The circulation of a foetus works differently to that of a newborn baby.

In the womb, the foetus is connected to the mother’s bloodstream through the placenta and the blood vessels in the umbilical cord. Blood rich in oxygen and nutrients is supplied directly from the mother to the foetus because the developing organs are unable to perform metabolic processes and the lungs are still inactive.

After reaching the foetus through the vessels in the umbilical cord, the oxygen-rich blood mixes together with the oxygen-poor blood from the vena cava veins (SVC, IVC) and reaches the heart where the foetal circulation begins. The blood available to the foetus is “mixed blood” which contains slightly less oxygen but is of sufficiently good quality for the foetus’ organs to thrive.

Every foetus has an opening or tunnel in the wall of tissue separating the right and left atriums (interatrial septum). This opening is known as the foramen ovale. Most of the blood that reaches the child’s right atrium (RA), flows through this opening into the left atrium (LA). It continues through the mitral valve into the left ventricle (LV) and flows into the aorta and to the organs. Only a small amount of blood flows through the tricuspid valve into the right ventricle (RV) and the pulmonary artery (PA). The foetal lungs are supplied with enough blood for the healthy development of the tissue and the pulmonary (lung) vessels which, until birth, are held in a “contracted” state by the muscles. For this reason, the pulmonary vascular resistance (resistance that must be overcome to push blood through the veins in the lungs) is particularly high. As a result, much of the blood in the pulmonary artery escapes through a connection between the trunk of the pulmonary artery and the proximal descending aorta; this vessel is known as the ductus.

At birth, a newborn baby takes its first breath and activates the lungs. This causes the pulmonary vessels to “relax”, lowering the pulmonary vascular resistance and allowing the blood to flow into the tiniest recesses of the pulmonary vascular tree (system of vessels in the lungs). With every breath, air is drawn into the bronchial tubes, allowing the process of gas exchange to begin. Now that more blood from the lungs is also flowing back through the pulmonary veins into the left atrium, the blood no longer needs to flow from right to left through the foramen ovale, which usually closes completely.

The child no longer depends on the blood supply from the placenta and the umbilical cord can be cut. The open ductus arteriosus is not needed anymore and it closes on its own within a matter of hours or days. In many heart defects, malformations can make it more difficult for the blood to reach the lungs or the aorta, sometimes blocking the blood flow altogether. The blood can no longer escape through the foramen ovale and ductus arteriosus as it did when the baby was still in the womb. Without medical intervention, these infants would die within hours or days of being born. In intensive care, the newborn is given prostaglandin, a highly effective form of medication that stops the ductus from closely spontaneously until corrective surgery can be performed in the first few days of the baby’s life. In the case of newborns who need an open foramen ovale, the connection may be widened in a cardiac catheterisation procedure (balloon atrioseptostomy or Rashkind manoeuvre). Cardiac catheterisation is when a long thin tube or catheter is inserted in an artery or vein and threaded through the blood vessels to the heart.

It usually takes a few weeks for the infant’s pulmonary vascular resistance (see above) to fall. This means it may be several weeks before the full extent of a heart problem becomes clear, e.g. in children with significant defects in the wall of tissue separating the right atrium from the left atrium (septum), causing large amounts of blood to flow from the left ventricle into the right ventricle and also into the lungs.

Foetal Circulation
SVC – Superior vena cava
IVC – Inferior vena cava
RA – Right atrium
RV – Right ventricle
PA – Pulmonary artery
LA – Left atrium
LV – Left ventricle
Aorta
Foramen ovale
Ductus arteriosus

VSD is the most common congenital heart defect.
It consists of a congenital hole in the septum (wall of tissue)[DA1] between the ventricles.

Given that the pressure is higher in the left than in the right ventricle, with every beat of the heart, blood flows from the left into the right ventricle (left-to-right shunt) and into the lungs. This results in pulmonary flooding (flooding of the lungs).

The larger the defect, the greater the blood flow and the more serious the repercussions.

Surgeons decide on a case-by-case basis whether and when an operation should be performed to close the hole.

Where the defect is so large that it causes high blood pressure in the pulmonary arteries (pulmonary hypertension), surgery is recommended within the baby’s first year, or preferably within the first six months.

ASD is a congenital hole in the septum or wall of tissue between the atriums. The defect in the atrial septum leads to a left-to-right shunt (blood diverting from the left to the right side of the heart) and therefore to flooding of the lungs (pulmonary flooding).

In the child’s first year, small ASDs frequently close on their own.
Depending on the size and location of the defect, a cardiac catheterisation procedure or surgery may be needed to close the hole. Cardiac catheterisation is when a long thin tube or catheter is inserted in an artery or vein and threaded through the blood vessels to the heart. Together with VSD (ventricular septal defect), ASD accounts for half of all congenital heart defects.

The interventional closure of an ASD with an umbrella (cardiac catheterisation) is a common procedure and is the method of choice for many ASDs. Success crucially lies in choosing the patients best suited for this procedure.

The intervention is carried out under general anaesthetic or sedation. A transesophageal echocardiogram (TEE image) is done to check the position of the umbrella before it is released. The risk of complications is no greater than for a surgical ASD closure.

The foramen ovale is a natural hole in the wall of tissue between the atriums (interatrial septum), which is needed while the foetus is in the womb and normally closes in the child’s first year.

Sometimes, the hole does not close completely. This condition is known as PFO and has no medical implications during childhood.

In the foetal circulatory system, the ductus arteriosus, also known as the ductus Botalli, is a normal and necessary connection between the pulmonary artery and the aorta.

Several days after birth, the ductus closes spontaneously. If this does not happen within the first few weeks, the infant has a patent ductus arteriosus.

Children with a small PDA do not display any symptoms. Those with a large PDA are more susceptible to infections and may even suffer from heart failure.

Given that all children with a PDA have a higher risk of inflammation of the heart valves, a ductus arteriosus should be closed if it persists beyond the child’s second year, or sooner in the case of a large ductus with increased blood flow to the lungs.

Three procedures can be used to close the ductus

• Operation
• Endoscopic closure with a metal clip
• Closure with a coil during cardiac catheterisation

The cardiologist will decide which procedure is most suitable based on the size of the ductus.

AVS is a narrowing of the aortic valve opening in the left ventricle caused by a thickening of the valve leaflets and/or an underdeveloped aortic root. The narrowing can be located beneath the valve (subvalvular), at the level of the valve (valvular) or above the valve (supravalvular).

The left ventricle must work against more resistance and so it thickens (hypertrophied). The extent of the narrowing determines the severity and risk of disease. In cases where treatment is considered necessary, subvalvular and supravalvular aortic stenosis can only be corrected surgically. Valvular aortic stenosis can usually be rectified with a balloon catheter.

At most centres, valvular aortic stenosis is dilated from a gradient of more than 70 mmHg (as measured by an echocardiogram). The procedure is carried out under general anaesthetic or sedation.

Pulmonary valve stenosis is a condition where a deformity on or near the pulmonary valve narrows the pulmonary valve opening. Exposed to greater resistance, the right ventricle has to work harder and forms more muscle mass as a result (hypertrophied).

A mild narrowing of the pulmonary valve does not give rise to any symptoms, but may result in a heart murmur.
Higher grade stenoses can lead to a bluish colouring of the skin (cyanosis) due to reduced blood flow through the lungs.

Depending on the complexity of the required surgical valve correction, the procedure may take place with or without a heart-lung machine (cardio-pulmonary bypass). Once the ribcage (thorax) has been opened, the paediatric surgeon makes an incision in the pulmonary artery above the valve to gain a direct view of the pulmonary valve. The deformed valve leaflets are cut open with a scalpel, taking care not to create a leaky valve. The pulmonary artery is sewn together and the ribcage is closed.

During cardiac catheterisation, a tube is inserted into a large vessel in the groin or arm and a cardiac catheter is pushed through to the right side of the heart, measuring the pressure gradient between the right heart ventricle and the pulmonary artery. By administering a contrast agent, the anatomy is displayed, and the team can decide which balloon size is needed to stretch the valve open. During balloon dilation (inflation), the valve leaflets tear along the deformed edges, enabling the blood to flow freely through the valve again. This procedure likewise involves the risk of creating a leaky valve. In the case of high-grade stenosis, this kind of exploratory examination of the pulmonary artery is associated with certain risks, as the blood flow to the lungs can sometimes be completely interrupted by the catheter even when the balloon is not inflated.

Aortic isthmus stenosis is a congenital vascular defect.

Just after the origin of the left subclavian artery at the aortic arch, there is usually a low-grade narrowing of the aorta. In the case of aortic isthmus stenosis, this narrowing is high-grade.

The narrowness of the aorta causes the left ventricle to work harder, whilst increasing the blood pressure in the arteries (arterial hypertension) in the upper body and decreasing the blood flow (hypoperfusion) in the lower body.

Surgery can normally take place without a heart-lung machine because the heart itself does not have to be opened up. The paediatric cardiac surgeon makes an incision between two ribs on the left side of the ribcage. For the duration of the surgery, the aorta is clamped behind and in front of the narrowing. Where the narrowing is short, the affected section is removed and the ends of the aorta are sewn together (end-to-end anastomosis).

Where the narrowing is longer, the affected section is removed and the lower end of the vessel is connected to the side of the aortic arch (end-to-side anastomosis). Occasionally, parts of the left subclavian artery are used to reconstruct the artery.

An AV canal defect can be described as complete when there is a large hole in the wall of tissue (the septum) that separates the left and right sides of the heart. The hole is in the centre of the heart, where the upper chambers (the atriums) and the lower chambers (the ventricles) meet, allowing blood to flow freely between all four heart chambers. In addition, rather than having separate valves on the right and left, there is only one large valve between the upper (atriums) and lower chambers (ventricles). This major defect at the centre of the heart causes oxygen-rich blood to flow from the left to the right side of the heart and into the lungs.

The increased flow of blood through the lungs damages the pulmonary vessels and causes high blood pressure in the lungs (pulmonary hypertension).

The AV canal defect can be surgically corrected only for as long as the pulmonary vascular resistance (resistance that must be overcome to push blood through the veins in the lungs) is not irreversibly raised.

For this reason, an AV canal defect is surgically corrected early on
(at around 3 months).

Tetralogy of Fallot is a complex heart defect (a combination of several heart defects) leading to a bluish colouring of the skin known as cyanosis.

The following defects are present:

Major septal defect

Pronounced narrowing between the right ventricle and the pulmonary artery

Incorrect positioning of the major vessels: the aorta is positioned too far to the right, directly over the ventricular septal defect (VSD), so that it is supplied with blood from the right and left ventricles.

The pressure is the same in both ventricles

Exposed to increased pressure, the right ventricle pumps against the narrowing of the pulmonary artery and thickens (hypertrophied). Some of the oxygen-poor blood is pressed into the aorta, causing the skin to turn blue (cyanosis).

The narrowing of the pulmonary artery often becomes more pronounced after birth which means that not enough blood can flow to the lungs.
Tetralogy of Fallot is corrected early on (at 2 to 3 months).

TGA is a condition where the aorta is supplied with blood from the right ventricle and the pulmonary artery receives blood from the left ventricle. When after birth the two connections between the pulmonary circulation (to the lungs) and the systemic circulation (to the body) close, the baby quickly becomes dangerously ill because no oxygen-rich blood can enter the systemic circulation.

To correct this defect, the arteries of the new-born must be switched.

The great arteries are disconnected from their original position on the heart and connected to the correct ventricles. The coronary vessels are likewise repositioned and connected to the correct vessels, ensuring that the heart itself is supplied with oxygen-rich blood.

HLHS is a condition where the entire left side of the heart, which supplies blood to the body (systemic circulation), is underdeveloped.

In the womb, the right ventricle secures the blood flow to the circulatory system. When, after birth, [DA1] the ductus arteriosus / Botalli closes (the connection between the aorta and the pulmonary artery to bypass the lungs), it becomes difficult for oxygen-rich blood to reach the body, leading to a life-threatening situation.

Life-saving medication can be administered to keep the ductus arteriosus / Botalli open. Until just a few years ago, HLHS always resulted in death.

There are two possible treatments:

• Heart transplant
• 3-step surgery
  
  Norwood operation: The Norwood operation is performed in the first few days of life. During the procedure, the trunk of the pulmonary artery is severed, and the underdeveloped aorta is extended with a patch. The two vessels are connected so that the right ventricle can pump blood to all organs in the body through this vessel. The trunk of the underdeveloped aorta is connected to the side of the new aorta and serves as the origin of the coronary vessels. The lungs are supplied with blood through a plastic tube (shunt), inserted between a branch of the aorta and the pulmonary artery. After this operation, the right ventricle has to pump blood not only to the body (systemic circulation) but also to the lungs (pulmonary circulation). To help the right ventricle cope with the extra workload, the infant is given medication to support the cardiovascular system.
  
  Glenn procedure: If the child’s oxygen levels in the arteries have fallen to unacceptable levels but the child has developed well, the second step – the Glenn procedure – is performed at 3 to 4 months. This step involves disconnecting the superior vena cava (SVC) from the heart and connecting it directly to the pulmonary artery. The abovementioned stent is removed. In contrast to newborns, the vascular pressure in infants of this age is high enough to drive the blood through the lungs without being pumped through a heart chamber first. The superior vena cava can be connected to the pulmonary artery in a variety of ways. While the oxygen-poor blood in the inferior vena cava flows directly to the heart, the blood from the upper body is oxygenated in the lungs which supplies the child with sufficient levels of oxygen. The advantage of this procedure is that the right ventricle no longer needs to work harder because the blood flows through the lungs passively, avoiding the right ventricle. This procedure can result in near-normal development.
  
  Fontan procedure: The third and final procedure (Fontan procedure) is performed at the age of 4-6 years and involves disconnecting the inferior vena cava from the heart and connecting it directly to the pulmonary artery. This procedure is also known as a total cavopulmonary anastomosis (TCPC). Now, all the venous blood flows to the lungs and the systemic (body) and pulmonary (lungs) circulatory systems are completely separate. This results in rosy skin. Named after its inventor, the procedure is also known as a “Fontan Circulation”. When the superior vena cava is connected to the pulmonary artery, the child has what is known as a “Hemi-Fontan” circulation.
  Since the lungs are still adapting to the changes in circulation, a small hole (fenestration) may be needed in the tunnel running through the atrium. This works like a “pressure relief valve”. When the pressure in the lungs increases (e.g. when the infant cries), the blood can only flow through the pulmonary vessels with a delay. To reduce the pressure, the blood is pressed through the fenestration. Depending on how much this connection is used, the infant’s colouring may alternate from rosy to blue to rosy. Even so, oxygen saturation levels are above 90 % in most Children.
  

Hypoplastic right heart syndrome (HRHS) is where parts of the right heart are underdeveloped in several possible ways. The condition affects the tricuspid valve (the heart valve between the right atrium and right ventricle), the right ventricle (right main chamber), the pulmonary valve (heart valve to the pulmonary artery) and the pulmonary arteries (lung arteries). The heart valves can be narrowed (stenotic) or completely closed (atretic). As a result, patients may also present with tricuspid atresia and pulmonary atresia. Given that the right half of the heart does not function properly, the baby is solely dependent on the left side of the heart to supply oxygen to the body and lungs. In children with HRHS, there is no way of stimulating growth of the underdeveloped right half of the heart.

The surgical procedure of choice depends on whether all or just some parts of the right heart are underdeveloped. In the case of tricuspid atresia, the right ventricle is so small that the left side of the heart has to do all the work.
In the case of pulmonary atresia, the situation may be slightly better in that the closed pulmonary valve can be opened through surgery or cardiac catheterisation which may allow the underdeveloped right main chamber to grow to normal size.

• Aortic pulmonary shunt: This operation is performed in the first few days after birth. Usually, the first surgical intervention involves connecting the aorta to the pulmonary artery. This is done by sewing a small plastic tube between the subclavian artery and the pulmonary artery. The aortic pulmonary shunt replaces the ductus arteriosus, which is surgically closed. This secures the oxygen supply although the child will still have a blueish colouring of the skin (cyanosis).
• Glenn procedure: If the overall situation is less favourable, the major vein in the upper body (SVC) is connected to the pulmonary artery at 4 to 6 months whilst the aortic pulmonary shunt or the stented ductus are surgically closed.
• Total cavopulmonary anastomosis (TCPC) | Fontan procedure: As in the case of hypoplastic left heart syndrome, all patients presenting with an undersized right ventricle will have the large blood vessel serving the lower body (inferior vena cava IVC) disconnected from the heart and connected to the pulmonary artery (Fontan circulation). The procedure is usually carried out when the child is 3 years of age.
  

When the embryological structure does not divide properly into the pulmonary trunk and aorta, it results in a condition known as truncus arteriosus communis. It presents as a single arterial trunk arising from the heart and providing mixed blood to the ascending aorta (supplying blood to the body – systemic circulation), the pulmonary arteries (supplying blood to the lungs) and the coronary arteries. This condition is also characterised by a large ventricular septal defect, or hole in the heart, beneath the trunk.

According to Collet and Edwards, there are four types, depending on where the pulmonary arteries are positioned:

• Type I displays a single dorsolateral pulmonary trunk arising from the truncal vessel.
• Type II displays right and left pulmonary arteries arising separately and at a similar level from the rear wall of the truncal vessel.
• Type III displays right and left pulmonary arteries arising separately but at different levels and to the side of the truncal vessel.
• Type IV displays no central pulmonary arteries. The blood is supplied to the lungs solely through the major aortopulmonary collateral arteries (otherwise known as “MAPCAS”).

The procedure is usually carried out in the first few months of life and is performed with the help of extracorporel circulation. The systemic circulation (body) is separated from the pulmonary (lung) circulation by closing the ventricular septal defect with a patch and creating a new right ventricular outflow tract.

The biggest problems are generally encountered with Type IV where unifocalisation is recommended. This is where the pulmonary arteries are brought together, as in the case of pulmonary atresia with VSD.

Accounting for less than 1% of all congenital heart defects, the Ebstein anomaly is a rare condition where the tricuspid valve (valve between the upper right and lower right heart chambers) is in the wrong position, has not formed properly and usually leaks. The right atrium has a thin wall and is enlarged, and the right ventricle is smaller as a result.

The deformed tricuspid valve is unable to close properly, causing blood to flow back and forth between the right atrium and the right ventricle.

Depending on the severity of the tricuspid valve deformity and the condition of the heart, this anomaly can cause right heart failure and therefore also risk to life. This can happen straight after birth, particularly when the baby also presents with underdeveloped, narrowed or closed (atresia[DA1] ) pulmonary arteries.

The infants are supported with medication for as long as possible and, under certain circumstances, are nourished through a feeding tube. Heart surgery is usually unavoidable given that the child’s health can be expected to deteriorate.

During the operation, the surgeon will try to reconstruct or, where this is not possible, to replace the deformed tricuspid valve. Patients who have had a tricuspid valve replacement will need to take blood-thinning medication throughout their lifetime. If the patient has an atrial septal defect, it is closed during surgery and the enlarged right atrium is reduced in size.

The surgical outcomes are generally good although the patient may encounter cardiac arrhythmia over time which may require a pacemaker.

If, in a newborn baby, valve replacement is not an option, the right ventricle is too small or the tricuspid valve cannot be reconstructed, a shunt is fitted (tunnel for the blood) and a multi-stage plan based on the Fontan principle is drawn up to alleviate the symptoms.
Occasionally, the surgeon may consider a heart transplant.

An enlarged heart can cause heart failure. Cardiomyopathy is a disease where the structure of the heart muscle changes. Frequently, this leads to the expansion (dilation) of the heart chambers and an enlarged heart.

The most common form is dilated cardiomyopathy (abnormally enlarged heart). It is frequently preceded by an inflammation of the heart muscle (myocarditis) which can be caused by a virus or bacteria. For example, the heart can become inflamed after a common cold where the virus is still in the body and affects the heart muscle.

It can also be caused by coronary heart disease. The coronary arteries are lined with fat and calcium deposits and have narrowed to such an extent that the heart muscle is no longer supplied with enough oxygen-rich blood and becomes damaged over time. Heart muscle cells slowly die off and are replaced by fibrous scar tissue. At the same time, the remaining healthy heart tissue tries to maintain the heart’s pumping capability by enlarging the heart chambers (hypertrophy). Over time, this compensation mechanism is no longer enough to offset the negative effects. The consequence is a thickened heart muscle that loses its elasticity and whose cavities do not fill with blood as they should. This restricts the pumping function and the ejection fraction (percentage of blood leaving the heart each time it contracts) to such an extent that it results in a chronically weak heart (chronic heart failure).

Once the cause of the enlarged heart has been diagnosed, the condition is usually treated with medication.
A heart transplant may become necessary over time.

An anomalous pulmonary venous connection is a condition where the pulmonary veins arising from the lungs do not connect properly to the left heart when the foetus is developing. As a result, rather than feeding the oxygen-rich blood to the left atrium, they supply it to the great veins to the right side of the heart.

There are four pulmonary veins.
If only some of them are affected, the condition is known as a partial anomalous pulmonary venous connection (PAPVC).
If all four veins are positioned incorrectly, we speak of a total anomalous pulmonary venous connection (TAPVC). This condition comes in many anatomical variations.

The symptoms in babies with a total anomalous pulmonary venous connection depend on the type of deformity and the degree of narrowing at the connection of the confluence.

If the narrowing causes the blood to collect in the lungs, the newborn baby becomes short of breath soon after birth, displaying a blue colouring of the skin (cyanosis) along with rapidly deteriorating health in the first few hours of life. In these cases, corrective surgery must be performed quickly.

Where the blood drains freely from the confluence into the venous system, the first symptom normally to appear is quickened breathing. Cyanosis is sometimes only slightly present. These infants display signs of a weak heart (heart failure), such as a weak sucking reflex when feeding and low weight gain. In these children, a diagnosis is often made later than in the abovementioned newborns.

When correcting a supra-cardiac (above the heart) anomalous pulmonary venous connection, the pulmonary venous confluence is connected directly to the dome of the left atrium between the superior vena cava and the aorta (known as side-to-side anastomosis). This allows the oxygen-rich blood from the common venous confluence to flow into the left atrium and reach the left heart chamber normally, before being pumped through the aorta into the systemic circulation (to the body). The previous connection between the common venous confluence and the systemic vein is closed. The atrial septal defect must be sewn together or closed with a patch. Procedures of this kind are associated with low mortality levels and rarely result in long-term complications.

The procedure to correct an infra-cardiac (beneath the heart) total anomalous pulmonary venous connection is considerably more complex. The pulmonary venous confluence drawing down through the diaphragm into the abdomen is sewn together at the bottom in the chest cavity. An incision is made along its length to where it connects with the pulmonary veins in order to remove the narrowing and to create a sufficiently wide connection to the left atrium. The mortality rate associated with this procedure is higher and complications are more frequent. Complications may include, for example, high blood pressure (hypertension) in the pulmonary vessels, caused by the previous accumulation of blood in the lungs. This may send the body into crisis making it more difficult to deliver intensive care.