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Interact CardioVasc Thorac Surg 2007;6:685-690. doi:10.1510/icvts.2007.156612 © 2007 European Association of Cardio-Thoracic Surgery
Defining Ebstein's malformation using three-dimensional echocardiographyWessex Congenital Cardiac Centre, Southampton University NHS Trust, Tremona Road, Southampton, SO16 6YD, UK Received 11 April 2007; received in revised form 24 July 2007; accepted 2 August 2007
*Corresponding author. Tel.: +44 23 8079 3546; fax: +44 23 8079 4526.
Ebstein's malformation is difficult to visualise, for both the echocardiographer and the surgeon. The essence of the problem in Ebstein's malformation is the deviation of the hingepoints of the leaflets towards the junctions of the inlet and apical trabecular parts of the right ventricle. Three-dimensional echocardiography offers new insights into the morphology and function of malformed valves, and allows elucidation of all the features. It allows clear visualisation of the valve leaflets, showing the precise morphology of the valve leaflets, the extent of their formation, the level of their attachment, and their degree of coaptation. Visualisation of the mechanism of regurgitation or stenosis is possible, as is more accurate quantification of the regurgitant jet or jets. Subchordal apparatus may be seen more clearly using three-dimensional echocardiography, and their functional anatomy understood. The multiplanar review modality allows examination of the three-dimensional data set even in patients with sub-optimal echocardiographic imaging. Previously, much of this information could only be well-understood at the time of surgery or post mortem, meaning that the majority of the specimens fully examined were at the poorly functioning end of the spectrum. This information is of use in furthering our understanding of this complex lesion as it functions in vivo, and demonstrating which anatomical pathology is significant in producing functional and physiological consequences. It is also of use for the clinician in selecting which patients are amenable to surgical intervention, for either single or biventricular repair, and for the surgeon in planning how to approach the operation. Correlation between three-dimensional echocardiographic findings and surgical findings has already been established, but the effect of this enhanced anatomical knowledge on surgical planning and surgical outcome requires further investigation.
Key Words: Ebstein; Echocardiography
According to conventional wisdom, Ebstein's malformation represents downward displacement of the hingepoints of the leaflets of the tricuspid valve [1, 2]. This concept is not only anatomically incorrect, but it probably contributes to many of the current misapprehensions that surround this congenital cardiac malformation. In reality, rather than being ‘downwardly displaced’, the larger parts of the leaflets of the tricuspid valve have failed to delaminate from the ventricular walls during ventricular development [3]. When we assess the location of the persisting valvar leaflets relative to the components of the right ventricle in attitudinally appropriate fashion [4], the hingepoints are rotated around the aortic root, with the effective valvar orifice closing at the junction of the inlet and apical trabecular components of the right ventricle, rather than at the atrioventricular junction [5]. The problem with appreciating the true abnormal morphology that characterises Ebstein's malformation is that it is remarkably difficult, even for the morphologist, to understand the three-dimensional arrangement of the valvar leaflets and their tension apparatus. Two-dimensional echocardiography has provided some basic anatomical insights, but remains limited in the information which it can provide [6, 7]. We believe these problems have now been resolved with the advent of three-dimensional echocardiography, which is rapidly emerging as an important new clinical tool in congenital heart disease, providing additional information regarding anatomy, and allowing further insights into in vivo morphology. Recently, three-dimensional echocardiography has immensely enhanced our understanding of the enormously difficult morphological enigma of Ebstein's malformation. Here we attempt to correlate three-dimensional observations with pathological findings, and in doing so, to explore the role of three-dimensional evaluation in understanding those perspectives pertaining to potential surgical intervention. 1.1. Analysis of the data sets Three-dimensional data sets may be analysed in two main ways. Firstly, ‘cropping’ or three-dimensional reconstruction of the data set allows the clinician to slice into the data set to the region of interest, and to display intra-cardiac structures from a chosen, clinically useful, aspect, for example, one may display the ‘surgeon's view’. The second method is analysis using the multiplanar review mode. This mode allows the operator to view the moving three-dimensional data set in three orthogonal planes simultaneously, and to review the image in infinite planes. The operator may position the planes through the structures under study, and for example, may study each valve leaflet individually, and in their relationship to each of the other two leaflets. ‘Sliding’ the planes across the whole width of the valve in each plane allows examination of the valve in its entirety. In this way, the morphology of the individual leaflets and their coaptation planes may be visualised, without losing sight of their anatomical relationships to the rest of the intracardiac structures.1.2. The features of the malformation Ebstein's malformation manifests itself as a wide spectrum of morphological and clinical features [8–10]. On the basis of three-dimensional echocardiographic findings, the morphological features can be divided into the following components, which are pivotal in defining a valve as Ebsteinoid, or merely dysplastic:
1.3. Displacement and rotation of the hinge points of the valvar leaflets: the essence of the malformation In the normal heart, the leaflets of the tricuspid valve, located in septal, inferior, and antero-superior positions, and closing in trifoliate fashion, are hinged at the right atrioventricular junction (Fig. 1). The position of the papillary muscles which support the valvar leaflets marks the junction between the inlet and the apical trabecular components of the right ventricle, with the leaflets closing towards the atrioventricular junction during ventricular systole. In Ebstein's malformation, the hingepoints of the leaflets are deviated towards the junctions of the inlet and apical trabecular parts of the right ventricle.
Three-dimensional echocardiography is the ideal tool with which to visualise the displacement and rotation of the valve leaflets. The data set may be cropped in such a way as to allow the clinician to view valves from whichever aspect provides most information. Fig. 1b demonstrates the rotational abnormality in Ebstein's malformation displayed in a cropped three-dimensional data set. In cases where the rotation is extreme, if a plane is chosen which cuts the tricuspid valve and right ventricle through their long axis, the mitral valve will be seen in short axis in the same plane. It is this rotation which is the single most significant pathogenomonic feature differentiating Ebstein's malformation from tricuspid dysplasia. Failure of delamination of the leaflets from the ventricular wall varies widely in the degree to which it occurs, and this is one of the major determinants of the valve's competence. The leaflet may be tethered only to a small degree near its septal attachment, or this may extend along virtually its entire length. If the leaflet remains largely tethered to the ventricular wall, its ability to coapt with its partners is compromised. The leaflet may be free along most of its length, but tethered at a point midway along, causing folding or ‘buckling’ of the leaflet, with the untethered portions of the valve leaflet prolapsing beyond the plane of coaptation during valve closure.Indeed, in some cases, the leaflets close in competent fashion at this junction between the ventricular inlet and the apical trabecular component. When closing in this fashion, however, they no longer meet in trifoliate fashion, but rather form a bifoliate valvar structure. And, because they meet at the entrance to the apical trabecular component, for the most part they lack the tension apparatus that characterises the normal valve, with the leaflets tending to be dysplastic, and meeting together as pouches rather than coapting leaflets. Within this arrangement, which is the essence of the lesion, nonetheless, there can be marked anatomical variation. It is this anatomic variation which probably determines the clinical presentation, and which certainly dictates the options for surgical intervention. Fig. 1d demonstrates the usefulness of using three-dimensional echocardiography to visualise the extent of delamination of the leaflets, and their manner of coaptation. 1.5. Valve dysplasia and abnormalities of the tension apparatus The major differences in morphology reflect the arrangements of the leaflets themselves. In particular, it is the nature of the distal attachments which dictates the options for surgical repair. Since the leaflets are hinged along a locus extending inferiorly from the site of the membranous septum, the septal and inferior leaflets are most severely afflicted, since the antero-superior leaflet is hinged along this locus even in the normal heart. Due to the rotation of the valvar orifice, there is little opportunity for formation of tension apparatus for the septal and inferior leaflets. Indeed, the septal leaflet is barely formed in some instances, being represented by no more than cauliflower-like excrescences on the septal surface. The inferior leaflet is also reduced in size, and forms a circular continuum with the antero-superior leaflet.It is the antero-superior leaflet itself, however, which shows the most significant variation, most significantly with regard to its distal rather than proximal attachments. This is because, as already explained, the hinge-line of the antero-superior leaflet remains at the atrioventricular junction, since this is coincident in the inner heart curve with the junction between the inlet and apical parts of the right ventricle. In less severe examples of Ebstein's malformation, the antero-superior leaflet retains its tension apparatus and papillary muscles, being attached between the medial and anterior papillary muscles. In the most severe cases, in contrast, the leading edge of the antero-superior leaflet is attached in linear fashion to a muscular shelf, the latter being formed at the junction of the inlet and apical ventricular components. In some examples with such linear attachment, the valvar mechanism thus formed seems to be competent. In others, in contrast, the valvar orifice is obviously stenotic, and forms a keyhole which points directly into the subpulmonary infundibulum (Fig. 2).
In still others, the valvar orifice becomes redundant and incompetent, with more florid dilation of the atrial and inlet components. Between these extremes of linear and focal attachments of the antero-superior leaflet, examples are seen with hyphenations along the leading edge of the leaflet (Fig. 1). The tension apparatus may have abnormal attachments between papillary muscles, contributing to tethering of the valve leaflets by restricting their mobility. The morphological substrate of tricuspid regurgitation is the competence of leaflet coaptation (Fig. 3). As previously described, in some cases the leaflets close in a competent fashion at the junction between the ventricular inlet and the apical trabecular component as a bifoliate valve. The anatomical variation in this arrangement contributes to the variability in degree of regurgitation. Three-dimensional echocardiography is an aid in understanding the mechanism of regurgitation, as it allows one to clearly visualise the entirety of the leaflets and their coaptation, and also aids in achieving accuracy in quantification of regurgitation (Video 1). The regurgitant jet may be accurately visualised and quantifiied using the multiplanar review mode.
1.6. Myocardial abnormality Because the valvar mechanism closes at the junction of the inlet and apical trabecular components of the right ventricle, the inlet ventricular component is effectively part of the right atrium. Irrespective of its precise structure, it is always at atrial rather than ventricular pressures, and hence is haemodynamically atrialised. In most instances, however, it is also anatomically atrialised, since its wall is typically thin. Indeed, in florid cases, in which the right atrium and the inlet component become grossly dilated because of regurgitation across the abnormal valve, the ventricular wall can become paper-thin, and is often confused with Uhl's malformation. These cases with gross dilation of the atrialised ventricular component typically present in the neonatal period with ‘wall-to-wall’ heart, and have a particularly poor prognosis. In cases surviving beyond the neonatal period, the degree of anatomic atrialisation is less severe, but still the wall of the inlet component of the right ventricle is thinned relative to the normal. 1.7. Functional component of the right ventricle The other significant variation when Ebstein's malformation is seen in isolation is the size and structure of the functional right ventricle. Since the inlet of the ventricle is atrialised in haemodynamic terms irrespective of the thickness of its walls, the functional right ventricle is made up of the apical trabecular and outlet ventricular components. Oftentimes this part of the ventricle is also dilated and thin-walled, but in less severe cases it can retain its muscular structure, and even be hypertrophied, albeit that fibrosis of the wall is frequent. Recent developments in three-dimensional echocardiographic analysis software allow quantification of effective volume of the functional right ventricle.1.8. Anatomy and function of the systemic ventricle If there is a large portion of the right ventricle which is atrialised, this may impinge upon the function of the left ventricle. This portion of the ventricle is haemodynamically as well as functionally atrialised, that is to say it is under low atrial pressure. The left ventricular side of this thin septum is, however, under systemic pressure, and this can lead to severely disco-ordinate left ventricular contraction. The left ventricle in Ebstein's malformation has been shown to have abnormal shape, as well as regional abnormalities of function, including of the lateral and posterior walls [11, 12].1.9. Co-existing cardiac abnormalities Ebstein's malformation, of course, does not always exist in isolation. Associated malformations are frequent, particularly an interatrial communication through the oval fossa. Other lesions can co-exist, such as pulmonary stenosis or atresia, and ventricular or atrioventricular septal defects. Ebstein's malformation frequently afflicts the tricuspid valve in the setting of congenitally corrected transposition. All of these features, particularly the location of any co-existing ventricular septal defect, should be diagnosed with three-dimensional echocardiography.Summary of morphological differentiation of Ebstein's malformation or dysplasia of tricuspid valve by three-dimensional echocardiography:
Three-dimensional echocardiography offers new insights into the morphology and function of Ebstein's malformation, and allows elucidation of all the features. The essence of the problem in Ebstein's malformation is the deviation of the hingepoints of the leaflets towards the junctions of the inlet and apical trabecular parts of the right ventricle. This may clearly be visualised using three-dimensional echocardiography, along with the precise morphology of the valve leaflets, and the mechanism of regurgitation or stenosis. This information is of use in furthering our understanding of this complex lesion as it functions in vivo, and in selection of patients for surgery, and in planning surgical approach. Correlation between three-dimensional echocardiographic findings and surgical findings has already been established [13, 14], but the effect of this enhanced anatomical knowledge on surgical planning and surgical outcome requires further investigation.
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Abstract
1. Introduction
