Ventricular septal defects: morphology of the doubly committed juxtaarterial and muscular variants

In our previous review of the phenotypic features of ventricular septal defects, we concentrated on the perimembranous variant, showing how its distinguishing feature, as viewed from the right ventricle, was fibrous continuity in its postero-inferior rim between the leaflets of the aortic and tricuspid valves. In this second review, we focus on the morphology of those defects which have exclusively muscular rims when viewed from their right side, and the variant with the phenotypic feature of fibrous continuity between the leaflets of the two arterial valves. As with the defects described as being perimembranous, once they have been characterised, it is the position of the defect relative to the components of the morphologically right ventricle that is the primary determinant of the options and strategies for treatment. Therefore, clarification of the morphology is the key to establishing the related risks for each particular defect.