Aortic root anatomy, including the aortic valve and coronary artery ostia, is complex [77–79]. The geometry and relationship of the aortic root structures change throughout the cardiac cycle [80–83]. Implantation of a stent/valve has incompletely understood the consequences of these structures and their relationships.

The aortic annulus describes the interface between the left ventricular outflow tract and the aortic root at the commissures of the aortic valve leaflets (Fig. 7.2). The three commissures extend upward into the aortic root similar to the shape of a crown or the struts of a bioprosthetic valve. The “annular” level at the lowest point of the valve hinge point (“inferior virtual basal ring”) defines the level where valve prostheses are sutured or secured. During valve surgery the annulus is fitted to the valve. On the other hand, when the transcatheter valve is deployed, the stent/valve must adjust to the “aortic root.” Therefore, in addition to size and shape, the composition and material properties of the surrounding structures have important implications for the interaction between device and root. Approximately 2/3 are in contact with ventricular myocardium, and the remaining 1/3 are composed of the aortic leaflet of the mitral valve [31].

The three individual cusps of the aortic valve are attached to the aortic wall along the commissures in a crescentic fashion (Fig. 7.3). Behind the cusps are the outward bulging sinuses of Valsalva, with the origins of the coronary arteries at the superior aspect of the left and right aortic sinuses. There is a wide variation in distance between the leaflet tips and the coronary ostia, and in about 50% of patients, the length of the left coronary leaflet exceeds the distance between the annulus and the ostium of the left coronary artery.

The sinotubular junction describes the margin between the aortic root and tubular ascending aorta and has an important role in maintaining valve competence (Fig. 7.4) [84]. During the TAVI procedures, the sinotubular junction provides support for the deployment balloon; depending on valve design (short vs. long), the sinotubular junction and proximal ascending aorta are important for proper implantation (distal anchor zone). Please see Chap. 2 for more information on the anatomy of the semilunar valves.

The position of the aortic root relative to the body axis and corresponding alignment of the X-ray plane are critically important for precise placement of the stent/valve. With angiography, overlap-free visualization of the three coronary cusps, which are oriented along the aortic valve plane, typically requires caudal angulation in the RAO projection and cranial angulation in the LAO projection. The current standard approach is based on the identification of X-ray root angiograms in one or preferably two orthogonal planes prior to the procedure after repeated root injections. Recent CT data demonstrates that a pre-procedural multi-detector CT angiography of the aortic root allows prediction of the optimal angulation of the root angiogram, which could facilitate the angiographic procedure and reduce the number of root injections (Fig. 7.5) [85, 86].

As described above, using imaging modalities, the annulus plane is defined as the plane created by the lowest hinge point of the three leaflets of the aortic valve (“inferior virtual basal ring”) (Figs. 7.2 and 7.4). Detailed 3D analysis demonstrates that this clinically defined annulus is typically elliptical [87–97], and therefore, maximal and minimal annular diameters are reported with CT. Mean annular diameter by CT correlates best but is typically slightly larger than that obtained with TEE. Measurement of the distance between the coronary arteries, artery ostia, and distal tip of the aortic valve leaflets is important and can be derived from angiography, CT, and TEE (Fig. 7.4). In the case of a low ostium or a long leaflet, there is increased risk of coronary (particular left main) occlusion [87, 89, 90, 94].

Imaging allows detailed description of the presence and distribution of valve and root calcification (Fig. 7.6) [98–104]. For example, calcification frequently extends from the aortic valve commissures to the base of the anterior mitral leaflets and sinotubular junction. The amount and distribution of calcification in the proximal device landing zone at the annulus affect sealing of the prosthesis. Aortic calcification of the sinotubular junction can influence precise placement of the valve during TAVI by restricting balloon expansion and potentially leading to the ventricular displacement of device at the time of deployment.

Direct observation of the aortic valve opening area allows for correlation of the pattern of valve opening with leaflet anatomy and leaflet calcification. Direct planimetry of the aortic valve opening area with CT has been shown to provide reproducible results in comparison to TEE and MRI (Fig. 7.7) [105–112].

During periprocedural 3D TEE, the biplane imaging mode is valuable in simultaneously imaging the aortic valve in both the short- and long-axis views, both in 2D and in color Doppler (Fig. 7.8). This allows the accurate positioning of the prosthetic device in the center of the stenotic valve in both orientations, as well as rapidly localizing postimplantation paravalvular regurgitation.

The annulus of the mitral valve is an oval, saddle-shaped structure which is formed by continuity of the left atrial tissue with the left ventricular tissue, as well as the base of the mitral valve leaflets (Figs. 7.9 and 7.10) [113, 114]. The mitral valve apparatus consists of the annulus, leaflet, chordae, and the papillary muscles. The annulus is divided into anterior and posterior parts by the commissures. The anterior leaflet is larger in length but covers only about 1/3 of the circumference of the annulus. The posterior leaflet is shorter in length but covers approximately 2/3 of the annulus. The chordae arise from the papillary muscle tips and then span to the leaflets in a fan-shaped manner (Fig. 7.11). There are two main chordae arising from each head of the papillary muscle, reaching each of the leaflets. However, there is a considerable variation in the origin and distribution of the chordae.

The coronary sinus (CS) extends along the left atrioventricular groove close to the mitral annulus and drains into the right atrium. In the context of sinus annuloplasty procedures, a major concern is the close proximity of the CS to the left circumflex artery (LCX) andthe potential risk of CS-based devices potentially impinging on the LCX [115]. See Chap. 1 for more information on the anatomy of the atrioventricular valves.

Three-dimensional imaging allows a detailed understanding of the mitral valve apparatus including the mitral annulus and leaflets and has been extensively described with echocardiography [116–121]. Description of mitral valvular anatomy is critical for procedures involving the mitral leaflets, including mitral valve clip procedures and percutaneous closure of paravalvular regurgitation. Real-time 3D and full-volume acquisition with TEE allows imaging of the entire mitral valve and annulus over full cardiac cycles [47, 122–125]. Therefore, 3D echocardiography is a critical part of the pre-procedural assessment of patients with mitral regurgitation and allows clarification of etiology and assessment of amenability of the mitral valve to percutaneous procedures (Fig. 7.12). For periprocedural guidance, full-volume 3D echocardiography data acquisition is less useful because of the need for offline analysis. However, real-time 3D echocardiography with its enface mitral valve view from the left atrium similar to the surgeon’s view, as well as simultaneous biplane imaging with its high temporal and spatial resolutions both in 2D and color Doppler modes, is invaluable for procedures such as mitral valve clip (Fig. 7.13) and percutaneous closure of paravalvular regurgitation (Fig. 7.14).

For CS-related procedures, fluoroscopy, CT, and TEE are helpful for proper positioning of the device and evaluating the effectiveness of the intervention. Several studies have used angiography and CT to describe the in vivo anatomical relationships between mitral annulus and CS as well as CS and LCX [126–129]. These studies observed significant variance of CS to mitral annulus separation. The LCX crossed between the CS and mitral annulus in 74–97% of patients at a variable ­distance from the ostium of CS, depending on coronary dominance. In addition, obtuse marginal branches and posterolateral branches were also in a position to potentially be compressed by a device placed within the CS. Therefore, evaluation of the relationship between the CS/great cardiac vein and the LCX is an important factor in determining the safety of CS-based devices.

For all transcatheter valvular procedures, assessment of vascular access is important and relies on different imaging modality (Fig. 7.15). Absolute size, amount and extent of calcification, as well as tortuosity of iliac and femoral determine suitability for the procedure [130, 131]. Vascular complications are the major cause of mortality and morbidity in patients undergoing TAVI, and this should therefore be considered as transcatheter valve procedures increase in number.