Aortic Regurgitation: Etiologies and Left Ventricular Responses

Anatomy of the Aortic Valve

The aortic valve is a semilunar valve, which typically has three cusps that are attached to the aortic wall to form the sinuses of Valsalva. The highest point of attachment at the leaflet commissures defines the sinotubular junction, and the most ventricular point (i.e., the nadir of the cusps) defines the annular plane. Note that the aortic annulus is not a real (physical) structure but rather a virtual “structure” defined by the bottom of the aortic cusps. The coaptation zone of the leaflets may include slight thickening or prominences at the central contact point (midpoint) of each cusp known as nodules of Arantius. Fenestrations at the free edges of the cusps are common but seldom cause aortic regurgitation (AR) because they are above the closure line. Large fenestrations or torn fenestrations, however, can lead to AR. Normally, the integrity of the aortic orifice during diastole is maintained by an intact aortic root and firm apposition of the coaptation zone. The proper functioning of the valve depends on the proper relationship between the leaflets within the aortic root.

Etiology of Aortic Regurgitation

AR is caused by a variety of disorders affecting the valve cusps, aortic root, or both ( Table 86.1 ). With rheumatic heart disease becoming less common, nonrheumatic causes currently account for the majority of the underlying causes of aortic insufficiency, including congenitally malformed aortic valves, infective endocarditis, and connective tissue diseases. ^, Disorders affecting the aortic root also account for a large number of patients with AR. These conditions include cystic medial necrosis, Marfan syndrome, aortic dissection, and inflammatory diseases. At the tissue level, the aorta shows cystic medial necrosis, loss of elastic fibers, increased apoptosis, and altered smooth muscle cell alignment. Note that the term “cystic medial necrosis” is actually a misnomer because this form of medial degeneration contains neither true cysts nor necrosis. Bicuspid aortic valve (BAV) is the most common congenital cardiac abnormality and is a common cause of AR ( Fig. 86.1 and Video 86.1 ). Most BAVs consist of one free leaflet and two leaflets that are conjoined (or have failed to separate during embryonic development) instead of the typical three leaflets. The term “raphe” defines the conjoined area of the two underdeveloped leaflets turning into a malformed commissure between both leaflets. Raphe may be complete, incomplete, or absent. Various causes have been suggested to explain the mechanism of AR in BAV, including cusp prolapse, endocarditis, dilated aortic root, and myxoid degeneration of the valve. Less common types of congenital aortic valves include unicuspid and quadricuspid valves. These are discussed in greater detail in Chapter 78 .

Video 86.1 . Two-dimensional and color Doppler images of a bicuspid aortic valve. Midesophageal transesophageal echocardiography (TEE) long-axis view with X-plane at the level of the aortic valve ( A ) demonstrates doming of the leaflet (arrow) , and the X-plane short-axis view demonstrates a bicuspid aortic valve with fusion of the right and left coronary cusp with a raphe (arrow) with fish-mouth appearance of valve orifice. TEE long-axis view of the aortic valve with color Doppler ( B ). The aortic regurgitation jet is eccentric (arrow) . AO, Aorta; IAS, interatrial septum; LA, left atrium; RA, right atrium.

Calcific aortic valve disease can cause calcification spots or more extensive calcification of all the cusps, interfering with cusp motion and resulting in AR. Even in the absence of any obvious pathology of the aortic valve or root, severe systemic hypertension has been reported to cause significant AR.