Tetralogy of Fallot (TOF)

Heart with Tetralogy of Fallot

An animation of a heart with tetralogy of Fallot (TOF)

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Anatomy

The four components that make up the "tetralogy" include:
  1. a ventricular septal defect (VSD);
  2. pulmonary stenosis (subvalvar, valvar and/or supravalvar);
  3. an overriding aorta; and
  4. right ventricular hypertrophy.

The primary problem is the malalignment VSD, in which the infundibular or conal septum is malaligned anteriorly, thereby blocking the right ventricular outflow tract. The conal septum pulls the aorta anteriorly with it, into a position overriding the ventricular septum. The right ventricular hypertrophy occurs secondary to high pressure in the right ventricle (RV), created by the pulmonary stenosis and the large VSD. In the extreme situation, the right ventricular outflow tract is completely blocked off, in which case you have tetralogy of Fallot with pulmonary atresia.

Physiology

The physiology is variable despite similar anatomy. The degree of RV outflow tract obstruction strongly influences the degree of cyanosis. With increasing degrees of obstruction, more and more of the desaturated (blue) blood is forced across the VSD and out into the aorta (a right to left shunt), thus never reaching the lungs to become oxygenated. On the other hand, if there is only mild RV outflow tract obstruction, there may be less resistance to blood flowing out the pulmonary artery than flowing to the systemic circulation. In this situation, excess blood tends to flow from the left ventricle to the right ventricle; i.e. a net left to right shunt. These patients are acyanotic ("pink Tetralogy of Fallot") and may actually develop congestive heart failure.

A patent ductus arteriosus (PDA) can play a very important role by providing an alternate pathway for blood to reach the lungs, allowing adequate pulmonary blood flow even in the face of very severe RV outflow obstruction. The flow across the PDA goes from left (the aorta) to right (the pulmonary artery) in this setting.

Children with tetralogy of Fallot are at risk of having hypercyanotic spells or "Tet spells". Spasm of the infundibular region (below the pulmonary valve) and/or a sudden increase in pulmonary vascular resistance produces a sudden decrease in the amount of blood getting to the lungs. Concomitantly, more blood is shunted from right to left and exits the aorta as desaturated blood. The resultant hypoxemia further increases the pulmonary vascular resistance and a downward spiral begins with the rapid development of acidosis. Older children learn to squat in order to prevent or alleviate a spell. It is believed that the squatting kinks the large arteries in the lower extremities, thus increasing the systemic vascular resistance and forcing more blood across the pulmonary outflow tract.

Surgical Management of Tetralogy of Fallot (TOF)

Definitive treatment of tetralogy of Fallot consists of surgical correction. Timing of surgery remains controversial but most agree that the presence of severe cyanosis or hypercyanotic spells necessitates surgical intervention. Complete repair consists of closing the ventricular septal defect with a patch and enlarging the right ventricular outflow tract. The latter usually requires incision across the pulmonary valve annulus and placement of a patch of synthetic material to widen the outflow tract at all levels of obstruction.

When surgical intervention is necessary in a patient who is not a good candidate for complete repair (i.e., very small patient size, tiny pulmonary arteries or an anomalous coronary artery course), a palliative procedure is performed. Palliation consists of placement of a shunt from the aorta to the pulmonary artery to increase pulmonary blood flow. The most commonly performed shunt today is the modified Blalock-Taussig shunt, in which a tube of Gore-Tex is placed between the subclavian artery and the pulmonary artery.


What is Normal Cardiac Anatomy?

When your child has a congenital heart defect, there's usually something wrong with the structure of his or her heart's structure.

 
Learn More About Normal Cardiac Anatomy

Heart with Normal Cardiac Anatomy

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When your child has a congenital heart defect, there's usually something wrong with the structure of his or her heart's structure.

The heart is composed of four chambers. The two upper chambers, known as atria, collect blood as it flows back to the heart. The two lower chambers, known as ventricles, pump blood with each heartbeat to the two main arteries (the pulmonary artery and the aorta). The septum is the wall that divides the heart into right and left sides. The atrial septum separates the right and left atria; likewise, the ventricular septum separates the two ventricles.

There are four valves that control the flow of blood through the heart. These flap-like structures allow blood to flow in only one direction. The tricuspid and mitral valves, also known as the atrioventricular valves, separate the upper and lower chambers of the heart. The aortic and pulmonary valves, also known as the arterial valves, separate the ventricles from the main arteries. Oxygen-depleted blood returns from the body and drains into the right atrium via the superior and inferior vena cavas. The blood in the right atrium then passes through the tricuspid valve and enters the right ventricle.

Next, the blood passes through the pulmonary valve, enters the pulmonary artery, and travels to the lungs where it is replenished with oxygen. The oxygen-rich blood returns to the heart via the pulmonary veins, draining into the left atrium. The blood in the left atrium passes through the bicuspid, or mitral, valve and enters the left ventricle.

Finally, the oxygen-rich blood flows through the aortic valve into the aorta and out to the rest of the body.

Coarctation of the Aorta

What Is Coarctation?

The aorta is the major blood vessel that carries blood away from the heart to the body. When someone has coarctation of the aorta, the aorta is narrowed at some point.

Here's how a healthy heart and aorta work: Blood that needs oxygen comes from all over the body and enters the right side of the heart, which pumps it to the lungs. The lungs fill the blood with oxygen, and this oxygen-rich blood returns from the lungs to the left side of the heart. The left side of the heart finishes up by pumping the blood out through the aorta. From the aorta, the blood travels through arteries that reach all of the body's organs and tissues, bringing them oxygen. Then the blood returns to the heart through veins and begins the cycle once again.

When part of the aorta is narrowed (this is a coarctation), that defect can affect the body's blood circulation because the left side of the heart has to work harder to pump blood through the narrowed aorta.

Sometimes the narrowing is minor and might not even cause symptoms. In other cases, the aorta is more constricted, placing a strain on the heart's left ventricle (the chamber that pumps blood to the aorta and out to the body).

A coarctation can occur anywhere in the aorta, but most often is found after the point where the arteries that carry blood to the upper body and head branch off from the aorta.

Causes

Coarctation of the aorta (or COA) is a congenital defect, meaning that someone is born with it. About 1 in 100 children is born with a heart problem, and coarctation represents about 8% of those cases. Doctors don't know for sure why certain people are born with this narrowing of the aorta.

Coarctation occurs more commonly in boys, but is often seen in girls with Turner syndrome, in which one of two X chromosomes is incomplete or missing. COA may occur with other birth defects or congenital heart conditions, such as a ventricular septal defect (a hole in the wall between the heart's left and right ventricles).

Coarctation also can be associated with other structures abnormalities of the left side of the heart. A common association is a bicuspid aortic valve, in which the aortic valve between the left ventricle and aorta has two leaflets instead of the normal three.

Most people with COA are diagnosed as babies or young children, although some aren't diagnosed until they're teens or even adults. Usually, in this case, the narrowing in the aorta is not severe enough to cause serious symptoms while the person is very young. But even those who do not have major symptoms usually need to be treated because the coarctation can eventually cause problems. COA will not go away on its own.

Signs and Symptoms

Often an abnormal blood pressure test is the first detected sign of COA. During a physical exam, a doctor may find that a child with a coarctation has a higher blood pressure in the arms than in the legs, and also might hear a heart murmur or notice that the pulse in the groin is weak or difficult to feel. Any person diagnosed with high blood pressure should be checked for coarctation of the aorta.

Kids who have COA often do not have any symptoms and have only mild signs that are discovered by accident during a regular visit to the doctor. A child who does have symptoms may experience some or all of these:

  • cold legs and feet
  • shortness of breath, especially when exercising
  • chest pain

Diagnosis and Treatment

Doctors may refer a child with the signs or symptoms of COA to a pediatric cardiologist (a doctor who specializes in diagnosing and treating heart disease in kids and teens). The cardiologist will listen to the heart, feel the pulses, and check blood pressure.

The doctor probably will order an echocardiogram, a test that uses sound waves to create a picture of the heart and its circulation. Other tests that produce images of the heart, such as a chest X-ray, a magnetic resonance imaging (MRI) test, or a computerized tomography (CT) scan, also may be used to help the cardiologist look for a narrowing of the aorta.

A severe coarctation is usually diagnosed shortly after birth and repaired by surgery immediately. In an older patient, doctors often recommend that COA be treated quickly, since it can cause persistent high blood pressure and cause heart enlargement. The defect can also cause dissection or rupture of the aorta, which can be fatal in many people by the age of 40.

Coarctation of the aorta can be repaired either by surgery or other procedures. Different types of surgery can repair a narrowing of the aorta, but one of the most common ways to fix COA is to remove the narrow section and reconnect the two ends of the aorta.

In some cases, doctors may do a procedure known as balloon dilation or balloon angioplasty. They insert a tiny balloon into a blood vessel in the leg and use a very thin wire to thread it up to the aorta, across the narrow area. When the doctor inflates the balloon, the narrow area is expanded. After the area has been widened, the balloon is removed. The cardiologist also may implant a device called a stent to keep the area open after the procedure.

Home Care

Once the defect has been fixed, most symptoms of COA disappear right away because the blockage that caused those symptoms is now gone. Some people will still have high blood pressure for a while and might have to take medicine to control it.

Kids and teens who have had surgery often feel completely better after a week or two, and those who have had the balloon treatment feel better even sooner, often within a couple of days.

But doctors recommend that all patients avoid some physical activities — especially lifting heavy objects or sports that could cause an impact to the chest — for several weeks or months to give the body enough time to heal. Someone whose blood pressure remains high may have to continue to limit certain activities as long as the blood pressure remains high.

Kids who've had a COA corrected will still need to be monitored over time. In some, the narrowing of the aorta can return after surgery or balloon dilation treatment. Regular visits to a cardiologist — often every year or two after recovery — let the doctor monitor blood pressure and look for signs that COA could be returning.

If your child has COA or has had a coarctation repaired, call the doctor if you see shortness of breath, chest pain, or fainting.

Overall, kids who have had coarctation of the aorta can expect to lead a normal life after treatment.

Reviewed by: Steven B. Ritz, MD
Date reviewed: May 2013