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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Ventricular Septal Defect
VSDs are the most common congenital heart defect, and in most cases they're diagnosed and treated successfully with few or no complications.
What Is a Ventricular 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 of the heart 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 travels 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-sided pumping chambers (ventricles) are separated by shared wall, called the ventricular septum.
Kids with a VSD have an opening in this wall. As a result, when the heart beats, some of the blood in the left ventricle (which has been enriched by oxygen from the lungs) is able to flow through the hole in the septum into the right ventricle. In the right ventricle, this oxygen-rich blood mixes with the oxygen-poor blood and goes back to the lungs. The blood flowing through the hole creates an extra noise, which is known as a heart murmur. The heart murmur, can be heard when a doctor listens to the heart beat with a stethoscope.
VSDs can be located in different places on the ventricular septum, and they can be different sizes. The symptoms and medical treatment of the VSD will depend on those factors. In some rare cases, VSDs are part of more complex types of congenital heart disease.
What Causes a VSD?
Ventricular septal defects occur during fetal heart development and are present at birth. During the first weeks after conception, the heart develops from a large tube, dividing into sections that will eventually become the walls and chambers. If a problem occurs during this process, it can create a hole in the ventricular septum.
In some cases, the tendency to develop a VSD may be due to genetic syndromes that cause extra or missing pieces of chromosomes. The vast majority of these defects, though, have no clear cause.
Signs and Symptoms
VSDs are usually found in the first few weeks of life by a doctor during a routine checkup. The doctor will be able to detect a heart murmur, which is due to the sound of blood as it passes between the left and right ventricles. The murmur associated with a VSD has certain features that allow a doctor to distinguish it from heart murmurs due to other causes.
The size of the hole and its location within the heart will determine whether a VSD causes any symptoms. Small VSDs will not typically cause any symptoms, and may ultimately close on their own. Older kids or teens who have small VSDs that persist usually don't experience any symptoms other than the heart murmur that doctors hear. They might need to see a doctor regularly to check on the heart defect and make sure it isn't causing any problems.
Moderate and large VSDs that haven't been treated in childhood may cause noticeable symptoms. Babies may have faster breathing and get tired out during attempts to feed. They may start sweating or crying with feeding, and may gain weight at a slower rate.
These signs generally indicate that the VSD will not close by itself, and cardiac surgery may be needed. This usually is done within the first 3 months of life to prevent other complications. A cardiologist can prescribe medication to lessen symptoms before surgery.
People with a VSD are at greater risk in their lifetime of developing endocarditis, an infection of the inner surface of the heart. This occurs when bacteria in the bloodstream infect the lining of the heart. Bacteria are always in our mouths, and small amounts are introduced into the bloodstream when we chew and brush our teeth. The best way to protect the heart from endocarditis is to to reduce oral bacteria by brushing and flossing daily, and visiting the dentist regularly. In general, it is not recommended that patients with simple VSDs take antibiotics before dental visits, except for the first 6 months after surgery.
Diagnosing a VSD
If your child is discovered to have a heart murmur, a doctor may refer you to a pediatric cardiologist, a doctor who specializes in diagnosing and treating childhood heart conditions.
In addition to doing a physical exam, the cardiologist take your child's medical history. If a VSD is suspected, the cardiologist may order one or more of these tests:
- a chest X-ray, which produces a picture of the heart and surrounding organs
- an electrocardiogram (EKG), which records the electrical activity of the heart
- an 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 a VSD.
- a cardiac catheterization, which provides information about the heart structures as well as blood pressure and blood oxygen levels within the heart chambers. This test is usually performed for VSD only when additional information is needed that other tests cannot provide.
Treating a VSD
Once an VSD is diagnosed, treatment will depend on the child's age and the size, location, and severity of the defect. A child with a small defect that causes no symptoms may simply need to visit a cardiologist regularly to make sure that there are no other problems.
In most kids, a small defect will close on its own without surgery. Some might not close but do not get any larger. Kids whose VSD is small and has not closed generally won't have to restrict their physical activities.
For kids with medium to large VSDs, surgery may be necessary. In most cases, this takes place within the first few weeks to months of life. In this procedure, the surgeon makes an incision in the chest wall and a heart-lung machine will maintain circulation while the surgeon closes the hole. The surgeon can stitch the hole closed directly or, more commonly, sew a patch of manmade surgical material over it. 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.
Certain types of VSDs may be closed by cardiac catheterization. A thin, flexible tube (a catheter) 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, shaped into two disks formed of flexible wire mesh, is positioned into the hole in the septum. The device is designed to flatten against the septum on both sides to close and permanently seal the VSD.
After healing from surgery or catheterization, kids with VSDs are considered cured and should have no further symptoms or problems.
Caring for a Child With a VSD
Some kids with VSDs may take heart medication prior to surgery to help lessen the symptoms from the defect. Those who have surgery for larger VSDs usually leave the hospital within 4 to 5 days after surgery if there are no problems.
In most cases, kids who have had VSD surgery recover quickly and without problems. But doctors will closely monitor the child for signs or symptoms of any problems.
Your child may undergo another echocardiogram to make sure that the heart defect has closed completely. If your child is having trouble breathing, call your doctor or go to the emergency department immediately.
Other symptoms that may 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 you notice any of these signs in your child after closure of the VSD.
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 a VSD corrected have a normal life expectancy and go on to live healthy, active lives.
Reviewed by: Steven B. Ritz, MD
Date reviewed: August 2010