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:

  • 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.

Anatomy of the heart | Cleveland Clinic

This illustration shows the normal heart structures.

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.

Hypoplastic left heart | Cleveland Clinic

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 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.

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

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