Imaging
Table 1: Common Clinical Applications of 3D Transthoracic Echocardiography and 3D Transoesophageal Echocardiography
Advantages of 3D Echocardiography Qualitative
Accurate depiction of anatomy
Demonstration of spatial relationships between cardiac structures Quantitative
Accurate and reproducible chamber volumes and mass (TTE FV) Regional timings and dyssynchrony (TTE FV) Accurate mitral valve area planimetry (TTE FV and RT TEE) Precise multidimensional measurements of defects such as PFO/ASD (RT TEE)
Indications for 3D Echocardiography Established Indications
Accurate left ventricular volumes and ejection fraction Assessment of mitral regurgitation/stenosis
Intraoperative guidance of transcatheter interventional procedures Assessment of prosthetic valve function/dysfunction Assessment of congenital heart disease
Emerging Indications
Assessment of aortic stenosis/regurgitation Accurate right ventricular volumes and ejection fraction Intraoperative guidance of mitral valve surgery Assessment for cardiac resynchronisation
Useful in Theory but No Clear Indication Yet Assessment of tricuspid/pulmonary valve disease
ASD = atrial septal defects; FV = full volume; PFO = patent foramen ovale; RT = realtime; TEE = transoesophageal echocardiography; TTE = transthoracic echocardiography.
intervention, requires accurate delineation of the actual valve pathology but also assessment of any consequent cardiac dysfunction, including assessment of ventricular size and function. 3D methods can also be used for assessment of ventricular dyssynchrony and for morphological assessment in congenital lesions, but these applications will not be discussed further in this review. Table 1 shows common clinical applications of 3D TTE and 3D TEE. The clinical utility of 3D echocardiography in valvular disease is well illustrated by its use in mitral valve disease, which will be covered in more detail below.
What Is the Role of 3D Echocardiography in the Assessment of Mitral Regurgitation?
The role of 3D echocardiography in the assessment of mitral regurgitation is best understood in terms of the assessment of valve morphology (aetiology and mechanism) and then assessment of the severity of regurgitation.
Understanding Mitral Valve Morphology
Mitral regurgitation can arise from a variety of mechanisms that may occur in combination. Traditionally described by Carpentier’s classification based on leaflet motion (normal motion, prolapse or restriction of a leaflet segment), the location and extent of leaflet motion abnormality guides treatment options. Guidelines emphasise the benefits of valve preservation by repair on patient outcomes.2 An accurate description of the mechanism of valve failure is required to predict the complexity of the techniques needed and hence the likelihood of achieving a successful mitral repair. This helps to guide the decision on the best time to intervene and offer surgery; this has become increasingly relevant as mitral repair is being performed in asymptomatic patients with severe mitral
62 regurgitation.3,4
However, if there is a high chance that the valve may be replaced, surgery is better delayed until symptoms develop or other parameters are met, such as a dilating ventricle or falling left ventricular ejection fraction.
Transthoracic 3D Echocardiography in the Assessment of Mitral Valve Morphology
Assessment of the mitral valve by 2D echocardiography requires the operator to obtain multiple views through all segments of the two leaflets. This requires considerable expertise and experience, but even then errors in interpretation may occur.
Surgical View of the Mitral Valve
3D TTE can provide a rapid overview of the mitral valve using the en face or ‘surgical’ view from the left atrium. This is unobtainable with the 2D approach. Realtime 3D (live 3D or ‘zoom’ mode) is performed preferably from the parasternal window in either the long or short axis. The resolution is optimal from these windows since the mitral valve is in close proximity to the probe. The live image is rotated to view the left atrial aspect of the mitral valve and the image is optimised by gentle probe angulation to bring the leaflets, coaptation line and annulus into view in their entirety. Visualising the heart from the transthoracic approach means one of the main limitations is image quality. Frame rates and image resolution are the main factors that limit precise details of valve anatomy. However, in the majority of patients at least adequate image quality allows a useful and rapid overview of the valve morphology. The extent of any prolapsing or restricted leaflet segments, the commissures, leaflet coaptation line and mitral annulus can be seen.
Segmental Analysis of the Mitral Valve
3D echocardiography also provides the ability to perform accurate segment-by-segment analysis.5
The preferred format is full-volume
acquisition, as frame rates and image resolution are greatest. Again, the parasternal long-axis window is preferred as anatomical landmarks using standardised analysis protocols mean this approach is simple and reproducible;6
where such windows are poor, the apical
windows can be used. Rapid online segmental analysis can be performed by viewing the data set in a multiplanar reconstruction format to define short- and long-axis views of the mitral valve. Using established landmarks, the entire coaptation line can be assessed from the anterolateral commissure, P1 and A1 segments through P2, A2 and then P3, A3 and the posteromedial commissure. The relationship of each segment to the annulus can be accurately assessed. Measurements can be made of segment prolapse or tenting7
in relation to the annulus. Acquisition times and the time needed for analysis of the data sets are reasonable and can easily be incorporated into the standard 2D echocardiography examination. Figure 1 gives an example of segmental analysis.
The literature confirms the clinical utility of 3D echocardiography in mitral valve morphology diagnosis. Comparison of real-time 3D TTE with 2D TEE has shown comparable high sensitivity, specificity and accuracy for identifying prolapsing mitral segments;8
a small proportion
(11%) of patients were excluded due to insufficient image quality by 3D TEE. Pepi et al.,9
in a series of 102 patients, showed that the time needed to obtain and analyse the 3D TTE images was 7±4 minutes. The quality of 3D TTE was insufficient in 8% of cases, sufficient in 16%, good in 55% and optimal in 21%. They performed a comprehensive 3D protocol taking views from both parasternal and apical windows. A
EUROPEAN CARDIOLOGY
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