Tetralogy of Fallot: Definition, Causes and Treatment

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  • 0:01 When Everything Goes Wrong
  • 0:30 Tetralogy of Fallot
  • 3:36 The Consequences of…
  • 6:10 Tet Spells
  • 8:04 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will go over a congenital problem known as Tetralogy of Fallot, the four major components that are involved, and how they act together to cause quite a few problems.

When Everything Goes Wrong

It's bad enough in life when one thing goes wrong, like a flat tire. It's even worse two things go wrong. But when four things go haywire then you're in pretty dire straits as a result. Just imagine having four flat tires all at once, you just came to a dead stop right away then.

Horribly so, some people are born with a congenital heart defect where four things, on their own bad enough, combine in one terrible condition.

Tetralogy of Fallot

This condition is known as Tetralogy of Fallot and again is a congenital heart condition that has four distinct heart defects present during birth. This problem is sometimes associated with DiGeorge Syndrome, a genetic condition that causes Tetralogy of Fallot, a cleft palate, underdeveloped thymus, and hypoparathyroidism. Since DiGeorge Syndrome occurs as a result of an abnormality on chromosome 22, this and the problems associated with it have a mnemonic known as CATCH-22 as a brief memory aid.

C- Cardiac abnormalities

A- Abnormal facies

T- Thymic hypoplasia

C - Cleft palate

H - Hypoparathyroidism (causing Hypocalcemia)

In our lesson's case, 'Tetra' means 'four' and Fallot stands for the last name of a French physician who described this condition in detail.

Tetralogy of Fallot includes the following four components:

  • A ventricular septal defect, or VSD, which is a hole in the tissue wall separating the ventricles of the heart. It's basically like having a hole in the wall between your room and a sibling at home. It's bound to lead to a lot of problems when sights and sounds from each room mix with one another. You'll see why in a little bit.
  • Another component is overriding aorta, an aorta that sits in the middle of both ventricles as opposed to coming off the left ventricle only. This is sometimes called dextroposition of the aorta. I liken this to a factory chimney that usually comes out of the roof at one end of the building all of a sudden being shifted to the middle of the building, thereby collecting exhaust from both sides of the factory at the same time.
  • The third component is a pulmonary valve - or infundibular - stenosis. This refers to the obstruction of the right ventricular outflow as a result of the narrowing of the pulmonary valve (known as valvular stenosis) or the section of the right ventricle right below the pulmonary valve (which refers to infundibular stenosis). The right ventricle pumps blood through this valve to the lungs, so if it becomes narrower, the outflow of blood to the lungs is obstructed. It's just like taking a water hose and squeezing your hand around it, less water will get out through the hose.
  • And the fourth component is right ventricular hypertrophy, or the increase in thickness of the wall of the right ventricle. Just like your muscles get larger when they work harder, so does the heart muscle. And because the right ventricle has to work harder than normal to pump blood due to pulmonary stenosis, it gets more muscular. Eventually, just as your muscles tire from too much exercise, the heart can fail as a result of all of this.

The Consequences of Tetralogy of Fallot

Now that you know the four components of Tetralogy of Fallot in more detail, it's important to understand how they all come together to cause a person a lot of problems.

Problem #1: Pulmonary valve (or infundibular) stenosis causes the improper oxygenation of blood.

Let's think about this logically. Pulmonary valve stenosis is the narrowing of the pulmonary valve, the thing that allows deoxygenated blood to flow from the right ventricle into the lungs via the pulmonary artery, in order to get oxygenated. If the outflow of this blood into the lungs is obstructed, less blood gets oxygenated regardless of any other defect present in this condition.

Problem #2: The mixing of oxygenated with deoxygenated blood.

Depending on the amount of pulmonary stenosis that occurs and some other factors, there will either be a left-to-right or right-to-left shunt of blood through the VSD (and sometimes a mixture of both). In any case, this means oxygenated (red blood in the left heart) and deoxygenated (blue blood in the right side of the heart) will mix together. So, just like sights and sounds mixing through a hole in the wall in a house cause people a lot of heartache, so too does a hole in the wall diving the ventricles.

Problem #3: The pumping of mixed blood into circulation.

Normally, the aorta connects only to the left ventricle. This is the side of the heart that normally only contains and pumps oxygenated blood. But, because the aorta now sits in the middle of both ventricles, it receives a mixture of deoxygenated and oxygenated blood from the right and left ventricles, respectively. This issue is further compounded by the already present problem #2 I described before.

Problem #4: The failure of the heart.

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