What is the most prevalent type of atrial septal defect (ASD)?

The most prevalent type of atrial septal defect (ASD) is ostium secundum, which accounts for the majority of ASD cases. This defect occurs in the middle of the atrial septum and is characterized by a failure of the septum primum to fuse completely with the septum secundum during fetal development.

Ostium secundum ASDs can vary in size, but they typically allow significant left-to-right shunting of blood, which can lead to volume overload of the right atrium and right ventricle over time. The clinical manifestations of this type of ASD might not present until late childhood or adulthood, allowing for adequate compensation in many cases.

The other types of ASDs, such as ostium primum, sinus venosus, and sinus atrial defects, are less common. Ostium primum ASDs are typically associated with atrioventricular septal defects, which are more complex anomalies. Sinus venosus and sinus atrial defects are also rare and are located in different areas of the atrial septum, contributing to their lower prevalence compared to ostium secundum.