Hypoplastic Left Heart Syndrome

Basics of Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a severe cardiovascular malformation that is a leading cause of infant mortality. In HLHS, the left side of the heart is underdeveloped and the aortic and mitral valves are narrowed or closed completely, impairing the heart’s ability to supply oxygen-rich blood to a child’s body. It is a congenital (present at birth) syndrome, meaning the heart defects occur due to abnormal underdevelopment of sections of the fetal heart during the first eight 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.

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

  • Mitral valve. The valve that controls blood flow between the heart’s left atrium and left ventricle.
  • Left ventricle. The heart’s lower left-hand chamber. 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 strong and muscular in order to pump enough blood to the body to meet its needs.
  • Aortic valve. The valve that regulates blood flow from the heart into the aorta.
  • Aorta. The body’s largest artery and 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 does not function effectively and cannot 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.

Fast Facts of Hypoplastic Left Heart Syndrome

  • Hypoplastic left heart syndrome occurs in 2 to 3 out of every 10,000 live births or 1 in every 4,344 babies born in the U.S. each year.
  • The syndrome comprises 2 percent to 3 percent of all cases of congenital heart disease.
  • HLHS occurs slightly more often in boys than girls.

Causes of Hypoplastic Left Heart Syndrome

Some congenital heart defects may have a genetic link, due to a gene defect, chromosome abnormality or environmental exposure, causing heart problems to occur more often in certain families. But research on whether genetics plays a large or relatively minor role in the development of HLHS has been inconclusive.

Symptoms of Hypoplastic Left Heart Syndrome

Infants with HLHS usually develop symptoms shortly after birth. Each child may experience symptoms of HLHS differently, but the most common ones include:

  • Cyanosis (blue color of the skin, lips and nail beds)
  • Pale skin
  • Sweaty or clammy skin
  • Cool skin
  • Heavy and/or rapid breathing
  • Fast heart rate
  • Cold feet, diminished pulses in the feet

Health problems associated with Hypoplastic Left Heart Syndrome

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

The first-stage procedure poses the highest risk. Specialized centers where a greater number of procedures are performed typically achieve higher survival rates than centers where fewer procedures are performed.

Infants and children who undergo the staged surgical procedures require special care and treatment to support growth and nutrition. These children often need support due to diminished physical strength and slowed developmental progress.

There is significant risk for progressive development of complications such as heart failure, dysrhythmias, and protein-losing enteropathy liver congestion, resulting in cirrhosis and/or liver congestion. Some children will eventually need a heart transplant to survive to adulthood.

Regular follow-up care at a center offering highly-specialized congenital cardiac care should continue throughout a child’s life.

Tests, procedures and diagnosis of Hypoplastic Left Heart Syndrome

When a child’s physician hears a heart murmur during a physical examination, the physician may refer the child to a pediatric cardiologist, who specializes in the diagnosis and treatment of congenital heart defects and other heart problems that may develop later in childhood. In making a diagnosis, the cardiologist performs a physical examination, listens to the heart and lungs, and makes other observations. Diagnostic testing for congenital heart disease varies by a child's age and clinical condition, and may include:

  • Chest X-ray. This diagnostic test uses X-ray energy beams to produce digital images of internal tissues, bones and organs.
  • Electrocardiogram (ECG or EKG). This test records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias) and detects heart muscle damage.
  • Echocardiogram (or “echo”). This procedure uses sound waves recorded on an electronic sensor to produce a moving picture of the heart and its valves. All patients with HLHS are diagnosed by echocardiography.

Treatment of Hypoplastic Left Heart Syndrome

A child’s doctor determines the specific treatment needed for hypoplastic left heart syndrome based on:

  • A child's age, overall health and medical history
  • Severity of the disease
  • A child's tolerance for specific medications, procedures or therapies
  • Expectations for the course of the disease
  • Parents’ opinions or preferences

A child will likely be admitted to the intensive care unit (ICU) or special care nursery after symptoms are noted. Initially a child may be placed on oxygen, and possibly 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. A child's cardiologist and cardiac surgeon can explain the risks and benefits of each. The surgical options include heart transplantation or a series of three operations that are done in stages: the first one shortly after birth, the second at about 3 to 9 months of age, and the final at about 18 months to 4 years of age. (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.

The series of operations are described below:

  • Stage I Norwood procedure. The goal of the operation is to make the right ventricle the main pumping chamber for blood flow to the body. During this procedure, the aorta is made larger to increase blood flow to the body. The outflow from the right ventricle (pulmonary artery) and outflow from the left ventricle (aorta) are connected side-by-side to allow all blood from either the right or left ventricles to reach the body. A connection is also made to enable the blood traveling through the aorta toward the body to "shunt" through this connection and flow into the pulmonary artery to receive oxygen. This allows blood to flow to the lungs and may be accomplished with either a modified Blalock-Taussig shunt or a modified Sano procedure. However, the infant will still have cyanosis because 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 shunt with another connection to the pulmonary artery. In this operation, the Blalock-Taussig 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 passively flows into the pulmonary artery and proceeds to the 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, greatly improving the blood’s oxygenation. The Glenn shunt, connecting the superior vena cava to the right atrium, is left in place. A second connection is made that directs blood from the inferior vena cava to the right pulmonary artery. This connection can be created in slightly different variations, depending on the method a child's surgeon prefers, and what is best for a child.