tetralogy of fallot

NOTES ON TETRALOGY OF FALLOT

What is Tetralogy of Fallot? It’s a congenital heart defect that is characterized by FOUR structural defects of the heart.

Quick Facts about TOF:

• It’s the most common complex congenital heart defect.

• It occurs when the baby is developing in the womb.

• According to the CDC.gov, 1 in 2518 babies born in the US will have TOF.

• It’s a cyanotic heart defect. This means the patient will have cyanosis due to a decrease in pulmonary blood flow.

When studying pediatric congenital heart defects, always let the name of the defect help you. With TOF, that are FOUR structural problems that you need to commit to memory.

The word tetra or tetrad (tetralogy) means it’s a condition that consists of FOUR problems.

What are the heart defects in tetralogy of fallot?

Remember the mnemonic: “RAPS”

Right ventricular hypertrophy

Aorta displacement

Pulmonary stenosis

Septal defect (ventricular)

To understand tetralogy of fallot, let’s talk about NORMAL blood flow because then the defects make complete sense.

Normal blood flow through the heart:

It starts on the RIGHT SIDE (goal of the right side is to get the UNOXYGENATED blood to the LUNGS)

1. The un-oxygenated blood (this is blood that has been “used-up” by your body that needs to be resupplied with oxygen) enters to the heart through the SUPERIOR AND INFERIOR VENA CAVA.

2. Blood enters into the RIGHT ATRIUM

3. Then it is squeezed through the TRICUSPID VALVE

4. Blood then enters into the RIGHT VENTRICLE

5. Then it is squeezed into the PULMONIC VALVE

6. Blood is then shot-up through the PULMONARY ARTERY and then enters into the lungs for some oxygen

Left Side of the Heart (goal of this side is to get the richly, oxygenated blood to the body to feed the brain, tissue, muscles, organs etc.)

7. Blood enters from the lungs through the PULMONARY VEIN that has just been refreshed with oxygen to go

8. into the LEFT ATRIUM

9. Down through the BICUSPID VALVE (also called mitral valve)

10. Then blood is squeezed into the LEFT VENTRICLE

11. Up through the AORTIC VALVE

12. Lastly up through the AORTA, where it pumped throughout the body

Tetralogy of Fallot Blood Flow:

Let’s start on the right side:

As blood enters in from the superior and inferior vena cava it goes into the right atrium, down through the tricuspid, and then the left ventricular

• But we have a problem at this point and it’s called a VENTRICULAR SEPTAL DEFECT (VSD).
This is a fancy word that means there is a hole in the ventricular wall. Normally this wall separates the RIGHT and LEFT ventricle, but in TOF the blood is mixing….this is a problem because we will have exhausted, unoxygenated blood mixing with fresh oxygenated blood.

Unfortunately, the problem doesn’t stop here. The blood that is in the right ventricle has a strong desire to reach the lungs to get oxygenated. To do this, it must go up through the pulmonic valve and pulmonary artery.

• In TOF, there is NARROWING of the pulmonary valve and artery (proper term STENOSIS). Therefore, blood can NOT easily go up through the pulmonary artery to go to the lungs to get oxygenated. Now depending on the severity of the stenosis or obstruction (if very severe), it will cause a right to left shunt of blood which causes even more unoxygenated blood to enter back into the system. SO, THE RIGHT VENTRICLE HAS TO WORK HARDER(when you overwork a muscle it enlarges). Therefore, right ventricle hypertrophy occurs (another way of saying enlargement of the right ventricle), which can lead to heart failure in the long run.

• Then on the left side of the heart, the aortic valve is enlarged and this causes the aorta to be displaced. Normally, the aortic valve just connects to the left ventricle, but now it is actually connecting to the septal defect and is collecting all the blood that is mixing at the ventricular septal defect. This will cause poorly oxygenated blood to go throughout the body.

Signs and Symptoms of Tetralogy of Fallot

“Afflict”

Activity (feeding, crying, playing) causes cyanosis “TET spells”… cyanosis, shortness of breath, increased breathing, fainting…think “activity intolerance”

• Nurse’s role with a “Tet spell”: knee-to-chest position, calm infant, and apply oxygen. Patient may need medication to calm or to increase systemic vascular resistance (IV fluids etc.)

Fingernail changes (clubbing due to hypoxia) noticeable at about 6 months

Fatigues or faints easily (especially during a “tet spell”….due to low oxygen levels)

Lift knees-to-chest position or squatting (children) WHY? squatting and the knee-to-chest position increases systemic vascular resistance, which will decrease the right to left shunting in the ventricles and helps increase oxygen levels.

Inability to grow properly due to hypoxemia

Cardiac: HARSH systolic murmur: WHY and WHERE? Due to pulmonary stenosis and is found left of the sternal border at the 2nd intercostal space (where you would find the pulmonic valve) and a systolic thrill may be present

Trouble feeding and thriving (not gaining weight, small for age, doesn’t achieve developmental milestones etc. )…think “failure to thrive”

Quick Review over Treatment for TOF

This heart defect will require surgery, which can be temporary (a.k.a. palliative) or complete repair.

Temporary surgery is performed to help with cyanosis and improve blood flow. It can include shunt placement to shunt oxygenated blood through the heart so oxygen levels are increased or stent placement to open up the stenosis. In addition, complete repair can be performed when the child is older enough to tolerate surgery (about 6-12 months of age). This includes placing a patch over the septal wall defect to prevent blood mixing in the ventricles.

If a child has a severe case of TOF, where there is a severe defect to the pulmonary valve (blood won’t be able to get to the lungs) and the newborn is very cyanotic at birth, a temporary surgery may be performed and a prostaglandin infusion started.

Aprostadil (prostaglandin E) will keep the ductus arteriosus open (this normally closes shortly after birth) to allow more blood to flow to the lungs for oxygenation.