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The diagnostic features of atrioventricular septal defect with common atrioventricular junction

THE CONGENITAL CARDIAC MALFORMATION variously known as endocardial cushion defect,atrioventricular canal malformation, 3 and, more recently, atrioventricular septal defect, is instantly recognizable in terms of its underlying morphology. These morphologic features lend themselves to cross-sectional echocardiographic recognition.' In terms of clinical presentation, it is well recognized that there are two major categories within the overall entity. In the first subset, shunting occurs only at atrial level. Patients with this arrangement are often described simply as having an "ostium primum" defect. The morphology is then often interpreted as representing a "partial" form of the basic lesion. In the other subset, there is also the potential for shunting at ventricular level. Patients with this variant are usually considered to exhibit the complete form of the defect. Yet the basic structure of the hearts is constant throughout the group irrespective of the level of shunting. The essence of the malformation is presence of a common atrioventricular junction, which bears scant anatomic resemblance to the junctional structures seen in the normal heart. This abnormal junctional morphology is to be found irrespective of the clinical presentation. Yet surprising discrepancies are still to be found with regard to interpretations of the junctional morphology seen in the "ostium primum" defect.