The four components that make up the "tetralogy" include:
- a ventricular septal defect (VSD);
- pulmonary stenosis (subvalvar, valvar and/or supravalvar);
- an overriding aorta; and
- 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.
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.
Heart With 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.
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.
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Heart Murmurs and Your Child
Many parents fear the worst when their child is diagnosed with a heart murmur, but this diagnosis is actually extremely common. In fact, many kids are found to have a heart murmur at some point during their lives. Most murmurs are not a cause for concern and do not affect the child's health at all.
What exactly is a heart murmur? By itself, the term heart murmur isn't a diagnosis of an illness or disorder. To better understand what it does mean, it's important to know how the heart works.
How the Heart Works
The normal heart has four chambers and four valves (which function like one-way doors). The two lower pumping chambers of the heart are called the ventricles, and the two upper filling chambers are the atria (singular is atrium).
Here's how blood moves in normal circulation:
- Blood that returns from the body to the filling chamber on the right side (the right atrium) is low in oxygen.
- This blood passes across a valve (the tricuspid valve) to the pumping chamber on the right side (the right ventricle) and then travels across the pulmonary valve to the lungs to receive oxygen.
- The oxygen-enriched blood returns to the filling chamber on the left side (the left atrium), then across a valve (the mitral valve) to the pumping chamber on the left side (the left ventricle).
- The blood is then pumped across the aortic valve out to the body through the aorta, a large blood vessel that carries blood to the smaller blood vessels in the body to deliver oxygen.
Using a stethoscope, a doctor examines the heart by listening to the sounds it makes. The familiar "lub-dub" sound of a normal heartbeat is caused by the closing sound of the valves as the heart squeezes to push blood through the body.
A heart murmur describes an extra sound 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.
Diagnosing a Heart Murmur
A murmur is heard during the heart listening exam, using a stethoscope held at different areas on the front of the chest as the heart beats. Heart murmurs can be heard in infants as well as older kids and teens.
Of course, if the child is crying, uncooperative, or breathing loudly, it might not be possible to hear a murmur. It helps if the child is quiet when the doctor listens, since some heart murmurs are very soft. The doctor may have a parent help by calming the child or having the child sit in the parent's lap during the exam.
Heart murmurs are rated on a scale from 1 to 6 in intensity (loudness). Grade 1 is barely audible, whereas grade 6 is very loud. The doctor will note where on the chest the murmur is best heard, the characteristics of the murmur (for example, whether it's harsh and high-frequency or soft and blowing), where it occurs in the heartbeat cycle, and whether it changes when your child changes position. After this initial discovery, the doctor may refer your child to a pediatric cardiologist for further evaluation.
It's not unusual for a murmur to be noticed during a checkup, even though none was heard before. Innocent murmurs tend to come and go, depending on a child's heart rate, position during the exam, and the presence of fever. Some new murmurs might be a sign of a newly developed heart problem. And some heart problems present from birth (congenital heart problems) at first might not be severe enough to cause a murmur that can be detected during an exam.
Because of the common misconception that all heart murmurs are serious, it's important for parents to understand which type of murmur their child has and if it needs further evaluation.
What's an Innocent Murmur?
The most common type of heart murmur is called functional or innocent. This diagnosis means the murmur is produced by a normal, healthy heart. It can come and go throughout childhood. It usually goes away on its own as the child gets older and doesn't pose any health threat.
Kids with innocent heart murmurs don't require a special diet, restriction of activities, or any other special treatment. They do not need to take a dose of antibiotic before going to the dentist. Those old enough to understand that they have a heart murmur should be reassured that they aren't any different from other kids.
In other words, an innocent murmur is the sound of normal blood moving through a normal heart in a normal way. Just as we can sometimes hear the sound of air moving in an air duct or water flowing through a plumbing pipe, we can often hear the sound of blood moving through the heart even if there is not a heart problem.
Congenital Heart Defects
Some murmurs can indicate a problem with the heart. If the doctor suspects something other than an innocent heart murmur, your child will see a pediatric cardiologist, who might order or perform additional tests, such as a chest X-ray, an EKG (an electrocardiogram), or an echocardiogram. An echocardiogram, or "echo," is an ultrasound picture of the heart structures (chambers, walls, and valves). It records the motion of the blood through the heart and can measure the direction and speed of blood flow within the heart structures.
About 1 out of every 100 babies is born with a structural heart problem, or congenital heart defect. These babies may show signs of their defect as early as the first few days of life or they may appear completely healthy until later in childhood. Some kids won't show any symptoms beyond a heart murmur, while others will have symptoms that could be mistaken for other illnesses or disorders.
Symptoms of a significant heart defect in newborns and infants can include:
- rapid breathing
- difficulty feeding
- blueness in the lips (called cyanosis)
- failure to thrive
Symptoms in an older child or adolescent may be:
- difficulty exercising or doing physical activity
- chest pain
Contact your doctor if you notice any of these symptoms.
Congenital heart defects can be seen in chromosomal disorders such as trisomy 21 (Down syndrome) or might be associated with specific gene abnormalities. Babies with other birth defects may also have heart defects. Exposure to certain chemicals, including alcohol, or medications before birth can be associated with congenital heart disease.
While some parents may have more than one child with a heart defect, most heart defects aren't considered to be hereditary. In most cases, however, children with congenital heart defects have no known risk factors.
Maternal health also plays a role. At a higher risk of having a baby with a heart defect are pregnant women who:
- contract rubella (German measles)
- have uncontrolled or poorly regulated diabetes
- have PKU (phenylketonuria, a genetic error of the body's metabolism)
Common Heart Defects
Several different categories of heart problems can cause heart murmurs. These include septal defects, valve abnormalities, abnormalities of flow between the heart chambers and the exits (outflow tract obstruction), and heart muscle disorders.
- Septal defects involve the walls (or septum) between the upper or lower chambers of the heart. A hole in the septum can result in blood flowing 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 and may cause the heart to enlarge. Some holes can be large enough to produce symptoms in addition to a heart murmur; others are smaller and may close on their own in time.
- Valve abnormalities are caused by heart valves that are narrow, too small, too thick, or otherwise abnormal. Valves that are misshapen don't allow smooth blood flow across them, and this creates turbulent flow. Sometimes, abnormal valves may allow backflow of blood within the heart. Either condition 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) can make the heart muscle abnormally thick or weak. This can impair the heart's ability to pump blood to the body normally.
A heart murmur is an exam finding, not a disease. Your doctor and 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, a pediatric cardiologist will know how to best take care of it.
Reviewed by: Steven B. Ritz, MD
Date reviewed: May 2013