Brief Summary of Tetralogy of Fallot- A Congenital Heart Disorder

Tetralogy of Fallot is a cyanotic congenital heart disorder which is defined by the following four defects

1. Ventricular septal defect (hole between the right and left ventricles)
2. Narrowing of the pulmonary outflow tract (the valve and artery that connect the heart with the lungs)
3. Overriding aorta (the artery that carries oxygen-rich blood to the body) that is shifted over the right ventricle and ventricular septal defect, instead of coming out only from the left ventricle
4. Thickened wall of the right ventricle (right ventricular hypertrophy)

Tetralogy of Fallot is rare, but it is the most common form of cyanotic congenital heart disease. Patients with tetraology of Fallot are more likely to also have other congenital defects.

Historical Information
Louis Arthur Fallot, after whom the name tetralogy of Fallot is derived, was not the first person to recognize the condition. Stensen first described it in 1672; however, it was Fallot who first accurately described the clinical and complete pathologic features of the defects.

Etiology
The cause(s) of most congenital heart diseases (CHDs) are unknown, although genetic studies suggest a multifactorial etiology.

Prenatal factors associated with a higher incidence of tetralogy of Fallot (TOF) 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.

Pathology
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.

Clinical Presentation
The clinical features of tetralogy of Fallot (TOF) are directly related to the severity of the anatomic defects.

Signs and symptoms may include:

• A bluish coloration of the skin caused by blood low in oxygen (cyanosis)
• Shortness of breath and rapid breathing, especially during feeding
• Loss of consciousness (fainting)
• Clubbing of fingers and toes — an abnormal, rounded shape of the nail bed
• Poor weight gain
• Tiring easily during play
• Irritability
• Prolonged crying
• A heart murmur

Tet spells
Sometimes, babies with tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying, feeding, having a bowel movement, or kicking his or her legs upon awakening. These episodes are called Tet spells and are caused by a rapid drop in the amount of oxygen in the blood. Toddlers or older children may instinctively squat when they are short of breath. Squatting increases blood flow to the lungs. Tet spells are more common in young infants, around 2 to 4 months old.

Diagnosis
Before more sophisticated techniques became available, chest x-ray was the definitive method of diagnosis. Congenital heart defects are now diagnosed with echocardiography, which is quick, involves no radiation, is very specific, and can be done prenatally.

The abnormal boot-like appearance of a heart with tetralogy of Fallot is classically visible via chest x-ray, although most infants with tetralogy may not show this finding. Absence of interstitial lung markings are another classic finding in tetralogy.

Other tests may include

• Complete blood count (CBC)
• Electrocardiogram (EKG)
• MRI of the heart (generally after surgery)

Treatment

Surgery is the only effective treatment for tetralogy of Fallot.

The primary role of medical therapy is in preparation for surgery. Most infants have adequate saturations and usually undergo elective repair.

The timing of complete surgical repair is dependent on numerous variables, including symptoms and any associated lesions (eg, multiple ventricular septal defect [VSD], pulmonary atresia).

Currently, the trend is to perform a complete surgical procedure (often electively) before the age of 1 year and preferably by the age of 2 years.

Sometimes more than one surgery is needed. When more than one surgery is used, the first surgery is done to help increase blood flow to the lungs.

Surgery to correct the problem may be done at a later time. Often only one corrective surgery is performed in the first few months of life. Corrective surgery is done to widen part of the narrowed pulmonary tract and close the ventricular septal defect.

Prognosis
Most cases can be corrected with surgery. Babies who have surgery usually do well. More than 90% survive to adulthood and live active, healthy, and productive lives. Without surgery, death usually occurs by the time the person reaches age 20.