Hypoplastic Left Heart Syndrome

Anatomy of the heart, normal

What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome (HLHS) is a combination of several abnormalities of the heart and great blood vessels. It is a congenital (present at birth) syndrome, meaning that the heart defects occur due to underdevelopment of sections of the fetal heart starting during the first 8 weeks of pregnancy.

In the normal heart, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped out to the body through the aorta.

Anatomy of a heart with hypoplastic left heart syndrome

In hypoplastic left heart syndrome, most of the structures on the left side of the heart are small and underdeveloped. The degree of underdevelopment differs from child to child. The structures affected usually include the following:

  • Mitral valve. The valve that controls blood flow between the left atrium and left ventricle in the heart.

  • Left ventricle. The lower left-hand chamber of the heart. It receives oxygen-rich (red) blood from the left atrium and pumps it into the aorta, which takes the blood to the body. The left ventricle must be well-developed, strong, and muscular in order to pump enough blood to the body to meet its requirements.

  • Aortic valve. The valve that regulates blood flow from the heart into the aorta.

  • Aorta. The largest artery in the body and the primary blood vessel leading from the heart to the body.

Perhaps the most critical defect in HLHS is the small, underdeveloped left ventricle. This chamber is normally very strong and muscular so it can pump blood to the body. When the chamber is small and poorly developed, it will not function effectively and can't provide enough blood flow to meet the body's needs. For this reason, an infant with hypoplastic left heart syndrome will not live long without surgical intervention. HLHS occurs slightly more often in boys than in girls.

What causes hypoplastic left heart syndrome?

Some congenital heart defects may be due to a genetic defect  that causes heart problems to occur more often in certain families. In hypoplastic left heart syndrome, there may be abnormalities of other organs.

In many children, HLHS occurs by chance, with no clear reason for its development.

What are the symptoms of hypoplastic left heart syndrome?

Infants with HLHS usually develop symptoms shortly after birth. However, each child may experience symptoms differently. Symptoms may include:

  • Cyanosis (blue color of the skin, lips, and nailbeds)

  • Pale skin

  • Sweaty or clammy skin

  • Cool skin

  • Heavy and/or rapid breathing

  • Fast heart rate

  • Cold feet, diminished pulses in the feet

The symptoms of hypoplastic left heart syndrome may look like other medical conditions and heart problems. Always consult your child's doctor for a diagnosis.

How is hypoplastic left heart syndrome diagnosed?

In many cases, hypoplastic left heart syndrome is diagnosed while the fetus is still in the womb. After birth, you or your doctor may have noticed that your baby is listless, breathing rapidly, or cyanotic (blue). 

A pediatric cardiologist specializes in the diagnosis and medical management of congenital heart defects, as well as heart problems that may develop later in childhood. The cardiologist will examine the child, listen to the heart and lungs, and make other observations that help in the diagnosis. Diagnostic testing for congenital heart disease varies by the child's age, clinical condition, and institutional preferences. Some tests that may be recommended include the following:

  • Chest X-ray. A diagnostic test that uses invisible X-ray energy beams to produce images of internal tissues, bones, and organs onto film.

  • Electrocardiogram (ECG). A test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle damage.

  • Echocardiogram (echo). A procedure that evaluates the structure and function of the heart by using sound waves recorded on an electronic sensor that produce a moving picture of the heart and heart valves. People with HLHS are almost always diagnosed by echocardiography.

Treatment for hypoplastic left heart syndrome

Your child will most likely be admitted to the intensive care unit (ICU) or special care nursery once symptoms are noted. Initially, your child may be placed on oxygen, and possibly even on a ventilator, to assist with breathing. Intravenous (IV) medications may be given to help the heart and lungs function more efficiently.

There are two surgical approaches offered to treat HLHS. Your child's cardiologist and cardiac surgeon will explain the risks and benefits to you. The surgical options include the following:

  • Series of 3 operations that are done in stages. The first one shortly after birth, the second at about 4 to 6 months of age, and the final at about 2 to 3 years of age (the timing of these stages may vary). In this series of operations, the right ventricle is used as the main pumping chamber to the body, and blood flow is redirected to the lungs and the body with various surgical connections:

    • Stage I Norwood procedure. The first operation serves to make the right ventricle the main pumping chamber for blood flow to the body. The outflow from the right ventricle (the pulmonary artery) and the outflow from the left ventricle (the aorta) are connected side-by-side in order to allow all blood from either the right or left ventricles to reach the body. A connection is also made to make a pathway for blood to flow into the lungs to receive oxygen. This may be accomplished with either a modified Blalock-Taussig shunt, in which the tube to the lungs is connected to the aorta,  or a modified Sano procedure, in which the tube is connected to the right ventricle. However, the infant will still have cyanosis since oxygen-poor (blue) blood from the right atrium and oxygen-rich (red) blood from the left side of the heart mix and flow through the aorta to the body.

    • Glenn shunt. A second operation replaces the Blalock-Taussig or Sano shunt with another connection to the pulmonary artery. In this operation, the Blalock-Taussig or Sano shunt is removed, and the superior vena cava (the large vein that brings oxygen-poor blood from the head and arms back to the heart) is connected to the right pulmonary artery. Blood from the head and arms then passively flows into the pulmonary artery and lungs to receive oxygen. However, oxygen-poor (blue) blood returning to the heart from the lower body through the inferior vena cava will still mix with oxygen-rich (red) blood in the left heart and travel to the body, so the child will remain cyanotic. This operation helps create some of the connections necessary for the final operation, the Fontan procedure.

    • Fontan procedure. This operation allows all the oxygen-poor (blue) blood returning to the heart to flow into the pulmonary artery and lungs, greatly improving the oxygenation of the blood. The Glenn shunt, connecting the superior vena cava to the right pulmonary artery, is left in place. A second connection is made directing blood from the inferior vena cava to the right pulmonary artery as well. This connection can be created in slightly different variations, depending on the method your child's surgeon prefers, and what is best for your child.

  • Heart transplantation (less common) 

Postoperative care for your child

After surgery, infants will return to the intensive care unit (ICU) to be closely watched during recovery. The chest may be left open, and covered with sterile drapes. The open chest prevents compression of the heart by the rib cage. The chest is then closed several days later after the swelling in the chest has gone down and the heart has had a chance to adjust to the new circulation.

While your child is in the ICU, special equipment will be used to help him or her recover, and may include the following:

  • Ventilator. A machine that helps your child breathe while he or she is under anesthesia during the operation. A small, plastic tube is guided into the windpipe and attached to the ventilator, which breathes for your child while he or she is too sleepy to breathe effectively. After a HLHS operation, children will usually benefit from remaining on the ventilator for at least a few days.

  • Intravenous (IV) catheters. Small, plastic tubes inserted through the skin into blood vessels to provide IV fluids and important medicines that help your child recover from the operation.

  • Arterial line. A specialized IV placed in the wrist or other area of the body where a pulse can be felt, that measures blood pressure continuously during surgery and while your child is in the ICU.

  • Nasogastric (NG) tube. A small, flexible tube that keeps the stomach drained of acid and gas bubbles that may build up during surgery.

  • Urinary catheter. A small, flexible tube that allows urine to drain out of the bladder and measures how much urine the body makes. This helps determine how well the heart is functioning. Immediately after surgery, the heart will be a little weaker than it was before, and the body may start to hold onto fluid, causing swelling and puffiness. Diuretics may be given to help the kidneys to remove excess fluid from the body.

  • Chest tube. A drainage tube may be inserted to keep the chest free of blood that would otherwise accumulate after the incision is closed. Bleeding may occur for several hours, or even a few days after surgery.

  • Heart monitor. A machine that constantly displays a picture of your child's heart rhythm, and monitors heart rate, blood pressure, and other values.

Your child may need other equipment not mentioned here to provide support while in the ICU, or afterwards. The hospital staff will explain all of the necessary equipment to you.

Your child will be kept as comfortable as possible with several different medications; some that relieve pain, and some that relieve anxiety. The staff will also be asking for your input as to how best to soothe and comfort your child.

After discharge from the ICU, your child will recuperate on another hospital unit before going home. You will learn how to care for your child at home before your child is discharged. Your child may need to take medications for a while, and these will be explained to you. The staff will give you instructions regarding medications, activity limitations, and follow-up appointments before your child is discharged.

Infants who spent a lot of time on a ventilator, or who were fairly ill while in the ICU, may have trouble feeding initially. These babies may have an oral aversion; they might equate something placed in the mouth, such as a pacifier or bottle, with a less pleasant sensation, such as being on the ventilator. Some infants are just tired, and need to build their strength up before they will be able to learn to bottle-feed. Strategies used to help infants with nutrition include the following:

  • High-calorie formula or breast milk. Special nutritional supplements may be added to formula or pumped breast milk to increase the number of calories in each ounce, thereby allowing your baby to drink less and still consume enough calories to grow.

  • Supplemental tube feedings. Feedings given through a small, flexible tube that passes through the nose, down the esophagus, and into the stomach, that can either supplement or take the place of bottle-feedings. Infants who can drink part of their bottle, but not all, may be fed the remainder through the feeding tube. Infants who are too tired to bottle-feed at all may receive their formula or breast milk through the feeding tube alone.

Caring for your child at home following a HLHS surgical repair

Pain medications, such as acetaminophen or ibuprofen, may be recommended to keep your child comfortable at home. Your child's doctor will discuss pain control before your child is discharged from the hospital.

If any special treatments are to be given at home, the nursing staff will ensure that you are able to provide them, or a home health agency may assist you.

You may receive additional instructions from your child's doctors and the hospital staff.

Long-term outlook for hypoplastic left heart syndrome

Without intervention, most infants with HLHS will not survive longer than a few days to a few weeks. Heart transplantation is an option, but because of the difficulty in obtaining a donor heart for an infant, the series of surgical procedures described above is most often recommended.

The first-stage procedure poses the highest risk for poor outcomes and death. Some specialized centers where a greater number of procedures are done have achieved survival rates that are higher than at centers where fewer procedures are done. Survival rates are higher with later stage procedures.

Infants and children who have the staged surgical procedures will require special care and treatment to support growth and nutrition. These children often have diminished physical strength as well as slowed developmental progress and may need support.

In the long-term, there is significant risk for progressive development of complications, such as heart failure, heart rhythm problems, protein-losing enteropathy, and liver congestion resulting in cirrhosis.

Some cases will require heart transplantation to survive into adulthood.

Regular follow-up care at a center offering highly-specialized congenital cardiac care should continue throughout the individual's lifespan.

Consult your child's doctor regarding the specific outlook for your child.