Tetralogy of Fallot

Tetralogy of Fallot is a serious and complex heart defect that is present at birth. A baby's heart begins to form shortly after conception and is complete by the end of the second month of pregnancy. During this time, tetralogy of Fallot can occur. Tetralogy of Fallot involves four specific defects in the development of different parts of the heart:

Pulmonary valve stenosis
Ventricular septal defect (VSD)
Overriding aorta
Right ventricular hypertrophy

These defects can cause:

Less blood flow to the lungs.
Mixing of oxygen-rich (red) and oxygen-poor (blue) blood inside the heart.
Low levels of oxygen in the blood. When oxygen levels are low, the baby's skin, fingertips, or lips have a bluish tint. This condition is called cyanosis. An infant with cyanosis is sometimes called a "blue baby."

Figure A shows the normal anatomy and blood flow of the interior of the heart. Figure B shows a heart with the four defects of tetralogy of Fallot.

Each year in the United States, about 3,000 babies are born with tetralogy of Fallot. It is the congenital heart defect that causes the most cases of cyanosis.

Every infant or child with tetralogy of Fallot needs surgery, usually within the first year of life. Because of advances in surgery and treatment, many children born with tetralogy of Fallot have successful surgery and live to adulthood.

Symptoms

The signs and symptoms in a baby with tetralogy of Fallot depend on the size and severity of the defects.

Common Signs and Symptoms

A heart murmur may be the first sign found by your doctor. It is an extra or unusual sound heard during the baby's heartbeat. Most babies with tetralogy of Fallot have a heart murmur. The heart murmur may not be heard until after the baby is a few days old.

Cyanosis is a common sign of tetralogy of Fallot. Cyanosis is the bluish tint of skin, lips, and nail beds caused by low levels of oxygen in a baby's blood. Cyanosis usually occurs within the first few days to the first 2 weeks of life. The level of oxygen in the blood depends on:

The amount of narrowing of the pulmonary valve and surrounding area. Narrowing of the pulmonary valve reduces blood flow to the lungs, lowering the amount of oxygen getting to the body.
The presence of a patent ductus arteriosus (PDA). PDA is a persistent connection between the aorta and the pulmonary artery after birth. Before birth, the aorta and the pulmonary artery are normally connected by a blood vessel called the ductus arteriosus. In most babies, the vessel normally closes off within a few hours or days after birth as the baby’s circulation shifts from the placenta to the baby’s own lungs. In some babies, however, the ductus arteriosus fails to close off as it should and remains open (patent). With PDA, blood flows directly from the aorta into the pulmonary artery. More blood is sent back to the lungs to pick up oxygen, putting a strain on the heart and the lungs.

Other signs

Your baby may have other signs, such as:

Rapid breathing
Cool and clammy skin
Pale skin color
Poor feeding because the baby tires easily while nursing
Poor weight gain
Fussiness or irritability

Tetralogy "Spells"

Some babies with tetralogy of Fallot have what are called tetralogy "spells." A spell occurs when there is a sudden drop in the oxygen level in the blood. This causes the baby to become very blue. The baby may also:

Have a hard time breathing
Become very tired and limp
Not respond to your voice or touch
Become very fussy
Have a seizure

The cause of these spells is not known. They can happen when the baby:

Is upset
Has a low red blood cell count (anemia)
Has not gotten enough fluids

Babies who have a tetralogy spell need surgery as soon as possible.

Diagnosis

Doctors diagnose tetralogy of Fallot by doing a physical exam of the baby and ordering medical tests. The signs and symptoms usually appear during the first weeks of life. Your infant's doctor may see the signs or symptoms during a routine checkup. Some parents also notice signs of cyanosis or poor feeding and bring the baby to the doctor.

If the doctor suspects that there is a problem with your baby's heart, you and your infant will be referred to a pediatric cardiologist (a specialist who treats heart problems in children). The specialist will take a family and medical history, do a physical exam, and order several tests.

Physical Exam

During the physical exam, the doctor:

Listens to your baby's heart. The doctor uses a stethoscope to check for a heart murmur.
Looks for signs such as bluish color of skin and lips and rapid breathing.
Looks at general appearance. Some children with tetralogy of Fallot have a characteristic facial appearance that is associated with DiGeorge syndrome.
Listens to your baby's lungs.

Testing

An echocardiogram, which is harmless and painless, uses sound waves to create a moving picture of your baby's heart. During an echocardiogram, reflected sound waves outline the heart's structure completely. The test allows the doctor to clearly see any problem with the way the heart is formed or the way it's working. An echocardiogram is the most important test available to your baby's cardiologist to both diagnose a heart problem and follow the problem over time. In babies with tetralogy of Fallot, the echocardiogram outlines all of the defects and shows the cardiologist how severe each one is. The test also shows the doctor how well your baby's heart is adapting to the structural problems, and it helps the doctor to decide when and what kind of surgery should be performed.

During pregnancy, if your doctor suspects that your baby has a congenital heart defect, a special test called a fetal echocardiogram can be done. This test uses sound waves to create a picture of the baby's heart while the baby is still in the womb. The test is usually done during the fifth month of pregnancy. If your child is diagnosed with a congenital heart defect before birth, your doctor can plan treatment before the baby is born.

Cardiac catheterization is another test often performed to diagnose heart problems. In this test, a thin, flexible tube is placed in the top of your baby's leg or arm and passed through an artery or vein to reach the heart. Using x rays, your baby's doctor can see the baby's blood vessels and heart. The doctor can also measure the pressure inside the heart chambers and determine how much oxygen-rich and oxygen-poor blood is mixing between the two sides of the heart. A cardiac catheterization can also show if the arteries that supply the heart with blood (the coronary arteries) are normal. Cardiac catheterization is sometimes performed if the results of the echocardiogram are not clear or if the doctor suspects other heart problems.

Other tests performed include:

Pulse oximetry. This test uses a sensor to see the level of oxygen in the baby’s lungs. This provides information on how well your baby's lungs are passing oxygen into the blood and if oxygen-rich and oxygen-poor blood are mixing. The sensor (like an adhesive bandage) is placed on the baby's fingertip or toe. A small computer unit shows the amount of oxygen in the blood sensed through the skin. This test is painless.
Chest x ray. A chest x ray takes a picture of your baby's heart and lungs. It can show if your baby’s heart is enlarged or if there is any fluid in his or her lungs.
EKG (electrocardiogram). This test measures the rate and regularity of your baby's heartbeat.
Blood work to measure blood counts and oxygen levels.
A special blood test to see if your baby has DiGeorge syndrome.

Causes

Doctors do not know the cause of most cases of tetralogy of Fallot.

Heredity may play a role. In rare cases, more than one child in a family is born with a congenital heart defect like tetralogy of Fallot. Also, parents who have a congenital heart defect may be more likely than other parents to have a child with tetralogy of Fallot.

Babies who have other birth defects, such as DiGeorge syndrome or Down syndrome, are also more likely to have tetralogy of Fallot.

Other factors that increase the risk of a mother’s having a child with tetralogy of Fallot are:

Using alcohol or street drugs during pregnancy
Taking medications to control seizures during pregnancy
Having a condition called phenylketonuria
Having viral infections, such as German measles (rubella), during pregnancy

Research is ongoing to find the causes of congenital heart defects.

Reference:

National Heart, Lung, and Blood Institute, USA.