Fig. 5.1
Biplane Mode (X-plane) acquisition with 3D transoesophageal echocardiography. Left side panel: the reference plane is mid-oesophageal four chamber view. Right side panel: 2D image of the mitral valve from a plane rotated 95° from the reference plane. AML anterior mitral leaflet, PML posterior mitral leaflet
Real Time 3D acquisition or Live 3D – enables a real-time display of a 30° × 60° pyramidal volume of the MV. It has the disadvantage of not being able to display the entire MV valve apparatus. However, due to the high temporal resolution, it is the modality of choice for guiding interventions on the MV. Rapid switch between “en face” and ventricular view of the MV leaflets can be performed according to the clinical question to be answered. Advances to live 3D now allow increase of the real time display to as high as a 90° × 90° sector; however, this comes at the cost of reduced temporal resolution.
Focused Wide Sector or 3D Zoom – enables a real time, focused, wide-sector view of the MV apparatus with good spatial resolution and satisfactory temporal resolution (Fig. 5.2). The temporal resolution can be improved by using a “stitched” 3D acquisition over 4–6 heart beats with some vendors. Live 3D Zoom is probably the most important 3D imaging modality for MV morphology assessment by 3D TEE. It is the modality of choice when analyzing valvular morphology in SMR patients. Care should be taken to optimize the spatial and temporal resolution of the acquired images. The acquisition should be started from the mid esophageal bi-commissural view with the sector width adjusted to cover the entire commissure and the elevational plane adjusted to cover the antero-posterior aspect of the MV. The height of the volume sector should also be adjusted to cover the entire mitral annulus, leaflets (both in systole and diastole) and subvalvular apparatus. The key to an optimal temporal and spatial resolution is to set the elevational plane as narrow as possible. Care should be taken to include in the acquired volume some of the landmarks surrounding the MV, such as the aortic valve and the left atrial appendage. This will allow the correct recognition of each MV leaflet and a correct orientation of the MV as seen from the atrial perspective (Movie 5.1) or ventricular perspective (Movie 5.2)
Fig. 5.2
3D Zoom acquisition of the mitral valve as seen from the atrial perspective by 3D transoesophageal echocardiography. The image is then rotated in such a way that the aorta is located anteriorly (flipped image indicated by arrow). Ao aorta
Full Volume Gated Acquisition – enables optimal spatial and temporal resolution. This modality has the largest acquisition sector available (a volume size of 75° × 75°) that allows imaging of the MV apparatus and of the left ventricle in the same volume (Fig. 5.3). It requires ECG gating. This type of acquisition may be very important in SMR when assessing the relationship between MV apparatus, chords, and distortion and LV with regional or global remodeling. When used as a multi-beat stitched acquisition it has also a higher temporal resolution, necessary when analyzing patterns of leaflet motion, such as in SMR. However, because the acquisition modality involves stitching together several smaller pyramidal volumes, each of them acquired during one cardiac cycle, this type of acquisition is predisposed to stitching artifacts especially in patients with irregular heart rhythms. Even in patients with regular heart rhythms stitching artifacts can often occur due to difficulties with breath-holding in a semi-conscious patient during TEE. Therefore care should be taken to look through the acquired data set to save images with minimal or no stitching artifacts to ensure accurate analysis.
Fig. 5.3
Full Volume Gated Acquisition with 3D transoesophageal echocardiography. Acquisition is done over four cardiac cycles that enables a good temporal resolution (32 volumes per second)
Full Volume Color Flow Doppler (Movie 5.3) – this technique is similar to the full volume gated acquisition with color Doppler on. With this method the full volume with color Doppler is constructed by stitching together multiple narrow pyramidal sets, each acquired during a single cardiac cycle (Fig. 5.4). Inadequate breath-holding and irregular heart rhythm can lead to stitching artifacts. With TTE this technique is highly dependent on transthoracic image quality, being less suitable in patients with poor apical acoustic windows. With TEE image quality is adequate but acquisition might be hampered by stitching artifacts related to inadequate breath-holding. Real-time 3D color Doppler acquisition and 3D zoom mode with color Doppler on are also available techniques with 3D TEE.
Fig. 5.4
Full Volume Color Flow Doppler acquisition with 3D transthoracic echocardiography. The full volume color Doppler is reconstructed by stitching together four narrow pyramidal sets. Off line analysis enables evaluation of vena contracta area by direct planimetry
Mitral Valve Morphology Assessment by 3D Echocardiography
3D echocardiography offers both qualitative and quantitative information in the evaluation of mitral valve morphology in patients with SMR.
3D TEE provides, undoubtedly, the best morphological details of the mitral valve. However, in patients with good acoustic windows, 3D TTE is able to provide satisfactory information regarding MV morphology and function (Figs. 5.5 and 5.6).
Fig. 5.5
3D transthoracic echocardiography evaluation in a patient with dilated cardiomyopathy and secondary mitral regurgitation. Apical systolic displacement of the mitral valve leaflets coaptation point as seen from a lateral aspect (Panel a, yellow arrow, the blue dotted line represents the mitral annulus plane). Apical and lateral displacement of the papillary muscles exerting a tethering effect on the mitral leaflets in mid-systole as seen from the ventricular view (Panel b, yellow arrows). For rapid recognition of the anatomic landmarks the ventricular aspect of the mitral valve apparatus is also shown in diastole (Panel c). Funnel shape morphology of the mitral valve as seen from the atrial perspective in the same patient (Surgeon’s view, Panel d). All images are reconstructed from the same 3D pyramidal data set. AML anterior mitral leaflet, PML posterior mitral leaflet, Ao aorta
Fig. 5.6
Surgeon’s view of the mitral valve in a patient with secondary mitral regurgitation (SMR) and idiopathic dilated cardiomyopathy showing the funnel shape of the mitral valve as seen from the atrial perspective (3D transthoracic echocardiography, Panel a). The chosen frame is in mid-systole, tethering on the MV leaflets being maximal (Panel a, yellow arrow indicating mid-systole on the ECG tracing). For easy recognition of the anatomic landmarks the valve is also shown in diastole (Panel b). Ao aorta, ALC anterolateral commissure, PMC posteromedial commissure
Through the “en face” view, 3D echocardiography allows direct examination of the atrial surface of the mitral leaflets, coaptation line, and commissures throughout the cardiac cycle (Fig. 5.2). This view provides a qualitative inspection of the mitral valve geometry, as seen from the atrial perspective, also known as the “surgeon’s view” (Figs. 5.2 and 5.5, Panel d; Fig. 5.6, Movie 5.1).
In SMR, due to the tethering of the leaflets, the geometry of the valve can be markedly changed. The MV usually has a funnel shape, with the lowest points of the funnel at the level of the coaptation line (Fig. 5.6). In normal MVs the coaptation line normally describes a slightly upward concavity as seen from the atrial side, but in SMR, it becomes even more concave (symmetric tethering) or completely changes its shape pointing towards the LV cavity (asymmetric tethering). This simple qualitative assessment of MV geometry from the “en face” view by 3D echocardiography providing a quick insight into the mechanism of SMR, helping the clinician to distinguish between symmetrical or asymmetrical tethering pattern (Movie 5.1).
In some cases of severe SMR, an orifice, representing the anatomic regurgitant orifice area (AROA), can be visualized from the atrial perspective of the valve, and planimetry of this orifice can be made using multi-planar reformat of the 3D data or with some vendors directly from the 3D image. Care should be taken to adequately set the gain and line density on each 3D echo machine during the acquisition to eliminate dropouts that might lead to overestimation of the regurgitant orifice by planimetry.
After this initial on-line qualitative assessment of MV morphology, all necessary 3D datasets of the MV apparatus are acquired. This will enable later off line analysis, and a more quantitative assessment of MV morphology in SMR patients.
Each of the possible mechanisms involved in SMR are carefully inspected while performing the off-line analysis of the acquired data to measure: mitral annulus size and shape, mitral annulus dynamics (change in shape between diastole and systole), MV leaflet surface area computation, and subvalvular apparatus geometry and its relative position to the MV annular plane.
Mitral Annular Geometry in SMR
For a more comprehensive analysis of MV morphology in SMR, off line reconstruction of the MV leaflets and annulus is possible from the 3D data sets with the help of various commercial software applications available on the market (Fig. 5.7). Mitral annulus antero–posterior diameter, the inter–commissural diameter, the perimeter of the mitral annulus, the length of each annular segment (anterior annulus length vs. posterior annulus length), the height of the annulus, i.e. the distance between the highest and the lowest points on the annulus, can be measured during each frame of the cardiac cycle to characterize mitral annular morphology and its dynamic properties in patients with SMR. Many of these measurements can be obtained without any geometric assumptions.
Fig. 5.7
Mitral annular reconstruction from 3D transoesopageal datasets with measurement of the antero-posterior diameter of the mitral annulus (green continuous line)
Studies that analyzed MV annular morphology, by 3D echocardiography, have shown that annular perimeter and area are increased, and that the annulus is less elliptical and more flattened in patients with SMR as compared to normal subjects [5, 6]. These studies have also shown that the degree of mitral annular deformation in ischemic SMR is more pronounced following anterior MI than inferior MI [7].
An attenuation of the sphincter function of the mitral annulus, i.e. the annular area change between diastole and systole, has been described as one of the mechanisms that contribute to SMR [8]. The annular sphincter function is decreased in these patients [9], while in normal subjects annular contraction is around 25 % [10].
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