Atrial Septal Defects in the Adult

Nomenclature and Classification There are 3 major types of ASDs or interatrial communications: ostium secundum, ostium primum, and sinus venosus (Figure 1A) defects. The ostium secundum is a true defect of the atrial septum and involves the region of the fossa ovalis. The ostium primum defect is within the spectrum of the atrioventricular (AV) septal defects (Figure 1B; also known as AV canal defects or endocardial cushion defects), the complete form of which also includes a large ventricular septal defect and a common AV valve. The sinus venosus defect is usually located at the junction of the right atrium and superior vena cava and is almost always associated with partial anomalous pulmonary venous return. Two very uncommon types of ASDs may be mentioned briefly: the inferior vena cava form of the sinus venosus defect and the coronary sinus septal defect (in which a defect between the coronary sinus and the left atrium allows a left-to-right shunt to occur through an “unroofed” coronary sinus).