Understanding Hypoplastic Left Heart Syndrome

Hypoplastic Left Heart Syndrome is a congenital heart defect that affects the normal flow of blood through the heart. 

If a baby is born with this condition, the left side of the heart can’t pump blood. Instead, the right side of the heart must pump the blood to the lungs and the rest of the body. 

Can children live a normal life with Hypoplastic Left Heart Syndrome?

Hypoplastic Left Heart Syndrome is a sliding scale with some affected only marginally and others profoundly. It is a non life compatible condition at birth and each child must have surgery to make corrections; many  children will have lifelong complications and may need follow up visits with a cardiologist. 

How often does Hypoplastic Left Heart Syndrome occur in children?

It is estimated that Hypoplastic Left Heart Syndrome occurs in approximately 1 in 5,000 children in the UK and Ireland. 

There are estimated to be 200 diagnoses made in the UK and Ireland per year. 

What causes Hypoplastic Left Heart Syndrome?

Like many congenital septal defects, the cause of Hypoplastic Left Heart Syndrome is unknown. Some babies may suffer from HLHS because of changes in their genes or chromosomes. 

Environmental factors during pregnancy are sometimes thought to increase the risk of HLHS in babies, especially with mothers who have taken medication or undergone medical procedures. 

Genetics are also thought to be a potential cause too. 

How is Hypoplastic Left Heart Syndrome diagnosed in children?

During pregnancy

During pregnancy, prenatal tests are used to check birth defects and other conditions. Hypoplastic Left Heart Syndrome can be diagnosed during pregnancy with an ultrasound scan and if it is suspected, an echocardiogram can be used to confirm the diagnosis. 

After birth 

After the baby is born, symptoms of Hypoplastic Left Heart Syndrome may not be present immediately, but some signs can quickly develop after the first few hours or days after birth. These signs include:

• Breathing problems 
• Pounding heart
• Weak pulse 
• Bluish skin colour

During a physical examination, a doctor might hear a heart murmur, which is an abnormal whooshing sound caused by blood not flowing properly. If a murmur is heard or other signs are present, your child’s doctor may request more tests. An echocardiogram is the most common type of test that will be used. 

Hypoplastic Left Heart Syndrome can also be detected with newborn pulse oximetry screening, which is a simple test used to determine the amount of oxygen in the baby’s blood. Low levels of oxygen can be a sign of HLHS. 

What are the symptoms of Hypoplastic Left Heart Syndrome?

Hypoplastic Left Heart Syndrome can present itself through many symptoms, including:

• Difficulty breathing 
• Difficulty feeding
• Lack of energy 
• Rapid heartbeat but weak pulse
• Sweaty, clammy or cool skin
• Greyish or bluish skin 
• Discoloured nails and lips 

Newborns don’t always show symptoms of HLHS immediately, but they will usually develop within a few hours or days after birth. 

Treatments for Hypoplastic Left Heart Syndrome

The type of treatment your child receives for HLHS usually depends on the severity of the condition. 

Medicine 

Some babies may need medicine to help strengthen the heart muscle, lower the blood pressure and help to get rid of the extra fluid. 

Surgery

Soon after a baby is born with Hypoplastic Left Heart Syndrome, surgeries will need to be undertaken to increase the blood flow to the body and bypass the poorly functioning left side of the heart. The surgery is usually completed in three stages:

• Norwood Procedure – This surgery is usually done in the first 2 weeks of a baby’s life. Surgeons create a ‘new’ aorta and connect it to the right ventricle. A tube is also placed from either the aorta or the right ventricle to the vessels to supply the lungs with oxygen. After the surgery, the baby’s skin may still look discoloured because oxygen-rich and oxygen-poor blood is still in the heart.

• Bidirectional Glenn Shunt Operation – At 4 – 6 months of age, the next procedure is complete. This procedure creates a connection between the pulmonary artery and the vessel returning oxygen-poor blood to the heart. This reduces the work the right ventricle has to do by allowing blood returning from the body to flow directly to the lungs.

• Fontan Procedure – This procedure is conducted during the period when a baby is aged 18 months to 3 years of age. Doctors will connect the pulmonary artery and the vessel returning oxygen-poor blood to the heart, allowing the rest of the blood coming back from the body to go to the lungs. Once this surgery is complete, the oxygen-rich blood will no longer mix with the oxygen-poor blood in the heart. 

Sometimes your child’s surgeon may recommend a heart transplant instead of the 3-part surgery. Babies who have a heart transplant will need lifelong medications. 

What happens as your child grows up?

As your child grows up, they will need lifelong follow up visits at least once a year with a cardiologist. These appointments will ensure that their heart, lungs and other vital organs continue to function as they should be. 

When your child becomes an adult, they will need to move to seeing specialists in adult congenital heart disease. 

Most children who have had surgery for Hypoplastic Left Heart Syndrome will need some form of heart medication for the rest of their life. They will also likely need antibiotics before any other surgeries to help prevent the risk of a heart infection. 

Are there any other conditions associated with Hypoplastic Left Heart Syndrome?

As we’ve mentioned, some babies born with Hypoplastic Left Heart Syndrome may also suffer from atrial septal defects. 

However, a small proportion of babies may have other abnormalities, including those relating to chromosome irregularities such as Turner Syndrome and Jacobsen Syndrome. Your child’s cardiologist will discuss this further with you if necessary.