Single Ventricle Defects

What are single ventricle heart defects?

In a normal heart there are four chambers. The two lower chambers are ventricles and they pump blood out of the heart. A child with a single ventricle heart defect has only one ventricle that is large enough to work effectively. The other ventricle may be small, underdeveloped or missing a valve.

Single ventricle heart defects are rare. They occur in about five out of every 100,000 live births.

There are different types of single ventricle heart conditions, some of which are:

• Hypoplastic Left Heart Syndrome (HLHS): This heart defect comprises a number of problems on the left side of the heart. The left ventricle is small (hypoplastic) and the mitral and/or the aortic valve may be narrow, blocked or not formed at all. The aorta is often small.
• Tricuspid atresia:  A heart defect where the valve between the right atrium and right ventricle doesn’t form at all.
• Pulmonary atresia with intact ventricular septum: A heart defect where the valve that controls the flow of blood between the right ventricle and the main pulmonary artery doesn’t form properly and there is no hole between the right and left ventricles
• Univentricular heart (Double inlet or outlet ventricle) In these conditions there is a single large pumping chamber (ventricle) which both collecting chambers (atria) empty their blood into. There may be a valve at the end of each collecting chamber or just one between the two. The two major blood vessels leaving the heart may leave from either the left or right sides of the ventricle and they may be swapped around (transposed).

How can they be spotted?

Most single ventricle heart defects can be detected at the 20-week anatomy scan or after birth by echocardiogram.

If it is not picked up in the antenatal period, once the baby is born it will display the following signs:

• Bluish skin colour
• Difficulty breathing
• Difficulty feeding
• Lethargy (sleepy or unresponsive)

In most cases, children with single ventricle heart defects require intensive medical intervention soon after birth.

How can they be treated?

Single ventricle heart defects cannot be corrected. However, the symptoms can be improved by surgery. Normally several stages of surgery are required to balance and optimise blood flow to the lungs and the body.

These will be open heart surgeries performed under general anaesthetic, the timing of which will depend on the severity of the anomaly, and the general condition of the baby.

Once baby has been born, the cardiologist will assess whether:

• There is too much blood going to the lungs
• Not enough blood going to the lungs

If there is too much blood flow to the lungs pulmonary banding will be needed to restrict this excessive flow.

If there is not enough blood flow to the lungs then a shunt or a stent will be needed to increase the blood going to the lungs.

Some babies with univentricular hearts balance themselves out regarding blood flow and don’t need any intervention in the immediate neonatal period.

Other surgeries offered can include:

Norwood procedure: This is the first surgery that is usually done in the first few weeks after birth. The surgeons will build a new larger aorta and use a small tube to direct blood flow to the lungs. 

Glenn procedure: The second surgery is usually done when the baby is around 6 months of age and the surgeons direct the blood flow from the upper body to the pulmonary artery so that the blood can collect oxygen from the lungs without having to go through the heart

Fontan procedure: This is the third surgery that is usually done when the child is 2 – 6 years old. The surgeons will now be separating the circulation so that no mixing of blood occurs. This also decreases the workload on the single ventricle. This procedure does not create a normal blood circulation in the body but it does improve the circulation.

General advice & information for the future

Babies and children with a single ventricle will need lifelong followup. Most will be on medicines for the rest of their lives.

They will need repeat tests like echocardiogram, ECG and sometimes cardiac Magnetic Resonance Imaging (MRI) scans. The aim of these check ups is to monitor your child’s heart function so that any future heart problems are diagnosed and treated quickly. 

Your cardiologist will advise you about any restrictions on activity that you should be aware of. As complicated as these conditions are, children are encouraged to be as active as they possibly can be. As your baby will have had open heart surgery, they will have a scar down the middle of the chest, and there will be small scars where drain tubes were used, but these will fade over time.

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