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.
From Nemours' KidsHealth
- Cardiac Catheterization
- ECG (Electrocardiogram)
- If Your Child Has a Heart Defect
- Atrial Septal Defect
- When Your Child Needs a Heart Transplant
- Heart Murmurs
- Patent Ductus Arteriosus (PDA)
- Coarctation of the Aorta
- Congenital Heart Defects
- Ventricular Septal Defect
- Tetralogy of Fallot
- A to Z: Atrial Flutter
- A to Z: Hypoplastic Left Heart Syndrome
- A to Z: Patent Ductus Arteriosus (PDA)
- A to Z: Tetralogy of Fallot
- Heart and Circulatory System
- Congenital Heart Defects Special Needs Factsheet
Trusted External Resources
It's normal to be nervous about a procedure that involves your child's heart. But cardiac catheterizations are usually no cause for alarm. These procedures are often successful in kids and teens and carry a very low risk of complications.
Kids are usually released from the hospital the very same day and can resume most regular activities within a week.
About Cardiac Catheterizations
Cardiac catheterizations help doctors perform diagnostic tests on the heart and its blood vessels, and even treat some heart conditions. During the procedure, doctors put a long, thin tube (catheter) into a blood vessel and thread it through blood vessels to the heart. Once the catheter is in place, doctors can use instruments to see into the heart and its chambers (via X-ray) and perform certain procedures.
Often, a cardiac catheterization can make open-heart surgery unnecessary, although for more serious heart problems, it's common for cardiac catheterization to be done in addition to open-heart surgical procedures.
Cardiac catheterization is what is called an invasive procedure, meaning it involves going into the body through the skin. However, it is a minimally invasive procedure and is not considered "open" surgery since it's performed without making any large incisions. Usually the only sign that a person has had the procedure is a small puncture hole where the catheter was inserted, usually in the groin area, but sometimes in the arm or neck.
Diagnostic Tests & Treatments
By performing a cardiac catheterization for diagnostic purposes, a doctor can:
- obtain a sample of heart tissue (biopsy)
- evaluate congenital heart defects (those that are present from birth)
- measure the blood pressure inside the heart
- measure the amount of oxygen in the heart
- check for problems with heart valves
- locate narrowed or blocked blood vessels
- determine the need for further treatment or surgery
A number of treatments for heart conditions can be performed during a cardiac catheterization. These include:
- closing holes in the heart that are the result of a congenital defect
- repairing leaky or narrow heart valves
- treating an irregular heartbeat (arrhythmia) by destroying the abnormal heart tissue that's causing the heart to beat irregularly
- removing blood clots
- inflating tiny balloons in obstructed blood vessels or heart valves to increase blood flow (angioplasties or valvuloplasties)
- placing wire devices (stents) in narrowed blood vessels to help keep them open
Cardiac catheterizations are generally safe procedures, particularly in comparison with open-heart surgery. Although complications are rare, any procedure that involves the heart and blood vessels does carry risks, such as:
- bruising or bleeding at the site where the catheter is inserted
- an allergic reaction to the medications or contrast material used during the procedure. Contrast material is a special dye put into the blood vessels that helps doctors see the vessels, valves, and chambers of the heart more clearly.
- skin reactions (similar to a sunburn) from exposure to X-rays
- chest pain
- blood clots
- heart attack, stroke, or kidney damage
Your doctor will discuss these risks with you and your child before the procedure is performed.
Preparing for the Procedure
Before the procedure, the doctor will perform a number of diagnostic tests, including an echocardiogram (ECHO), which uses sound waves to create a picture of the heart. The doctor also might do an electrocardiogram (EKG or ECG) to record the electrical activity of the heart. In rare cases, the doctor might call for a cardiac magnetic resonance imaging (MRI) scan or a CAT scan.
Before the procedure, make sure you discuss any allergies your child has with the doctor, particularly if they involve contrast material, iodine, seafood, latex, or rubber products. Also discuss any medications your child takes. The doctor might have your child stop taking medications or adjust the doses for a few days before the procedure. Bring a list of your child's medications and dosages with you to the hospital.
Your child will be instructed not to eat or drink anything for about 8–12 hours before the procedure. Having something in the stomach can increase the risk of complications from anesthesia. After the procedure, your child will be able to eat and drink.
When it's time to go to the hospital, have your child wear comfortable clothes and remove any jewelry, especially necklaces that may interfere with the pictures to be taken of the heart. At check-in, your child's blood pressure and pulse will be recorded. It's important to keep your child relaxed and distracted at this point so that the heart beats at a normal rate.
If there's a possibility that your child may have to stay in the hospital after the procedure, bring toiletries and any other items that can make the stay more comfortable.
The cardiac catheterization will be performed by a pediatric cardiologist in a catheterization lab. The lab has special X-ray and imaging machines not found in normal operating rooms.
A team of doctors and nurses will be on hand to make sure your child is comfortable and the procedure goes smoothly. In the lab, your child will lie on a small table surrounded by heart monitors and other equipment. The room is kept cool to protect this sensitive equipment, so your child may be offered blankets to keep warm.
First, an intravenous (IV) line will be inserted into your child's arm to deliver medications and fluids during the procedure. A sedative will be given to help your child relax and sleep. Small, sticky patches called electrodes will be placed on the chest; these are attached to an electrocardiograph (ECG) monitor, which will monitor the heartbeat during the procedure.
A nurse will clean and possibly shave the area where the catheter will be inserted, and your child will be given an injection of a local anesthetic (a drug that numbs only a small, specific part of the body, like a hand or patch of skin). Once the area is numb, a plastic sheath (a short, hollow tube used to guide the catheter into the blood vessel) will be inserted into the groin or arm, and then the catheter will follow.
The cardiologist will use X-rays to help guide the catheter as it moves up the blood vessels toward your child's heart. When the catheter is in place, a small amount of contrast material will be injected into the blood vessels and heart.
X-rays will be taken of the heart and if your child needs a treatment (like a valve repair or angioplasty), it will be performed at this time.
After the cardiac catheterization is finished, the catheter will be removed and the site where it was inserted will be bandaged. Your child will recover for several hours while the nursing staff monitors his or her progress. If the catheter was inserted into the groin, your child will need to keep the affected leg straight for a few hours after the procedure to minimize the chances of bleeding at the catheterization site.
If you have a long drive home, stop every hour and have your child walk for 5-10 minutes. If you'll be on a plane, have your child stretch his or her legs and walk in the aisle at least once an hour.
The day after the catheterization, your child may remove the bandage. This is easily done by getting it wet in the shower and taking it off. Once the area is dry, replace the bandage with a small adhesive bandage. It's normal for the site to be bruised, red, or slightly swollen for a couple of days after the procedure.
Have your child gently wash the site with soap and water at least once a day, but he or she should avoid baths, hot tubs, and swimming for 1 week after the catheterization. Don't use any creams, lotions, or ointments on the area.
The doctor will tell you when it's safe for your child to resume activities. In general, your child can expect to feel tired and weak the day after the procedure and will need to take it easy for the first couple of days. This means no heavy lifting (more than 10 pounds) and no sports. After about a week, your child probably will get the go-ahead to return to all normal activities./p>
Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: September 05, 2017