Demonstration of living anatomy clarifies the morphology of interatrial communications

Inferences made regarding the postnatal anatomy of the atrial septum still tend to be based on developmental evidence. Although atrial septation is a well-defined process, it is remarkably complex and remains poorly understood. It is now established, however, that the process involves the conjugation of several myocardial structures and mesenchymal tissues of both intracardiac and extracardiac origin. The resultant postnatal morphology is equally complex, evidenced by the fact that, in the normal heart, only the floor of the oval fossa, along with its anteroinferior muscular buttress, are true anatomical septums. In this regard, septums can be defined as partitions that can be removed without creating communications with the extracavitary space. The true septal components are surrounded by grooves, which themselves largely represent infolding of the atrial walls. These anatomical features can now accurately be revealed using virtual dissection of CT data sets. These images, when carefully reconstructed, demonstrated the anatomy with as much accuracy as when hearts are dissected in the autopsy room. Such virtual dissection, furthermore, shows the components as they are seen within the chest, thus facilitating understanding for those intending to undertake interventional therapeutic procedures. By preparing such images, we show the complexity of the normal atrial septum and its surrounds. We show that it is only defects within the oval fossa, or the much rarer vestibular defects, which can appropriately be illustrated in the context of a normally constructed heart.