Tetralogy of Fallot (ToF) is the most common cyanotic congenital heart defect, consisting of four anatomical abnormalities occurring together: a ventricular septal defect (VSD, a hole between the lower chambers), pulmonary stenosis (narrowing obstructing blood flow from the right ventricle to the lungs), right ventricular hypertrophy (thickening of the right ventricular muscle in response to the obstruction), and an overriding aorta (the aorta sits over the VSD, receiving blood from both ventricles rather than only the left).
The degree of pulmonary stenosis determines the clinical presentation. When obstruction is severe, deoxygenated blood from the right ventricle preferentially passes through the VSD into the overriding aorta, bypassing the lungs, causing significant cyanosis. In milder cases (the ‘pink Fallot’), flow may be left-to-right with less cyanosis. Infants with severe obstruction may suffer ‘tet spells’ (episodes of acute desaturation triggered by crying, feeding, or exertion) which can be dangerous.
Surgical repair is typically performed in the first six to twelve months of life, closing the VSD with a patch and relieving the right ventricular outflow tract obstruction. Since routine surgical correction was established, over 85% of surgically repaired patients now survive to age 30 and beyond.
Long-term follow-up in adult congenital heart disease (ACHD) services is essential. Most repaired ToF patients develop pulmonary regurgitation over time, causing progressive right ventricular dilation. Ventricular arrhythmias and sudden cardiac arrest are recognised long-term risks, making arrhythmia surveillance and timely pulmonary valve replacement important aspects of ongoing ACHD care.
« Back to Glossary Index