Session 4: Congenital Heart Disease

Question 1

Give causes of congenital heart disease.

Answer 1

Genetics:
Downs, Turner’s, Marfan’s etc
Environmental:
Teratogenicity from drugs, alcohol etc.
Maternal infections such as rubella and toxoplasmosis

Question 2

Explain what happens during a left to right shunt as a result of congenital heart disease.

Answer 2

There is an opening that allows blood to flow from left to right.
Blood from the left heart is returned to the lungs instead of going to the rest of the body.
Increased lung blood flow by itself is not damaging but increased pulmonary artery or pulmonary venous pressure is.

Question 3

Explain what happens during a right to left shunt as a result of congenital heart disease. How does this differ to left to right shunt?

Answer 3

It requires an opening but also a distal obstruction! This means that the right heart pressure will have to increase due to the distal obstruction.

Question 4

What is the consequence of left to right shunt.

Answer 4

Blood goes to the lungs again instead of the body.

Increased pulmonary artery and venous pressure.

Question 5

What is the consequence of right to left shunt?

Answer 5

Oxygen deprived blood bypasses the lungs and so oxygen deprived blood is going out in the body resulting in cyanosis.

Question 6

Congenital heart disease can be classified into two categories. Which?

Answer 6

Acyanotic and cyanotic CHD

Question 7

Give examples of acyanotic CHD.

Answer 7

Left to right shunt such as atrial septal defect, ventricular septal defect and patent ductus arteriosus.
Also obstructive lesions such as aortic stenosis, pulmonary stenosis, coarctation of the aorta and mitral stenosis.

Question 8

Give examples of cyanotic CHD.

Answer 8

Right to left shunts.
Tetralogy of Fallot
Transposition of the great arteries
Total anomalous pulmonary venous drainage
Univentricular heart

Question 9

Explain atrial septal defect and the complications.

Answer 9

Opening of the septum between the two atria persisting after birth.
pLA > pRA means that blood flows from left atrium to right atrium.
This means that there will be no mix of oxygen deprived and oxygen rich blood in the systemic circulation. However there will be in pulmonary circulation.

Question 10

Explain patent foramen ovale and its complications.

Answer 10

Not a true atrial septal defect and this is because PFOs may be fairly common and present in around 20% of the population but still clinically silent.

Question 11

Why might patent foramen ovale be clinically silent?

Answer 11

Because the left atrial pressure is higher than the right atrial pressure so the ‘flap’ is generally closed.

Question 12

Explain ventricular septal defect and its complications.

Answer 12

Abnormal opening of the interventricular septum. Since ventricular is usually higher than in the left heart than the right blood will flow from the left to right and again there will be no mix of oxygenated and oxygen deprived.

Question 13

Where does ventricular septal defect most commonly occur?

Answer 13

Membranous portion of the septum.

Question 14

Explain patent ductus arteriosus and its complications.

Answer 14

When there is a failure to close the ductus arteriosus. The ductus arteriosus is a shunt which allows blood to flow from the pulmonary artery to the aorta in utero.
If this fails to close blood from the aorta will flow into the pulmonary artery. It does not cause cyanosis however usually because it doesn’t affect the amount of oxygen that arrives to tissue that much.

Question 15

Explain coarctation of the aorta.

Answer 15

A narrowing of the aortic lumen in the region of the ligamentum arteriosum which is the bit that is left of the ductus arteriosum after it has closed.

Question 16

What are the complications of coarctation of the aorta?

Answer 16

Increased after load on the left ventricle which can lead to LV hypertrophy. The vessels to the upper limbs and head usually emerge proximal to the coarctation meaning that there will be no reduction in blood flow there. However in the lower limbs the blood flow may be reduced and a delayed or weak pulse might be experienced in the femoral artery.

Question 17

What is Tetralogy of Fallot?

Answer 17

A cyanotic defect which is a group of 4 lesions.
• Ventricular septal defect
• Overriding aorta
• Pulmonary stenosis
• RV hypertrophy

Question 18

How does Tetralogy of Fallot cause cyanosis?

Answer 18

The pulmonary stenosis causes RV hypertrophy and those to conditions together causes an increase in the pressure of the right ventricle. As this pressure is increases, along with the VSD and the overriding aorta it will allow blood to flow from right to left which mixes oxygen deprived blood with oxygenated blood in the systemic circulation.

Question 19

What is tricuspid atresia?

Answer 19

A lack of development of the tricuspid valve which leaves no inlet to the right ventricle.

Question 20

How can tricuspid atresia be suitable for life?

Answer 20

If there is a complete right to left shunt in form of atrial septal defect or patent foramen ovale along with a ventricular septal defect in order to make blood go from left ventricle to right ventricle.

Question 21

What is transposition of the great arteries?

Answer 21

It means that the arteries have swapped with their corresponding ventricles:
Right ventricle -> aorta
Left ventricle -> pulmonary trunk

Question 22

What are the complications of transposition of the great arteries?

Answer 22

That the two systems (pulmonary and systemic) are now separate.

Question 23

Transposition of the great arteries is not suitable for life after birth. How can this be treated?

Answer 23

It is usually treated by prostaglandins which cause vasodilation and keep the ductus arteriosus open allowing blood to flow from the aorta to the pulmonary trunk. This is however not a long term solution, it just ensures that the baby survives for the time being. After this the baby is put into surgery to reroute the arteries and ventricles.

Question 24

What is hypoplastic left heart?

Answer 24

When the left ventricle and ascending aorta fail to develop correctly.

Question 25

Is hypoplastic left heart suitable for life?

Answer 25

Yes and no.
In a short term a PFO or ASD will be present blood supply to the systemic circulation will occur via a patent ductus arteriosus.
This is not long term and needs to be corrected surgically.

Question 26

What embryonic germ layer contributes to the cardiovascular system?

Answer 26

Mesoderm

Question 27

Is the flow of blood into the primitive heart tube always at its caudal end?

Answer 27

No. The primitive heart tube will loop by twisting and folding upwards resulting in both inflow and outflow being no longer caudally but instead superior.

Question 28

Do both the left and right atria develop entirely from structures present in the primitive heart tube?

Answer 28

No.
RA = most of primitive atrium and sinus venosus
LA = only a small part of the primitive atrium but most of it comes from parts of the pulmonary veins resulting in a smooth wall of the left atrium.

Question 29

What is the difference between the course of the left and right recurrent laryngeal nerves in relation to the great vessels?

Answer 29

LLN: Hooks around the 6th arch around the ductus arteriosus between the pulmonary trunk and the aorta.
RLN: Hooks around the 4th arch around the right subclavian artery.

Question 30

Why is right to left flow between the atria necessary in utero?

Answer 30

Because the lungs are not fully developed yet. A large volume would be damaging. Instead blood flow skips the lungs and oxygenated blood is supplied by the placenta from the mother instead.

Question 31

How is right to left flow between the atria maintained in utero?

Answer 31

Due to higher pressure in right atrium.

Also due to a shunt which is called the foramen ovale.

Question 32

How is the primitive ventricle of the heart divided into right and left ventricles?

Answer 32

Ventricular septum forms. It has 2 components which are membranous and muscular.
The muscular portion will grow upwards towards the fused endocardial cushions.
Most of the ventricular septum consists of the muscular portion.

Question 33

At birth, the three cardiovascular shunts necessary for fetal survival cease to function. What are these shunts and what happens to them at birth.

Answer 33

Ductus venosus
Foramen ovale
Ductus arteriosus
They shut.

Question 34

In what direction will blood flow through a ventricular septal defect, assuming there are no other abnormalities? Will the patient by cyanosed?

Answer 34

Left to right. The patient will not be cyanosed.

Question 35

Ventricular septal defect can eventually cause cyanosis. How?

Answer 35

It can lead to RV hypertension and if that is left untreated it can lead to cyanosis due to higher pressure in the right ventricle.

Question 36

Explain why transposition of the great arteries is compatible in utero but not after birth.

Answer 36

Since oxygenated blood already comes from the mother the lungs are not needed. This means that the left ventricular to pulmonary trunk malformation is not needed. Blood can flow into the right ventricle and enter the aorta and the systemic circulation directly.

Question 37

What proportion of babies born with Down’s syndrome have a congenital cardiac defect?

Answer 37

Around 40%

Question 38

Which congenital cardiac defect is most common with children with Down’s syndrome?

Answer 38

Atrioventricular septal defect where there is a defect of the endocardial cushions.

Question 39

What will patent ductus arteriosus sound like?

Answer 39

Due to the pressure being higher in the aorta at all times there will be constant flow from the aorta to the pulmonary trunk.
This increases at systole and reaches its peak just before the second heart sound as the aortic pressure is at its highest.
This means that the murmur crescendos at S2 and decrescendos on the way to S1.

Question 40

Why can it be hard to hear S2 in PDA?

Answer 40

Because the murmur is at its loudest at S2 so it might make it difficult.