Hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) is a rare, complex, serious form of congenital heart disease in which the left ventricle (or chamber) of the heart is underdeveloped. As a result, HLHS is called a “single-ventricle heart defect.” In general, the other left-sided structures of the heart are also small— including the mitral valve, aortic valve and ascending aorta. In the past without treatment, babies with HLHS could not survive, but there are now good surgical options that can help these babies.

Some, but not most, infants with HLHS may also have other birth defects and genetic syndromes. HLHS is found more often in male infants than in females.

As is often the case with congenital heart defects, there is no known single cause of hypoplastic left heart syndrome.

Symptoms manifest within a few days of birth if left untreated. They include:

• Pale skin color
• Cyanosis — blue-tinged skin, lips, and nailbeds, caused by lack of oxygen in the bloodstream
• Difficult or fast breathing
• Difficulty in feeding
• Rapid heartbeat
• Skin that is cool, clammy, or sweaty to the touch
• Cold limbs
• Fatigue, lethargy
• Weak pulse or shock

A standard prenatal ultrasound may indicate a problem that requires further testing with a fetal echocardiogram. A fetal echocardiogram is a specialized ultrasound to create pictures of the developing heart. If the diagnosis is not known before birth, an echocardiogram will be obtained and will show the diagnosis.

If the infant is cyanotic (has skin or membranes that appear blue or purple), it requires intensive support prior to surgical intervention. A surgical approach requiring multiple operations—known as staged reconstruction—is necessary to redirect blood flow through the heart. Through these surgeries the single ventricle is asked to do the work of pumping the blood to the body, while the blood to the lungs is “passive” (flows without a pump). Sometimes, a cardiac catheterization is performed prior to the second and third operations to assess the child's circulation. The three stages of staged reconstruction are:

• Stage 1: Norwood procedure. Performed in the first week or so of life, this procedure reconfigures the ventricles so that the right chamber can act as the main “pump” both into and out of the heart.
• Stage 2: Bidirectional cavopulmonary anastomosis. Sometimes known as the bidirectional Glenn procedure or the hemi-Fontan procedure, this procedure is performed at around 4 to 6 months of age. It reroutes the patient’s circulation so that deoxygenated blood from the brain can drain straight into the lungs and deliver oxygenated blood to the organs.
• Stage 3: Fontan procedure. Usually performed between the ages of 18 months and 3 years, the Fontan procedure reroutes blood flow from the lower body to the lungs by creating a channel outside of the heart. This channel is joined with the connection made in the Glenn procedure.

Children with hypoplastic left heart syndrome and other “single ventricle” problems will require a lifetime relationship with a cardiologist and a team with expertise in caring for these problems. This is one of the most serious heart problems seen in children and it is important for the family and the team to be aware of possible problems. Some of the most common problems include: leakage from valves, narrowing of lung or body blood vessels, weakening of the heart muscle over time, heart rhythm problems, loss of protein in the stool (protein losing enteropathy or PLE), Fontan associated liver disease (FALD), as well as others. Because of these problems some children with HLHS may require heart transplantation as they get older.