the sinuses of Valsalva progressively diminishes as it approaches the annulus to which it is firmly attached.
The size and shape of the sinuses of Valsalva analyzed by casts under physiological pressures ( Fig. 20-5 ) are slightly different with frequent individual variations.
Precise measurements of the intercommissural distance and height show that the left coronary sinus is usually smaller than either the right coronary sinus or the non–coronary sinus ( Table 20-1 ). The systolic circumference of the aortic root at the level of the sinuses is approximately 50% larger than the sino-tubular junction circumference, with large individual variations. The right and left coronary orifices arise from the right and left sinuses at different levels, with the right coronary orifice usually located at a higher level, to the point that it may be hidden by the sino-tubular ridge ( Fig. 20-6 ).
| Intercommissural Distance | Height of Sinuses | |
|---|---|---|
| Right coronary sinus | 18.8 (1.8) * | 19.4 (1.9) * |
| Non-coronary sinus | 17.4 (1.9) * | 17.7 (1.7) * |
| Left coronary sinus | 15.2 (1.8) * | 17.4 (1.4) * |
The annulus is a well-delineated scallop-shaped fibrous structure firmly attached to the trigones, the aorto-mitral curtain, and the muscular and membranous septa ( Fig. 20-7 ). The nadir of the non–coronary scallop is generally situated at a lower level than those of the two other scallops. The plane joining the nadirs of the aortic annulus (annular plane) forms an approximate 120° angle with the plane of the mitral valve orifice ( Fig. 20-8 ). The planar projection of the scalloped annulus is a circle 10% larger than the circumference of the sino-tubular junction. The average length of this circumference is 70 ± 7 mm for a diameter of approximately 22 mm. The scalloped shape of the annulus delineates three commissural tips that attach the leaflet commissures.
The subaortic segment , which forms the junction between the aortic root and the ventricular outflow tract, is composed of three triangular subcommissural structures ( Fig. 20-9 ). The triangle between the right and non–coronary sinuses partially includes the membranous septum. The triangle between the non–coronary and left coronary sinuses is part of the aorto-mitral curtain. The triangle between the right and left coronary sinuses, in continuity with the ventricular septum, is muscular at its base and fibrous at its summit. Through the aortotomy, below the aortic annulus, the ventricular aspect of the anterior mitral leaflet and the attachment sites of secondary chordae are visualized.
