Discussion
As we have shown, multiple, or seemingly multiple, ventricular septal defects can be found in three discrete patterns. In the first arrangement, separate and discrete defects co-exist within different parts of the ventricular septum. Most usually this is because of a combination of perimembranous and muscular defects. This variant is of particular surgical significance when the muscular defect opens to the inlet of the right ventricle. This is because the atrioventricular conduction axis is particularly vulnerable in this setting (Figure 7). The second arrangement is found when the muscular ventricular septum has failed properly to coalesce during cardiac development. This then produces two variants according to the extent of coalescence. When less severe, multiple discrete holes can be observed within the muscular septum, usually at the borders between the right ventricular inlet and outlet and the apical part of the septum. It is the more severe end of the spectrum of failure of coalescence that manifests as the so-called Swiss-cheese septum. This variant poses perhaps the greatest challenge for surgical correction. The final arrangement is not truly an example of multiple defects. It is found when a large, but solitary, defect in the apical part of the muscular septum is crossed in the right ventricle by trabeculations, giving the spurious impression of multiple defects.4 The surgical approach to each of these variants will itself vary, although several options have been proposed for each specific sub-set. It is those options that we will discuss in the our surgical review.