Thoracic Aorta
The aorta is a complex tubular structure divided into five segments: aortic root, tubular portion of the ascending aorta, aortic arch, descending thoracic aorta and abdominal aorta. Various imaging modalities such as echocardiography, MSCT and MRI have been used to evaluate the aorta. Each has it is own advantages and disadvantages. Overall, conventional 2D echocardiography is used to evaluate the aortic root, proximal ascending aorta, and aortic arch dimensions. 3D echocardiography can improve these measurements by identifying real maximum diameters of each part. The best possible 3D images of the ascending aorta can be obtained from the parasternal long-axis view. A recent 3DTTE study has shown visualization of longer segments of the ascending aorta utilizing the right parasternal approach compared to 2DTTE. In addition, right parasternal examination views the right pulmonary artery behind the ascending aorta unlike the left parasternal approach which most often images the superior vena cava rather than the pulmonary artery posterior to the aorta (Figure 8 A-C).34 The trunk/right pulmonary artery often serves not only as a landmark to divide the ascending aorta into proximal and distal segments and but also to measure the mid ascending aorta diameter by MSCT. Suprasternal view may identify aortic arch. The use of 3D echocardiography has become more relevant after the introduction of TAVI. Planning for TAVI requires precise aortic annulus measurements for appropriate valve sizing. 3D measurements of the aortic valve area, annulus, root dimensions and annulus distance to the coronary ostia have been validated against MSCT and MRI. Another major advantage of 3D TEE compared to 2D imaging is guidance during TAVI procedures to assist with appropriate device positioning and assessment of procedural success and identifying any potential complications such as paravalvular leak.
Among patients with thoracic aneurysm and dissection, 3D TEE has greater accuracy than 2D TEE in identifying the type and location of aneurysm as well as the dissection.38 Our lab showed that in a study of 67 patients with aortic disease, 20 with aortic aneurysm without dissection, 21 with aortic aneurysm and dissection, and 26 with aortic dissection without aneurysm, the use of live 3D TEE increased the level of confidence in the diagnosis and allows the localization of the rupture site (Figures 9, 10 A-D, Movies 9 A-C).39 The use of 3D TEE can easily distinguish linear artifact occasional seen within the aorta from a true dissection flap, which will appear like a curvilinear sheet rather than a thin linear echo density (Figure 11 A and B, Movies 10 A and B).40