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 cm ² . 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. 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 ). 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. The body of the aortic valve leaflets is well seen by RT3DE, as opposed to 2DE ( Figure 4-3 ).

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. 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. My own experience with closing the Gerbode defect with vascular plugs using RT3DTEE guidance has been extremely favorable.

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. 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.

One of the first reports specific for RT3DE imaging of the aortic valve, performed by Blot-Souleti, looked at the accuracy of aortic stenosis quantitation using RT3DTTE. Previously, there had been multiple reports of the general use of RT3DTTE to visualize many structures, including the aortic valve. Blot-Souleti's study was, however, a comprehensive evaluation of the first experience with RT3DTTE. Later, several case reports of imaging bicuspid aortic valves by RT3DTTE appeared. Imaging of a quadricuspid aortic valve by RT3DTTE was described by Aggarwal, Burri, and Chen, and that of the unicuspid aortic valve by Matsumoto. In the first report, the right upper sinus of Valsalva ruptured into the right atrium, which was well visualized by RT3DTTE as well as color RT3DTTE. Figure 4-8 shows a quadricuspid valve by 2DE and RT3DTEE ( Videos 4-18 and 4-19 ).

As previously mentioned, the accuracy of imaging the aortic valve area in aortic stenosis by RT3DTTE has been compared with the 2D continuity equation and TEE planimetry, with a correlation of 0.82 and 0.94, respectively. Furthermore, aortic stenosis imaging accuracy by RT3DTTE was compared with catheterization and planimetry by 2DTEE, and only very small absolute differences (between 0.01 and 0.15 cm) were noted. Aortic annular motion is a significant pitfall in measuring the aortic valve area by 2DTEE planimetry. This seems to be at least partially overcome by using the volumetric data obtained by RT3DTEE.

Aortic regurgitation severity has been evaluated by RT3DE using the 3D color vena contracta method. In this comparison, the vena contracta severity was favorably compared with a gold standard of magnetic resonance imaging phase contrast regurgitant volume and regurgitant fraction.