Hypoplastic Left Heart Syndrome (HLHS)

Overview

What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome (HLHS) is a complex and rare heart condition that’s present at birth (congenital). It’s a single-ventricle heart defect. This means one side of your baby’s heart didn’t develop correctly.

In babies born with hypoplastic left heart syndrome, some structures in the left side of their heart didn’t develop completely, including:

  • Left ventricle: This is your heart’s lower left chamber, which pumps oxygen-rich blood to your aorta.
  • Aorta: This is your largest blood vessel. It takes blood from your heart to the rest of your body.
  • Mitral and aortic valves: These flaps of tissue open and close to control how your blood moves through your heart. Your aortic valve allows blood to pass from your left ventricle to your aorta. Your mitral valve controls blood flow from your top heart chamber (atrium) to your lower heart chamber (ventricle).

Also, a baby with hypoplastic left heart syndrome may have an opening (atrial septal defect) between the two upper heart chambers. Normally, this would be a solid wall of tissue.

Hypoplastic left heart syndrome vs. normal heart

Each side of a normal heart has a job. The right side moves oxygen-poor blood to your lungs to get oxygen. The left side sends oxygen-rich blood to your body.

In a baby with hypoplastic left heart syndrome, the heart’s left side is too small to pump enough blood to the rest of the body. Their right ventricle or right lower chamber of their heart then takes over to pump blood to both their lungs and whole body. It does this through a blood vessel called the ductus arteriosus.

The ductus arteriosus is a vessel that all fetuses have. It typically gets smaller until it closes soon after birth. With a closed ductus arteriosus, hypoplastic left heart syndrome is usually fatal if babies don’t receive treatment.

How common is hypoplastic left heart syndrome?

About 1 in 3,800 babies are born with hypoplastic left heart syndrome each year in the U.S. This condition accounts for about 2% to 3% of all congenital heart diseases (CHD). Hypoplastic left heart syndrome affects more men and people assigned male at birth (67%) than women and people assigned female at birth.

Symptoms and Causes

What are the symptoms of hypoplastic left heart syndrome?

Hypoplastic left heart syndrome symptoms may include:

  • Cyanosis, or a grayish (in dark-skinned people) or bluish (in light-skinned people) discoloration of skin, lips and nails.
  • Difficulty breathing.
  • Difficulty feeding.
  • Lack of energy (lethargy).
  • Rapid heartbeat.
  • Sweaty, clammy or cool skin.
  • Weak pulse.

Newborns with HLHS don’t always show symptoms immediately. Instead, symptoms may develop within a few hours or days of birth.

What causes hypoplastic left heart syndrome?

Most of the time, there is no known cause for hypoplastic left heart syndrome. Sometimes, the cause is genetic. Babies with mutations (changes) in specific genes may have a higher risk of HLHS. These genes are known as GJA1 or NKX2-5.

Some babies with genetic disorders (such as Turner syndrome or trisomy 18) may also have hypoplastic left heart syndrome.

Diagnosis and Tests

How is hypoplastic left heart syndrome diagnosed?

A healthcare provider can make a hypoplastic left heart syndrome diagnosis with information from harmless imaging.

Your provider may do this during your pregnancy or soon after your baby is born.

During pregnancy, healthcare providers use painless and non-invasive imaging methods such as:

  • Ultrasound.
  • Fetal echocardiogram (ultrasound) to evaluate your baby’s heart before birth.

After your baby is born, healthcare providers diagnose the condition by observing symptoms and examining test results. They may hear a heart murmur while using a stethoscope to listen to your baby’s heart. This means blood isn’t flowing the way it should.

What tests will be done to diagnose hypoplastic left heart syndrome?

Tests for a hypoplastic left heart syndrome diagnosis may include:

  • Chest X-ray: This shows the size and shape of your baby’s heart and lungs.
  • Echocardiogram: This ultrasound shows internal heart structures.
  • Electrocardiogram (EKG): This measures electrical changes during a heartbeat.
  • Pulse oximetry screening: This tells how much oxygen is in your baby’s bloodstream.

Management and Treatment

Is hypoplastic left heart syndrome treatable?

Yes. First, your baby will need a medication called prostaglandin. This keeps their ductus arteriosus open and functioning. Other medicines can help your baby’s heart work more efficiently. Your baby also may need help with breathing.

Then they’ll need a series of surgeries to direct blood flow to their lungs and body. These operations put their heart’s workload on their right ventricle, which does all the pumping.

How is hypoplastic left heart syndrome treated?

Surgeons perform three separate operations. Hypoplastic left heart syndrome surgery stages are the Norwood, Glenn and Fontan procedures. Your baby’s provider will need to do the surgeries in that order.

Norwood procedure: Babies with HLHS need Norwood surgery within the first two weeks of life. During the procedure, surgeons:

  1. Reconstruct your child’s underdeveloped aorta to provide blood flow to their body.
  2. Place a shunt (tube) to reroute blood either from their right ventricle or aorta to their pulmonary arteries, which go to their lungs.
  3. Create a connection between the upper chambers of their heart. This drains oxygen-rich blood from their lungs to supply their body.

Bidirectional Glenn shunt operation: At 4 to 6 months of age, babies need a second operation. During the Glenn procedure, surgeons:

  1. Remove the old shunt.
  2. Place a new shunt to attach your baby’s superior vena cava to their pulmonary arteries. The superior vena cava (SVC) is a large vein that carries oxygen-poor blood from their upper body to their heart.
  3. Use this shunt to reduce the strain on your child’s right ventricle by letting blood flow right into their lungs.

Fontan procedure: Between 18 months and 4 years of age, babies need a final surgery. This final procedure allows all blood returning from their body to go straight to their lungs instead of mixing in their heart. During a Fontan procedure, surgeons will connect your baby’s inferior vena cava (IVC) to their pulmonary arteries. Similar to the SVC, the IVC is the large vein that carries oxygen-poor blood from your child’s lower body to their heart.

Complications of the treatment

Some children may not make it from one surgery to the next. Also, they may have problems after each surgery, such as:

  • Issues with their right ventricle not working right.
  • An aortic valve leak.
  • Liver disease.
  • Abnormal heart rhythms.
  • Blood clots.
  • Infection.
  • Trouble eating.
  • Seizures.
  • Kidney problems.
  • Cardiac arrest.

Is a heart transplant a good treatment for hypoplastic left heart syndrome?

Sometimes, your baby’s surgeon may recommend a heart transplant instead of the three-part surgery series. However, babies with heart transplants need lifelong medications.

Can hypoplastic left heart syndrome (HLHS) be treated before birth?

Operating during pregnancy is not a treatment for hypoplastic left heart syndrome. A fetal surgeon may choose to operate only to correct some conditions that might be associated with poor HLHS outcomes or in babies who are developing HLHS.

Prevention

Can I reduce the risk of hypoplastic left heart syndrome (HLHS)?

Many HLHS cases don’t have an obvious cause. However, providers always encourage healthful habits during your pregnancy, including:

  • Avoiding alcohol and smoking.
  • Controlling any medical conditions, such as diabetes.
  • Eating a healthy diet.
  • Taking a daily prenatal vitamin with at least 400 micrograms (mcg) of folic acid.

If you or the other prospective parent has hypoplastic left heart syndrome in their family, you may want to talk with a genetic counselor before getting pregnant.

Outlook / Prognosis

What can I expect if my child has hypoplastic left heart syndrome?

Your child will need lifelong follow-up visits at least once a year with a cardiologist (heart doctor). These visits ensure that their heart, lungs and other organs continue to work properly. When your child becomes an adult, they’ll transition to care from a specialist in adult congenital heart disease.

Most children with hypoplastic left heart syndrome will need heart medications. They’ll also need to take antibiotics before any other surgeries, such as dental surgeries. These medications reduce the risk of endocarditis (a heart infection).

Outlook for hypoplastic left heart syndrome

Without treatment, hypoplastic left heart syndrome is fatal days or weeks after birth.

A hypoplastic left heart syndrome prognosis depends on the complexity of your child’s heart deformity. Ask your baby’s healthcare provider about the risks associated with each surgery.

Some children may have decreased physical endurance for the rest of their lives. Usually, healthcare providers recommend limiting physical activities such as competitive sports.

What is the survival rate of hypoplastic left heart syndrome?

About 20% to 60% of babies with hypoplastic left heart syndrome survive their first year of life. After that, the survival rate for the next five, 10 and 15 years is about 40%. Babies who have a normal birth weight and aren’t premature do better than babies with lower birth weights. One study found that most babies who survived their first year were still alive at age 18.

Living With

How do I take care of my child?

Children born with this condition can live a healthy life with long-term monitoring from a cardiologist.

You can care for your child in these ways:

  • Make sure your child gets vaccinated against the flu every year and against COVID-19.
  • Bring your child to cardiologist appointments every six months or every year.
  • Make sure your child takes their medications.
  • Limit your child’s intense physical activity based on their provider’s recommendations.
  • Work with them if they have learning difficulties.

What questions should I ask my doctor?

If your baby has hypoplastic left heart syndrome, you may want to ask your healthcare provider:

  • What are the risks of surgery?
  • Are there potential surgery complications to watch for?
  • What medications does my child need?
  • Are there any medication side effects?
  • How will HLHS affect my child’s life?
  • What follow-up care does my child need after surgery?
  • If I have another baby, does that child have a higher risk of HLHS?

A note from Cleveland Clinic

Having a child with hypoplastic left heart syndrome can be stressful and lonely. It’s important to find a support group or other source of emotional support while you deal with the stresses and uncertainties of your child’s heart defect. Feeling emotionally strong will help you manage the highs and lows of your child’s health.

Last reviewed by a Cleveland Clinic medical professional on 07/29/2022.

References

  • American Heart Association. Single Ventricle Defects. (https://www.heart.org/en/health-topics/congenital-heart-defects/about-congenital-heart-defects/single-ventricle-defects) Accessed 7/29/2022.
  • Centers for Disease Control and Prevention. Facts about Hypoplastic Left Heart Syndrome. (https://www.cdc.gov/ncbddd/heartdefects/hlhs.html) Accessed 7/29/2022.
  • Chaix M, Khairy P. Single Ventricle Post Fontan Palliation: Tricuspid Atresia, Pulmonary Atresia, and Hypoplastic Left Heart Syndrome. In: Fuster V, Narula J, Vaishnava P, Leon MB, Callans DJ, Rumsfeld J, Poppas A, eds. Fuster and Hurst's The Heart. 15th ed. McGraw Hill; 2022. Accessed 7/29/2022.
  • National Center for Advancing Translational Sciences. Hypoplastic left heart syndrome. (https://rarediseases.info.nih.gov/diseases/6739/hypoplastic-left-heart-syndrome) Accessed 7/29/2022.
  • National Organization for Rare Disorders. Hypoplastic Left Heart Syndrome. (https://rarediseases.org/rare-diseases/hypoplastic-left-heart-syndrome/) Accessed 7/29/2022.
  • Roeleveld PP, Axelrod DM, Klugman D, et al. Hypoplastic left heart syndrome: from fetus to fontan. (https://pubmed.ncbi.nlm.nih.gov/30223915/) Cardiol Young. 2018 Nov;28(11):1275-1288. Accessed 7/29/2022.
  • Siffel C, Riehle-Colarusso T, Oster ME, Correa A. Survival of children with hypoplastic left heart syndrome. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4663985/) Pediatrics. 2015;136(4):e864-e870. Accessed 7/29/2022.

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