Understanding Congenital Heart Disease

Question 1

What are the main common causes of congenital heart disease?

Answer 1

• Genetic
– Down’s, Turner’s, Marfan’s syndromes

• Environmental
– Teratogenicity from drugs, alcohol etc

• Maternal infections
– Rubella, Toxoplasmosis, etc

Question 2

What is the difference in shape between the left and right ventricle?

Answer 2

Left ventricle is cylindrical

Right ventricle wraps around the left ventricle
- It contracts agains the left ventricle

Each ventricle is morphologically adapted for its task
- The pressure in the left atria is slightly higher than the right atria

• The systolic pressure in the ventricles is similar to the blood pressure

Question 3

What is the oxygen saturation in the different compartments of the heart?

Answer 3

Right side of heart - 67%

Left ventricle - 99%

Question 4

What are the pressures (mmHg) in the different compartments of the heart?

Answer 4

Right atrium - 4mmHg

Right ventricle - 25/3mmHg

(Because the blood moves down a pressure gradient during diastole)

Pulmonary artery - 25/10mmHg

Left atrium - 5mmHg

Left ventricle - 4/80mmHg

Aorta - 80/40mmHg

(Systemic resistance is higher, it has further to go, has to go against gravity)

Question 5

What are the Haemodynamic effects of shunts?

Answer 5

• Left to right shunt :
– Requires a hole !
– Blood from the left heart is returned to the lungs instead of going to the body
– Increased lung blood flow by itself is not damaging, but increased pulmonary artery or pulmonary venous pressure is.

• Right to left shunt :
– Requires a hole and distal obstruction !
– De-oxgenated blood bypasses the lungs and is found in the arterial circulation- This is called cyanosis

Question 6

What is a shunt?

Answer 6

A communication between two sides of the circulation

A hole

Instead of blood going round the body, it falls out of systemic circulation and goes around the pulmonary circulation again.

This can damage the lungs at higher pressures

Question 7

What is cyanosis? How is it caused

Answer 7

It is the presence of deoxygenated haemoglobin in the arterial circulation

1) Via a right to left shunt
2) presence of deoxygenated blood in pulmonary circulation caused by poorly lungs

Question 8

How are congenital heart diseases classified?

Answer 8

• Acyanotic
– Left to right shunts: ASD,VSD,PDA
– Obstructive lesions: Aortic stenosis (Hypoplasia)
- Pulmonary stenosis (Valve, outflow, branch)
- Coarctation of the Aorta, Mitral stenosis

• Cyanotic (Complex, Right to Left shunts)
– Tetralogy of Fallot (VSD/Pulm stenosis …)
– Transposition of the Great Arteries
– Total Anomalous Pulmonary Venous Drainage
– Univentricular Heart

Question 9

What is a cyanotic congenital heart lesion?

Answer 9

Cyanosis refers to the blue- purple discolouration of the skin and mucous membranes caused by an elevated blood concentration of deoxygenated haemoglobin.

In congenital heart disease, cyanosis results from defects that allow poorly oxygenated blood from the right side of the heart to be shunted to the left side, bypassing the lungs

They are very complex

Examples include =
– Tetralogy of Fallot (VSD/Pulm stenosis …)
– Transposition of the Great Arteries
– Total Anomalous Pulmonary Venous Drainage
– Univentricular Heart

Question 10

What is an acyanotic congenital heart lesion? Give examples

Answer 10

They are heart defects that result in left to right shunting of blood

Large left to right shunts at the atrial, ventricular or great vessel level, cause the pulmonary artery volume and pressure to increase

It can therefore be associated with later development of of pulmonary arteriolar hypertrophy and subsequently increased resistance to flow.

Examples of left to right shunts include: Atrial septal defects (ASD), Ventricular septal defects (VSD) and Patent ductus arteriosus (PDA)

Examples of obstructive lesions include = Aortic stenosis (Hypoplasia) Pulmonary stenosis (Valve, outflow, branch) Coarctation of the Aorta, Mitral stenosis

Question 11

What is Tetralogy of Fallot?

Answer 11

Tetralogy of Fallot results from a single developmental defect and abnormality of the interventricular septum.

It is generally characterised by a group of four structural abnormalities within the heart that occur together.
These are:

1) pulmonary stenosis – a narrowing at, under or above the valve between the right pumping chamber (right ventricle) and the large blood vessel that carries blood to the lungs to pick up oxygen (pulmonary artery)
2) ventricular septal defect – a hole between the right and left pumping chambers (ventricles)
3) Over-riding aorta – the entrance to the large blood vessel that takes blood away from the heart to the rest of the body (aorta) is next to the ventricular septal defect, allowing oxygen-poor blood to flow through it
- The aorta receives blood from both ventricles

4) Thick right ventricle (hypertrophy)
– the heart has to work harder to pump blood through the narrowed pulmonary artery, causing the muscle to thicken

Question 12

What is the pathophysiology of Tetralogy of Fallot?

Answer 12

Increased resistance caused by the pulmonary stenosis causes deoxygenated blood returning from the systemic veins to be diverted to the RV through the VSD to the LV (due to the difference in pressure) and into the systemic circulation because of the overriding aorta

This results in hypoxemia (an abnormally low concentration of oxygen in the blood) and cyanosis.

The increased resistance in the PA means the RA has to work really hard to pump blood to the pulmonary circulation. This results in RV hypertrophy.

Question 13

What are the presenting symptoms of TOF?

Answer 13

Mild cyanosis mostly on the lips, mucous membranes and digits

Clubbing of fingers and toes due to chronic hypoxemia caused by the right to left shunt

Question 14

How is TOF treated/

Answer 14

Usually undergo surgery to close the VSD and enlarge the pulmonary artery using a pericardial patch

This usually occurs at 6-12 months to decrease the likelihood of further complications

Question 15

What is tricuspid atresia?

Answer 15

Tricuspid atresia is a form of congenital heart disease whereby there is a complete absence of the tricuspid valve.

Therefore, there is an absence of right atrioventricular connection.

This leads to a hypoplastic (undersized) or absent right ventricle.

This defect is contracted during prenatal development, when the heart does not finish developing.

It causes the heart to be unable to properly oxygenate the rest of the blood in the body.

Because of this, the body does not have enough oxygen to live, so other defects must occur to maintain blood flow.

Because of the lack of an A-V connection, an atrial septal defect (ASD) must be present to fill the left ventricle with blood.

Also, since there is a lack of a right ventricle there must be a way to pump blood into the pulmonary arteries, and this is accomplished by a ventricular septal defect (VSD).

The causes of Tricupsid atresia are unknown.

Question 16

How are tricuspid atresia’s treated?

Answer 16

Treatment for tricuspid atresia involves surgery to ensure adequate blood flow through the heart and into the lungs, allowing your baby’s body to receive the proper amount of oxygen-rich blood.

Often, this requires more than one surgical procedure.

Medications also may be given before surgery.

Question 17

What is hypoplastic left heart syndrome (HLHS)?

Answer 17

1) Left ventricle is underdeveloped
2) Ascending Aorta very small
3) Right ventricle supports systemic circulation
4) Obligatory Right to Left shunt

ASD and PDA are vital for survival.

Hypoplastic left heart syndrome is a condition where the left lower pumping chamber (left ventricle) of the heart does not develop properly so is much smaller than usual.

The mitral valve between the left ventricle and the upper left filling chamber (left atrium) is often closed or very small.

In addition, the main blood vessel that carries blood from the heart to the rest of the body (aorta) is also smaller than usual.

This means that the heart is unable to pump blood around the body effectively.

Question 18

What causes hypoplastic left heart syndrome (HLHS)?

Answer 18

There is no known cause in the majority of HLHS cases.

There is likely a genetic component, as HLHS has been shown to be heritable and associated with specific gene mutations.

HLHS usually occurs as an isolated cardiac defect.

Question 19

How is HLHS treated?

Answer 19

Usually reconstructive surgery

Without life-prolonging interventions, HLHS is fatal, but with intervention, an infant may survive.

A cardiothoracic surgeon may perform a series of operations or a full heart transplant.

While surgical intervention has emerged as the standard of care in the United States, other national health systems, notably in France, approach diagnosis of HLHS in a more conservative manner, with an emphasis on termination of pregnancy or compassionate care after delivery.

Before surgery, the ductus must be kept open to allow blood-flow using medication containing prostaglandin.

Air with less oxygen than normal is used for infants with hypoplastic left heart syndrome. These low oxygen levels increases the pulmonary vascular resistance (PVR) and thus improve blood flow to the rest of the body, due to the greater pressure difference between the lungs and body.

Question 20

Describe the pathophysiology of transposition of the great arteries

Answer 20

In this disease, each great vessel (the aorta and pulmonary artery) arise from the opposite and wrong ventricles..

So the right ventricle is connected to Aorta and the left ventricle is connected to Pulmonary Artery

The systemic and pulmonary circuits are now in parallel rather than being in series

This arrangement forces desaturated blood from the systemic venous system to pass through the RV and then return to the systemic circulation through the aorta without undergoing normal oxygenation to the lungs.

In a similar way, oxygenated pulmonary venous return passes through the LV and then back to the pulmonary artery to the lungs without imparting oxygen to the systemic circulation.

This results in extreme hypoxia and and a cyanotic neonate

Not viable unless the two circuit communicate ie via atrial, ventricular or ductal shunts

Example of bi-directional shunting

Question 21

Why is TGA compatible with life in utero?

Answer 21

Because flow through the ductus arteriosus and Foraman ovale allows communication between the two circulations

Oxygenated fetal blood flows from the placenta through the umbilical vein to the right atrium and then most of it travels into the left atrium through the Foraman ovale.

The oxygenated blood in the the left atrium passes into the LV and is pumped out to the pulmonary artery

Most of the pulmonary artery flow travels through the ductus arteriosus into the aorta, instead of the high-resistance pulmonary vessels, such that oxygen is provided to the developing tissues.

However, after birth, normal physiologic closure of the ductus and the Foraman ovale eliminates the shunt

Question 22

How is transposition of the great arteries treated?

Answer 22

It is a medical emergency

The ductus arteriosus must be maintained using prostaglandin

Inter atrial communication must be created too - This is called the Rashkind procedure, and it uses a balloon catheter to open up communication

The Rashkind procedure allows aqequate mixing of the two circulations until surgery can be performed

The current surgical procedure of choice is called the “arterial switch”

Question 23

Why is it that babies born with a univentricular heart (with or without transposition of the great arteries) are able to survive for a while?

Answer 23

Because the systemic circulation is still getting some oxygenated blood, even though it is mixed with deoxygenated blood, it is better than nothing.

This means that tissues can be slightly perfused to some extent

Question 24

What is pulmonary atresia?

Answer 24

Pulmonary atresia is a birth defect of the pulmonary valve.

Pulmonary atresia is when this valve didn’t form at all, and no blood can go from the right ventricle of the heart out to the lungs.

In a baby without a congenital heart defect, the right side of the heart pumps oxygen-poor blood from the heart to the lungs through the pulmonary artery.

The blood that comes back from the lungs is oxygen-rich and can then be pumped to the rest of the body. In babies with pulmonary atresia, the pulmonary valve that usually controls the blood flowing through the pulmonary artery is not formed, so blood is unable to get directly from the right ventricle to the lungs.

In pulmonary atresia, since blood cannot directly flow from the right ventricle of the heart out to the pulmonary artery, blood must use other routes to bypass the unformed pulmonary valve.

The foramen ovale, a natural opening between the right and left upper chambers of the heart during pregnancy that usually closes after the baby is born, often remains open to allow blood flow to the lungs.

Additionally, doctors may give medicine to the baby to keep the baby’s patent ductus arteriosus open after the baby’s birth. The patent ductus arteriosus is the blood vessel that allows blood to move around the baby’s lungs before the baby is born and it also usually closes after birth

Question 25

What is coarctation of the aorta?

Answer 25

A discreet narrowing of the aorta

Often occurs in patients with Turner syndrome

Question 26

What are the consequences of coarctation of the aorta?

Answer 26

The LV has an increased after load

Blood flow to the head and upper extremities is preserved because the vessels supplying these areas usually branch off the aorta proximal to the obstruction

However, flow to the descending aorta and lower extremities may be diminished

Could also result in:

• LV hypertrophy
• dilatation of collateral blood vessels from the intercostal arteries that bypass the coarctation and provide blood to the more distal descending aorta
• These collateral vessels will eventually enlarge and can erode the undersurface of the ribs

Question 27

How is coarctation of the aorta treated?

Answer 27

Prostaglandin infusion given to keep the ductus arteriosus patent

Surgery

Question 28

What is an atrial septal defect?

Answer 28

A persistent opening in the intertribal septum after birth that allows direct communication between the left and right atria

It causes oxygenated blood from the LA to be shunted to the RA

This can lead to RV hypertrophy

In more severe cases this shunt can reverse

Flow through the defect is a function of its size and not the filling properties (compliance) of the ventricles into which the atria pass their contents

Question 29

How is ASD treated?

Answer 29

Most patients with ASD are asymptomatic

However, if the volume of the shunted blood is haemodynamically significant (even in the continued absence of symptoms), elective surgical repair is recommended to prevent heart failure

Question 30

What is ventricular septal defect (VSD)?

Answer 30

It is an abnormal opening in the interventricular septum

They are relatively common

The impact depends on the size of the shunt

If a large ventricular septal defect (VSD) is untreated, extra blood flow goes from the left side of the heart back to the lungs.

Because this blood already carries oxygen from the lungs, passing through the lungs again does not add more oxygen and results in inefficient flow through the heart.

The lungs can become congested (too full) and unable to properly do their job of exchanging oxygen from the air with carbon dioxide from blood.

The extra blood flow can cause the heart to enlarge.

Because of this inefficiency in the circulation, the heart and lungs work harder than normal, expending extra energy, which can result in poor growth in infants.

Question 31

What is Patent Ductus Arteriosus?

Answer 31

Patent ductus arteriosus (PDA) is a condition wherein the ductus arteriosus fails to close after birth.

The ductus arteriosus is a fetal blood vessel that closes soon after birth. In a PDA, the vessel does not close and remains “patent” (open), resulting in irregular transmission of blood between the aorta and the pulmonary artery.

A PDA allows a portion of the oxygenated blood from the left heart to flow back to the lungs by flowing from the aorta (which has higher pressure) to the pulmonary artery.

If this shunt is substantial, the neonate becomes short of breath: the additional fluid returning to the lungs increases lung pressure, which in turn increases the energy required to inflate the lungs.

This uses more calories than normal and often interferes with feeding in infancy.

Question 32

When can PDA be useful?

Answer 32

In some congenital heart defects (such as in transposition of the great vessels) a PDA may need to remain open, as it is the only way that oxygenated blood can mix with deoxygenated blood.

In these cases, prostaglandins are used to keep the DA open until surgical correction of the heart defect is completed.

Question 33

What is the impact of congenital aortic stenosis?

Answer 33

Aortic stenosis is a heart valve disorder that narrows or obstructs the aortic valve opening. Narrowing of the aortic valve prevents the valve from opening properly and obstructs the flow of blood from the left ventricle to the aorta.

There are specific types of aortic stenoses:
- Subaortic stenosis refers to a narrowing of the left ventricle just below the aortic valve, which blood passes through to go into the aorta. This stenosis limits the flow of blood out of the left ventricle. This can reduce the amount of blood that flows to the body.

• Supravalvular aortic stenosis (SVAS) is a congenital narrowing of the ascending aorta which can occur as a congenital defect itself or as one component of Williams syndrome.

All increase the work the heart has to do to pump blood forward, causing pressure inside the left ventricle to increase which results in ventricular hypertrophy.

Unlike other muscles, thick heart muscles are not desirable.

Over a long period of time, a thick ventricle can enlarge and fail.

The thick muscle, increased pressure and decreased flow of oxygen rich blood to the heart muscle make the heart prone to rhythm disturbances (arrhythmia) and may cause sudden cardiac death.

Question 34

What are the consequences of pulmonic stenosis?

Answer 34

Pulmonic stenosis is an obstruction to right ventricular outflow at the pulmonary valve, within the body for the RV or the pulmonary artery.

It leads to impairment of right ventricular outflow, which leads to increased RV pressures and RV hypertrophy

The clinical course is determined by the severity of the obstruction

Although mild pulmonic stenosis rarely progresses and is unlikely to affect RV function, untreated severe pulmonic stenosis typically results in right- sided heart failure.

Can be treated with a balloon stent.

Question 35

Outline the natural history of these common congenital heart diseases:

ASD

VSD

Coarctation

Tetralogy of Fallot

Transposition/ hypoplastic left heart/Pre-ductal
Coarctation/Pulmonary atresia

Answer 35

• ASD:

• Usually asymptomatic late into adulthood.
• Late onset Arrythmia and Right Heart Failure

• VSD:

• Unless very small, present in infancy with Left Heart Failure
• Untreated, can lead to in-operable pulmonary hypertension

• Coarctation
– Neonatal variety: associated with PDA, R to L shunt
– Adult variety: complicated by Renal Hypertension, Left Vent
Hypertrophy, often associated Aortic Valve Stenosis

• Tetralogy of Fallot:
- Present in infancy or early childhood with
Cyanotic spells. Mild cases compatible with adulthood

• Transposition/ hypoplastic left heart/Pre-ductal
Coarctation/Pulmonary atresia:
- Presenting as Neonatal emergencies, often due to reduced pulmonary blood flow