Introduction
Deficient ventricular septation is the commonest abnormality found when the heart is congenitally malformed. It can be found in isolation, or as an integral part of multiple lesions. When encountered as the major problem, the arrangement is appropriately described in terms of ventricular septal defects. When deficient septation is part of lesions such as double outlet right ventricle, or common arterial trunk, the channel between the ventricles is more accurately considered as an interventricular communication.1 Such distinctions, however, are largely of semantic interest. The understanding of the differences in the terms, nonetheless, is key to appropriate surgical management. This is also the case when the defects are multiple. It is now agreed that, when considered as an overall group, and taking account of the fact that the communications can also be part of more complex lesions, the defects themselves, when assessed in isolation, exhibit one of three phenotypic patterns. There are the muscular, perimembranous, and juxta-arterial variants.2 When approached on this basis, it should be no surprise that the perimembranous, or juxta-arterial, variants can co-exist with additional channels within the muscular ventricular septum. Several discrete channels can also be found within the confines of the muscular septum itself. On occasion, furthermore, the multi-fenestrated septum is justifiably compared to Swiss cheese. Yet another subtly different arrangement is found when a solitary channel within the apical part of the muscular septum is crossed, on the right ventricular side, by multiple trabeculations.3 This gives the spurious impression of multiple defects.4 The recent analysis of the trawl of surgical results made by the Society of Thoracic Surgeons revealed that both mortality and morbidity were increased in the setting of multiple as opposed to solitary ventricular septal defects.5-9The surgical approach in presence of multiple defects, however, is likely to be different depending on the combinations of individual defects. It is unlikely that the same operative intervention will be optimal for each of the different patterns. To the best of our knowledge, the significance of these different associations between multiple defects has yet to be explored in the context of therapeutic management. In this, the introduction to a review of such management, we have described the developmental background to the existence of multiple defects. We demonstrate the phenotypic combinations, and discuss their anatomical features. In our subsequent review, we will discuss the significance of the anatomical variations to diagnosis and options for treatment.