Tetralogy of Fallot
Congenital heart defects result from abnormal changes in the structure of the heart that occur early in pregnancy and are present at birth. They are the most common birth defects, occurring in about 1 in 125 births. Tetralogy of Fallot (TOF) is a common defect in which obstruction to the flow of blood from the heart to the lungs causes low oxygen levels in the blood. Open heart surgery to correct the heart defect is the only treatment that gives long-term survival.
What Is TOF?
TOF is a defect combining 4 abnormalities that are all related (Figure):
Right ventricular outflow tract obstruction. The connection between the right ventricle of the heart and the lungs is narrowed, and the blood flow to the lungs is reduced. The main area of narrowing is under the pulmonary valve, caused by thick muscle in this area. The valve may also be narrow (stenotic), and the pulmonary artery may also be small (hypoplastic).
Ventricular septal defect. There is a hole in the wall (septum) between the right and left ventricles (pumping chambers) of the heart.
Overriding of the aorta. The major blood vessel from the heart to the body, the aorta, is positioned more rightward than normal and sits above the ventricular septal defect.
Hypertrophy of the right ventricle. The right ventricle is more muscular than normal as a result of the right ventricular outflow tract obstruction and the need to pump harder.
TOF can …