Tetralogy of Fallot is a common syndrome of congenital heart defects. This condition, present in utero, is caused by the narrowing of the pulmonary artery and a hole between the ventricles. When the baby is born and begins to breathe on its own, the baby turns cyanotic, or blue, due to the deoxygenated blood that bypasses the lungs because the narrowed pathway and the hole between the ventricles has remained open. (Illustration by Electronic Illustrators Group.)

  Definition

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

  Description

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 changes 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 and symptoms

Tetralogy of Fallot 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.

  Diagnosis

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.

  Treatment

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 corrections removed.

  Prognosis

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

   Key Terms:

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

   Resources:

Books

• Friedman, William F., and John S. Child. "Congenital Heart Disease in the Adult." In Harrison's Principles of Internal Medicine, ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.
• Nelson Textbook of Pediatrics. Ed. Richard E. Behrman. Philadelphia: W. B. Saunders Co., 1996.