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What is Hypoplastic Left Heart Syndrome (HLHS)?

Hypoplastic left heart syndrome (HLHS) is a congenital heart defect, where the left ventricle of the baby’s heart is underdeveloped. It happens when an abnormality of the left-sided heart valve(s) occurs, and less blood flow passes through the left ventricle inhibiting its development. This means the left side of the heart cannot pump oxygen-rich blood to the rest of body. In a baby with untreated HLHS, the right side of the heart is able to pump the oxygen-rich blood for a few days after birth, but the heart cannot function this way in the long term.

How is HLHS diagnosed and managed during pregnancy?

The Fetal Heart Team can diagnose HLHS through a fetal echocardiogram (ECHO), or an ultrasound of the fetus’ heart. After diagnosing HLHS during your pregnancy, our team monitors your baby closely, and helps your family create a plan for delivery.

How does HLHS impact delivery?

Most babies with HLHS can be delivered vaginally, unless there are obstetric indications for another mode of delivery. It is best for these babies to be delivered at a medical center where there is immediate access to a team of pediatric cardiologists and neonatologists, along with an established NICU (Neonatal Intensive Care Unit).

After delivery, the baby needs PGE, a special medicine that gives a blood vessel the ability to remain patent, or open, after birth. This allows blood flow from the right ventricle to provide blood flow to the body. The baby will also be prepared for the first HLHS surgery, which typically occurs within a week of delivery.

The Fetal Heart Program at the St. Louis Fetal Care Institute has the experience, facilities and technology to handle the most medically challenging deliveries. In the most severe cases the team can perform cesarean sections and EXIT procedures at SSM Cardinal Glennon Children’s Medical Center. The EXIT procedure allows the fetal and cardiothoracic surgeons to perform life-saving procedures on the baby before cutting the umbilical cord. If additional intervention is needed, the baby is next door to the pediatric operating room and the pediatric hybrid cardiac catheterization suite.

What is the surgery for HLHS, and how does it work?

Within the first week of the baby’s birth, the first of three heart surgeries to increase blood flow to the body and bypass the poorly functioning left side of the heart will be conducted.

Through these surgeries, the right ventricle becomes the main pumping chamber to the body. The later surgeries allow non-oxygenated blood to be directed directly to the lungs, bypassing the heart. These surgeries do not cure Hypoplastic Left Heart Syndrome, but help restore heart function.

The three-step procedure to treat HLHS

1. Norwood Procedure or Hybrid Palliation In the first week of life.

In this surgery, the surgeon uses the pulmonary artery to recreate the aorta and inserts a surgical tube to provide blood flow to the lungs. There is still mixing of oxygen poor and oxygen rich blood.

In this alternative first stage procedure, a stent is placed in the ductus arteriosus, and bands are placed over the right and left branches of the pulmonary artery. This limits over-circulation to the lungs. There is still mixing of oxygen-poor and oxygen-rich blood.

2. Glenn procedure 4-6 months of age

This surgery creates a direct connection between the pulmonary artery and the superior vena cava (vessel returning oxygen-poor blood from the upper part of the body to the heart). This reduces the work the right ventricle has to do by allowing blood returning from the body to flow directly to the lungs.

3. Fontan procedure 2-4 years of age

This procedure completes the repair of Hypoplastic Left Heart Syndrome. Surgeons connect the pulmonary artery and the inferior vena cava (vessel returning oxygen-poor blood from the lower part of the body to the heart), 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.

What happens after the surgeries?

After the first surgery the baby may be fragile and have feeding difficulties because the heart is still working very hard. These babies will require a stay in the Neonatal Intensive Care Unit (NICU) until they overcome any feeding and breathing difficulties. Following these surgeries, these children will need regular follow-up visits with a cardiologist to monitor their progress.

What is the long-term prognosis for babies with HLHS?

The three-step procedure for HLHS was only introduced in the 1980’s. Overall, the long-term prognosis is quite good. Over 75% of babies who are treated with the 3-step procedure survive for at least 5 years, but many survive well beyond that. Since it has been performed since the 1980’s, many of the earliest patients are still alive and well, now in their 20’s or early 30’s.

Children with very complex HLHS, or children whose hearts become weak after the surgeries, may need heart transplants, but many can lead healthy lives.