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.

Heart Murmurs and Your Child

What Are Heart Murmurs?

The human heartbeat is usually steady: lub-dub, lub-dub. In some people, though, the blood makes an extra noise as it flows through the heart. This sound is called a murmur.

Doctors hear a heart murmur as a whooshing sound between heartbeats. The whoosh is just an extra noise that the blood makes as it flows through the heart.

What Happens in a Heart Murmur?

Depending on a person's age, the heart beats about 60 to 120 times every minute. Each heartbeat is really two separate sounds. The heart goes "lub" with the closing of the valves that control blood flow from the upper chambers to the lower chambers. Then, as the valves controlling blood going out of the heart close, the heart goes "dub."

A heart murmur describes an extra sound heard in addition to the "lub-dub." Sometimes these extra sounds are simply the sound of normal blood flow moving through a normal heart. Other times, a murmur may be a sign of a heart problem.

Who Gets Heart Murmurs?

Parents might worry if they're told that their child has a heart murmur. But heart murmurs are very common, and many kids are found to have one at some point. Most murmurs are not a cause for concern and won't affect a child's health at all.

How Are Heart Murmurs Diagnosed?

Doctors listen to the heart by putting a stethoscope on different areas of the chest. It helps if kids are quiet as the doctor listens, because some heart murmurs are very soft. It's not unusual for a murmur to be noticed during a routine checkup, even if none was heard before.

Heart murmurs are rated on a scale from 1 to 6 based on how loud they are. Grade 1 is very soft, whereas grade 6 is very loud. If a murmur is found, the doctor may refer a child to a pediatric cardiologist for further evaluation.

What Causes Heart Murmurs?

Innocent Heart Murmurs

The most common type of heart murmur is called functional or innocent. An innocent heart murmur is the sound of blood moving through a normal, healthy heart in a normal way. Just as you might hear air moving through an air duct or water flowing through a pipe, doctors can hear blood moving through the heart even when there's no heart problem.

An innocent heart murmur can come and go throughout childhood. Kids with these murmurs don't need a special diet, restriction of activities, or any other special treatment. Those old enough to understand that they have a heart murmur should be reassured that they aren't any different from other kids.

Most innocent murmurs will go away on their own as a child gets older.

Congenital Heart Defects

Some murmurs can indicate a problem with the heart. In these cases, doctors will have a child see a pediatric cardiologist. The cardiologist will order tests such as:

  • a chest X-ray: a picture of the heart and surrounding organs
  • an EKG: a record of the heart's electrical activity
  • an echocardiogram: a picture of the heart made using sound waves

About 1 out of every 100 babies is born with a structural heart problem, or congenital heart defect. These babies may show signs of the defect as early as the first few days of life or not until later in childhood. Some kids won't have any symptoms beyond a heart murmur, while others will such signs as:

  • rapid breathing
  • difficulty feeding
  • blueness in the lips (called cyanosis)
  • failure to thrive

An older child or teen might:

  • be very tired
  • have trouble exercising or doing physical activity
  • have chest pain

Call your doctor if your child has any of these symptoms.

Pregnant women have a higher risk of having a baby with a heart defect if they get rubella (German measles), have poorly controlled diabetes, or have PKU (phenylketonuria, a genetic error of the body's metabolism).

Common Heart Defects

Several kinds of heart problems can cause heart murmurs, including:

  • Septal defects, which involve the walls (or septum) between the upper or lower chambers of the heart. A hole in the septum can let blood flow through it into the heart's other chambers. This extra blood flow may cause a murmur. It can also make the heart work too hard or become enlarged. Bigger holes can cause symptoms besides a heart murmur; smaller ones may eventually close on their own.
  • Valve abnormalities, caused by heart valves that are narrow, too small, too thick, or otherwise abnormal. These valves don't allow smooth blood flow across them. Sometimes, they can allow backflow of blood within the heart. Either problem will cause a murmur. Outflow tract obstruction might be caused by extra tissue or heart muscle that blocks the smooth flow of blood through the heart.
  • Heart muscle disorders (cardiomyopathy), which can make the heart muscle abnormally thick or weak, hurting its ability to pump blood to the body normally.

Your doctor and a pediatric cardiologist can determine if the murmur is innocent (which means your child is perfectly healthy) or if there is a specific heart problem. If there is a problem, the pediatric cardiologist will know how best to take care of it.

Reviewed by: Steven B. Ritz, MD
Date reviewed: August 03, 2017