Atrial Septal Defect (secundum)

What is atrial septal defect (secundum)

Ostium secundum atrial septal defect (ASD) represents an opening between the right and left atria through the ostium secundum which results from abnormal embryological cardiac development.

Epidemiology of atrial septal defect

ASDs are the most common congenital heart defect to present in adulthood. Ostium secundum ASDs account for 80–90% of all ASDs. They are more common in females, with a female-to-male ratio estimated at approximately 2:1.

Higher pressures in the left side of the heart ➔ Left-to-right shunt ➔ Volume overload in right side heart ➔ Right side heart dilatation / enlargement of pulmonary artery (increased pulmonary vascular markings on chest radiograph)

Atrial left-to-right shunt ➔ decreased volume load on the aorta ➔ decreased size of aorta (underdeveloped)

Eisenmenger reaction

In rare cases, when the defect is large or the shunt persists for a long time, Eisenmenger physiology may develop.
In these cases, the right heart stiffens and the pulmonary artery pressure increases in response to volume overload and attains pressures higher than those in the left heart, resulting in reversal of the left-to-right shunt(Right-to-left shunt), cyanosis, right heart failure, and pulmonary hypertension.
The only treatment for Eisenmenger reaction is heart lung transplantation.

Imaging finding of ASD

– Increased pulmonary vascularity (due to Left-to-right shunt)
– Prominent pulmonary conus
– RA, RV enlargement
– Small aorta

Differential diagnosis of ASD

– VSD : Aorta size is normal
– TOF : Right-to-left shunt, decreased pulmonary vascularity
– Pulmonic stenosis : Only main and left pulmonary artery are enlarged. (the systolic jet of blood passing through the stenosed valve preferentially enters the left pulmonary artery)