Tetralogy of Fallot ( TOF)

Tetralogy of Fallot ( TOF)
TOF is a congenital heart defect. A congenital heart defect is a problem with the heart's structure that's present at birth. This type of heart defect changes the normal flow of blood through the heart.
Tetralogy of Fallot is a rare, complex heart defect that occurs in about 5 out of every 10,000 babies. It affects boys and girls equally.

Tetralogy of Fallot involves four heart defects:

☛ Ventricular Septal Defect
The heart has a wall that separates the two chambers on its left side from the two chambers on its right side. This wall is called a septum. The septum prevents blood from mixing between the two sides of the heart.
A VSD is a hole in the part of the septum that separates the ventricles, the lower chambers of the heart. The hole allows oxygen-rich blood from the left ventricle to mix with oxygen-poor blood from the right ventricle.

☛ Pulmonary Stenosis
This defect is a narrowing of the pulmonary valve and the passage through which blood flows from the right ventricle to the pulmonary artery.
Normally, oxygen-poor blood from the right ventricle flows through the pulmonary valve, into the pulmonary artery, and out to the lungs to pick up oxygen. In pulmonary stenosis, the heart has to work harder than normal to pump blood, and not enough blood reaches the lungs.

☛ Right Ventricular Hypertrophy
This defect occurs if the right ventricle thickens because the heart has to pump harder than it should to move blood through the narrowed pulmonary valve.

☛ Overriding Aorta
This is a defect in the aorta, the main artery that carries oxygen-rich blood to the body. In a healthy heart, the aorta is attached to the left ventricle. This allows only oxygen-rich blood to flow to the body.

In tetralogy of Fallot, the aorta is between the left and right ventricles, directly over the VSD. As a result, oxygen-poor blood from the right ventricle flows directly into the aorta instead of into the pulmonary artery to the lungs.

Together, these four defects mean that not enough blood is able to reach the lungs to get oxygen, and oxygen-poor blood flows out to the body.

Signs - clubbing, loud ejection systolic murmur (radiates to back), cyanosis, tet spells ( a tet spell occurs when the oxygen level in the blood suddenly drops. This causes the baby to become very blue.)

Surgery to repair tetralogy of Fallot is done to improve blood flow to the lungs and to make sure that oxygen-rich and oxygen-poor blood flows to the right places. 

Surgeon will:
1. Widen the narrowed pulmonary blood vessels. The pulmonary valve is widened or replaced, and the passage from the right ventricle to the pulmonary artery is enlarged. These procedures improve blood flow to the lungs. This allows the blood to get enough oxygen to meet the body's needs.

2. Close the ventricular septal defect (VSD). A patch is used to cover the hole in the septum. This patch stops oxygen-rich and oxygen-poor blood from mixing between the ventricles.

Fixing these two defects resolves problems caused by the other two defects. When the right ventricle no longer has to work so hard to pump blood to the lungs, it will return to a normal thickness. Fixing the VSD means that only oxygen-rich blood will flow out of the left ventricle into the aorta.

References:
http://www.heart.org/HEARTORG/Conditions/CongenitalHeartDefects/AboutCongenitalHeartDefects/Tetralogy-of-Fallot_UCM_307038_Article.jsp
https://circ.ahajournals.org/content/100/suppl_2/II-157.full
http://surgery.ucsf.edu/conditions--procedures/tetralogy-of-fallot.aspx
http://en.wikipedia.org/wiki/Tetralogy_of_Fallot
Image: comparison between normal heart and heart with TOF via UCSF