Tetralogy of Fallot

Tetralogy of Fallot (TOF) is a congenital heart defect that affects how blood flows through the heart. TOF involves four defects:

  1. Ventricular septal defect: A hole in the heart wall, between the heart’s two lower chambers (ventricles), allows oxygen-poor blood to mix with oxygen-rich blood.
  2. Pulmonary stenosis: The pulmonary valve guards blood flow from the heart to the lungs. When the valve is small as in TOF, it reduces blood flow to the lunges and deprives the body of oxygen. The heart then must work harder.
  3. Right ventricular hypertrophy: The muscle of the right ventricle thickens because the heart is working harder than usual due to the narrow pulmonary valve.
  4. Overriding aorta: In a healthy heart, the aorta (the largest artery in the body) connects to the left ventricle and delivers only oxygen-rich blood to the body. An overriding aorta is connected to the left and right ventricles, directly over the ventricular septal defect. This defect directs oxygen-poor blood into the aorta and to the body.


Tetralogy of Fallot Causes and Risk Factors

In most cases, TOF has no known cause. Doctors suspect that in some cases, changes to genes or chromosomes may cause this condition.

Children with chromosomal disorders such as DiGeorge syndrome or Down syndrome have a higher risk of developing TOF. Approximately 25% of babies with TOF have other birth defects not related to the heart.

Some factors that affect a mother during pregnancy also increase the risk of a baby developing TOF. These maternal risk factors include:

  • Alcohol use
  • Diabetes
  • Viral illness, such as rubella
  • Phenylketonuria (PKU), an inherited metabolic disorder
  • Poor prenatal nutrition
  • Pregnancy after age 40


Tetralogy of Fallot Symptoms

Tetralogy of Fallot symptoms vary and depend on the level of blood flow blockage to the lungs. Babies and children who have Tetralogy of Fallot experience episodes of cyanosis (lack of oxygen). Cyanosis is visible in the skin, lips and fingernails—these areas appear blueish on light skin and greyish on dark skin.

Other signs and symptoms may include:

  • Shortness of breath and rapid breathing, especially during feeding or exercise
  • Tiring easily during play or exercise
  • Heart murmur
  • Loss of consciousness (fainting)
  • Clubbed fingers and toes—an abnormal, rounded nail bed shape
  • Poor weight gain
  • Irritability
  • Prolonged crying
  • Tet spells—sudden cyanosis, breathing difficulties and restlessness while crying or feeding (most common in infants)


Tetralogy of Fallot Diagnosis

If your child experiences cyanosis or a heart murmur, the doctor may order additional tests to look for TOF. Diagnostic tests may include:

  • Echocardiogram
  • Fetal echocardiogram, for diagnosis during pregnancy
  • Chest X-ray
  • Newborn screening using pulse oximetry, which measures blood oxygen levels


Tetralogy of Fallot Treatment

Tetralogy of Fallot is a critical congenital heart defect, meaning children with this defect may need surgery soon after birth. Open-heart surgery is the only definitive treatment for TOF.

While the exact timing of the procedure depends on your child’s condition, doctors generally perform surgery when a child is 3 to 6 months old.

Some babies need immediate surgery after birth because of very low oxygen levels. Full surgical repair may not be possible for newborns, so surgeons can perform a procedure to temporarily improve oxygenation. Babies then can get the full repair when they are older and strong enough for the complex surgery.

Complete surgical repair of TOF includes:

  • Closing the hole between the pumping chambers of the heart
  • Relieving the obstruction to blood flow from the right side of the heart to the lungs
  • Widening or replacing the pulmonary valve when needed


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