Atrial septal defects (ASDs)
Atrial septal defects are defined by the presence of a deficiency within the atrial septum. These defect can range from a single hole in the fossa ovale to multiple small fenestrations.
- The most common defect is the secundum type ASD which occurs because of a deficiency in the septum primum.
- Patent foramen ovale is a critical communication during fetal development. It allows for blood oxygenated by the placenta to bypass the non-functional lungs. Following birth, right atrial pressure drop and the flap created by the septum secundum opposes the septum primum, effectively closing the communication. The lack of cooptation may result in a persistent atrial communication past the fetal period. It is often regarded as an insignificant finding in infancy, but in adulthood it can be associated with strokes due to shunting of emboli from the left to right atrium in older patients (Keane)
- A Sinus Venosus ASD exists in the venosus region of the atrial septum. This may occur either anteriorly or inferiorly, with the anterior type being most frequent. These defects are most often associated with partial anomalous pulmonary venous return.
- Unroofed coronary sinus results from a defective formation in all or parts of the areas the atrial wall separating the left atrium and coronary sinus. These defects can be strongly associated with the presence of a left superior vena cava, which in known as “Raghib Syndrome”. In this case, the left superior vena cava drains into the superior aspect of the left atrium often communicating with the coronary sinus.
- A common atrium results from an absence of the septum primum, septum secundum, and septum of the atrioventricular canal. This defect is typically associated with “Heterotaxy Syndrome”.
- Atrial septal defects allow blood to shunt from the left atrium to right atrium. Shunting is minimal during infancy, but typically increases with age, as the right ventricle becomes more compliant.
- Most infants are asymptomatic but may develop congestive heart failure or elicit growth failure, if the left-to-right shunt is significant. In these cases, the infants often have additional heart defects as well as extracardiac anomalies, which may contribute to their overall slowed growth. Older adults may develop congestive heart failure, atrial fibrillation, and more rarely, pulmonary vascular obstructive disease.
- It is recommended that atrial septal defects 8mm or larger with presence of a left-to-right shunt to be closed upon identification; in order to prevent pulmonary vascular disease and/or arrhythmias. Smaller defects, particularly those less than 3mm often close spontaneously.