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.

Arrhythmias

An arrhythmia is an abnormal heart rhythm usually caused by an electrical "short circuit" in the heart.

The heart normally beats in a consistent pattern, but an arrhythmia can make it beat too slowly, too quickly, or irregularly. This can cause the heart muscle's pumping function to work erratically, which can lead to a variety of symptoms, including fatigue, dizziness, and chest pain.

What Causes Arrhythmias?

The heart has its own conduction system, or electrical system, that sends electrical signals around the heart, telling it when to contract and pump blood throughout the body. The electrical signals originate from a group of cells in the right atrium, called the sinus node. The sinus node functions as the heart's pacemaker and makes sure the heart is beating at a normal and consistent rate. The sinus node normally increases the heart rate in response to factors like exercise, emotions, and stress, and slows the heart rate during sleep.

However, sometimes the electrical signals flowing through the heart don't "communicate" properly with the heart muscle, and the heart can start beating in an abnormal pattern — an arrhythmia (also called dysrhythmia).

Arrhythmias can be temporary or permanent. They can be caused by several things, but also can occur for no apparent reason. Arrhythmias can be congenital (meaning kids are born with it), sometimes due to a birth defect of the heart but sometimes even when the heart has formed normally.

Other causes of arrhythmias in kids include chemical imbalances in the blood, infections, or other diseases that cause irritation or inflammation of the heart, medications (prescription or over-the-counter), and injuries to the heart from chest trauma or heart surgery. Other factors (such as illegal drugs, alcohol, tobacco, caffeine, stress, and some herbal remedies) also can cause arrhythmias.

Signs and Symptoms

Because arrhythmias can cause the heart to beat less effectively, blood flow to the brain and to the rest of the body can be interrupted. If the heart is beating too fast, its chambers can't fill with the proper amount of blood. If it's beating too slowly or irregularly, the proper amount of blood can't be pumped out to the body.

If the body doesn't get the supply of blood it needs to run smoothly, these symptoms can occur:

  • dizziness
  • fatigue
  • lightheadedness
  • weakness
  • palpitations (a feeling of fluttering or pounding in the chest)
  • shortness of breath
  • chest pain
  • fainting

Arrhythmias can be constant, but usually come and go at random. Sometimes arrhythmias can cause no detectable symptoms at all. In these cases, the arrhythmia can only be discovered during a physical examination or a heart function test.

What's a Normal Heart Rate?

Heart rate is measured by counting the number of beats per minute. Normal heart rate varies depending on factors like age and whether the person leads an active lifestyle or not. (For example, athletes often have a lower resting heart rate).

The resting heart rate decreases as kids get older. Typical normal resting heart rate ranges are:

  • babies (birth to 3 months of age): 100–150 beats per minute
  • kids 1-3 years old: 70-110 beats per minute
  • kids by age 12: 55-85 beats per minute

Your doctor should help you determine whether or not your child's heart rate is abnormally fast or slow, since the significance of an abnormal heart rate depends on the situation. For example, an older child or adult with a slow heart rate might begin to show symptoms when his or her heart rate drops below 50 beats per minute. However, trained athletes have a lower resting heart rate — so a slow heart rate in them isn't considered abnormal if no symptoms are associated with it.

Types of Arrhythmias

There are several types of arrhythmias, including:

Premature Atrial Contraction (PAC) and Premature Ventricular Contraction (PVC)

Premature contractions are usually considered minor arrhythmias, in which the person may feel a fluttering or pounding in the chest caused by an early or extra beat. PACs and PVCs are very common, and are what happens when it feels like your heart "skips" a beat. It doesn't skip a beat — an extra beat actually comes sooner than normal. Occasional premature beats are common and considered normal, but in some cases they can indicate an underlying medical problem or heart condition.

Tachycardias

Tachycardias are arrhythmias that involve an abnormally rapid heartbeat. They fall into two major categories — supraventricular and ventricular:

  • Supraventricular tachycardia (SVT): is the most common significant arrhythmia, it's characterized by bursts of fast heartbeats that originate in the upper chambers of the heart. The bursts can happen suddenly, and episodes can last anywhere from a few seconds to several days. Specific treatment is usually recommended if incidents of SVT are long-lasting or happen often.
  • Ventricular tachycardia: is a serious but relatively uncommon condition that originates in the lower chambers of the heart and can be dangerous.

Bradycardias

Bradycardias — arrhythmias characterized by an abnormally slow heartbeat — include:

  • Sinus node dysfunction: is when the heart's sinus node isn't working correctly, most commonly following surgery to correct a congenital heart defect. An abnormally slow heartbeat is typically seen in this condition; however, episodes of rapid heartbeat due to SVT also can occur.
  • Heart block: is often caused by a congenital heart defect, but also can be the result of disease or injury. Heart block happens when electrical impulses can't make their way from the upper to lower chambers of the heart. When this happens, another node in the lower chambers takes over and acts as the heart's pacemaker. Although it sends out electrical impulses to keep the heart beating, the transmission of the signals is much slower, leading to a slower heart rate.

Diagnosing Arrhythmias

Doctors use several tools to diagnose arrhythmias. It's very important to know your child's medical history and give this information to your doctor, who will use it, along with a physical examination, to begin the evaluation.

If an arrhythmia is suspected, the doctor will probably recommend an electrocardiogram (EKG) to measures the heart's electrical activity. There is nothing painful about an EKG — a series of electrodes (small metal tabs) are fixed to the skin with sticky papers, then information about the electrical activity of the heart is transferred to a computer, where it's interpreted and drawn as a graph.

The doctor might recommend the following types of EKG tests:

  • Resting EKG. This measures resting heart rate and rhythm, and lasts about a minute.
  • Exercise EKG (also called a stress test). This measures heart rate and rhythm while exercising, like riding a stationary bicycle or walking on a treadmill.
  • Signal-average EKG. This measures heart rate much like a resting EKG. The only difference is the signal-average EKG monitors the heartbeat over a longer time period (around 15–20 minutes).
  • Holter monitor. This is an EKG done over a long period of time, usually 24 hours or more. The electrodes are connected to the chest, and the wires are attached to a portable EKG recorder. The child is encouraged to continue normal daily activities, but must be careful to not get the electrodes wet (for example, no swimming, showering, or activities that cause a lot of sweating). The two kinds of Holter monitoring are: continuous recording, which means the EKG is on throughout the entire monitoring period; and event monitoring, which means data is recorded only when the child feels symptoms and then turns the Holter monitor on.

Treating Arrhythmias

Many arrhythmias don't require treatment; however, some can pose a health problem and need to be evaluated and treated by a doctor.

Depending on the type and severity of the arrhythmia, one of these options might be recommended:

  • Medications. Many types of prescription anti-arrhythmic medications are available to treat arrhythmias. The doctor will determine which is best by considering the type of arrhythmia, possible underlying medical causes, and any medications a child is taking. Sometimes, anti-arrhythmic medications can increase symptoms and cause unwanted side effects, so their use and effectiveness should be closely monitored by the doctor, you, and your child.
  • Pacemakers. A pacemaker is a small, battery-operated device implanted into the body (near the collarbone) through a surgical procedure. Connected to the heart by a wire, pacemakers can help treat bradycardia. Through a sensing device, a pacemaker can detect if the heart rate is too slow and sends electrical signals to the heart to speed up the heartbeat.
  • Defibrillators. Like a pacemaker, a defibrillator can deliver electrical impulses to the heart. A small battery-operated implantable cardioverter defibrillator (ICD) can be implanted near the left collarbone through a surgical procedure. Wires run from the defibrillator to the heart. It senses if the heart has developed a dangerously fast or irregular rhythm and delivers an electrical shock to restore a normal heartbeat.
  • Catheter ablation. "Ablation" literally means removal or elimination. In the case of catheter ablation, a catheter (a long, thin wire) is guided through a vein in the leg to the heart. Arrhythmias are often caused by microscopic defects in the heart muscle. Once the problem area of the heart is pinpointed, the catheter heats or freezes the muscle cells and destroys them.
  • Surgery. Surgery is usually recommended only if all other options have failed. In this case, the child is put under anesthesia, the chest is opened, and the heart is exposed. Then, the tissue causing the arrhythmia is removed.

When to Call the Doctor

Although many arrhythmias are minor and don't represent a significant health threat, some can indicate a more serious problem. If your child has been having symptoms of an arrhythmia, call your doctor.

Reviewed by: Joel D. Temple, MD
Date reviewed: August 2012