Hypoplastic Left Heart Syndrome (HLHS)

What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome is a congenital heart defect in which there are a number of problems with the structures on the left side of the heart.

• The left ventricle (the chamber that pumps oxygen rich blood to the body) is small and underdeveloped.
• The mitral valve that allows blood flow from the left atrium into the left ventricle may be blocked, narrow or not formed at all.
• The aortic valve that controls the flow of blood from the left ventricle to the body may be blocked, narrow or not formed at all.
• The aorta, the vessel that carries oxygen rich blood to the body is small (hypoplastic)
• There may be a hole between the two upper chambers (atria) of the heart.

This means the left ventricle and aorta are too small to pump enough blood to the body.

Instead, the right ventricle which normally only pumps blood to the lungs, must pump blood to the lungs and also to the rest of the body. The blood is pumped to the rest of the body through a small blood vessel called the ductus arteriosus. During pregnancy, this structure allows blood to bypass the lungs and go straight to the descending aorta to supply oxygen rich blood to the body. A couple of days after birth, this vessel usually closes on its own. In a baby with an hypoplastic left heart syndrome, when the duct closes, blood can no longer reach the lower body. This can cause the baby to suddenly become very ill and without treatment HLHS is fatal.

1. Mitral atresia
2. Hypoplastic left ventricle
3. Hypoplastic aorta
4. Persistent ductus arteriosus
5. Atrial septal defect

How can hypoplastic left heart syndrome be spotted?

Hypoplastic left heart syndrome can be detected at the 20 week anatomy scan or after birth by echocardiogram.

If HLHS is not picked up in the antenatal period, once the baby is born and the ductus arteriosus closes the baby will display the following signs:

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

If HLHS is diagnosed during the pregnancy, plans can be made to give the baby a medicine at birth called prostaglandin which keeps the ductus arteriosus open until the baby can have surgery. 

In most cases, children with HLHS require intensive medical intervention soon after birth. 

How can hypoplastic left heart syndrome be treated?

Immediate treatment will be gaining intravenous access after birth and the medicine prostaglandin started to keep the duct open. This will enable blood to reach the body until surgery can take place.

Hypoplastic left heart syndrome 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.

Norwood procedure: This is the first surgery that is usually done in the first week 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 between 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 HLHS will need lifelong follow-up. 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 tests 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. They are encouraged to live as normal a life as they possibly can. 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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