Tetralogy of Fallot (TOF) is a cyanotic heart disease (a congenital heart defect that causes blood with lower oxygen levels to circulate in the body). It involves a combination of four cardiac anomalies: an enlarged aorta that is positioned directly above the VSD, a large ventricular septal defect (VSD), pulmonary stenosis (PS) and thickening of the wall of the right ventricle or right ventricular hypertrophy (RVH). These defects together cause oxygen-poor blood to flow to the rest of the body.
Rarer variations involve differences in the degree of PS from pulmonary atresia (PA; the pulmonary valve does not form properly and blood cannot flow from the right ventricle to the lungs) to absent pulmonary valve (the pulmonary valve did not form at all causing backflow of blood into the right ventricle).
Cyanosis, or a blue tinge of the skin, nail beds and lips is the earliest and most visible effect of TOF. It can be observed in infancy and oxygen levels in the body will depend on the amount of blood flow there is to the lungs. I don’t understand how the two sentences are related.
Pulmonary atresia or severe pulmonary stenosis causes more cyanosis than the less severe forms because of the decreased amount of blood that enters the lungs. Poor blood flow to the lungs causes the pulmonary artery branches (left and right lung vessels) to be smaller than normal.
Infants with an absent pulmonary valve have difficulty breathing. Unrestricted blood flow between the right ventricle and pulmonary arteries causes the main lung vessels to enlarge and physically compress the airways.
Infants can have sudden episodes of cyanosis after prolonged crying, feeding or when agitated. These are called “tet spells” and caused by a rapid drop in oxygen when they are agitated. They typically resolve when the infant or child calms down.
TOF can be detected during pregnancy when the fetus has an ultrasound of the heart. If undetected before birth, it is often diagnosed as a newborn when a murmur is heard on the infant’s chest, when cyanosis is observed and oxygen levels are lower than normal.
A chest xray can provide clues such as a decrease in the visibility of blood vessels in the lungs or a characteristic “boot-shape” of the heart. An ECG can show changes relating to the thickness of the right ventricle and other nonspecific signs. An echocardiogram can show details of the heart anatomy and confirm the diagnosis.
All children with TOF require surgical repair. The type and timing of repair will depend on the type of TOF and if there are any other associated heart defects. For the most common forms of TOF, full repair is typically done at 4-6 months of age.
In infants with pulmonary atresia or severe pulmonary stenosis, an intervention may be needed to provide enough blood flow to the lungs. This can be done by:
Regular and frequent cardiology visits are needed before complete repair for monitoring of any clinical changes and changes seen in their cardiac anatomy. Infants and children who experience tet spells may need medications to control the frequency and severity of tet spells, or may be candidates for earlier surgical repair.
Long term follow up is also needed to monitor for any changes as the child grows. Children can develop pulmonary stenosis or pulmonary regurgitation with time and may require additional interventions through cardiac catheterization or surgery.
Complete repair includes closure of the VSD with a patch, removal of any obstruction below the pulmonary valve and allowing good blood flow to the lungs by enlarging the area of the pulmonary valve or providing a tube to connect the right ventricle and the lung arteries.
TOF with absent pulmonary valve can require early repair within the first few days or weeks because of airway obstruction. The large main pulmonary arteries and branches are surgically made smaller to relieve compression of the airways.
Long term follow up is needed. Antibiotics before dental procedures (bacterial endocarditis prophylaxis) will be needed for at least 6 months after surgical repair or longer depending on the nature of repair and presence of residual cardiac defects. Your dentist would prescribe the antibiotics, when needed.
Heart rhythm issues (arrhythmias), or an increase in the size of the right ventricle may develop over time. Talk to your cardiologist about physical activity to review the risks.
The BC Children's Hospital Heart Hub is a clinically reliable and accurate online resource for patients and families living with congenital and acquired heart disease.
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