Hypoplastic Left Heart Syndrome (HLHS)
What is hypoplastic left heart syndrome?
Normal heart (click to enlarge)Hypoplastic left heart syndrome (HLHS) is a congenital (present at birth) syndrome that involves a combination of several abnormalities of the heart and great blood vessels.
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.
See
About the Heart and Blood Vessels for more information on how the heart normally works.
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 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 cannot provide enough blood flow to meet the body's needs. For this reason, an infant with hypoplastic left heart syndrome is in a very critical situation.
Hypoplastic left heart syndrome occurs in up to four out of every 10,000 live births. The syndrome comprises 8 percent of all cases of congenital heart disease. It is one of the top three heart abnormalities to cause problems in the newborn. HLHS occurs slightly more often in boys than in girls. In many children, HLHS occurs by chance, with no clear reason evident for their development.
What causes hypoplastic left heart syndrome?
Hypoplastic left heart syndrome is the result of abnormal underdevelopment of sections of the fetal heart during the first 8 weeks of pregnancy. Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality, or environmental exposure, causing heart problems to occur more often in certain families. In hypoplastic left heart syndrome, there may be abnormalities of other organs.
What are the symptoms of hypoplastic left heart syndrome?
Infants with HLHS usually develop symptoms shortly after birth. The following are the most common symptoms of hypoplastic left heart syndrome. 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
The symptoms of hypoplastic left heart syndrome may resemble other medical conditions and heart problems. Always consult your child's physician for a diagnosis.
How is hypoplastic left heart syndrome diagnosed?
Hypoplastic left heart syndrome (click to enlarge)Your child's physician may have heard a heart murmur during a physical examination and referred your child to a pediatric cardiologist for a diagnosis. A heart murmur is simply a noise caused by the turbulence of blood flowing through a narrow region. Symptoms your child experiences also will help with the diagnosis.
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 perform a physical examination, listening to the heart and lungs, and make other observations that help in the diagnosis. Other tests are needed to help with the diagnosis.
Chest X-ray — A diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones and organs onto film.
Electrocardiogram (ECG or EKG) — 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.
Cardiac Catheterization — A procedure that gives function and information about the structure inside the heart. Under sedation, a small, thin, flexible tube (catheter) is inserted into a blood vessel in the groin and guided to the inside of the heart. Blood pressure and oxygen measurements are taken in the four chambers of the heart, as well as in the pulmonary artery and aorta. Contrast dye also is injected to more clearly visualize the structures inside the heart.
Cardiac Magnetic Resonance Imaging (MRI) — A non-invasive test that uses magnets and radio waves to make pictures of structures and blood flow inside the body.
What are the treatments for hypoplastic left heart syndrome?
Specific treatment for hypoplastic left heart syndrome will be determined by your child's physician based on:
your child's age, overall health and medical history
extent of the disease
your child's tolerance for specific medications, procedures or therapies
how your child's doctor expects the disease will progress
your opinion or preference
Your child most likely will be admitted to the intensive care unit (ICU) or special care nursery once symptoms are noted. Initially, your child may be placed on oxygen, or a ventilator to assist his/her breathing. Intravenous (IV) medications may be given to help the heart and lungs function more efficiently.
Surgical repair
The surgical approach to HLHS is directed toward using the one good ventricle to do the work that is normally done by two ventricles, and to separate the "blue" or pulmonary circulation from the "red" or systemic circulation, as is the case in the normal heart. Treatment consists of three stages ending with the Fontan procedure.
The Fontan procedure takes advantage of the fact that blood flows so easily through the mature lung that it does not need the force of the right ventricle to push it through. In fact, the great veins bringing "blue" blood back to the heart, called the superior vena cava and inferior vena cava, can be channeled directly to the lungs through the pulmonary artery, bypassing the right ventricle altogether. When this is achieved, the right ventricle (in HLHS, the only ventricle) can be devoted to pumping "red" blood to the rest of the body. In this way, "blue" blood pathways and "red" blood pathways are separate, with "blue" blood reaching the lungs passively, where it is oxygenated before returning to the single ventricle as "red" blood, then pumped to the body.
The blood vessels of the lungs change over the first year of life. The Fontan procedure depends on sufficiently easy flow through the lungs to not require the force of a ventricle to conduct blood through the pulmonary circuit. This is not possible in the first months of life, and two operations must precede the Fontan procedure until the lungs are ready.
The Stage I operation (Norwood Procedure) connects the right ventricle to the aorta so that its flow, which will eventually be "red" blood, will be delivered to the body through branches of the aorta. This usually involves rebuilding a small aorta and connecting it to the ventricle. To survive the newborn period, blood flow to the immature lungs must be forceful. Blood flow to the lungs is provided through a tube from a branch of the aorta to the pulmonary artery called the Modified Blalock-Taussig Shunt.
Usually, at between three and eight months of age, the lungs mature to the point that blood flows more easily through, and ventricular force is no longer necessary. The Stage II, or Bi-directional Glenn Shunt, is a direct connection between the superior vena cava and the pulmonary artery, diverting half of the "blue" blood directly to the lungs without the assistance of the ventricle.
Finally, with still further lung maturity, the vessels of the lungs can accommodate all the body's "blue" blood and the Stage III, or Fontan procedure, can be done. The Fontan procedure connects the inferior vena cava to the pulmonary artery by creating a channel, or baffle, through the heart to direct its flow to the pulmonary artery. Now all the "blue" blood flows passively to the lungs, and the single ventricle pumps exclusively "red" blood to the body.
What is the long-term outlook after treatment for hypoplastic left heart syndrome?
Children with hypoplastic left heart syndrome will need follow-up care throughout their life to make sure their heart continues to work correctly. Most will require heart medicines. Consult your child's physician regarding the specific outlook for your child.
What is the latest research on hypoplastic left heart syndrome?
Complementing the Cardiovascular Program of Children's Hospital Boston is the nation's most intensive clinical and basic research program focused on pediatric heart disease. Children's is a world leader in opening new avenues of "translational research," bringing laboratory advances to the bedside and doctor's office as quickly as possible. All senior medical staff members of the Cardiovascular Program participate in clinical research activities.
