Types of Atrial Septal Defects

Atrial septal defects (ASDs) can be divided into four types based on location. From anterior to posterior, they are:

• Ostium primum atrial septal defect: Second most common type of ASD. Occurs in the lower septum. Associated with complete or partial mitral valve cleft and endocardial cushion defects.
• Ostium secundum atrial septal defect: Most common type of ASD. Occurs in the central septum. Patent foramen ovale is a variant. Not associated with endocardial cushion defects.
• Sinus venosus atrial septal defect: Involves the posterior atrial septum near the inferior or superior vena cava (mnemonic vena cava = venosus). May be associated with anomalous drainage of the pulmonary veins to the right atrium.
• Coronary sinus atrial septal defect: Least common type. The anatomy is important here. On its way to drain into the right atrium, the coronary sinus shares its roof with the posterior wall of the left atrium. Defects in the roof of the coronary sinus allow left atrial blood to be shunted into into the right atrium. For this reason, it is also known as an unroofed coronary sinus. Associated with a left superior vena cava (common) and heterotaxy syndromes.