Atrioventricular septal defects (AVSDs) represent approximately 5% of congenital cardiac abnormalities
and are bound by a variable deficiency of the atrioventricular (AV) septum immediately above and below the AV valves. These defects are frequently associated with other cardiac malformations. About 30-40% of the cardiac abnormalities observed in patients with Down syndrome are AVSDs.
The AV valves are invariably abnormal in patients with atrioventricular septal defects. At one end of the spectrum of atrioventricular septal defects, incomplete atrioventricular septal defects, also termed ostium primum atrial septal defects (ASDs), have only a deficiency in the inferior portion of the atrial septum immediately superior to the AV valves and have 2 valve orifices. The other end of the spectrum encompasses complete atrioventricular septal defects, with both ASDs and ventricular septal defects (VSDs) and a single common AV valve.
In addition to the term “atrioventricular septal defects,” these congenital abnormalities have been described by several other terms, including AV canal defects, endocardial cushion defects, and AV communis.