Hello doctor, In Tetralogy of Fallot, after systemic to pulmonary artery shunt is done, the mixed-blood goes through the pulmonary artery, then to the lungs to get oxygenated. This blood gets oxygenated, then enters the heart through the pulmonary vein. Now is it the same mechanism happening? So how does this method help to increase the oxygen level in the blood?
Hello. I am a cardiologist, and I am glad to clarify your doubt. In Tetrology of Fallot, the defect between the two ventricles is significant and non-restrictive. Hence both ventricles will function at the same pressure. Also, the aorta lies directly above the ventricular septal defect (VSD).  Therefore how much pulmonary and systemic circulation occurs is determined by the degree of pulmonary stenosis. If the pulmonary stenosis is severe, a large amount of impure blood gets pumped from the RV to the aorta leading to cyanosis (bluish discoloration of extremities). If the pulmonary stenosis is mild, less blood gets shunted to the left side, and the patient may not be cyanotic at rest.