What is Hypoplastic Left Heart Syndrome (HLHS)?

Hypoplastic left heart syndrome (HLHS) is a rare congenital heart defect. Babies born with HLHS have a combination of abnormalities of the heart as well as the major blood vessels. With HLHS, the entire left side of the heart is underdeveloped. This includes the aorta, aortic valve, left ventricle, and mitral valve. Sometimes these structures are unusually small and other times they are closed all together. The condition is very serious because these are the structures responsible for transporting oxygen-rich blood to the body. Because of this, babies with HLHS are not able to properly circulate blood. Without surgery, HLHS patients with die within hours or days.

Who gets HLHS?

HLHS is congenital, meaning it is present at birth. It occurs in about four out of every 10,000 live births. It affect boys slightly more than girls. Until recently, not much was known about HLHS and how it occurs. However, according to a new study, HLHS appears to have high heritability. This suggests that the condition may be genetic.

What causes HLHS?

The exact cause of HLHS is not known. In the past, it was believed that environmental factors and pure chance lead to HLHS. However, the most recent research suggests that HLHS is genetic. This means that mutations in certain genes likely lead to HLHS. Scientists currently hypothesize that HLHS occurs as a result of a defect in growth of muscle tissue while the heart is developing in utero.

What are the symptoms of HLHS?

In some cases, the defect is caught before birth. This is usually because of abnormal genetic testing results and/or an ultrasound. In cases where it is not caught, infants usually appear normal and healthy at birth. This is because when the baby was in utero, a structure known as the patent ductus arteriosus made it possible to have relatively normal circulation. After birth, however, this structure closes up. That is when signs and symptoms of HLHS begin to appear. These signs and symptoms include cyanosis, pale skin, sweaty and/or clammy skin, cool skin, heavy and/or rapid breathing, fast heart rate, poor oxygen saturation, a murmur, weak pulse, lethargy, and poor feeding. If the condition is not diagnosed, the symptoms will continue to get worse. Eventually, severe respiratory distress, severe shock, seizures, renal failure, liver failure, and worsening cardiac function will develop. These complications may or may not be reversible. That is why it is so important that HLHS be diagnosed early.

How is HLHS diagnosed?

If an infant's doctor suspects HLHS, the infant will usually be referred to a pediatric cardiologist. The pediatric cardiologist will first perform a physical examination and look at all observable signs. If HLHS is still suspected, tests will be ordered to aid in diagnosis. These tests may include a chest x-ray, electrocardiogram (EKG), echocardiogram, and cardiac catheterization. In cases where HLHS is suspected before birth, many tests will be run. Most importantly, an ultrasound. Parents are usually referred to a pediatric cardiologist. In these cases, the diagnosis will still need to be confirmed after birth.

How is HLHS treated?

Babies with HLHS need to be stabilized before other treatment can take place. There are basically two treatment options: a series of three surgeries or a heart transplant. The pediatric cardiologist will work with the parents to help decide what the best treatment option is. The three-stage surgery is almost always the treatment of choice. Following surgery, infants will be in the hospital for quite a while. Even once they get home, individualized treatment will continue for the rest of the individual's life.

What is the prognosis of those with HLHS?

Assuming HLHS is diagnosed and treated promptly, patients have a relatively good prognosis. Prior to the development of the three-stage surgery, there were no survivors. Those who received the three-stage surgery after its invention in the 1980s are now in their twenties. The long-term prognosis is not known. Most patients who die from HLHS die within the first days of life. If patients survive until six months of age, they have about a ninety percent chance of survival.

Sources

Children's Hospital of Wisconsin

Cincinnati Children's Hospital

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