What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome is a medical condition in which the structures of the left side of the heart are underdeveloped. The degree of underdevelopment can vary, but the structures involved usually include the following:

This illustration shows the normal heart structures.

  • The left ventricle: This is the left lower chamber of the heart, which pumps oxygen-rich blood out to the body. In hypoplastic left heart syndrome, this chamber is very small and poorly developed, and cannot provide enough blood flow to meet the body's needs.
  • The mitral and aortic valves: The mitral valve directs the oxygenated blood (which comes from the lung) from the left atrium (the left upper chamber of the heart) into the left ventricle. The aortic valve is between the left ventricle and the aorta. In hypoplastic left heart syndrome, these valves can be narrowed or closed, blocking the flow of oxygenated blood out to the body.
  • The aorta: This is the largest artery in the body. It receives the oxygenated blood from the left ventricle and distributes it to the body. In hypoplastic left heart syndrome, the aorta is small and very narrowed, which can block the flow of oxygenated blood out of the heart and to the body.

What causes hypoplastic left heart syndrome?

Hypoplastic left heart syndrome is a congenital condition (the baby is born with it). Underdevelopment of the heart structures occurs during the first eight weeks of pregnancy. There is often no clear reason for the development of congenital heart defects. In some cases, there might be a genetic (inherited) link or an environmental exposure that makes the defects occur more often in some families. In other cases, there is simply no known cause.

How common is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome occurs in four to 16 of every 10,000 live births, and accounts for about 8 percent of congenital heart disease in babies. It occurs more often in males (55 percent to 70 percent) than in females. Babies with this syndrome tend to also have other cardiovascular and neurologic (nervous system) organ defects.

This illustration shows some of the malformations seen in hypoplastic left heart syndrome, which includes a narrowing (in diameter) of the aorta; a pinching of the aorta; a narrowing or closure of the mitral and/or aortic valves; and underdevelopment of the left ventricle.

What are the symptoms of hypoplastic left heart syndrome?

Symptoms usually appear within a few hours or days after the baby is born, and can include the following:

  • Pale skin color
  • Cyanosis (blue coloring to skin, lips, and nailbeds)
  • Difficulty breathing
  • Difficulty feeding
  • Rapid heartbeat
  • Sweaty, clammy, or cool skin

How is hypoplastic left heart syndrome diagnosed?

Hypoplastic left heart syndrome can be detected while the baby is still in the uterus. After the baby is born, it is diagnosed based on a physical exam (listening to the heart and lungs), observation of symptoms, and the results of other tests, including the following:

  • Echocardiogram: Uses sound waves to create a moving picture of the heart's internal structures. This test can also be done while the baby is still in the womb.
  • Doppler ultrasound: Uses sound waves to measure blood flow; often combined with an echocardiogram to evaluate both the internal structure of the heart and blood flow across the heart's valves.
  • Chest X-ray: Shows the size and shape of the heart and lungs.
  • Electrocardiogram (ECG or EKG): Records the electrical changes that occur during a heartbeat. This test also reveals abnormal heart rhythms (arrhythmias) and detects heart muscle stress.

How is hypoplastic left heart syndrome treated?

Babies with this condition will die within days to weeks if they are not treated. Babies can be treated in a series of operations that re-route the function of the left side of the heart. Heart transplantation is another option, though it is limited by the number of infant hearts that are available. Children who have a heart transplant must take drugs to prevent organ rejection for the rest of their lives.

After birth

Once the baby is born, three surgical procedures—which are timed to coincide with the development of the lungs—are performed:

  • The Norwood Procedure: This surgery, which re-routes the blood flow to avoid the left side heart problems, is performed shortly after the child is born. The surgery turns the right ventricle—the non-defective ventricle—into the main “workhorse” ventricle that will pump blood to both the lungs and the body. The main pulmonary artery and the aorta are surgically connected with a shunt (tube), linking a branch of the aorta or the right ventricle to the pulmonary artery to supply blood to the lungs. Oxygenated blood is supplied to the body through other branches of the aorta.
  • Bi-directional Glenn Operation: This operation usually is performed about three to six months after the Norwood procedure, when the lungs are more mature and don't require ventricular force to send blood to the lungs. During this operation, the shunt to the pulmonary arteries is disconnected and a new shunt attaches the superior vena cava (major vein that drains de-oxygenated blood from the upper body to the right upper chamber of the heart) to the pulmonary artery. This new shunt diverts half of the de-oxygenated blood directly to the lungs without the need to go through the ventricle.
  • Fontan Operation: This operation is usually performed about 18 to 36 months after the Glenn operation, a time when the lungs have further matured and the vessels of the lungs can accommodate all the de-oxygenated blood from the lower part of the body. This operation connects the inferior vena cava (the major blood vessel that carries de-oxygenated blood from the lower part of the body back to the heart) with the pulmonary artery. This is done by creating a channel through or just outside the heart to direct blood to the pulmonary artery. After this operation, blood flows passively through the lungs, and the single ventricle pumps exclusively oxygenated blood to the body.

The decision about which surgical approach to take will depend on:

  • The baby's overall health;
  • The extent of the disease;
  • The surgeon's expertise;
  • Expectations about how the baby's disease might develop in the future, and;
  • The wishes of the parents.

Because these surgeries are complex and need to be personalized for each baby, your heart doctor will help you decide which medical and surgical approach will be best for your baby.

Before birth

Two new approaches to treating hypoplastic left heart syndrome while the baby is still in the uterus are being explored:

  • In a small group of fetuses in which the hole between the atria is closed, a procedure known as fetal balloon atrial septostomy opens the hole before the baby is born.
  • Another group of children develop a problem with the aortic valve, which leads to enlargement of the left ventricle. The left ventricle then shrinks, causing hypoplastic left heart syndrome. One proposed surgery is to open the aortic valve before the left ventricle shrinks.

There are significant risks to these procedures, and the outcomes are still mixed.

How successful are the treatments for hypoplastic left heart syndrome? Can my child expect to have a full, normal length of life?

The outlook is different for each baby. Ask your heart doctor about what to expect for your baby. Each stage of the different surgical repair procedures carries different risks and complications. Also, the outcomes at each medical facility are different, based on the number of cases performed and the surgeon's experience. Be sure to ask your heart doctor about these concerns.

Children with hypoplastic left heart syndrome will need check-up appointments throughout their lives to evaluate how well their hearts and other organs, such as livers and kidneys, are working. Other tests, such as cardiac MRI or cardiac catheterization, will also be performed periodically. Many children will require heart medicines, as well as antibiotics before dental work or other surgeries, to reduce the risk of infection to the heart valves (a condition called endocarditis).


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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 2/14/2017...#12214