Tetralogy of Fallot

Tetralogy of Fallot (TOF) is a type of congenital heart disease that affects about five of every 10,000 babies, accounting for about 10% of all congenital heart disease. The severity of TOF can vary, but it is always a significant problem that requires surgical treatment.

What Is Tetralogy of Fallot?

As originally described by Dr. Etienne-Louis Arthur Fallot in 1888, TOF consists of a combination of four distinct cardiac anatomic defects.

These are:

• Right ventricular outflow tract obstruction (RVOT): Stenosis (narrowing) reduces the amount of blood entering the pulmonary artery from the right ventricle
• Large ventricular septal defect: A hole in the wall between the right and left ventricles
• Deviation of the aorta toward the right ventricle
• Right ventricular hypertrophy (muscle thickening)

Normal Heart Function

In TOF, the heart's structures don't form the way a healthy heart is expected to develop. This leads to many dangerous effects.

How the heart normally works:

• After oxygen is consumed by the body's tissues, the blood from all over the body returns to the heart through the veins and enters the right atrium, and then the right ventricle.
• The right ventricle pumps the blood through the pulmonary artery to the lungs, where it is replenished with oxygen.
• The freshly oxygenated blood returns to the heart through the pulmonary veins and enters the left atrium, and then the left ventricle.
• The left ventricle (the main pumping chamber) then pumps the oxygenated blood into the aorta and out to the body's tissues to provide oxygen and nutrients. 

In a healthy heart, the right and left ventricles are separated from one another by a muscular wall called the ventricular septum. This keeps oxygen-poor blood in the right side of the heart from mixing with the oxygen-rich blood in the left side of the heart,

Why Tetralogy of Fallot Causes Problems

A large portion of the ventricular septum is missing in TOF. This is a ventricular septal defect. The result of this septal defect is that oxygen-poor blood returning from the body becomes mixed with oxygen-rich blood returning from the lungs.

Because of the defect in the septum, blood from either side can flow to either the RVOT or the aorta when the ventricles contract. Because the pulmonary artery is narrow, the aorta usually receives more than its share.

The blood that's pumped into the aorta includes freshly oxygenated blood, as well as oxygen-poor blood, so the overall oxygenation of blood reaching the tissues is low.

Variability of Pulmonary Artery Stenosis in TOF

The clinical severity of TOF can vary with the degree of pulmonary artery stenosis. The most severe cases of TOF are those with a high degree of pulmonary artery stenosis.

With severe pulmonary artery obstruction, a large portion of the pumped blood will enter the aorta, when the ventricles contract. And relatively little will enter the pulmonary artery. When relatively little blood gets to the lungs to become oxygenated, oxygen-poor blood enters the circulation. This is a dangerous condition known as cyanosis.

If pulmonary artery stenosis is not very severe, then a reasonable amount of blood gets pumped to the lungs and becomes oxygenated. With less cyanosis, TOF often won't cause symptoms at birth.

Fluctuations in Pulmonary Artery Stenosis with Activity

A well-described feature of TOF, seen in many children with this condition, is that the degree of pulmonary artery stenosis may fluctuate. In these cases, cyanosis may come and go. Cyanotic episodes may occur, for instance, when a baby with TOF becomes agitated or begins crying, or when an older child with TOF exercises.

These “spells” of cyanosis, often called “tet spells” or “hypercyanotic spells,” may become severe and can require emergency medical treatment.

If your child is having cyanotic spells, they will have a comprehensive cardiac evaluation after they are stabilized with emergency treatment.

Symptoms of Tetralogy of Fallot

The symptoms of TOF, and the age at which symptoms begin, largely depend on the degree of pulmonary artery obstruction.

Severe Obstruction

When fixed pulmonary artery obstruction is severe, a newborn can experience profound cyanosis (a condition that used to be called a “blue baby”). These infants have immediate and severe distress and require urgent treatment.

Moderate Obstruction

The majority of people with TOF have moderate pulmonary artery stenosis and are diagnosed during early childhood if the condition is not recognized at birth

A healthcare provider may hear a heart murmur during a routine physical examination, or parents might notice cyanotic spells when the child becomes agitated.

Other symptoms of TOF may include difficulty feeding, failure to develop normally, dyspnea, fatigue, and poor exercise tolerance. Symptoms of TOF tend to worsen as time goes by.

Squatting

Older children with TOF often learn to squat to reduce their symptoms. Squatting increases resistance in the arterial blood vessels, which has the effect of causing resistance to blood flow in the aorta, thus directing more of the cardiac blood into the pulmonary circulation. This reduces cyanosis in people with TOF.

Sometimes children with TOF are first diagnosed when their parents mention their frequent squatting to a doctor.

When TOF Doesn't Cause Symptoms

People who have TOF with only minor pulmonary artery stenosis may not have any spells of cyanosis, and years may pass before a diagnosis is made.

Sometimes, TOF may not be diagnosed until adulthood. Despite the lack of symptoms, people who are diagnosed during adulthood need to be treated, since they often develop significant heart failure by early adulthood.

What Causes Tetralogy of Fallot?

The cause of TOF is not known. The condition occurs with higher frequency in children with Down syndrome and with certain other genetic abnormalities.

It is almost always sporadic in nature and is not inherited. TOF has also been associated with maternal rubella, poor maternal nutrition, maternal alcohol use, and maternal age of 40 years or older.

Most of the time none of the risk factors are present when a baby is born with TOF.

Diagnosing Tetralogy of Fallot

If you or your child has signs or symptoms of heart disease, your provider will likely order an electrocardiogram (ECG, ECG), which is a quick, noninvasive test.

The diagnosis of TOF can be made with an echocardiogram or a cardiac MRI, non-invasive imaging tests that can visualize the heart's structure.

A cardiac catheterization is also often used to help plan the surgical repair.

Treating Tetralogy of Fallot

Current practice for TOF treatment is corrective surgery during the first year of life, ideally between 3 and 6 months of age.

Surgery involves:

• Closing the ventricular septal defect to separate the right and left ventricles
• Relieving the pulmonary artery obstruction

After surgery, blood flow through the heart is largely normalized.

With modern techniques, corrective surgery for TOF can be performed with a mortality risk of 0% to 3% in infants and children. The surgical mortality rate for TOF repair in adults can be higher than 10%. Fortunately, it is very uncommon for TOF to be “missed” into adulthood.

Palliative Surgery

For young babies, a form of palliative surgery may be necessary to stabilize the baby until they are strong enough for corrective surgery. This generally involves creating a shunt between one of the systemic arteries (usually a subclavian artery) and one of the pulmonary arteries to improve blood circulation to the lungs.

What Is the Long-Term Outcome of Tetralogy of Fallot?

Without surgical repair, almost half of people born with TOF die within a few years of birth, and very few (even those with “milder” forms of the defect) live to be 30.

With early corrective surgery, long-term survival is now excellent. The majority of people with corrected TOF survive well into adulthood. Because modern surgical techniques are only a few decades old, we still do not know what survival will be. But it is becoming common for cardiologists to see patients with TOF in their sixth and even seventh decades of life.

Still, cardiac problems are fairly common in adults with repaired TOF. Pulmonary valve regurgitation, heart failure, and cardiac arrhythmias (especially atrial tachycardia and ventricular tachycardia) are the most frequent problems that occur as the years go by. For this reason, anyone who has had corrected TOF needs to be under the care of a cardiologist who can evaluate them regularly so that any cardiac problems that subsequently develop can be treated.

A Word From Verywell

With modern treatment, the tetralogy of Fallot has been transformed from a condition that usually resulted in death during childhood to a correctable problem. With continuous medical care, people born with this condition can live well into late adulthood. Today, parents of babies born with TOF have every reason to expect the same happiness and heartbreak they might expect with any other child.