CT and MR imaging prior to transcatheter aortic valve implantation: standardisation of scanning protocols, measurements and reporting-a consensus document by the European Society of Cardiovascular Radiology (ESCR)

Abstract

Transcatheter aortic valve replacement (TAVR) is a minimally invasive alternative to conventional aortic valve replacement in symptomatic patients with severe aortic stenosis and contraindications to surgery. The procedure has shown to improve patient's quality of life and prolong short- and mid-term survival in high-risk individuals, becoming a widely accepted therapeutic option which has been integrated into current clinical guidelines for the management of valvular heart disease. Nevertheless, not every patient at high-risk for surgery is a good candidate for TAVR. Besides clinical selection, which is usually established by the Heart Team, certain technical and anatomic criteria must be met as, unlike in surgical valve replacement, annular sizing is not performed under direct surgical evaluation but on the basis of non-invasive imaging findings. Present consensus document was outlined by a working group of researchers from the European Society of Cardiovascular Radiology (ESCR) and aims to provide guidance on the utilisation of CT and MR imaging prior to TAVR. Particular relevance is given to the technical requirements and standardisation of the scanning protocols which have to be tailored to the remarkable variability of the scanners currently utilised in clinical practice; recommendations regarding all required pre-procedural measurements and medical reporting standardisation have been also outlined, in order to ensure quality and consistency of reported data and terminology. KEY POINTS: • To provide a reference document for CT and MR acquisition techniques, taking into account the significant technological variation of available scanners. • To review all relevant measurements that are required and define a step-by-step guided approach for the measurements of different structures implicated in the procedure. • To propose a CT/MR reporting template to assist in consistent communication between various sites and specialists involved in the procedural planning.

Keywords: Aortic valve stenosis; Consensus; Magnetic resonance imaging; Multidetector computed tomography; Transcatheter aortic valve replacement.

Fig. 1

CT images of a Medtronic self-expandable Corevalve (a) and Edwards Lifesciences balloon-expandable Sapien valve (d). After deployment, a self-expandable valve will conform itself to the normal annular contour, acquiring an oval cross-sectional morphology (b). Compared with a balloon-expandable valve, the self-expandable Corevalve is larger in size and contains an inflow (I), waist (w), and outflow (O) functional part (c). This outflow part is by design intended to extend into the ascending aorta, covering but not obstructing the coronary ostia. The balloon-expandable Sapien valve (d) is shorter, with a mostly circular cross-sectional contour after deployment (e) as it forces this circular morphology on the annulus through the radial forces of the expanding balloon. In contrast to the self-expandable Corevalve, it remains within the aortic sinus (f). Within both THVs, the pericardial leaflets can be appreciated as fine hypodense linear structures (arrowheads in c, f), its visibility dependent on image quality. Small interposing calcifications (arrows in b, e) have in these examples only a minimal effect on THV expansion. Reused from reference [40], with permission

Fig. 2

3D volume rendering CT image of the heart containing the aortic root. The aortic root has a double-oblique orientation within the heart. Therefore, standard orthogonal imaging planes, like the axial plane indicated with the dotted white line, are not suitable to correctly visualise the aortic root and containing structures. For this reason, intrinsic 3D imaging modalities like CT are necessary to correctly assess the aortic root and annulus and obtain accurate measurements

Fig. 3

The aortic sinus contains the aortic valve, in most patients composed of three leaflets (asterisk in a, coloured dotted lines in b, c). They are named according to the adjacent sinus of Valsalva (a): right coronary sinus (red), left coronary sinus (green) and non-coronary sinus (blue). As such, we distinguish (b, c) a right coronary cusp (red), left coronary cusp (green) and non-coronary cusp (blue). The dotted dark blue line in (c) indicates the sinotubular junction, marking the roof of the aortic sinus

Fig. 4

Most TAVI candidates will present with an aortic valve containing significantly calcified valve leaflets. The majority of patients will have a clearly identifiable tricuspid aortic valve (a). However, a significant portion will have a bicuspid aortic valve, which is an important feature to report as its presence is associated with some specific complications. However, in some cases, valve cuspidity can be difficult to assess in heavily degenerated valves, where extensive calcification can make differentiation between tricuspid and (functionally) bicuspid valves difficult (b)

Fig. 5

Incomplete and asymmetric deployment of a self-expandable THV due to interposition of extensive native leaflet calcifications (arrow in a, b) between the prosthetic valve and the wall of the aortic sinus. Severe calcifications can complicate prosthesis deployment as in this case, leading to a deformed THV. Nevertheless, caution should be taken when extrapolating morphological findings into a potential dysfunction. While in this case the residual gap between the THV and the aortic wall would suggest a severe paravalvular leakage, this was not the case on Doppler echocardiography examination, with the calcification apparently acting as an additional seal. Valvular function was acceptable, and no further intervention was deemed necessary

Fig. 6

Incorrect positioned THV, which is tilted and does not fully extend into the aortic annulus. As such, parts of the native right aortic valve leaflet is protruding into the inflow part of this self-expandable THV (arrow), causing a residual valve gradient on Doppler echocardiography. CT is very useful in detecting the cause of THV dysfunction in cases where Doppler echocardiography does not provide an answer. In this case, function was improved after balloon dilatation of the inflow part of the THV, further crushing the remaining valve leaflets against the adjacent aortic wall

Fig. 7

Relation between the coronary ostia and the deployed THV. Both self-expandable and balloon-expandable THVs are designed not to obstruct the coronary ostia, with self-expandable Corevalve and Evolut protheses extending into the ascending aorta by design, leaving the coronary ostia open (a, b). When coronary obstruction occurs, it is not by the THV but secondary to displaced calcified native leaflet remnants that migrate during deployment of the THV in the aortic sinus to the vicinity of the coronary ostia. Nevertheless, while CT can detect these migrated calcifications in or near the coronary ostia (c), the evaluation of luminal patency is less obvious, mostly dependent on local expertise and the quality of the CT scanner used

Fig. 8

CT images of the aortic valve illustrating different degrees of valvular calcification depositions: none (a), mild (b), moderate (c) and severe (d). Also note the differences in the affected cusps and distribution (leaflet edges, commissures and attachment sites)

Fig. 9

Double-oblique CT image of the aortic root in a TAVI candidate. While most calcification will be on a supra-annular level (arrowhead), occasionally, calcifications can also be found on an infra-annular subvalvular level (arrow). Reporting of these latter calcifications is important, as they can hamper proper deployment and attachment of the prothesis

Fig. 10

3D CT image of the aortic root containing the sinuses of Valsalva (asterisk). As the aortic valve leaflets extend within these sinuses up to the sinotubular junction, connecting their most basal attachment sites forms a virtual ring which is named the aortic annulus (red dotted line, arrows). It also marks the transition to the LVOT

Fig. 11

a Schematic drawing illustrating the crownlike suspension of the aortic valve leaflets within the aortic root extending across the length of the aortic sinus (a). AR, virtual annular ring representing the annulus (green), formed by joining the basal attachments of the aortic valve leaflets; STJ, sinotubular junction (blue); VAJ, ventriculo-arterial junction (yellow). Red, aortic leaflet insertion sites in the sinus of Valsalva forming a crownlike ring. b Coronal contrast-enhanced CT image demonstrates the levels of the sinotubular junction (STJ) (blue line), ventriculo-arterial junction (VAJ) (yellow line) and annular ring (AR) (green line). Double-headed arrow, anatomic range of the sinuses of Valsalva. CAU, caudal; CRA, cranial. c–f Double-oblique reformatted images further clarify the changing shape of the aortic root contour. c The sinotubular junction forms the top of the crown, where the outlet of the aortic root in the ascending aorta (Ao) is a true circle. A, anterior; P, posterior; L, left; R, right. d The aortic root gradually becomes less circular, with a more cloverleaf shape at its midportion (i.e. at the sinuses of Valsalva). At this level, the aortic valve leaflets are clearly seen. e The aortic valve leaflets (asterisk) are just barely visible at the level of the ventriculo-arterial junction, where the left ventricular structures give rise to the fibroelastic walls of the aortic valvar sinuses. Note that the aortic root contour is now becoming increasingly ellipsoid. f The bottom of the aortic root is formed by the virtual ring, or aortic annulus (Aoann), which has an oval shape in most patients. Reused from reference [39], with permission

Fig. 12

For all measurements of the aortic root as illustrated in Figs. 12, 13 and 14, the use of a (simple) multiplanar reconstruction viewer is mandatory. The three imaging planes should be perpendicular to each other at 90° angles and the reference lines should be “locked” so rotating one reference line automatically rotates the other planes. Care should be taken to have the screen layout setting in such a way that all three imaging planes (starting with axial, coronal and sagittal) are visible simultaneously. The CTA dataset (preferably a systolic phase) is loaded into the viewer. a First, in the coronal plane the aortic valve is located and the centre of the reference lines is placed approximately at the centre of the aortic valve. In the coronal image plane, the references lines are rotated so one of the two lines is at approximately 45° to the horizontal level. This results in the images seen in b. In the plane that was the original sagittal reconstruction (middle panel in b), the reference line is also rotated to be approximately parallel to the aortic valve. This generally provides a pretty good imaging plane that is perpendicular to the aortic valve (right panel in b). The essential step (illustrated in c) is to scroll up and down through this image stack (as indicated by the straight arrows in the other views in c) and determine if all three aortic valve cusps are seen symmetrically in each image (i.e. scrolling from the level of the LVOT to the aortic valve, the three cusps should appear symmetrically and simultaneously in one image). This is often not yet the case. By tweaking the angulation of the plane by slight rotation of the crosshairs in the other views (as indicated by the curved arrows in c) while assessing its effect on the symmetry of the valve leaflets in the in-plane image is needed to have the cusps appear symmetrically. Once this has been established, by scrolling through the image stack in-plane with the aortic valve towards the LVOT, the leaflets will increasingly appear smaller and closer to the aortic wall (d, see arrowheads in right panel). The first image just below the level of the lowest image (i.e. closest to the LVOT) that no longer shows the leaflets is selected and represents the annulus (e)

Fig. 13

The annular plane image obtained through the steps outlined in Fig. 12 is used for the measurements. The long- and short-axis diameters are measured using a simple distance tool (a). In the annular plane, the circumference of the annulus is traced using a planimetry tool (b). Most software systems then automatically display the area, perimeter and area-derived diameter of the traced area (c). Alternatively, parameters can be calculated as described in the text

Fig. 14

Standardised way to perform measurements of the distance of the annular plane to the ostium of the right coronary artery and left main. The starting points are the annular plane images (obtained through the steps outlined in Fig. 12) as displayed in a–c above. In this image stack, in plane with the annulus, the origin of the RCA is located by scrolling through the images in the direction of the aorta (arrows in a, b). Subsequently, the reference lines are rotated (curved arrow in c) in such a way that one of the reference lines passes through the RCA ostium (asterisk in f); then, by scrolling toward the LVOT (arrows in d, e), the annulus plane is again displayed (i) and in one of the two other panels (h), the origin of the RCA is visible (asterisk in h), as well as the reference line which corresponds to the annulus plane level (red line in h). The distance is measured as the distance of the lower border of the RCA ostium (asterisk in j, k) to the attachment of the coronary cusp (j) or perpendicular to the reference line of the annulus plane (k). For the distance of the annulus to the left main, the steps mentioned above are repeated

Fig. 15

The target point (T) in case of a transaortic THV delivery. When the usual endovascular or transapical delivery routes are not possible, the transaortic pathway offers an alternative for patients in which no other access is possible. The recommended entry point for self-expandable THV is located at least 6 cm above the level of the aortic annulus (annular plane in red dotted line). Furthermore, the status of the aortic wall around this location needs to be scrutinised, as e.g. extensive calcification increases procedural feasibility and risk, and may as such make this access path unsuitable. However, even for transaortic access caution is needed. The TAVI candidate might have previous coronary bypass grafts, including a venous bypass over the RCA (arrow in c). The origin of this bypass (asterisk in c) might be near the targeted entry point, in this case about 6 cm above an annular plane with a heavily calcified aortic valve (arrowhead in c). Also, the anterior wall of the ascending aorta may show extensive calcification (arrow in d), making transaortic access impossible. Note incidental visualisation of an extensive calcified RCA (asterisk in d)

Fig. 16

Compromised delivery paths. A safe endovascular trajectory is needed for safe transportation of the THV to the aortic root. CT is in his respect an essential tool in order to avoid vascular complications and guide to the intervention through the safest possible passage. Potential complications may arise due to luminal narrowing or even chronic iliac artery occlusion with extensive collaterals (a) and pronounced vascular tortuosity and kinking (arrows in b). In this last case, there is an additional short dissection in the left external iliac artery (arrowhead) due to a previously performed conventional coronary angiography. For these patients, the preferred transfemoral access approach is therefore not possible, and other options have to be considered. Nevertheless, other access paths may also pose significant challenges, like bilateral subclavian artery narrowing and occlusion (arrows in c), and the presence of post-infarct thrombus and wall calcification in the left ventricular apex (asterisk in d), making a transapical approach with a balloon-expandable valve impossible. Therefore, vascular access examination must include all anatomic possible entry points for a full assessment of the different options