What is tetralogy of Fallot?
Tetralogy of Fallot is a rare, complex congenital (present at birth) heart defect. Named after the physician who first described this condition in 1888, tetralogy of Fallot is the name for a cluster of four heart defects:
A large ventricular septal defect: The ventricles are the heart’s two lower chambers, and the septum is the wall that separates the left and right chambers. A ventricular septal defect is a hole in the septum that allows oxygen-rich blood to flow from the left ventricle back into the right ventricle and mix with the oxygen-poor blood there, instead of flowing to the aorta and out to the rest of the body.
Alternatively, oxygen-poor blood can flow across the defect at times (right to left), bypassing the lungs and leading to cyanosis (low oxygen levels in the systemic circulation).
Pulmonary stenosis: Blood normally flows from the right ventricle through a valve or flap into the pulmonary artery in the lungs where it gets loaded with oxygen. Pulmonary stenosis is a narrowing of the valve between the right ventricle and the pulmonary artery, or the muscle growth immediately below the valve (subpulmonic stenosis). Often, the narrowing not only involves the valve, but also the muscle directly below it. The constriction of the passageway causes the heart to pump harder to push the blood through and reduces the amount of blood flowing through the valve.
Right ventricular hypertrophy: The extra pumping required by the pulmonary stenosis causes the right ventricle to thicken (hypertrophy).
Overriding aorta: The aorta is the main artery that carries oxygen-rich blood from the heart to the rest of the body. Normally the aorta is connected to the left ventricle, and oxygenated blood flows out of the ventricle into the aorta. In tetralogy of Fallot, the aorta is positioned between the left and right ventricles, above the ventricular septal defect. This location allows the aorta to receive blood from both sides of the heart, so that oxygen-poor blood from the right ventricle mixes with oxygenated blood from the left ventricle.
How common is tetralogy of Fallot and what causes it?
Tetralogy of Fallot is relatively rare, occurring in about 5 of every 10,000 births. Although this heart defect has been recognized for 120 years, the exact cause is still unknown. The defect occurs during the heart's development before birth. About 15 percent of people with Tetralogy of Fallot have a specific genetic abnormality that is also linked with other birth defects such as cleft palate.