What is the most common type of ASD?

The most common type of atrial septal defect (ASD) is the septum secundum. This defect occurs due to incomplete closure of the foramen ovale, which normally closes shortly after birth. The septum secundum ASD is characterized by an opening in the upper part of the atrial septum, allowing blood to flow from the left atrium to the right atrium.

This type of defect is often asymptomatic in childhood and may not be detected until adulthood during routine evaluations or when symptoms arise. It significantly contributes to the volume overload of the right atrium and ventricle, which can lead to complications such as pulmonary hypertension or atrial arrhythmias if left untreated.

In comparison, septum primum defects are less common and are typically associated with other cardiac anomalies. Sinus venosus defects are also rare and occur at the junction between the superior vena cava and the right atrium, often involving the right pulmonary veins. Endocardial cushion defects, frequently associated with Down syndrome, are typically more complex and involve a combination of atrial and ventricular septal defects. Therefore, the septum secundum ASD is the most prevalent variation among these described types.