Definition of Tetralogy of Fallot:

Tetralogy of Fallot refers to a group of four types of heart defects present at birth (congenital).

Causes, incidence, and risk factors:

Tetralogy of Fallot is classified as a cyanotic heart defect because the condition causes low oxygen levels in the blood, which leads to cyanosis (a bluish-purple coloration to the skin).

The classic form of Tetralogy includes 4 defects within the heart structures:

• Ventricular septal defect (hole between the right and left ventricles)
• Narrowing of the pulmonary outflow tract (tube that connects the heart with the lungs)
• An aorta (tube that carries oxygenated blood to the body) that grows from both ventricles, rather than exclusively from the left ventricle
• A thickened muscular wall of the right ventricle (right ventricular hypertrophy)

At birth, infants may not show the signs of the cyanosis, but later may develop sudden frightening episodes (called "Tet spells") of bluish skin from crying or feeding.

Tetralogy of Fallot is considered rare. Patients with tetraology of Fallot have a higher incidence of major non-heart congenital defects.

The cause of most congenital heart defects is unknown. Multiple factors seem to be involved. Prenatal factors associated with higher than normal risk for this condition include maternal rubella or other viral illnesses during pregnancy, poor prenatal nutrition, maternal alcoholism, mother over 40 years old, and diabetes.

There is a high incidence of chromosomal disorders in children with tetralogy of Fallot, such as Down syndrome and Di George's syndrome (a partial gene deletion that results in heart defects, low calcium levels, and immune deficiency.)