Tetralogy Of Fallot- A Congenital Heart Defect.

Tetralogy of Fallot (TOF) is a congenital heart disorder that is present at birth. The condition is caused by a combination of four heart defects hence the name tetralogy.

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)

These defects, cause oxygen-poor blood to flow out of the heart and to the rest of the body. Infants and children with tetralogy of Fallot usually have blue-tinged skin because their blood doesn't carry enough oxygen. It is classified as a cyanotic heart disease and is the most common form of cyanotic congenital heart disease.

Causes: 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 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.

Clinical Features: 

Tetralogy of Fallot symptoms vary, depending on the extent of obstruction of blood flow out of the right ventricle and into the lungs. 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 or exercise
• Loss of consciousness (fainting)
• Clubbing of fingers and toes — an abnormal, rounded shape of the nail bed
• Poor weight gain
• Tiring easily during play or exercise
• Irritability
• Prolonged crying
• A heart murmur

Tet spells: Sometimes, babies who have tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying or feeding, or when agitated. These episodes are called tet spells and are caused by a rapid drop in the amount of oxygen in the blood. Tet spells are most common in young infants, around 2 to 4 months old. Toddlers or older children might instinctively squat when they're short of breath. Squatting increases blood flow to the lungs.

Diagnosis: 

1. Chest X ray: Before more sophisticated techniques became available, chest x-ray was the definitive method of diagnosis. The abnormal boot-like appearance of a heart with tetralogy of Fallot is classically visible via chest x-ray,  ( see the picture given above) although most infants with tetralogy may not show this finding. Absence of interstitial lung markings are another classic finding in tetralogy.

2. Echocardiography: Congenital heart defects are now diagnosed with echocardiography, which is quick, involves no radiation, is very specific, and can be done prenatally.

3. 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.