Tetralogy of Fallot is a congenital condition that affects the structure of the heart. Tetralogy of Fallot is characterized by the combination of four cardiac defects: (1) pulmonary valve stenosis, or narrowing of the pulmonary valve, (2) ventricular septal defect (VSD), (3) overriding aorta, which means that the main artery leading from the heart out to the body is shifted to the right, lying directly above the ventricular septal defect, allowing oxygen-rich (red) blood to mix with oxygen-poor (blue) blood in the lower chambers of the heart, and (4) right ventricular hypertrophy, meaning that the muscle of the right ventricle, or lower chamber of the heart, thickens due to over-pumping.
Tetralogy of Fallot is one of the most common congenital cardiac malformations, accounting for 5% to 10% of all congenital heart defects diagnosed in infants born alive. Tetralogy of Fallot has an incidence rate of 2 to 3 per 10,000 live births.
Tetralogy of Fallot is not a fatal condition, but the condition can be fatal, depending on the severity of the defects and the presence of any additional anomalies. Tetralogy of Fallot is associated with additional cardiac defects such as atrial septal defects (ASD) as well as the absence of the pulmonary valve, which occurs in 3-6% of cases.
Fetal karyotype testing is recommended following a diagnosis of Tetralogy of Fallot, as 12-50% of cases have an associated chromosomal abnormality, with trisomy 13, trisomy 18, and trisomy 21 (Down syndrome) being the most common. When chromosomal abnormalities are present, the risk of intrauterine fetal demise increases. Hydrops fetalis is also associated with tetralogy of fallot, and when this condition is present, the prognosis for tetralogy of fallot is poor.
The cause of tetralogy of fallot is unknown. The recurrence risk for tetralogy of fallot is 2.5% if one sibling has the condition, 8% if two siblings have the condition, 2.5% if the mother has the condition, and 1.5% if the father has the condition.