Tetralogy of Fallot (TOF) is a complex congenital heart defect. It is one of the most common anomalies of heart present at birth.

These are the eight things you should know about this disease:

#1. Tetralogy of Fallot is a group of heart abnormalities that you are born with.

Classically there are four defects :

• Pulmonary stenosis, narrowing of the exit from the right ventricle
• Ventricular septal defect, a hole between the two ventricles
• Right ventricular hypertrophy, thickening of the right ventricular muscle
• An overriding aorta, which allows blood from both ventricles to enter the aorta.

Other defects like Atrial septal defect and Right aortic arch are also present occasionally.

#2. TOF is a cyanotic heart defect.

A cyanotic heart defect is a type of congenital heart anomaly that occurs due to deoxygenated blood bypassing the lungs and entering the systemic circulation or a mixture of oxygenated and deoxygenated blood entering the systemic circulation. It is caused by structural defects of the heart. TOF is one of such structural defects.

#3. "Tet-spell" is a tell-tale sign of TOF.

In most cases of tetralogy of Fallot, the defect is severe enough at birth that lack of oxygen causes a bluish tint, called cyanosis, to develop in a baby’s skin, lips, and fingernails. The bluish tint occurs because the oxygen level in the blood leaving the heart is below normal.

When affected babies cry or have a bowel movement, they may develop a "tet spell" where they turn very blue, have difficulty breathing, become limp, and occasionally lose consciousness. Cyanosis usually gets progressively worse over the first few weeks of life, and TOF usually is diagnosed quite early, although it can go undiagnosed for a few months or even up to several years.

Other clinical manifestations may include a heart murmur (ejection systolic murmur), finger clubbing, failure to thrive, and shortness of breath.

#4. The cause of the disease is unknown.

What really causes TOF is not known. It is thought to be due to environmental or genetic factors or a combination. It is associated with chromosome 22 deletions and DiGeorge syndrome.

Risk factors include a mother who uses alcohol, has diabetes, has age above 40, or gets rubella during pregnancy. It may also be associated with Down's syndrome.

#5. TOF is diagnosed by Echocardiography.

Nowadays, all congenital heart defects are diagnosed with echocardiography. More commonly known as the "Echo", this diagnostic tool is actually a sonogram of the heart. It is quick, accurate, and involves no radiation. Tetralogy of Fallot can also be diagnosed prenatally, with fetal echocardiograms.

Before cardiac echo became a gold-standard, chest x-ray was the first investigation of choice. In TOF, a boot-shaped heart is classically seen on CXR, although most infants with tetralogy may not show this finding. Other classic findings in TOF patients are the absence of interstitial lung markings secondary to pulmonary oligaemia, as is the pulmonary bay sign.

#6. Treatment of tetralogy of Fallot involves surgery.

Surgery is recommended to tetralogy patients. TOF is typically treated by open-heart surgery in the first year of life. The timing of surgery depends on the baby's symptoms and size. The complete repair procedure for TOF involves closing the ventricular septal defect and relieving the pulmonary stenosis.

When these repairs are done, the overriding aorta is incorporated into the correct left ventricle and the right ventricular thickening regresses. Also, a temporary shunt can be placed to relieve the cyanosis if there are issues that prohibit complete repair in infancy. BT shunt is mostly used for this purpose.

#7. Tetralogy of Fallot is rare.

By some estimates, 1 in 2,000 babies is born with this cardiac defect. Boys and girls are affected equally. About 15% of people with tetralogy of Fallot have a specific genetic abnormality that is also linked to other birth defects such as cleft palate.

#8. TOF is a lifelong medical condition.

Unquestionably over the past few decades, the diagnosis and treatment of tetralogy have improved significantly yet it remains a lifelong condition. Most children who have this cardiac defect survive to adulthood. They require life-long follow up with a cardiologist to ensure the best possible health outcome.