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.

Atrial Septal Defect

About Atrial Septal Defects

An atrial septal defect (ASD) — sometimes referred to as a hole in the heart — is a type of congenital heart defect in which there is an abnormal opening in the dividing wall between the upper filling chambers of the heart (the atria).

In most cases ASDs are diagnosed and treated successfully with few or no complications.

Atrial Septal Defect

To understand this defect, it first helps to review some basics about the way a healthy heart typically works.

The heart has four chambers: The two lower pumping chambers are called the ventricles, and the two upper filling chambers are the atria.

In a healthy heart, blood that returns from the body to the right-sided filling chamber (right atrium) is low in oxygen. This blood passes to the right-sided pumping chamber (right ventricle), and then to the lungs to receive oxygen. The blood that has been enriched with oxygen returns to the left atrium, and then to the left ventricle. It's then pumped out to the body through the aorta, a large blood vessel that carries the blood to the smaller blood vessels in the body. The right and left filling chambers are separated by a thin shared wall, called the atrial septum.

Kids with an atrial septal defect have an opening in the wall (septum) between the atria. As a result, some oxygenated blood from the left atrium flows through the hole in the septum into the right atrium, where it mixes with oxygen-poor blood and increases the total amount of blood that flows toward the lungs. The increased blood flow to the lungs creates creates a swishing sound, known as a heart murmur. This heart murmur, along with other specific heart sounds that can be detected by a cardiologist, can be clues that a child has an ASD.

ASDs can be located in different places on the atrial septum, and they can be different sizes. The symptoms and medical treatment of the defect will depend on those factors. In some rare cases, ASDs are part of more complex types of congenital heart disease. It's not clear why, but ASDs are more common in girls than in boys.

Causes

ASDs occur during fetal development of the heart and are present at birth. During the first weeks after conception, the heart develops. If a problem occurs during this process, a hole in the atrial septum may result.

In some cases, the tendency to develop a ASD might be genetic. Genetic syndromes can cause extra or missing pieces of chromosomes that can be associated with ASD. For the vast majority of children with a defect, however, there's no clear cause.

Signs and Symptoms

The size of an ASD and its location in the heart will determine what kinds of symptoms a child experiences. Most kids who have ASDs seem healthy and appear to have no symptoms. Generally, they feel well and grow and gain weight normally.

Children with larger, more severe ASDs, however, might have some of these signs or symptoms:

  • poor appetite
  • poor growth
  • fatigue
  • shortness of breath
  • lung problems and infections, such as pneumonia

If an ASD is not treated, health complications can develop later, including an abnormal heart rhythm (known as an atrial arrhythmia) and problems with how well the heart pumps blood. As kids with ASDs get older, they also might be at an increased risk for stroke, since a blood clot that develops can pass through the hole in the wall between the atria and travel to the brain. Pulmonary hypertension (high blood pressure in the lungs) also can develop over time in older patients with larger untreated ASDs.

Fortunately, most kids with ASD are diagnosed and treated long before the heart defect causes physical symptoms. Because of the complications that ASDs can cause later in life, pediatric cardiologists often recommend closing ASDs early in childhood.

Diagnosis

Generally, a child's doctor hears the heart murmur caused by ASD during a routine checkup or physical examination. ASDs are not always diagnosed as early in life as other types of heart problems, such as ventricular septal defect (a hole in the wall between the two ventricles). The murmur caused by an ASD is not as loud and can be harder to hear than other types of heart murmurs, so it may be diagnosed any time between infancy and adolescence (or even as late as adulthood).

If a doctor hears a murmur and suspects a heart defect, the child may be referred to a pediatric cardiologist (a doctor who specializes in diagnosing and treating childhood heart conditions). If an ASD is suspected, the cardiologist might order one or more of the following tests:

  • chest X-ray, which produces an image of the heart and surrounding organs
  • electrocardiogram (EKG), which records the electrical activity of the heart and can indicate volume overload of the right side of the heart
  • echocardiogram (echo), which uses sound waves to produce a picture of the heart and to visualize blood flow through the heart chambers. This is often the primary tool used to diagnose an ASD.

Treatment

Once an ASD is diagnosed, treatment will depend on the child's age and the size, location, and severity of the defect. In kids with very small ASDs, the defect may close on its own. Larger ASDs usually won't close, and must be treated medically. Most of these can be closed in a cardiac catheterization lab, although some will require open-heart surgery.

A child with a small defect that causes no symptoms may simply need to visit a pediatric cardiologist regularly to ensure that there are no problems; often, small defects will close spontaneously without any treatment during the first years of life. In general, kids with a small ASD won't require restrictions on physical activity.

In most children with ASD, though, doctors must close the defect if it has not closed on its own by the time a child is old enough to start school.

Depending on the defect's position, many can be corrected by cardiac catheterization. In this procedure, a catheter (a thin, flexible tube) is inserted into a blood vessel in the leg that leads to the heart. A cardiologist guides the tube into the heart to make measurements of blood flow, pressure, and oxygen levels in the heart chambers. A special implant is positioned into the hole in the septum and will flatten against the septum on both sides to close and permanently seal the ASD.

In the beginning, the natural pressure in the heart holds the device in place. Over time, the normal tissue of the heart grows over the device and covers it entirely. This non-surgical technique for closing an ASD eliminates the scar on the chest needed for the surgical approach, and has a shorter recovery time, usually just an overnight stay in the hospital.

There's a small risk of blood clots forming on the closure device while new tissue heals over it, so kids who have their ASD closed with a device implantation are prescribed a low dose of aspirin for 6 months after the procedure.

If surgical repair for ASD is necessary, a child will undergo open-heart surgery. In this procedure, a surgeon makes a cut in the chest and a heart-lung machine is used to maintain circulation while the heart surgeon closes the hole. The ASD may be closed directly with stitches or by sewing a patch of surgical material over the defect. Eventually, the tissue of the heart heals over the patch or stitches, and by 6 months after the surgery, the hole will be completely covered with tissue.

For 6 months following catheterization or surgical closure of an ASD, antibiotics are recommended before routine dental work or surgical procedures to prevent infective endocarditis (an infection of the inner surface of the heart). Once the heart tissue has healed over the closed ASD, most patients no longer need to worry about having a higher risk of infective endocarditis.

Your doctor will discuss other possible risks and complications with you prior to the procedure. Typically, after repair and adequate time for healing, kids with ASD rarely have further symptoms.

Caring for Your Child

Kids who undergo cardiac catheterization to close an ASD usually spend the night in the hospital after the procedure and also should be kept out of gym class or sports practice for a week. After that, they can usually return to their normal physical activities, with their doctor's OK.

Kids who have surgery for their ASDs usually go home after a few days in the hospital if there are no complications. After surgical ASD repair, the main medical concern is the healing of the chest incision. In general, the younger patients are when they have their surgical repairs, the less pain they will have during recovery. The child will be watched closely for signs or symptoms that may indicate a problem. If your child has trouble breathing, is not eating, has fever, or redness or pus oozing from the incision, get medical treatment right away. In most cases, kids who have had ASD surgery recover quickly and without problems.

In the weeks following surgery or cardiac catheterization, your doctor will check on your child's progress. Your child may undergo another echocardiogram to make sure that the heart defect has closed completely. Kids who have undergone ASD repair will continue to have follow-up visits with the cardiologist.

Most kids recover from treatment quickly — you might even notice that within a few weeks, your child is eating more and is more active than before surgery. However, some signs and symptoms might indicate a problem. If your child is having trouble breathing, call the doctor or go to the emergency department immediately.

Other symptoms that can indicate a problem include:

  • a bluish tinge or color (cyanosis) to the skin around the mouth or on the lips and tongue
  • poor appetite or difficulty feeding
  • failure to gain weight or weight loss
  • listlessness or decreased activity level
  • prolonged or unexplained fever
  • increasing pain, tenderness, or pus oozing from the incision

Call your doctor if your child has any of these signs after closure of the ASD.

Any time a child is diagnosed with a heart condition, it can be scary. But the good news is that your pediatric cardiologist will be very familiar with this condition and how to best manage it. Most kids who've had an ASD corrected have a normal life expectancy and go on to live healthy, active lives.

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