Tetralogy of Fallot

What is tetralogy of Fallot?

Tetralogy of Fallot (TOF or "TET") is a complex condition of several congenital (present at birth) defects that occur due to abnormal development of the fetal heart during the first 8 weeks of pregnancy. These problems include the following:

  • ventricular septal defect (VSD) - an opening in the ventricular septum, or dividing wall between the two lower chambers of the heart known as the right and left ventricles.
  • pulmonary (or right ventricular outflow tract) obstruction - a muscular obstruction in the right ventricle, just below the pulmonary valve, that decreases the normal flow of blood. The pulmonary valve may also be small.
  • overriding aorta - the aorta is shifted towards the right side of the heart so that it sits over the ventricular septal defect.
Anatomy of the heart, normal
Anatomy of the heart, normal

"Tetralogy" refers to four heart problems. The fourth problem is that the right ventricle becomes enlarged as it tries to pump blood past the obstruction into the pulmonary artery.

Normally, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped through the aorta out to the body.

In tetralogy of Fallot, blood flow within the heart varies, and is largely dependent on the size of the ventricular septal defect, and how severe the obstruction in the right ventricle is.

  • With mild right ventricle obstruction, the pressure in the right ventricle can be slightly higher than the left. Some of the oxygen-poor (blue) blood in the right ventricle will pass through the VSD to the left ventricle, mix with the oxygen-rich (red) blood there, and then flow into the aorta. The rest of the oxygen-poor (blue) blood will go its normal route to the lungs. These children may have slightly lower oxygen levels than usual, but may not appear blue.
  • With more serious obstruction in the right ventricle, it is harder for oxygen-poor (blue) blood to flow into the pulmonary artery, so more of it passes through the VSD into the left ventricle, mixing with oxygen-rich (red) blood, and then moving on out to the body. These children will have lower than normal oxygen levels in the bloodstream, and may appear blue, especially whenever the pressure in the right ventricle is very high and large amounts of oxygen-poor (blue) blood passes through the VSD to the left side of the heart.

According to the National Heart, Lung, and Blood Institute (NHLBI), tetralogy of Fallot affects about 5 of every 10,000 babies and occurs equally in boys and in girls.

What causes tetralogy of Fallot?

Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality, or environmental exposure, causing heart problems to occur more often in certain families.

Maternal abuse of alcohol during pregnancy, leading to fetal alcohol syndrome (FAS), is linked to tetralogy of Fallot. Mothers who take medications to control seizures and mothers with phenylketonuria (PKU) are also more likely to have a baby with tetralogy of Fallot.

Most of the time, this heart defect occurs sporadically (by chance), with no clear reason evident for its development.

Why is tetralogy of Fallot a concern?

The amount of oxygen-poor (blue) blood that passes through the VSD to the left side of the heart varies. If the right ventricle obstruction is severe, or if the pressure in the lungs is high, a large amount of oxygen-poor (blue) blood passes through the VSD, mixes with the oxygen-rich (red) blood in the left ventricle, and is pumped to the body. The more blood that goes through the VSD, the less blood that goes through the pulmonary artery to the lungs, and the less oxygen-rich (red) blood that returns to the right side of the heart. Soon, nearly all the blood in the left ventricle is oxygen-poor (blue). This is an emergency situation, as the body will not have enough oxygen to meet its needs.

Some situations, such as crying, increase the pressure in the lungs temporarily, and increasing blueness might be noted as a baby with tetralogy of Fallot cries. In other situations, the pathway from the right ventricle to the pulmonary artery becomes tighter, preventing much blood from passing that way, and allowing oxygen-poor (blue) blood to flow through the VSD into the left heart circulation. Both of these situations are nicknamed "TET spells." Sometimes, steps can be taken to lessen the pressure or the obstruction, and allow more blood to flow into the lungs and less through the VSD. These steps, however, are not always effective.

What are the symptoms of tetralogy of Fallot?

The following are the most common symptoms of tetralogy of Fallot. However, each child may experience symptoms differently. Symptoms may include:

  • Because large amounts of oxygen-poor (blue) blood can flow to the body under certain circumstances, one of the indications of tetralogy of Fallot is blueness (blue color of the skin, lips, and nail beds) that occurs with such activity as crying or feeding, and quickly becomes more obvious.
  • Some babies do not have noticeable cyanosis (blue color of the skin, lips, and nail beds), but may instead be very irritable or lethargic due to a decreasing amount of oxygen available in the bloodstream.
  • Some children become pale or ashen in color, and may have cool, clammy skin.

Any of these can be symptoms of tetralogy of Fallot. The symptoms of tetralogy of Fallot may resemble other medical conditions or heart problems. Always consult your child's physician for a diagnosis.

How is tetralogy of Fallot diagnosed?

Your child's physician may have heard a heart murmur during a physical examination, and referred your child to a pediatric cardiologist for a diagnosis. A heart murmur is simply a noise caused by the turbulence of blood flowing through the obstruction from the right ventricle to the pulmonary artery. Symptoms your child exhibits will also help with the diagnosis.

A pediatric cardiologist specializes in the diagnosis and medical management of congenital heart defects, as well as heart problems that may develop later in childhood. The cardiologist will perform a physical examination, listening to the heart and lungs, and make other observations that help in the diagnosis. The location within the chest that the murmur is heard best, as well as the loudness and quality of the murmur (harsh, blowing, etc.) will give the cardiologist an initial idea of which heart problem your child may have. Diagnostic testing for congenital heart disease varies by the child's age, clinical condition, and institutional preferences. Some tests that may be recommended include the following:

  • chest X-ray - a diagnostic test which uses invisible X-ray beams to produce images of internal tissues, bones, and organs onto film.
  • electrocardiogram (ECG or EKG) - a test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle stress.
  • echocardiogram (echo) - a procedure that evaluates the structure and function of the heart by using sound waves recorded on an electronic sensor that produce a moving picture of the heart and heart valves.
  • cardiac catheterization - a cardiac catheterization is an invasive procedure that gives very detailed information about the structures inside the heart. Under sedation, a small, thin, flexible tube (catheter) is inserted into a blood vessel in the groin, and guided to the inside of the heart. Blood pressure and oxygen measurements are taken in the four chambers of the heart, as well as the pulmonary artery and aorta. Contrast dye is also injected to more clearly visualize the structures inside the heart.

Treatment for tetralogy of Fallot treated:

Specific treatment for tetralogy of Fallot will be determined by your child's physician based on:

  • your child's age, overall health, and medical history
  • extent of the condition
  • your child's tolerance for specific medications, procedures, or therapies
  • expectations for the course of the condition
  • your opinion or preference

Tetralogy of Fallot is treated by surgical repair of the defects. A team of cardiac surgeons performs the surgery, usually before an infant is 1 year old. In many cases, the repair is made at around 6 months of age, or even a little earlier. Repairing the heart defects will allow oxygen-poor (blue) blood to travel its normal route through the pulmonary artery to receive oxygen.

The operation is performed under general anesthesia, and involves the following:

  • The ventricular septal defect is closed with a patch.
  • The obstructed pathway between the right ventricle and the pulmonary artery is opened and enlarged with a patch. If the pulmonary valve is small, it may be opened as well or removed.

Postoperative care for your child:

Children will spend time in the intensive care unit (ICU) after tetralogy of Fallot repair. During the first several hours after surgery, your child will be very drowsy from the anesthesia that was used during the operation, and from medications given to relax him/her and to help with pain. As time goes by, your child will become more alert.

While your child is in the ICU, special equipment will be used to help him/her recover, and may include the following:

  • ventilator - a machine that helps your child breathe while he/she is under anesthesia during the operation. A small, plastic tube is guided into the windpipe and attached to the ventilator, which breathes for your child while he/she is too sleepy to breathe effectively on his/her own. After a truncus repair, children will benefit from remaining on the ventilator overnight or even longer so they can rest.
  • intravenous (IV) catheters - small, plastic tubes inserted through the skin into blood vessels to provide IV fluids and important medicines that help your child recover from the operation.
  • arterial line - a specialized IV placed in the wrist or other area of the body where a pulse can be felt, that measures blood pressure continuously during surgery and while your child is in the ICU.
  • nasogastric (NG) tube - a small, flexible tube that keeps the stomach drained of acid and gas bubbles that may build up during surgery.
  • urinary catheter - a small, flexible tube that allows urine to drain out of the bladder and accurately measures how much urine the body makes, which helps determine how well the heart is functioning. After surgery, the heart will be a little weaker than it was before, and, therefore, the body may start to hold onto fluid, causing swelling and puffiness. Diuretics may be given to help the kidneys remove excess fluid from the body.
  • chest tube - a drainage tube may be inserted to keep the chest free of blood that would otherwise accumulate after the incision is closed. Bleeding may occur for several hours, or even a few days after surgery.
  • heart monitor - a machine that constantly displays a picture of your child's heart rhythm, and monitors heart rate, arterial blood pressure, and other values.

Your child may need other equipment not mentioned here to provide support while in the ICU, or afterwards. The hospital staff will explain all of the necessary equipment to you.

Your child will be kept as comfortable as possible with several different medications; some of which relieve pain, and some of which relieve anxiety. The staff will also be asking for your input as to how best to soothe and comfort your child.

After discharge from the ICU, your child will recuperate on another hospital unit for a few days before going home. You will learn how to care for your child at home before your child is discharged. Your child may need to take medications for a while at home, and these will be explained to you. The staff will give you instructions regarding medications, activity limitations, and follow-up appointments before your child is discharged.

Caring for your child at home following tetralogy of Fallot repair:

Pain medications, such as acetaminophen or ibuprofen, may be recommended to keep your child comfortable at home. Your child's physician will discuss pain control before your child is discharged from the hospital.

After surgery, older children usually have a fair tolerance for activity. Your child may become tired easily, and sleep more right after surgery, but, within a few weeks, your child should be fully recovered.

Long-term outlook after tetralogy of Fallot surgical repair:

Most children who have had a tetralogy of Fallot surgical repair will live healthy lives. Activity levels, appetite, and growth will eventually return to normal in most children. Your child's cardiologist may recommend that antibiotics be given to prevent bacterial endocarditis after discharge from the hospital.

After initial repair of tetralogy of Fallot, pulmonary valve replacement is often indicated in the second or third decade of life to prevent complications such as enlargement of the right ventricle, dysrhythmias, and heart failure. For women wishing to have children, pre-conception evaluation by echocardiogram and/or magnetic resonance imaging (MRI) is recommended.

Consult your child's physicians regarding the specific outlook for your child.

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