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Fallot tetralogy

In medicine, the tetralogy of Fallot (described by Etienne Fallot, 1850 - 1911, Marseille) is a significant and complex congenital heart defect. more...

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The term blue baby syndrome is sometimes applied to the tetralogy of Fallot, but is less specific and includes other conditions.

Four malformations

It involves four different heart malformations:

  1. A ventricular septal defect (VSD): a hole between the two bottom chambers (ventricles) of the heart.
  2. Pulmonic stenosis: Right ventricular outflow tract obstruction, a narrowing at or just below the pulmonary valve.
  3. Overriding aorta: The aorta is positioned over the VSD instead of in the left ventricle.
  4. Right ventricular hypertrophy: The right ventricle is more muscular than normal.

Pseudotruncus arteriosus is a particularly severe variant of the tetralogy of Fallot, in which there is complete obstruction of the right ventricular outflow tract. In these individuals, there is complete right to left shunting of blood. The lungs are perfused via collaterals from the systemic arteries. These individuals are severely cyanotic and will have a continuous murmur on physical exam due to the collateral circulation to the lungs.


The tetralogy of Fallot generally results in low oxygenation of blood due to mixing of oxygenated and deoxygenated blood in the left ventricle and preferential flow of blood from the ventricles to the aorta because of obstruction to flow through the pulmonary valve. This is known as a right-to-left shunt. It is often evidenced by a bluish tint to the baby's skin (cyanosis). However there are "pink Fallots" in which the degree of obstruction in the pulmonary tract (right ventricular outflow, pulmonary valve and pulmonary arteries) is low. Blood flows preferentially from the ventricles to the lungs and only minimal desaturation occurs in the systemic circulation because of mixing of saturated and desaturated blood in the ventricles. This degree of desaturation may be undetectable to the eye and requires a pulse oximeter to identify it.

Even children who are generally not too deeply cyanosed (blue) may develop acute severe cyanosis or hypoxic "tet spells". The precise mechanism of spelling is in doubt but certainly this is a dangerous event and presumably results from an increase in resistance to blood flow to the lungs with increased preferential flow of desaturated blood to the body. Such spells may be treated with beta-blockers such as propranolol, but acute episodes may require rapid intervention with oxygen, morphine (to reduce ventilatory drive) and phenylephrine (to increase blood pressure). There are also simple procedures such as knee-chest position which reduces systemic venous return (to reduce the right-to-left shunting), increases systemic vascular resistance (and hence blood pressure) and provides a calming effect when the procedure is performed by the parent.


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Tetralogy of Fallot
From Gale Encyclopedia of Medicine, 4/6/01 by J. Ricker Polsdorfer


Tetralogy of Fallot is a common syndrome of congenital heart defects.


The heart is two pumps in one. The ventricle on the left side pumps blood full of oxygen through the body; the ventricle on the right side pumps the same blood through the pulmonary artery to the lungs to take up oxygen. The left ventricle operates at pressures about four times as high as the right ventricle. Blood is supposed to flow through one side, then the other.

Tetralogy of Fallot is a condition that is characterized by several congenital heart defects occurring at once. They include:

  • Ventricular septal defect (Abnormal passageway between the right and left ventricles)
  • Displaced aorta
  • Narrowed pulmonary valve
  • Thickened right ventricle wall.

Each defect acts in combination with the others to create a malfunction of the heart. The problem starts very early in the uterus with a narrowed pulmonary valve and a hole between the ventricles. This is not particularly a problem for a fetus because hardly any blood flows through the lungs until birth. It is only after birth that the defects pose a problem. The blood that is supposed to start flowing through the lungs cannot easily get there because of the narrowed valve, however the hole between the ventricles remains open. Because of the opening between ventricles, much of the blood that comes back to the heart needing oxygen is sent out without being properly oxygenated. In addition, the right heart has to pump at the same pressure as the left side. Several things follow. First, the baby turns blue (cyanotic) because of the deoxygenated blood that bypasses the lungs. Deoxygenated blood is darker and appears blue through the skin. Second, the right side of the heart (ventricle) hypertrophies (gets more muscular) from the extra exercise demanded of it. Next, the low oxygen causes the blood to get thicker and clot more easily. Clots in the veins can now pass through the hole in the heart and directly enter the aorta, where they can do much more damage than in the lungs--such as causing infarcts in the brain. In addition, these anomalies make the lining of the heart more susceptible to infection--endocarditis-- which can damage valves and lead to blood poisoning (septicemia).

Causes & symptoms

Tetralogy is a congenital defect with unknown causes.

Babies with tetralogy of Fallot are blue at birth (cyanosis). Sometimes the blue color appears only when they cry. They also have detectable heart murmurs. Infants with mild forms can have surgery postponed until they are older. Infants with more severe symptoms often have attacks of worsened cyanosis. During attacks, they turn very blue, have shortness of breath, and can faint. This usually occurs during heightened activity, such as crying.


A complete evaluation of the circulation is required, including testing the blood for its oxygen content, ultrasound and x rays of the heart accompanied by a contrast agent to determine the amount of blood flowing in the wrong direction. A search for other birth defects is also necessary, because they tend to happen together.


Correction of the defects are done through surgery. Surgery must be carefully timed with attention to the progression of the disease process, the size of the infant, and the size of the various defects. There are temporary surgical procedures that can prolong the time before corrective surgery while the baby grows larger and stronger.

During surgery, the pulmonary valve is widened, the ventricular septal defect is closed, and any interim fixes removed.


Surgical correction has a high rate of success, returning the child to near normal health.

Key Terms

Main arterial trunk that moves blood from the heart to the arteries, which transport the blood throughout the body.
Blue-colored skin due to oxygen-deficient blood.
Inflammation of the lining of the heart.
Death of tissue due to shutting off the blood supply.
Blood poisoning.
Systemic circulation
Through the body, as opposed to "pulmonary"--through the lungs.
The muscular chambers of the heart that do the pumping.

Further Reading

For Your Information


  • Friedman, William F. and John S. Child. "Congenital Heart Disease in the Adult." In Harrison's Principles of Internal Medicine, edited by Kurt Isselbacher, et al. New York: McGraw-Hill, 1998.
  • Nelson, Waldo E., et al., eds. Nelson Textbook of Pediatrics Philadelphia: W. B. Saunders, 1996.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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