Atrial septal defect

This condition accounts for a third of the adult cases of congenital heart disease, occurring two to three times more frequent in women.
It may occur in various positions in the atrial septum (see figure 20):1) lower part, ostium primum, 15% of cases;2) ostium secundum, in area of fossa ovalis (prior site of foramen avalis in the fetus, allowing both left and right atrium to communicate), 75%;3) upper atrial septum, sinus (site of sinus or pocket where inferior vena cava (IVC) and superior vena cava (SVC) empty into right atrium) venosus, 10%.
Most cases are due to spontaneous genetic mutations, but others are inherited.
The results of these defects come from the shunting of blood from one atrium to the other.
The direction and size of the shunting are determined by the size of the defect and compliance of the ventricles.
A small defect less than 0.5 cm in diameter is associated with a small shunt and no significant sequelae.
But a larger defect, more than 2 cm in diameter may be associated with a large shunt with important blood flow changes.
In most cases with atrial defects, the right ventricle is more flexible than the left; thus, the left atrial oxygenated blood is shunted to the right atrium causing increased blood flow and enlargement of the atria, right ventricle, and pulmonary arteries