What is Hypoplastic Left Heart Syndrome (HLHS)?
Hypoplastic left heart syndrome is a single ventricle congenital heart defect affecting normal blood flow through the heart. Each year, approximately 960 infants in the U.S., or 1 in every 4,344 babies, are born with HLHS, according to the Centers for Disease Control and Prevention (CDC).
As a fetus with HLHS develops during pregnancy, the left side of the heart, which normally pumps oxygen-rich blood from the lungs to the rest of the body, does not grow normally and ends up being very small, or hypoplastic. This means the right side of the unborn baby's heart must do all the work of pumping blood to the baby. A special blood vessel—the ductus arteriosus, open in the fetus before birth—allows the right heart to pump blood to the body and organs of the fetus. Unfortunately, within hours to days after birth, the ductus arteriosus closes and severely diminishes blood flow to the body, restricting blood flow to the vital organs and eventually causing the baby to go into shock. Without treatment, HLHS can be fatal—often within the first hours or days of life.
HLHS is among the most challenging congenital heart defects to manage, but the cardiology specialists at the Children's Healthcare of Atlanta's Heart Center are trained to treat this condition and support patients and families every step of the way.
Congenital Heart Defects Explained
Hypoplastic Left Heart Syndrome
It can be overwhelming to learn that your child has a congenital heart defect. Our team of experts is here to provide the best care possible for children with HLHS.
How is HLHS diagnosed?
HLHS may be diagnosed during pregnancy or shortly after a baby is born.
It is most readily diagnosed on a fetal echocardiogram and is one of the most common cardiac defects picked up on an obstetrical ultrasound. An echocardiogram, which uses sound waves to produce images of the heart, can give detailed information about how your child’s heart is affected by HLHS, as well as how it’s functioning. During a fetal echocardiogram, an unborn child will show a smaller than normal left ventricle and aorta, as well as abnormal heart valves.
A prenatal diagnosis allows doctors to create a plan that will allow your child to be delivered safely at birth.
After birth, your baby can be started on prostaglandins, a medicine that is infused through an intravenous catheter into your baby's bloodstream. Prostaglandins keep the ductus arteriosus—the special vessel that lets the right heart pump blood directly to the body—open, allowing the baby to remain stable and avoid the danger of going into shock as a result of the ductus arteriosus closing.
What are the symptoms of HLHS after a baby is born?
Newborns with HLHS might not have any trouble during the first few days of life, but if the condition is unrecognized, they may quickly develop the following symptoms:
- Breathing problems
- Loss of appetite
- Pounding heart
- Weak pulse
- Ashen or bluish skin color
How do you treat HLHS?
Shortly after birth, an infant with HLHS may need:
- Medicines to keep the ductus arteriosus open, like prostaglandins, as well as medicines that help strengthen the heart muscles and help the body get rid of extra fluid.
- Catheters—usually in the umbilical blood vessels—that allow the care team to give medicine and draw blood for testing.
- Respiratory treatments, such as mechanical ventilation, which may be necessary to help balance the flow of blood to the body and lungs.
- Monitoring in order to detect organ dysfunction and help maintain the stability of the heart and lungs.
Children with HLHS will typically undergo a series of operations to help reconfigure the cardiovascular system to make it as efficient as possible, despite the lack of an adequate left ventricle. These surgeries do not correct the lesion but can help the baby's heart achieve function that is as normal as possible given the abnormal cardiac structure. These surgeries include:
- Norwood procedure: This surgery, which can be very challenging, is usually performed within the first week of life. It involves a new or “neo” aorta being made from part of the pulmonary artery and the original, tiny aorta, which is reconstructed or enlarged to provide blood flow to the body. A small tube graft is placed either from an artery to the lung vessels (called a modified Blalock-Taussig shunt) or from the right ventricle to the lung vessels (called a Sano shunt).
- Bidirectional Glenn procedure: During this operation, which is performed when a child is 4 to 6 months old, a large vein called the superior vena cava is connected to the pulmonary arteries. It allows the superior vena cava to supply the lungs with blood and serves as a shunt, giving the patient several years to grow. This takes some stress off the right ventricle until the next surgery.
- Fontan procedure: This procedure is usually performed when a child is 3 to 4 years old. It involves connecting the large vein returning blood from the lower part of the body to the heart—the inferior vena cava—directly to the lung artery, allowing the rest of the blood coming back from the body to go to the lungs. Once this procedure is complete, oxygen-rich and oxygen-poor blood no longer mix in the heart, and the child's blood oxygen levels become normal.
What is the future like for a child born with HLHS?
Infants born with HLHS may have lifelong complications, requiring follow-up visits with a cardiologist to monitor progress. Children with HLHS often take long-term cardiac medicines that help the heart work as efficiently as possible and undergo frequent testing to monitor heart health. If the heart becomes weak over time, a heart transplant may be necessary. Children who undergo a heart transplant will need to take medication for the rest of their lives to help prevent the body from rejecting a new heart.
An adult who had a Fontan procedure as a child may experience specific problems that require ongoing monitoring by a cardiologist. These issues may include:
- An abnormal heart rhythm that requires treatment.
- Weakening of the pumping chamber or leakage of one or more valves in the heart.
- Developing an unusual condition called protein-losing enteropathy that requires very careful management.
- Having problems with liver or kidney function.
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