Tetralogy of Fallot

 Rajat Das Gupta

Tetralogy of Fallot Overview

Tetralogy of Fallot is the most common heart defect in children. The condition causes mixing of oxygen-poor blood with the oxygen-rich blood being pumped out of the heart and into the circulatory system of blood vessels.

• The blood leaving the heart has less oxygen than is needed by the organs and tissues of the body, a condition called hypoxemia.
  
• Chronic (ongoing, long-term) lack of oxygen causes cyanosis, a bluish color of the skin, lips, and membranes inside the mouth and nose.

The normal heart works as follows:  

• The heart is made up of 4 chambers: 2 upper chambers called atria and 2 lower, largerchambers called ventricles. Each atrium is separated from its paired ventricle by a valve.
  
• The heart has a left 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 returning by veins (superior vena cava and inferior vena cava) from the body.
  
• The blood flows from the right atrium through the tricuspid valve into the right ventricle, which pumps it through the pulmonic valve into the pulmonary artery, the main artery to the lungs.
  
• In the lungs, the blood absorbs oxygen and then returns to the left atrium through the pulmonary veins.
  
• From the left atrium, the blood is pumped through the mitral valve to the left ventricle. The left ventricle pumps the blood out of the heart into the circulatory system via a large artery known as the aorta.
  
• The blood moves throughout the body, supplying oxygen and nutrients to organs and cells.
  
• Organs cannot work properly if they do not receive enough oxygen-rich blood.

The 4 abnormalities (tetralogy) of the heart described by Fallot include the following:

• Right ventricular hypertrophy: Narrowing or blockage of the pulmonaryvalve and/or muscle under the pulmonary valvecoming out of the right ventricle.This restriction to blood outflow causes an increase in right ventricular work and pressure, leading to right ventricular thickening or hypertrophy.
  
• Ventricular septal defect (VSD): This is a hole in the heart wall (septum) that separates the 2 ventricles. The hole is usually large and allows oxygen-poor blood in the right ventricle to pass through, mixing with oxygen-rich blood in the left ventricle. This poorly oxygenated blood is then pumped out of the left ventricle to the rest of the body. The body gets some oxygen, but not all that it needs. This lack of oxygen in the blood causes cyanosis.
  
• Abnormal position of the aorta: The aorta, the main artery carrying blood out of the heart and into the circulatory system, exits the heart from a position overriding the right and left ventricles. (In the normal heart, the aorta exits from the left ventricle.) This is not of major importance in infants.
  
• Pulmonary valve stenosis (PS): The major issue with tetralogy of Fallot is the degree of pulmonary valve stenosis, since VSD is always present. If the stenosis is mild, minimal cyanosis occurs, since blood still mostly travels to the lungs. However, if the PS is moderate to severe, a smaller amount of blood reaches the lungs, since most is shunted right-to-left through the VSD.Tetralogy of Fallot accounts for 10-15% of all congenital (newborn) heart defects. Infants with this abnormality develop signs of the condition very early in life.
  

  Tetralogy of Fallot Causes

  Tetralogy of Fallot occurs during development of the fetus, before birth, and is therefore termed a congenital birth defect. An error occurs as the fetal heart separates into the chambers, valves, and other structures that make up the normal human heart. No one is really sure why this error occurs.
  

  Tetralogy of Fallot Symptoms

  Most infants with tetralogy of Fallot develop cyanosis in the first year of life.
• The skin, lips, and mucous membranes inside the mouth and nose take on a noticeably dusky blue color.
  
• Only some infants with very severe obstruction of the right ventricle outflow turn blue at birth.
  
• A small number of children with tetralogy of Fallot never turn blue at all, especially if the pulmonary stenosis is mild, the ventricular septal defect is small, or both.
  
• In some children, the cyanosis is quite subtle and may go undetected for some time.

The following symptoms suggest tetralogy of Fallot:

• Growth and development are slower, especially if the pulmonary stenosis is severe. Puberty may be delayed if the tetralogy is untreated.
  
• The child usually tires easily and begins panting with any form of exertion. He or she may play for only a short time before sitting or lying down.
  
• Once able to walk, the child often assumes a squatting position to catch his or her breath and then resumes physical activity. Squatting increases the pressure transiently in the aorta and left ventricle, causing less blood to move into the left ventricle, more out the pulmonary artery to the lungs.

Episodes of extreme blue coloring (called hypercyanosis or simply "tet spells") occur in many children, usually in the first 2-3 years of life.

• The child suddenly becomes blue, has difficulty breathing, and may become extremely irritable or even faint.
  
• Up to 20-70% of children with tetralogy of Fallot experience these spells.
  
• The spells often happen during feeding, crying, straining, or on awakening in the morning.
  
• Spells can last from a few minutes to a few hours.

  When to Seek Medical Care

  Sometimes tetralogy of Fallot goes undiagnosed for several months to a year. Diagnosing conditions such as tetralogy of Fallot is one of the goals of routine checkups with your doctor. Take your child to his or her health care provider if the child develops a bluish color, has breathing difficulties, seizures, fainting, fatigue, slow growth, or developmental delay. A medical professional should establish the cause of these problems.
  If you cannot reach your child's health care provider or if the child develops any of the following symptoms, take the child to a hospital emergency department right away:
• Bluish discoloration
  
• Trouble breathing
  
• Seizures
  
• Fainting
  
• Extreme fatigue or weakness

  Exams and Tests

  Even if the bluish color and other symptoms have resolved by the time the child reaches medical attention, the health care provider will immediately suspect a heart problem. Medical tests will focus on identifying the cause of the cyanosis.
• Lab tests: The red blood cell count and hemoglobin may be elevated as the body attempts to compensate for the lack of oxygen to the tissues.
  
• Electrocardiogram (ECG): This painless, quick test measures and records the electrical activity of the heart. Structural abnormalities of the heart usually produce abnormal recordings on ECG. In tetralogy of Fallot,right ventricular hypertrophy is almost always present.
  
• Chest x-ray imaging: This image may demonstrate the classic "boot-shaped heart." This occurs because the right ventricle is enlarged. It also may show an abnormal aorta.
  
• Echocardiography: This imaging test is key. It will demonstrate the ventricular septal defect or large hole between the left and right ventricles, the degree of pulmonary stenosis, and it will reveal other unanticipated defects.Many patients do not need cardiac catheterization if the clinical, ECG, and echocardiogram findings are routine and as expected.
  
• Cardiac catheterization: This is an invasive procedure accomplished by a cardiologist in a special laboratory with the patient under local anesthesia. This procedure was done on all patients with suspected tetralogy prior to echocardiography, since it was the only procedure that could be used to confirm the diagnosis. If needed, a small tube (catheter) is inserted through the skin into a blood vessel (usually in the groin) andadvanced up the inferior vena cavainto the heart. An x-ray imageis taken while a small amount of dye is infused. The dye helps highlightthe ventricular septal defect, pulmonary stenosis, overriding aorta, and the size of the pulmonary arteries.

  Medical Treatment

  Surgery is the primary way to correct the heart problem. Your child may be prescribed medication for tet spells. You will also be given information for dealing with future tet spells.
  
• The child will be placed on his or her back in the knee-to-chest position to increaseaortic resistance. The increased aortic and left ventricular pressure reduces the rush of blood through the septal hole from the right ventricle and improves blood circulation to the lungs, so more red blood reaches the tissues.
  
• The child may be given oxygen through a face mask to increase the amount of oxygen in the blood.
  
• The child may be given morphine, propranolol (or metoprolol), or, in extreme cases, phenylephrine (Alconefrin, Vicks Sinex). These medications decrease the frequency and severity of tet spells.

  Surgery

  The Blalock-Taussig operation: Apalliative procedure performed in smaller infants to increase blood flow to the lungs. This allows the child to grow big enough to have complete surgical repair.
  A connection is made between one of the majorarteries of the body, usually the right subclavian artery,and the right pulmonary artery, which increases the amount of red oxygenated blood reaching the lungs, relieving cyanosis with dramatic relief of the patient's symptoms.
  Total correction: The hole in the ventricular septum (between the ventricles) is closed with a patch and the obstruction to right ventricular outflow, pulmonic stenosis, isopened. These corrections allow blood flow to the lungs for oxygenation before being pumped out into the body.
  The timing of the operation depends on symptoms. Surgery usually is performed within the first 2 years of life. Operative mortality rates have dramatically dropped over the last 20 years. Still, about 1-5% of children who undergo complete correction die during or immediately after the procedure, secondary to other additional defects in the body and/or heart, and the heart lung bypass procedure itself.
  

  Follow-up

  Your health care provider should schedule regular follow-up visits for your child. At these visits, the child should be checked for abnormal heart rhythms, which may develop in children who have undergone surgical correction for tetralogy of Fallot.
  

  Outlook

  After successful surgery, children generally don't have any symptoms and lead normal lives with few, if any, restrictions. However, the surgery itself may have somelong-term complications. These include the following:
  
• Right ventricular failure: Right ventricular failure is possible, especially if surgery created severe pulmonary valve insufficiency, that is regurgitation of blood backwards from the pulmonary artery into the right ventricle.
  
• Electrical conduction abnormalities: Every patient with tetralogy of Fallot has right bundle branchblock secondary to the congenital ventricular septaldefect. But sewing the patch into the ventricular septum can create heart block or failure of the upper atria to conduct/communicate with the lower ventricles. Apermanent pacemaker is occasionally needed.
  
• Arrhythmias: Because of surgery on the ventricles, postoperative ventricular tachycardia (VT) is an infrequent risk. This is a life-threatening arrhythmia, so follow-up detection of risk for ventricular tachycardia is important.
  
• Residual hole in the ventricular septum: This is also possible, with oxygenated blood passing from the left side of the heart to the right (shunting).