Figure 1

The images show the problems existing in defining the boundaries of the area of space that represents the “ventricular septal defect”. Panel A shows a simulated five chamber echocardiographic cut in a specimen with overriding of the aortic root relative to the apical muscular septum. The yellow arrow shows the continuation of the long axis of the muscular ventricular septum. This area marks the true geometric interventricular communication, which is almost planar. This virtual plane, however, can never be closed, since its cranial margin is formed by the leaflets of overriding aortic root. The red double-headed arrow shows the margins of the curved surface that would be closed so as to restore septal integrity. Although shown as a planar entity, in reality the surface is markedly curved due to the non-planar configurations of its boundaries. It is shown in planar format for the sake of simplicity. As shown in Panel B, it is the margins of this curved surface, outlined by the red dots, that are taken as representing the ventricular septal defect when viewed from the right ventricle. Note that its cranial border is formed by the muscular outlet septum, which is malaligned relative to the apical muscular septum, accentuating the non-planar configuration of its surface.