Sub Aortic Membrane | Sub Aortic Tunnel | Complex LVOT
Components of the common atrioventricular(AV) valve: The common AV valve in AVSD is composed of 2 bridging leaflets and a mural leaflet in the left ventricle. The right atrioventricular junction is guarded by the two bridging leaflets and 2 resident leaflets in the right ventricle.
There is significant variation in the morphology of individual substrate for the sub aortic stenosis. Depending on the type of associated congenital malformation (eg. AVSD/ Isolated sub AS/ Part of Shone's anomaly etc) the nature and extent of the obstruction varies. In the first image (left corner) there is a prominent subcordal apparatus whcich is attached to the posterio-medial papillary muscle. This constantly moves between the septum and the anterior mitral leaflet in the LVOT. It is possible that there is denudation or destruction of the endocardial surface which leads to at least partly to the pathogenesis of progressive sub aortic stenosis in this case. The second image (centre) is demonstration of the subaortic tunnel between the LV and an anteriorly placed aorta following intraventricular repair of transposition using Rastelli approach. The LV end of the tunnel is progressively becoming narrow with time (the original VSD becoming small). The image on right is a 3D colour angio of the same subaortic tunnel and demonstrates the dynamic nature of the obstruction. As this is a cast of the suba aortic tunnel accurate dynamic volume changes can be appreciated.
Possible mechanisms of sub AS
In AVSD, the Left Atrioventricular valve is morphologically different from the mitral valve. Even when there are two seperate AV valve orifices, the left AV valve is formed of a posterior or mural leaflet and two bridging leaflets opposing each other. These leafflets together form the anterio-superior leaflet. The so called 'cleft' is the point of apposition between the two bridging leaflets as shown on the 3D echocardiographic picture in the adjacent panel. The mural leaflet guards only 50% of the Left AV valve as opposed to 2/3rd of that of the mitral valve. In congenital 'cleft' mitral valve the morphology of the mitral valve is different. The cleft is eccentric and the mral leaflet retains its normal extent of 2/3rd of the artioventricular junction as shown in this
The Dynamic nature of a complex sub aortic membrane is demonstrated here. There is a thick ridge in the septum jurting out in to the LVOT. This assymmetric and relatively less mobile than the dynamic element of the obstruction caused by complex thickining of the subcordal mapparatus. Here the obstruction is much below the usual anatomic position The AML is free of any membrane or obstructive element).
For related topics Ref: Multiplanar review analysis of three-dimensional echocardiographic datasets gives new insights into the morphology of subaortic stenosis. Bharucha T, Siew Yen Ho, Vettukattil JJ. Advance Access published online on February 20, 2008
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