Tetralogy of Fallot (TOF)

Tetralogy of Fallot is a rare condition caused by a combination of four heart defects that are present at birth (congenital).

These defects, which affect the structure of the heart, cause oxygen-poor blood to flow out of the heart and to the rest of the body. Infants and children with tetralogy of Fallot usually have blue-tinged skin because their blood doesn't carry enough oxygen.

Tetralogy of Fallot is often diagnosed during infancy or soon after. However, tetralogy of Fallot might not be detected until later in life in some adults, depending on the severity of the defects and symptoms.

The 4 abnormalities (tetralogy) of the heart described by Fallot include the following:



Right ventricular hypertrophy: Right ventricular thickening, or hypertrophy, occurs in response to narrowing or obstruction at or below the pulmonic valve, due to an increase in right ventricular work and pressure.
Ventricular septal defect (VSD): This is a hole in the heart wall (septum) that separates the 2 ventricles. The hole is usually large and allows oxygen-poor blood in the right ventricle to pass through, mixing with oxygen-rich blood in the left ventricle. This poorly oxygenated blood is then pumped out of the left ventricle to the rest of the body. The body gets some oxygen, but not all that it needs. This lack of oxygen in the blood causes cyanosis.

Abnormal position of the aorta: The aorta, the main artery carrying blood out of the heart and into the circulatory system, exits the heart from a position overriding the right and left ventricles. (In the normal heart, the aorta exits from the left ventricle.)
Pulmonary valve stenosis (PS): The major issue with tetralogy of Fallot is the severity of pulmonary valve stenosis, since VSD is always present. If the stenosis is mild, minimal cyanosis occurs, since the oxygen-poor blood from the right ventricle can pass through the pulmonic valve to the lungs and less of it passes through the VSD. However, if the PS is moderate to severe, a smaller amount of blood reaches the lungs, since most is shunted right-to-left through the VSD.

The 4 abnormalities (tetralogy) of the heart described by Fallot include the following:



Right ventricular hypertrophy: Right ventricular thickening, or hypertrophy, occurs in response to narrowing or obstruction at or below the pulmonic valve, due to an increase in right ventricular work and pressure.
Ventricular septal defect (VSD): This is a hole in the heart wall (septum) that separates the 2 ventricles. The hole is usually large and allows oxygen-poor blood in the right ventricle to pass through, mixing with oxygen-rich blood in the left ventricle. This poorly oxygenated blood is then pumped out of the left ventricle to the rest of the body. The body gets some oxygen, but not all that it needs. This lack of oxygen in the blood causes cyanosis.

Abnormal position of the aorta: The aorta, the main artery carrying blood out of the heart and into the circulatory system, exits the heart from a position overriding the right and left ventricles. (In the normal heart, the aorta exits from the left ventricle.)
Pulmonary valve stenosis (PS): The major issue with tetralogy of Fallot is the severity of pulmonary valve stenosis, since VSD is always present. If the stenosis is mild, minimal cyanosis occurs, since the oxygen-poor blood from the right ventricle can pass through the pulmonic valve to the lungs and less of it passes through the VSD. However, if the PS is moderate to severe, a smaller amount of blood reaches the lungs, since most is shunted right-to-left through the VSD.