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 of the Aorta?

Coarctation of the aorta (COA) is a narrowing of the aorta, the major blood vessel that carries blood away from the heart to the body. This narrowing causes the left side of the heart to work harder to pump blood through the aorta.

Sometimes the coarctation is minor and might not even cause symptoms. Other times, surgery or other procedures are needed to treat it.

What Causes COA?

Coarctation of the aorta is a congenital defect, meaning that a baby is born with it. Doctors aren't sure why some people develop COAs, but boys are almost twice as likely to have it than girls.

In many people, the defect shows up with other birth defects or conditions, such as a ventricular septal defect (a hole in the wall between the heart's left and right ventricles). It's also fairly common in girls born with Turner syndrome, a genetic disorder in which one of a girl's two X chromosomes is incomplete or missing.

Usually, COA is found early. But some people aren't diagnosed until they're teens or even adults. In those cases, it's usually because the narrowing in the aorta is not severe enough to cause serious symptoms until then. But even people who don't have major symptoms need treatment because COA can eventually cause problems. The defect doesn't go away on its own.

What Are the Signs & Symptoms of COA?

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

Often, kids don't have any symptoms and the COA is discovered during a regular visit to the doctor. Kids who do have symptoms might have:

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

How Is Coarctation of the Aorta Diagnosed?

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 problems). The cardiologist will listen to the heart, feel the pulses, and check blood pressure.

The cardiologist might order an echocardiogram — a test that uses sound waves to create a picture of the heart and its circulation — and other tests that produce images of the heart, like a chest X-ray, a magnetic resonance imaging (MRI) test, or a computerized tomography (CT) scan.

COA must be treated quickly because it can cause high blood pressure and enlarge the heart. It also can cause dissection or rupture of the aorta, which can be fatal. Severe coarctations usually are found shortly after birth and repaired by surgery immediately.

How Is COA Treated?

Coarctation of the aorta can be repaired with surgery or other procedures. One of the most common ways to fix a coarctation is to remove the narrow section and reconnect the two ends of the aorta.

In some cases, doctors may do a balloon dilation (also called balloon angioplasty). In this procedure, a tiny balloon is inserted into a blood vessel in the leg and a very thin wire is threaded up to the aorta, across the narrow area. When the balloon is inflated, the narrow area is widened. Then the balloon is removed. The cardiologist also may implant a stent to keep the area open after the procedure.

Looking Ahead

After the defect is fixed, most symptoms of COA disappear right away because the blockage that caused those symptoms is 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 until the blood pressure lowers.

Kids who've had a COA corrected will need to see their doctors regularly. Sometimes, the narrowing can return after surgery or balloon dilation treatment. Visits to the cardiologist every year or two after recovery will 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: October 30, 2017