Chapter 4 Evaluation of the Aortic Valve

Introduction

The aortic valve is the third largest valve in the body, behind the tricuspid and mitral valves, and has a typical valve area of 3 to 4 cm². Despite its smaller size, it is arguably the most important because it lies between the high-resistance aorta and the high pressure–generating left ventricle. Like the pulmonary valve, the aortic valve is semilunar in nature; the major difference between the two semilunar valves is that the left and right coronary arteries arise from the aortic valve and from the left and right coronary sinuses of Valsalva, respectively. However, the aortic valve is also a more resilient valve than the pulmonic valve, as has been shown when the pulmonic valve has been switched into the aortic position in the Ross procedure.¹ The anatomy of the semilunar valves is unique in that a discrete, well-defined annulus, as in the mitral and tricuspid valves, is not present. That is, there is no well-formed fibrous band of tissue encircling the aorta, even though clinicians, especially surgeons, speak of this. Rather, there is a curvilinear attachment of the aortic valve cusps to the aortic wall. Real-time three-dimensional transesophageal echocardiography (RT3DTEE) has been used to reconstruct the aortic valve annulus, which has been shown to have significant variation depending on whether it is tricuspid, bicuspid, calcified, or quadricuspid (Figure 4-1).² In fact, the aortic annulus has the appearance of a crown and is well visualized in Figure 4-1. Furthermore, the valve cusps attach to tissue in both the aortic wall as well as the left ventricular arterial junction in a curvilinear fashion. The aortic valve cusps have a main core of tissue with endocardial lining present on each side. The individual leaflets meet at a central line of coaptation, the center of which is a thickened nodule called the nodule of Arantius (Figure 4-2). This nodule has important anatomic significance for RT3DE imaging because the extent of the nodule thickening often cannot be completely appreciated by two-dimensional echocardiography (2DE), and complete visualization is important in pathology of the valve leading to aortic regurgitation.²^–⁴ The body of the aortic valve leaflets is well seen by RT3DE, as opposed to 2DE (Figure 4-3).

Figure 4-1 The varying shape of the aortic valve annulus reconstructed from real-time three-dimensional transesophageal echocardiography data. A1, normal trileaflet valve; A2, calcified tricuspid valve; A3, scalene tricuspid valve; A4, bicuspid aortic valve, and A5, quadricuspid aortic valve.

(From Ren B, Tang H, Kang Y: Visualisation of the aortic annulus using the real-time three-dimensional transesophageal echocardiography. Heart 97:862–863, 2011.)

Figure 4-2 The center nodule of Arantius is prominent in this real-time three-dimensional transesophageal echocardiography short-axis view of the aortic valve.

Figure 4-3 A, Short-axis two-dimensional transesophageal echocardiography (TEE) of normal aortic valve. B, Short-axis real-time three-dimensional (3D) TEE of a normal aortic valve. This case shows an advantage and disadvantage of real-time 3D echocardiography. The advantage is the ability to see the body of the aortic valve cusp. The disadvantage is that there is some dropout (arrow) of the leaflet rather than an actual hole in the leaflet. This problem is encountered more with the semilunar valves than the atrioventricular valves because the former are thinner.

Aortic Valve Pathology and Real-Time Three-Dimensional Echocardiography

The evaluation of the aortic valve, including the sinuses of Valsalva and the aortic root, by both 2DE and 3DE has become even more important in modern-day cardiology because of the advent of the percutaneously delivered aortic valve and the ability to close defects in the aortic root and sinuses of Valsalva by using percutaneously placed vascular plugs.⁵ The characteristic Gerbode defect, defined as right coronary sinus of Valsalva rupture into the right atrium, is just one example in which RT3DTEE can particularly perform well in terms of visualization of the many (right atrium, right coronary sinus of Valsalva, tricuspid valve, interatrial and interventricular septae) structures that are in proximity to each other (Figure 4-4; Video 4-1). The anatomic relationships of these structures are not trivial, and RT3DTEE can sort them out nicely in many, if not all, instances.^1,² My own experience with closing the Gerbode defect with vascular plugs using RT3DTEE guidance has been extremely favorable.

Figure 4-4 Gerbode defect. Clockwise from top, Right atrium (red arrow), interatrial septum, defect in right coronary sinus of Valsalva (green arrow), mitral valve, and right ventricle with pacemaker (white arrow) (see Video 4-1).

The most common clinically significant aortic valve lesion is calcific aortic stenosis; this problem is becoming more and more common as the population ages. Significant hemodynamic effects develop with aortic stenosis when the valve area reaches roughly one fourth its normal value, depending on patient size. In young and middle-aged patients with aortic stenosis, the cause is frequently bicuspid aortic valve.⁶ RT3DE of the aortic valve can produce quite satisfactory images, particularly of bicuspid aortic valves, although visualization of the valve leaflets typically is more challenging than that of the mitral valve because the leaflets are very thin in the former (Figure 4-5; Videos 4-2 to 4-8). The advantage of RT3DE over traditional 2DE is the ability to visualize the body of the valve leaflets as opposed to only the borders of the leaflets at the coaptation point and as they come together to form the commissures at the circumference of the aortic valve. This particular strength of RT3DE is shown in Figure 4-6 with direct comparison with 2DE imaging in the same patient. A step-by-step approach to acquisition of the RT3DTEE dataset, starting with the 2DTEE views and then moving to the 3D zoom mode, is described (Videos 4-9 to 4-14). Both RT3D transthoracic echocardiography (TTE) and RT3DTEE have been extensively used for evaluation of the disease of the cusp body. Because the most common cause of aortic stenosis is degenerative or calcific aortic stenosis, RT3DE is particularly useful because that type of aortic stenosis preferentially involves the body of the aortic cusps. The same is true for evaluation of the precursor of calcific aortic stenosis: aortic sclerosis (Figure 4-7; Videos 4-15 to 4-17). For aortic regurgitation, the second most common clinically significant aortic valve lesion, RT3DE can provide data about the degree of regurgitation, particularly by evaluating the 3D vena contracta of the regurgitation, especially with regard to the etiology of the aortic regurgitation.