What is the pathophysiology of tetralogy of Fallot (TOF) in children?

Updated: Nov 13, 2018
  • Author: Shabir Bhimji, MD, PhD; Chief Editor: Yasmine S Ali, MD, FACC, FACP, MSCI  more...
  • Print

The cause(s) of most congenital heart diseases (CHDs) are unknown, although genetic studies suggest a multifactorial etiology. Methylene tetrahydrofolate reductase (MTHFR) gene polymorphism may be a susceptibility gene for tetralogy of Fallot (TOF). [11, 12]  More recently, it appears that VEGF genetic polymorphisms, -2578C>A and -634C>G, may be associated with an increased risk for tetralogy of Fallot, whereas the risk is potentially reduced with 936C>T polymorphism. [13]

Prenatal factors associated with a higher incidence of tetralogy of Fallot include maternal rubella (or other viral illnesses) during pregnancy, poor prenatal nutrition, maternal alcohol use, maternal age older than 40 years, maternal phenylketonuria (PKU) birth defects, and diabetes. Children with Down syndrome also have a higher incidence of tetralogy of Fallot, as do infants with fetal hydantoin syndrome or fetal carbamazepine syndrome.

In addition, as one of the conotruncal malformations, tetralogy of Fallot can be associated with a spectrum of lesions known as CATCH 22 (cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, hypocalcemia). Cytogenetic analysis may demonstrate deletions of a segment of chromosome band 22q11 (DiGeorge critical region). Ablation of cells of the neural crest has been shown to reproduce conotruncal malformations.

These abnormalities are associated with the DiGeorge syndrome and branchial arch abnormalities.

The hemodynamics of tetralogy of Fallot depend on the degree of right ventricular (RV) outflow tract obstruction (RVOTO). The ventricular septal defect (VSD) is usually nonrestrictive, and the RV and left ventricular (LV) pressures are equalized. If the obstruction is severe, the intracardiac shunt is from right to left, and pulmonary blood flow may be markedly diminished. In this instance, blood flow may depend on the patent ductus arteriosus (PDA) or bronchial collaterals.

Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!