Imaging
Figure 4: 3D Transoesophageal Echocardiography Surgical View of a Mitral Valve with Complex Valve Anatomy
mitral valve annulus often clarifies an otherwise difficult assessment even with the use of segmental analysis, since such complicated anatomy can be a challenge to decipher with the naked eye (see Figure 4). In our laboratory analysis, the time taken averages approximately five to seven minutes. The ability to perform a segmental analysis post-repair and assess the degree of leaflet apposition along the whole length of coaptation, coupled with quantification of the reduction in annulus dimensions with MVQ software, is likely to provide further insights into durability of repair.
Assessment of Mitral Regurgitation Severity
Assessment of the severity of mitral regurgitation by 2D echocardiography can be challenging, particularly with eccentric jets. 3D colour Doppler allows better visualisation of the origin, size and shape of jets.16,17
The annulus lies at an angle and an appreciation of the multiple regions of prolapse and their extent is enhanced by the MVQ software images to the right of the image. Bileaflet prolapse is seen (red regions).
Figure 5: 3D Colour Transoesophageal Echocardiography of a P2 Prolapse
However, previous 3D methods of regurgitation quantification relied on gated acquisition, and although they were shown to be more accurate than the established 2D echocardiographic methods, they were time-consuming and not clinically applicable.18,19
The vena contracta and proximal isovelocity
surface area (PISA) assessment are methods used to quantify severity of mitral regurgitation, the latter allowing calculation of effective regurgitant orifice area and regurgitant volume.20
More recently, with
the advent of the 3D fully sampled matrix array probes, 3D colour flow can now be displayed with the greyscale image. The conventional PISA method assumes a hemispheric shape of the isovelocity surface, which very often is not the case (see Figure 5). These newer 3D methods allow assessment of the true shape of proximal flow convergence region and permit more accurate measurement of the PISA and vena contracta.21,22
understanding of the shape of the regurgitant orifice.23
Such data have improved our In degenerative
Left image shows the true anatomical regurgitant orifice of a P2 prolapse. Right image shows the same but with 3D colour superimposed, and depicts the shape of the proximal isovelocity surface area.
area) in early systole and saddle-shape deepening contributes to mitral competency. In mitral valve disease these early systolic changes were less pronounced despite a similar magnitude of ventricular contraction, suggestive of ventricular–annular decoupling. Subsequent area enlargement may contribute to mitral incompetence. In patients undergoing mitral repair, the annulus remained dynamic without systolic saddle-shape accentuation. Currently, such detailed analysis is time-consuming and requires offline analysis with customised software.
However, software is available online (including MVQ, Phillips Medical and Tomtec mitral quantification tool) that allows analysis of 3D TEE data sets in clinical practice. MVQ offers a semi-automated analysis package of mitral valve anatomy at end-systole. This can provide a very detailed assessment with accurate measurements of the annulus and leaflets, papillary muscle position and aortic–mitral angles, and is likely to play an important role in pre-operative planning of mitral valve repair in the future. Currently, little published data exist on its use in clinical practice. In our experience this software provides excellent information on mitral annulus dimensions and geometry. Useful parameters include antero-posterior diameter, commissural diameter, total circumference, annulus saddle height, total mitral orifice area and mitral annulus to aortic valve angle. In complex anatomy, depiction of the leaflet segments in relation to the
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mitral valve disease the PISA is more spherical, but in functional mitral regurgitation the PISA is elongated and elliptical. These differences in PISA geometry in part explain discrepancies in regurgitation severity by 2D PISA methods. Applying a hemi-ellipsoid formula reduces the underestimation of regurgitation from 49 to 26%.24
Despite these
advances, these methods are not in routine clinical use. Limitations include time-consuming analysis methods, image resolution and dependence on multiple cardiac cycles (seven to 14 cycles) with narrow sector acquisitions, which increase artefacts.
3D TEE provides excellent assessment of the mitral annulus dimensions, the location and extent of the regurgitant orifice and leaflet morphology, all of which are essential in planning the procedure. During the procedure, 3D TEE is also of considerable value.26
Percutaneous Catheter-based Interventions for Mitral Regurgitation and the Role of 3D Echocardiography While surgical repair remains the therapy of choice in severely regurgitant mitral valves, functional mitral regurgitation often involves significant left ventricular impairment. Such patients may face significant risk from conventional surgery, and percutaneous approaches are currently being explored. MitraClip (Evalve Inc.) is one example. It is based on the surgical Alfieri operation and inserted using a transvenous approach and atrial septal puncture. The ‘clip’ is positioned over the regurgitant orifice grasping both mitral leaflet free edges, creating a double orifice with significant reduction in mitral regurgitation.25
The position of transseptal puncture is crucial: if it is too high or too low on the atrial septum, the delivery system may either not reach the valve or assume an awkward angle, making clip deployment impossible. 3D imaging allows a precise atrial septal puncture and accurate positioning over the mitral valve leaflets
EUROPEAN CARDIOLOGY
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