The aortic valve is a complex structure that is best described as a functional and anatomic unit, the aortic root. The aortic root has four components: aorto-ventricular junction or aortic annulus, aortic cusps, aortic sinuses, and sinotubular junction. In addition, the triangles beneath the commissures of the aortic valve, although part of the left ventricular outflow tract, are also important for valve function.
The aortic annulus unites the aortic cusps and aortic sinuses to the left ventricle. It is attached to ventricular myocardium (interventricular septum) in approximately 45% of its circumference and to fibrous structures (anterior leaflet of the mitral valve and membranous septum) in the remaining 55% (Fig. 36-1). The aortic annulus has a scalloped shape. Histologic examination of the aortic annulus reveals that it is a fibrous structure with strands attaching itself to the muscular interventricular septum and has a fibrous continuity with the mitral valve and membranous septum. The fibrous structure that separates the aortic annulus from the anterior leaflet of the mitral valve is the intervalvular fibrous body. An important structure immediately below the membranous septum is the bundle of His. The atrioventricular node lies in the floor of the right atrium between the annulus of the septal leaflet of the tricuspid valve and the coronary sinus. This node gives origin to the bundle of His, which travels through the right fibrous trigone along the posterior edge of the membranous septum to the muscular interventricular septum. At this point, the bundle of His divides into left and right bundle branches that extend subendocardially along both sides of the muscular interventricular septum.
A photograph of a human left ventricular outflow tract and aortic root.
The aortic cusps are attached to the aortic annulus in a scalloped fashion (see Fig. 36-1). The aortic cusps have a semilunar shape whereby the length of the base is approximately 1.5 times longer than the length of the free margin, as illustrated in Fig. 36-2. There are three cusps and three aortic sinuses: left, right, and noncoronary. The aortic sinuses are also referred to as sinuses of Valsalva. The left coronary artery arises from the left aortic sinus and the right coronary artery arises from the right aortic sinus. The left coronary artery orifice is closer to the aortic annulus than is the right coronary artery orifice. The highest point where two cusps meet is called the commissure, and it is located immediately below the sinotubular junction. The scalloped shape of the aortic annulus creates three triangular spaces underneath the commissures. The two triangles beneath the commissures of the noncoronary cusp are fibrous structures, whereas the triangular space beneath the commissure between the left and right cusps is mostly muscular. These three triangles are seen in Fig. 36-1. The aortic annulus evolves along three horizontal planes within a cylindrical structure. ...