Figure Legends
Figure 1. The images show the arrangement of the developing heart at the stage of the beginning of formation of the muscular ventricular septum. The left hand panel shows a section from a murine embryo sacrificed on embryonic day 10, while the right hand panel shows a reconstruction of the cavities of the developing human heart at around 5 weeks of development, which is graded as Carnegie stage 13. The star shows the site of formation of the apical muscular septum, separating the ballooning apical ventricular components.
Figure 2. The images show the stages of remodelling of the primary interventricular communication to form the secondary and tertiary communications in the developing murine heart. Panel A shows the stage subsequent to expansion of the atrioventricular canal. Panel B, at a later stage, shows how the proximal outflow cushions have fused (dotted line) to form a shelf in the roof of the right ventricle. Panel C, from the same heart, shows the persisting tertiary interventricular communication between the aortic root and the cavity of the right ventricle.
Figure 3. The images show the different types of defects produced in developing mice in which the Furin enzyme has been perturbed. Panel A shows the non-compacted apical muscular septum in a heart which also shows an ostium primum defect. Panel B shows a perimembranous defect, while panel C shows an outlet defect that is juxta-arterial because of failure of formation of the subpulmonary infundibulum.
Figure 4. The images show the features of the different types of ventricular septal defects as determined on the basis of their borders. Panel A shows the features of a muscular inlet defect, with panel B showing a perimembranous defect, both in cuts replicating the echocardiographic four-chamber plane. Panel C shows a juxta-arterial defect in a cut simulating the parasternal long axis plane.
Figure 5. The images show multiple muscular defects found at the border between the inlet of the right ventricle and its apical component when there has been a degree of inappropriate coalescence of the septum during development. Panel A shows the view from the right ventricular aspect. As can be seen when assessing the situation from the left ventricular apex (Figure 5B). the most apical part of the septum is intact.
Figure 6. The images show the situation produced when there has been severe lack of coalescence of the muscular ventricular septum during cardiac development. Panel A shows the right ventricular aspect, with Panel B showing the view from the left side. Although the entire apical part of the septum has failed to coalesce, it is difficult to identify individual defects. Note also the excessive apical trabeculation in the left ventricle.
Figure 7. The images show multiple defects produced by the combination of perimembranous and muscular inlet defects. The red dashed line shows the location of the atrioventricular conduction axis, which runs through the myocardial bar separating the defects. The defects are shown from the right (panel A) and left (panel B) ventricular aspects.
Figure 8. The images show how a solitary defect when viewed from the left ventricle (panel A) can seem to represent multiple defects when viewed from the right ventricle (panel B).