3D Echocardiography in Mitral Valve Heart Disease – Is It the New Gold Standard?
during clip deployment. Once successfully deployed, assessment of residual regurgitant jets and how this relates to valve anatomy can also be performed using 3D TEE.
What Is the Role of 3D Echocardiography in the Assessment of Mitral Stenosis
Mitral stenosis severity is quantified in terms of mean transmitral gradient and mitral orifice area.27
Methods that calculate the
‘effective’ mitral orifice area include pressure half-time measurement (PHT), continuity equation and PISA methods. However, these have their limitations since the Doppler-derived methods are influenced by factors including tachycardia, heart rhythm, non-linear Doppler velocity curves and concomitant valvular disease, and are not applicable in the immediate period post-balloon valvuloplasty.
However, the stenotic mitral valve leaflets often form a funnel shape and the stenotic orifice may be situated obliquely within the ventricle. 2D planimetry is limited by difficulties in obtaining the minimum cross-sectional area during planimetry measurements. This method demands considerable experience and expertise to define the correct orientation of the true mitral valve orifice. 3D TTE helps locate the plane with the smallest mitral valve orifice as the image can be viewed using multiplanar reformatting to align with the orifice in both the long and the short axis (see Figure 6). Use of 3D has been shown to be an accurate method for assessing mitral valve area, and is faster and more reproducible, even in less experienced hands, than 2D echocardiography.29,30
If the
patient is in atrial fibrillation, instead of the full volume, live 3D imaging can be used to overcome stitching artefacts. Invasive catheter measurements using Gorlin’s method have also been compared with 3D echocardiography, and the latter appears to correlate more closely than other non-invasive methods.31
It seems likely that 3D techniques will become the new ‘gold standard’ for quantifying mitral valve area.
Another limitation of 2D planimetry is the presence of significant calcification, particularly within the leaflets. This can be overcome by 3D TEE imaging, as clear imaging of the orifice is possible from the left atrial en face view as calcific shadowing is cast into the left ventricle. Alternatively, the use of 3D TTE with colour Doppler is another solution.32
Percutaneous balloon valvuloplasty is an effective treatment for appropriately selected patients with rheumatic mitral stenosis. 3D TEE can provide accurate information on the functional significance and morphology of the valve to determine suitability for balloon valvuloplasty. Accurate peri-procedural evaluation of the mechanism and effect of valvuloplasty is also desirable. Assessment of complications can be better appreciated with 3D imaging, as with 3D assessment one can determine the increase in valve area and whether this has occurred due to commissural splitting as intended, or due to leaflet tearing (see Figure 7). It is also recognised that Doppler-derived measures of mitral valve area are inaccurate immediately post- valvuloplasty due to acute changes in left atrial compliance and transmitral gradient.33
The most reliable method of assessing change
in area is direct planimetry, and 3D TTE has been shown to correlate best with invasive measurements immediately post-procedure.34
EUROPEAN CARDIOLOGY
Direct planimetery can be used to measure the true ‘anatomical’ orifice area. This is considered to be the reference method in clinical practice, having been shown to correlate more precisely with direct measurement of anatomical orifice at surgery than Doppler methods.28
Figure 6: 3D Transoesophageal Echocardiography Live ‘Zoom’ Mode of a Stenotic Mitral Valve
Multiplanar reconstruction method to accurately locate and quantify true anatomical mitral valve orifice area by planimerty.
Figure 7: Peri-procedural Transoesophageal Echocardiography During Balloon Mitral Valvuloplasty – 3D Live ‘Zoom’ Mode and 2D Imaging with Colour Doppler
Top left image shows the left ventricular surface of a valve with severe mitral stenosis. The commissures are clearly identified with symmetrical fusion. Top right image shows the mild mitral regurgitation prior to balloon mitral valvuloplasty. The lower images show the complication post-ballooning. There is moderate regurgitation on the lower right image but 3D (lower left image) defines its nature. The anterolateral commissure (*) has been successfully split by the ballooning; however, there is a tear in the anterior leaflet that explains the mechanism of the regurgitant jet (arrow). This was not clear on 2D imaging.
The Place of 3D Echocardiography in Mitral Valve Disease in Clinical Practice In clinical practice, 3D used as part of the initial TTE study could largely replace the need for initial 2D TEE as it allows more confident assessment of leaflet morphology, and hence the likelihood of successful repair and timing of intervention. Once the decision for surgery is made, a TEE with 3D imaging could be performed to accurately define valve anatomy and dimensions used for pre- operative planning. In mitral stenosis, 3D planimetry is likely to become the method of choice in assessing severity of stenosis and is particulary useful immediately following balloon mitral valvuloplasty.
Conclusion
As with all new techniques there is a significant learning curve, and image quality is still dependent on echocardiographic windows. Once
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