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.

Figure 4-5 These figures are from the same patient and demonstrate two-dimensional (2D) and real-time (RT) three-dimensional (3D) echocardiography images of a bicuspid aortic valve. A, Bicuspid aortic valve by 2D transthoracic echocardiography (TTE) parasternal short-axis view. In this view, the valve has the typical “fish mouth” bicuspid look, and no raphe is clearly visible. B, 2DTTE parasternal short-axis view. In this image, the main closure of the bicuspid valve is shown from the 12:30 to 6:30 o’clock positions (arrow). There is also a small raphe shown at the 9:00 o’clock position, in the area where the right and noncoronary cusp would fuse if this were a trileaflet valve. C, 2DTTE, parasternal short-axis view. In this image, a small amount of aortic regurgitation is shown (red arrow). The raphe shown in B is seen again (white arrow). D, Image of the aortic regurgitation and the raphe shown in C (see Video 4-2). E, 2DTTE parasternal short axis view. The raphe seen in C is again seen, as well as the closure line of the bicuspid valve at the 1:00 and 6:30 o’clock positions (see Video 4-3). F, RT3D transesophageal echocardiography (TEE) image of the bicuspid aortic valve closed. The raphe seen by 2D in C is shown in 3D here. This emphasizes how the raphe is more complex and longer than appreciated by the 2D image. G, RT3DTTE image showing that there are two raphes, one at approximately the 11:00 o’clock position and one at the 5:00 o’clock position. Again, the anatomy of the raphes is appreciated better than in 2D (see Video 4-4). H, 2DTEE image of the bicuspid aortic valve taken at an angle of 33 degrees. Note that with the aortic valve completely open in mid-systole, the raphes are not seen. I, 2DTEE image of the bicuspid aortic valve. Note the aortic regurgitation; the orientation of the valve is now opposite the transthoracic orientation, with the posterior at the top of the image. Note the complex raphe near the anterior opening of the valve (arrow). J, RT3DTEE of the bicuspid aortic valve. Note the additional raphes seen with RT3DE that were not seen in the 2DTEE images (arrow). K, 2DTEE of the bicuspid aortic valve. Note the raphes present, but the lack of perception of depth in the 2D image (see Video 4-5). L, RT3DTEE of the bicuspid aortic valve. Note the “fish mouth” appearance of the aortic valve opening as well as the depth perception of the aortic valve leaflets. M, RT3DTEE of the bicuspid aortic valve. As opposed to L, the valve is more open as it is captured in mid-systole. Note that this is frame 9 of the cardiac cycle. N, RT3DTEE showing raphe formation at the 9:00 and 6:00 o’clock positions in this bicuspid aortic valve (see Videos 4-6 and 4-7). O, RT3DTEE of the bicuspid aortic valve taken from the opposite side of the valve. In this case, the image is taken from the aortic side of the valve (see Video 4-8). P, RT3DTEE with the transducer at 35 degrees shows the closed bicuspid valve with raphes present at the 9:00 and 6:00 o’clock positions and thickening of the tissue associated with the raphe.

Figure 4-6 Two-dimensional (2D) transesophageal echocardiography (TEE) views of the aortic valve. A, Short-axis view of the aortic valve by RT3DTEE with the transducer at 35 degrees. B, Long-axis view of the aortic valve with the transducer at 150 degrees (see Videos 4-9 and 4-10). C, The setup for going to RT3DTEE in the 3D zoom mode. Image of the biplane, or “X-plane,” view is shown at left. Note that the aortic valve is shown simultaneously in orthogonal views (35 degrees and roughly 150 degrees) (see Video 4-11). D, RT3DTEE in the 3D zoom mode. D1, Short-axis view of the aortic valve (closed); D2, short-axis view of the aortic valve (open); D3, long-axis view of the aortic valve. Note the coronary artery shown coming off the sinus of Valsalva (arrow). E, RT3DTEE in the 3D zoom mode. E1, Short-axis view of the aortic valve (with right ventricular outflow tract more anterior and tricuspid valve); E2, short-axis view of the aortic valve (zoomed); E3, long-axis view of the aortic valve. Note the coronary artery shown coming off the sinus of Valsalva (arrow) (see Videos 4-12 to 4-14).

Figure 4-7 Aortic sclerosis shown by (A) two-dimensional (2D) transesophageal echocardiography (TEE) and (B) real-time three-dimensional (3D) TEE. In both cases, a short-axis view at an angle near 35 degrees is shown. There is particular sclerosis of the noncoronary cusp seen in both 2D and 3D (arrows). The extent of the sclerosis throughout the entire cusp is more readily apparent on the 3D image (see Videos 4-15 to 4-17).

One of the first reports specific for RT3DE imaging of the aortic valve, performed by Blot-Souleti,¹² 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.⁷ 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.^8–11 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).

Figure 4-8 Quadricuspid valve. A, Two-dimensional transesophageal echocardiography (TEE) short-axis view of a quadricuspid valve. Note that the cusp at the 2 o’clock position is substantially smaller than the others. B, Real-time three-dimensional (RT3D) TEE short-axis view of the quadricuspid valve. The major difference and advantage appreciated in RT3DTEE is the ability to see the body of the aortic valve cusps. This also gives a more realistic perspective of the relative sizes of the cusps (see 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.¹² 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.¹³ 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.¹⁴

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.

Bicuspid Aortic Valve Pathology and Real-Time Three-Dimensional Echocardiography

Bicuspid aortic valves typically can be diagnosed with 2DTTE imaging, although in some patients transthoracic imaging is inadequate and 2DTEE is necessary. However, RT3DE imaging can visualize the presence or absence of a raphe between the fused cusps as well as the relationship of the raphe to the other cusps and the coronary arteries. This characterization is useful from a prognostic standpoint, since bicuspid aortic valves with an anterior or posterior orientation with the coronary arteries arising from the anterior cusp have more complications and less longevity than the right or left orientation. Furthermore, bicuspid valves with a raphe have a worse prognosis than those without.^15–17 Also, the presence or absence of a raphe as well as presence of a cleft have been reported to affect surgical repair in patients who have valve preservation surgery.¹⁸ Hence, imaging of the bicuspid valve morphology by RT3DE becomes important because (1) bicuspid aortic valve is the most common congenital heart defect, present in 2% of the population; and (2) RT3DE is the imaging test of choice to evaluate for the presence and extent of a raphe. Examples of RT3DTEE views of bicuspid aortic valves are shown in Figure 4-9 (Videos 4-20 and 4-21.)

Figure 4-9 A bicuspid valve with a possible vegetation present. The two-dimensional transesophageal echocardiography (2DTEE) image (A) has a higher frame rate (38 Hz) compared with the corresponding three-dimensional (3D) image (18 Hz) (B). As a consequence, it is easier to see that the mass on the aortic valve is undulating and has movement and is independent of the aortic valve. The real-time 3DTEE image shows the body of the aortic valve cusp in more detail compared with the corresponding 2D image. As it turned out, the patient’s blood cultures were negative and did not meet the Duke criteria for endocarditis despite having this mass (see Videos 4-20 and 4-21).

Endocarditis of the Aortic Valve and Real-Time Three-Dimensional Echocardiography

Endocarditis is a significant cause of aortic regurgitation in adult patients with trileaflet aortic valves. In addition, when an abscess cavity develops in endocarditis, the aortic valve is involved in 83% of the cases. Evaluation of endocarditis by RT3DE has been shown to improve the accuracy of vegetation size and morphology and also aid in the diagnosis of abscess cavity associated with the endocarditis process. For aortic valve endocarditis specifically, both RT3DTTE and RT3DTEE have been used extensively to determine aortic valve cusp integrity and to diagnose an abscess cavity associated with the aortic valve. Figure 4-10 shows several examples of aortic valve endocarditis visualized by RT3DTEE (Videos 4-22 to 4-26).

Figure 4-10 Endocarditis. Real-time (RT) three-dimensional (3D) transesophageal echocardiography (TEE) view of a patient with a vegetation on the aortic valve (right, arrow). The two-dimensional (2D) TEE view is shown for comparison (left, blue line). The 3D image reveals the actual shape of the vegetation to be papillary in nature. B1, 2DTEE with the transducer at 151 degrees showing the aortic valve vegetation (same view as A). B2, RT3DTEE image of a vegetation on the aortic valve. B3, A more zoomed RT3DTEE image of the vegetation on the aortic valve (see Videos 4-22 to 4-24). C, 2DTEE with the transducer at 151 degrees showing aortic regurgitation as a result of the vegetation on the aortic valve. Note that in this case aortic regurgitation is directed at the area where the aortic vegetation is located, possibly contributing to the reason that the vegetation was present in this location. D, 2DTEE (left) and RT3DTEE (right) of aortic regurgitation showing the aortic regurgitation jet hitting the area where the aortic vegetation is located. Hence, the aortic regurgitation jet is possibly contributing to why the vegetation was present in this location (see Videos 4-25 and 4-26).

Interventional Procedures and the Aortic Valve by Real-Time Three-Dimensional Echocardiography

Interventional procedures involving the aortic valve, including transcatheter aortic valve implantation, closure of paraaortic prosthetic aortic valvular leak, closure of sinus of Valsalva ruptured aneurysm, and closure of aortic root pseudoaneurysms have all been described with RT3DTTE or RT3DTEE guidance.¹⁹ Closure of paraaortic prosthetic aortic valvular leak, in fact, is quite difficult to perform without RT3DTEE. Figure 4-11 shows imaging of a transcatheter-placed aortic valve by RT3DTEE. Evaluation of the aortic annulus size has been shown to be more accurate by 3DTEE than by 2DTEE when compared with magnetic resonance imaging.

Figure 4-11 Transcatheter aortic valve implantation. Real-time three-dimensional transesophageal echocardiography of a properly positioned stent valve (A) and a stent valve that has prolapsed into the left ventricular outflow tract (B).

Prosthetic Aortic Valves

Although prosthetic valve imaging by RT3DE is covered in Chapter 8, it is important to mention RT3DE imaging specifically for the aortic position. The good news is that on the basis of my experience, there is less shadowing from the prosthetic valves with RT3DE than with traditional 2DE. This, however, is not easily explained, since RT3DE still uses ultrasound and shadowing artifact from prosthetic material remains a significant limitation. So, this is a small triumph. However, the unfortunate news is that compared with the mitral valve, the aortic valve remains much more difficult to image by any echocardiography modality. And, as in the 2D realm, although TEE helps dramatically with mitral imaging, TEE helps only to a certain extent for imaging the aortic valve. Finally, in the case of patients with mechanical prosthetic valves in both the mitral and aortic positions, aortic valve imaging remains a substantial challenge. Figure 4-12 shows an example of imaging of a prosthetic aortic valve by RT3DTEE. Further aortic valve images of interest are shown in Figures 4-13 to 4-18; Videos 4-27 to 4-34).

Figure 4-12 Real-time three-dimensional transesophageal echocardiography of a bioprosthetic valve, open, in the aortic position.

Figure 4-13 A, A bicuspid valve with a prominent nodule is seen by two-dimensional (2D) transesophageal echocardiography (TEE; A1) and real-time (RT) three-dimensional (3D) TEE (A2). The nodule seen in the 2D image (arrow) is seen also in RT3DTEE with added depth perception. B, Same patient as in A. B1, The same 2DTEE short-axis view is seen, again with the prominent nodule. B2, The 2DTEE long-axis view (125-degree view) is shown, with the nodule prolapsing into the left ventricular outflow tract. This lesion led to suspicion of endocarditis. The patient, however, did not have positive blood culture results for endocarditis and did not meet the Duke criteria for endocarditis (see Video 4-27). C, Repeat view of the RT3DTEE view of the nodule.

Figure 4-14 A, Early vintage real-time (RT) three-dimensional (3D) transthoracic echocardiography (TTE) showing an aortic valve with the pulmonary valve just to the right. This image was created via cropping in the software program QLab. B, Cropping in QLab. This is an image of a full volume of 3D data obtained by RT3DTTE. In this case, the volume set is cropped to show the aortic valve (see Video 4-28). C, Older vintage RT3DTTE showing simultaneous aortic valve (black arrow), mitral valve (yellow arrow), and pulmonary valve (white arrow) (see Video 4-29).

Figure 4-15 Real-time three-dimensional transesophageal echocardiography image of aortic valve showing the limitation of dropout. In this case, a notable dropout of the right coronary cusp (arrow) is seen (see Video 4-30). There is a tradeoff with the gain in these types of cases between showing increased gain to eliminate dropout but, at the same time, not being able to visualize the body of the aortic valve cusp.

Figure 4-16 Subaortic membrane (arrow) by real-time three-dimensional transthoracic echocardiography (see Video 4-31).

Figure 4-17 A patient with systemic lupus erythematosus has lack of cusp coaptation at the central point (arrow) (see Video 4-32).

Figure 4-18 Two-dimensional (2D) transesophageal echocardiography (TEE) (A) and real-time (RT) three-dimensional (3D) TEE (B) of the aortic valve showing the coronary arteries. The 2DTEE image of the aortic valve shows the bifurcation of the left main artery into the left anterior descending (LAD) and circumflex (Cx) coronary arteries (arrow). The RT3DTEE view uses the elevation dimension to show the left main as well as the two bifurcating arteries (LAD and Cx). In the 2D image, the LAD and Cx arteries are seen, but the left main artery is into the plane and therefore not seen simultaneously (see Videos 4-33 and 4-34).

Summary

Aortic regurgitation, particularly aortic stenosis, is a frequent problem. RT3DE has been shown to be useful in a variety of settings in which the aortic valve is involved in the disease process. The elevation dimension of RT3DE has proved to be particularly useful for viewing the aortic cusps and has definite advantages over the use of standard 2DE imaging. In the future, it would be expected that color Doppler using RT3DE would improve and would further aid in the quantification of aortic regurgitation. Finally, for some interventional procedures involving the aortic valve, RT3DTEE has proved to be indispensable.