When there is a defect in the interatrial septum the blood will flow from the LA to the RA (left to right shunt). This is because the LA empties into the thick less compliant LV while the right atrium empties into the thin more distensible RV.
Additional oxygenated blood will reach the RA and RV and pulmonary arteries. Pulmonary plethora will result,
If the pulmonary blood flow is excessive, pulmonary arteriolar vasoconstriction will occur and causes pulmonary hypertension. This will decrease then abolish the increased blood flow in the lungs. It will also cause further hypertrophy and dilatation of the RV, RA and pulmonary arteries.
Ultimately the shunt will be reversed resulting in Eisenmenger Syndrome.
X-ray Picture
- Plethoric lung fields.
- Dilatation of the right atrium, right ventricle and pulmonary artery.
- Small aortic arch due to low cardiac output.
- Marked pulsations of the pulmonary artery and its branches seen during fluoroscopy, i.e. hilar dance.
- As pulmonary hypertension develops the plethora will decrease then disappear and the picture will be transformed into that pulmonary hypertension.
