Tetralogy of Fallot

Tetralogy of Fallot occurs in about 400 out of a million live births. This congenital heart defect causes a mixture of oxygen-poor blood and oxygen-rich blood, which is then pumped out of the heart into the circulatory system of the blood vessels.

The blood leaving the heart contains less oxygen than the organs and tissues need, this condition is called hypoxemia.
Chronic (permanent, prolonged) lack of oxygen causes cyanosis, a bluish color of the skin, lips and mucous membranes of the mouth and nose.

A normal heart works like this:

The heart has 4 chambers: 2 upper chambers called atria and 2 large lower chambers called ventricles. Each atrium is separated from the paired ventricle by a valve.
The heart has a left side and a right side. The left and right sides of the heart are separated by a septum (wall). The right side of the heart receives oxygen-depleted or blue blood, which is returned through the veins (superior vena cava and inferior vena cava) from the body.
Blood flows from the right atrium through the tricuspid valve into the right ventricle, which pumps it through the pulmonary valve into the pulmonary artery, the main artery of the lungs.
In the lungs, blood absorbs oxygen and then returns to the left atrium through the pulmonary veins.
From the left atrium, blood is pumped through the mitral valve into the left ventricle. The left ventricle pumps blood from the heart to the circulatory system through a large artery known as the aorta.
Blood moves throughout the body, delivering oxygen and nutrients to organs and cells.
Organs cannot function properly if they do not receive enough oxygen-rich blood.

The four anomalies (tetralogies) of the heart described by Fallot are as follows:

Right ventricular hypertrophy: Right ventricular thickening or hypertrophy occurs in response to narrowing or obstruction at or below the pulmonic valve due to increased right ventricular work and pressure.
Ventricular septal defect: This is a hole in the wall of the heart (septum) that separates the 2 ventricles. The orifice is usually large and allows oxygen-poor blood into the right ventricle, mixing with oxygen-rich blood in the left ventricle. This poorly oxygenated blood is then pumped from the left ventricle to the rest of the body. The body gets some oxygen, but not all it needs. The lack of oxygen in the blood causes cyanosis.
Abnormal position of the aorta: the aorta, the main artery that carries blood from the heart to the circulatory system, exits the heart from a position that spans the right and left ventricles. (In a normal heart, the aorta emerges from the left ventricle.)
Pulmonary valve stenosis: The main concern with tetralogy of Fallot is the severity of pulmonic valve stenosis, since interventricular communication is always present. If the stenosis is mild, minimal cyanosis occurs because oxygen-poor blood from the right ventricle can pass through the pulmonic valve into the lungs, and less blood passes through the ventricular septal defect. However, if PS is moderate to severe, less blood reaches the lungs because more of it is shunted from right to left through a ventricular septal defect.

Tetralogy of Fallot accounts for 10-15% of all congenital heart defects (newborns). Infants with this anomaly show signs of the disease very early in life.

Causes of tetrology of Fallot

Tetralogy of Fallot occurs during fetal development, before birth, which is why it is called a congenital malformation. The error occurs when the fetal heart separates into the chambers, valves, and other structures that make up a normal human heart. Nobody really knows why this is happening.

Tetrology of Fallot's symptoms

Most children with tetralogy of Fallot develop cyanosis during the first year of life.

The skin, lips and mucous membranes of the mouth and nose become noticeably dark blue.
Only some babies with very severe right ventricular outflow obstruction turn blue at birth.
A small number of children with Fallot's tetralogy never have blue at all, especially if the pulmonary stenosis is minor, the ventricular septal defect is small, or both.
In some children, cyanosis is barely noticeable and may go unnoticed for some time.

The following symptoms are indicative of Fallot's tetrad:

Growth and development are slowed down, especially in severe pulmonary stenosis. Puberty may be delayed if the tetrad is not treated.
The child usually gets tired quickly and begins to suffocate with any effort. He or she can only play for a short time before sitting or lying down.
After walking, the child often squats down to catch his breath and then resumes physical activity. Squatting briefly increases pressure in the aorta and left ventricle, causing less blood to flow through the left ventricle and more from the pulmonary artery to the lungs.

Episodes of extreme blue coloration occur in many children, usually during the first 2-3 years of life.

The child suddenly turns blue, has difficulty breathing, may become very irritable or even pass out.
Between 20% and 70% of children with Fallot's tetrad experience these seizures.
Attacks often occur during feeding, crying, straining or when waking up in the morning.
Spells can last from several minutes to several hours.

When to seek medical care

Sometimes Fallot's tetrad remains undiagnosed for several months to a year. Diagnosing conditions such as Fallot's tetrad is one of the goals of routine checkups with a doctor. Take your child to the doctor if the child develops a bluish color, difficulty breathing, seizures, fainting, fatigue, slow growth, or developmental delay. The healthcare professional must determine the cause of these problems.

If you are unable to contact your child's primary care physician, or if the child develops any of the following symptoms, take the child to a hospital emergency room immediately:

Bluish discoloration
Trouble breathing
Seizures
Fainting
Extreme fatigue or weakness

Exams and tests

Even if the bluish color and other symptoms have disappeared by the time the child seeks medical help, the doctor will immediately suspect a heart problem. Medical tests will focus on identifying the cause of the cyanosis.

Lab tests: Red blood cell and hemoglobin counts may be elevated as the body tries to compensate for the lack of oxygen in the tissues.
Electrocardiogram: This quick and painless test measures and records the electrical activity of the heart. Structural abnormalities of the heart usually cause abnormal electrocardiogram recordings. With tetralogy of Fallot, right ventricular hypertrophy is almost always present.
Chest x-ray: this picture may show the classic "boot-shaped heart". This is due to the enlargement of the right ventricle. It may also show an abnormal aorta.
Echocardiography: This imaging study is essential. It will demonstrate a ventricular septal defect or a large opening between the left and right ventricles, the degree of pulmonary stenosis, and identify other unexpected defects. Many patients do not require cardiac catheterization if the clinical, electrocardiographic, and echocardiographic findings are general and consistent with expectations.
Cardiac catheterization: This is an invasive procedure performed by a cardiologist in a specialized laboratory with the patient under local or general anesthesia. This procedure was performed in all patients with suspected tetrad before echocardiography, as this was the only procedure that could be used to confirm the diagnosis. If necessary, a small tube (catheter) is inserted through the skin into a blood vessel (usually in the groin) and passed through the inferior vena cava to the heart. During the introduction of a small amount of dye, an x-ray is taken. The dye helps highlight the ventricular septal defect, pulmonary artery stenosis, aortic occlusion, and the size of the pulmonary arteries.

Treatment of tetralogy of Fallot

Medical treatment

Surgery is the main way to correct heart problems. Your child may be prescribed medication for tet periods. You will also receive information about future tet spells.

The child is placed on his back in a knee-chest position to increase aortic resistance. Increased pressure in the aorta and left ventricle reduces blood flow through the hole in the interventricular septum of the right ventricle and improves blood flow to the lungs, so more red blood is delivered to the tissues.
The child can receive oxygen through a face mask to increase the amount of oxygen in the blood.
The child can be given morphine, propranolol (or metoprolol) or, in extreme cases, phenylephrine. These drugs reduce the frequency and severity of tet episodes.

Surgery

Blalock-Taussig operation: a palliative procedure performed on young children to increase blood flow to the lungs. This allows the child to grow tall enough to undergo a complete surgical repair.

A connection is established between one of the major arteries in the body, usually the right subclavian artery, and the right pulmonary artery, which increases the amount of red oxygenated blood reaching the lungs, reducing cyanosis and drastically alleviating the patient's symptoms.

Total correction: the hole in the interventricular septum (between the ventricles) is closed with a patch and obstruction of the right ventricular outlet, pulmonary stenosis, is opened. These patches allow blood to flow through the lungs to be oxygenated and then pumped throughout the body.

The timing of the operation depends on the symptoms. Surgery is usually performed within the first 2 years of life. The operating mortality rate has dropped dramatically over the past 20 years. However, approximately 1% to 5% of children who undergo complete correction die during or immediately after the procedure due to other additional defects in the body and/or heart, as well as due to the cardiopulmonary bypass procedure itself.

Next steps

Your doctor should schedule regular follow-up visits for your child. During these visits, the child should be checked for cardiac arrhythmias that may develop in children who have undergone surgical correction of Fallot's tetrad.

After successful surgery, children are usually asymptomatic and lead normal lives with few or no restrictions. However, the surgery itself can have long-term complications. These include, in particular, the following:

Right ventricular failure: Right ventricular failure is possible, especially if surgery has caused severe pulmonary valve insufficiency, in which blood leaks backward from the pulmonary artery into the right ventricle.
Electrical conduction anomalies: Any patient with Fallot's tetrad develops right bundle branch block secondary to congenital interventricular communication. But suturing a patch to the ventricular septum can cause heart block or an inability of the upper atria to conduct/communicate with the lower ventricles. Sometimes a permanent pacemaker is needed.
Arrhythmias: Due to ventricular surgery, postoperative ventricular tachycardia is a rare risk. This is a life-threatening arrhythmia, so it is important to control the risk of ventricular tachycardia.
Residual hole in the interventricular septum: This is also possible when oxygenated blood passes from the left side of the heart to the right side.