BIOMED - Pathophysiology

🫀 𝘛𝘦𝘵𝘳𝘢𝘭𝘰𝘨𝘺 𝘰𝘧 𝘍𝘢𝘭𝘭𝘰𝘵 (𝘛𝘖𝘍)

©️ Cincinnati Children's

Here's an introduction video to get you started. 2min30sec.

Tetralogy for Fallot (TOF)
Right ventricular outflow tract obstruction
(RVOTO)

TOF is a a cardiac condition that is the term used when there are the presence of four related heart defects that commonly occur together. TOF is the most common chaotic congenital heart disease.

There four defects present in TOF are:

1. Ventricular Septal Defect VSD) ☞ see VSD chap for more info.

2. Overriding Aorta ☞ enlarged aorta arising from both left and right ventricles rather than the left only.

3. Pulmonary stenosis ☞ narrowing of pulmonary valve and outflow tract, creating an obstruction for blood from from right ventricle to pulmonary artery. (See more in chap on Pulmonary Stenosis/Atresia)

4. Right Ventricular Hypertrophy ☞ due to right ventricle pumping at high pressure.

However there may be multiple VSD's, the presence of an atrial septal defect (see chap ASD for more), or abnormalities in the coronary artery branching patterns.

1 | VSD
A defect between the ventricles that allows blood shunting between the chambers means that there is a reduced arterial oxygen saturation, leading to blue, cyanotic babies. This, paired with pulmonary stenosis, will determine how cyanotic the baby is.

3 | Pulmonary Stenosis
Depending on the extent of the pulmonary stenosis obstruction, there will be differentiated levels in decreased arterial oxygenation levels. Pulmonary stenosis (narrowed pulmonary valve and outflow tract) impedes upon blood delivery to the lungs, and so the more restrictive this obstruction is, the more we will see shunting of blood from the right ventricle to the aorta due to pressures in the heart, thereby lowering the O2 delivery.

Signs & Symptoms
A loud systolic heart murmur or cyanosis is usually the first presenting sign of TOF, leading to investigations and diagnosis. TOF babies usually have a patent ductus arteriosis (see chap on PDA for more), that allows additional blood flow to lungs, therefore meaning that severe cyanosis directly after birth is rare.

Once the ductus arteriosus closes however in the first days of life, cyanosis can develop thereafter.

We then see signs and symptoms associated with oxygenation and reduced pulmonary blood flow.

☞ tachypnea
☞ "tetralogy spell" ☞ arterial O2 dropping suddenly, usually due to sudden increased pulmonary stenosis in the outflow tract. This presents with babies with blue lips and skin, and more acute cyanosis, as well as behavioural irritation in response to critically low oxygen levels, and the sleepy/unresponsive if the severe cyanosis persists.

This may be treated by comforting the infant and flexing the knees forward and upward to decrease right to left shunting (pressures), but most often, immediate medical attention is necessary.

Diagnosis
Once cyanosis is first noticed, oxygen is administered, and if there is a failure to respond to this delivery, then it will begin to be suspected that there is a defect present. Echocardiography can pick up the four related defects, and cardiac catheterisation is sometimes necessary to evaluate the size and distribution of the pulmonary arteries, as well as determining whether there is an abnormal aorta pulmonary collateral (blood vessel).

Keep in mind that TOF may be associated with chromosomal abnormalities, and so it is important to identity and investigate this so that other conditions may be treated.

Treatment
Initially, treatment revolves around addressing cyanosis and ensuring oxygenation is adequate to avoid hypoxia. Prostaglandin may be initially given to keep the ductus arteriosus open to support oxygen levels in the body. However these babies will often need surgical intervention in the neonatal period, whereas infants with mild cyanosis or normal oxygen saturation levels are usually able to go home in their first week of life.

Surgical correction is always necessary and is usually done within the 4-6 months of age period, so long as oxygen levels remain safe. If this is not the case, intervention may been to be done earlier.

Corrective surgery involves closing the VSD with a Dacron patch to correct flow to the aorta. The pulmonary valve narrowing and right ventricular outflow tract are augmented and enlarged by resecting obstructive tissue in the right ventricle and enlarging the outflow pathway with a patch.

In babies where the coronary armies branch across the right ventricular outflow tract where the patch is usually placed, an incision in this area can damage the artery. Therefore, a hole is created in the front surface of the R) ventricle avoiding the coronary artery, and a conduit (tube) is sewn form the R) ventricle to the bifurcation of the pulmonary arteries to provide unobstructed blood flow from the R) ventricle to the lungs.

Results of Surgical Correction
Most babies are very sick in the first days after surgery, as the R) ventricle is stiff from previous hypertrophy and because an incision was made in the ventricle's muscle, weakening it. However this improves in the days coming.

Pulmonary regurgitation "leaky" pulmonary valve results from leaking back into the right ventricle from the pulmonary valve.

Some babies will experience rhythm issues post surgery which may require medication to treat, or even a temporary pacemaker. The rhythm will usually return to normal once the R) ventricle recovers.

Further surgical intervention or balloon dilation of vessels for pulmonary insufficiency post surgery may be necessary if this occurs, and long-term follow up with cardiology is necessary to detect recurrent or new problems through life, including into adulthood.

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