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What Are the 4 Defects in the Tetralogy of Fallot?

Tetralogy of Fallot or TOF is a congenital heart defect that affects the normal flow of blood in the heart.

Tetralogy of Fallot or TOF is a congenital (present since birth) heart defect that affects the normal flow of blood in the heart. According to the Centers for Disease Control and Prevention (CDC), around 1660 babies are born with this condition each year in the United States. Tetralogy of Fallot involves a defect in the heart structure that arises while the baby is still in the mother’s womb. The condition is characterized by the presence of four main defects in the structure of the heart:

  • Ventricular septal defect: The heart has two upper chambers called atria and two lower chambers called the ventricles. The ventricles, right and left, are separated from each other by a partition called the interventricular septum. Ventricular septal defect or VSD refers to a defect or hole in the interventricular septum.
  • Pulmonary stenosis: The pulmonary artery is the blood vessel that takes blood from the heart to the lungs for oxygenation. It is guarded by the pulmonary valve. An abnormal narrowing or obstruction in the pulmonary valve and the main pulmonary artery is called pulmonary stenosis.
  • Overriding aorta: The aorta is the large blood vessel carrying the oxygen-rich blood from the heart to the body. It normally arises from the left ventricle. Overriding of the aorta means the aorta is situated abnormally. Such aorta arises above both the ventricles instead of just the left ventricle.
  • Right ventricular hypertrophy: The abnormal thickening of the wall of the right ventricle is called right ventricular hypertrophy or RVH.

What are the symptoms of the tetralogy of Fallot?

The symptoms of tetralogy of Fallot may appear soon after birth or within the first year of life. The severity of symptoms may vary depending on the extent of the structural defects. The symptoms generally include:

  • Cyanosis or bluish discoloration of the skin: It gets worse when the baby is crying or being fed (also known as a tet spell). Cyanosis is the most common symptom of TOF.
  • Clubbing of fingers: This is a condition where the skin or bone around the fingernails becomes broad or rounded.
  • Poor feeding habits: The baby is unable to suckle to the breast. The effort is too much for the baby.
  • Poor weight gain or failure to gain weight
  • Fainting episodes while playing
  • Delayed milestones
  • Easy fatiguability
  • Irritability
  • Difficulty in breathing
  • Repeated flu infections and chest congestion
  • Convulsions in a baby

What causes the tetralogy of Fallot?

The cause of tetralogy of Fallot is not known in most cases. Certain conditions may increase the risk of having tetralogy of Fallot. They include:

  • Certain genetic conditions in the baby, such as Down syndrome, DiGeorge syndrome, and Alagille syndrome
  • A history of alcoholism in the mother
  • Presence of certain infections, such as rubella virus infection, during pregnancy
  • Advanced maternal age (pregnancy in women aged older than 40 years)
  • Maternal diabetes
  • Certain medication taken during pregnancy
  • Poor nutrition during pregnancy
  • One of the parents having tetralogy of Fallot

How is the tetralogy of Fallot treated?

Tetralogy of Fallot is a type of critical congenital heart disease. Most babies require major surgery or other procedures soon after the birth. Most surgeries are done before the baby turns 6 months of age. The surgery involves widening or replacing the stenosed pulmonary valve and enlarging the lumen (inner diameter) of the pulmonary artery. The surgeon also repairs the ventricular septal defect with a patch. The outcome of most surgeries done for TOF is good. A regular follow-up with a cardiologist is necessary after the surgery. The individuals do well but have exercise restrictions all their life.


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Medically Reviewed on 2/11/2021


Centers for Disease Control and Prevention. Facts about Tetralogy of Fallot.

Mancini MC. Tetralogy of Fallot. National Organization for Rare Disorders (NORD).,right%20and%20left%20ventricles%20(dextroposition

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