Hypoplastic left heart syndrome (HLHS) is a congenital heart defect affecting how the blood moves through the heart. It happens when the left side of the heart does not form correctly while the baby develops before birth. HLHS is considered a critical congenital heart defect, and your baby will need surgery soon after birth to correct the defect.
An infant with hypoplastic left heart syndrome has one of the highest risks for premature death from congenital heart defects. Only two out of three infants will survive the three surgeries necessary to modify the heart and restore function and proper blood flow.
In the United States, about one out of every 3,841 babies each year has hypoplastic left heart syndrome.
Normal healthy heart function
In a healthy heart, the left side of the heart is larger than the right and pumps oxygen-rich blood out to the entire body via a large artery called the aorta. The right side of the heart receives oxygen-depleted blood from the body and pumps it to the lungs via a large artery called the pulmonary artery. This artery splits into two separate arteries, which take blood to the two lungs. The blood picks up oxygen in the lungs and returns to the left side of the heart to circulate back out to the body.
Both large arteries come off the top of the heart very near each other, but oxygen-rich and oxygen-depleted blood never mixes.
Before an infant is born, they do not need their lungs to breathe, so circulation is slightly different.
Two holes allow blood to mix before birth, and pressure changes in the heart after birth cause them to close within the first few days, allowing blood flow to continue normally:
- The foramen ovale is a hole between the two sides of the heart.
- The ductus arteriosus is a hole between the two arteries coming off the top of the heart, the aorta and the pulmonary artery.
An infant with hypoplastic left heart syndrome has several defects in their heart:
- The left side of the heart and the valve inside it are too small and cannot pump blood out to the body effectively. After the two holes in the heart close a few days after birth, the left side of the heart is too small or weak to pump blood into the body effectively.
- The aortic valve, which prevents blood from returning to the left side of the heart, is not formed or is too small. Blood cannot leave the left side of the heart, as it should.
- The aorta, the large artery carrying blood to the body, is not formed or is too small. The body does not receive the oxygen-rich blood it needs.
- Frequently the infant will also have an atrial septal defect (ASD), an extra hole in the heart that allows oxygen-rich and oxygen-depleted blood to mix.
Before birth, the heart's right side pumps blood to the lungs and the body. However, a few days after delivery, when the two holes close and blood can no longer mix, the left side becomes unable to pump enough blood out to the body. Symptoms begin to develop at this point.
Your newborn may begin to show signs that his or her body is not getting the oxygen it needs, and the right side of their heart is working harder than it should. These symptoms could include:
- Ashen or bluish color to the skin
- Difficulty breathing
- Difficulty feeding
- Fast heart rate
- Weak pulse
Using prenatal tests, your doctor may detect a heart defect before a baby is born. If they see a cause for concern during these tests, they may want to take a closer look at your baby's heart with a fetal echocardiogram.
Suppose prenatal tests are not done or do not pick up on the defect. In that case, a newborn pulse oximetry reading showing low oxygen levels in your baby's hands and feet may alert your doctors to the possibility of a heart condition. At that point, they may be able to run some more tests and find the problem before the two holes in the heart close.
In some situations, the condition will first become apparent a few days after birth when the holes close.
Call your infant's doctor if you see any symptoms of HLHS in your child.
Call 9-1-1 if your infant is not responding to you or having difficulty breathing.
The doctor will listen to your baby's heart with a stethoscope and look at it with an echocardiogram. If they determine your baby has HLHS, they must begin treatment immediately.
Hypoplastic left heart syndrome is one of the most challenging congenital heart defects. Treatment will differ based on how severe the heart defect is and whether other heart defects are present in addition to the HLH. You will need to discuss with a pediatric cardiologist the right treatments for your child.
If the defect is detected before birth or immediately after, medical staff can give your baby IV medication to keep the ductus arteriosus open until surgery.
Your child will probably receive medication to lower their blood pressure, remove extra fluid, or help the heart pump more efficiently. They will need this medicine before the surgery and probably after as well.
You may need to feed your baby a high-calorie formula to help them gain weight if they are not eating well. In extreme cases, they may need a feeding tube.
In most situations, your child will need multiple surgeries in a particular order. These surgeries will not cure your child, but they will help restore heart function.
Norwood procedure: Within two weeks of birth, a surgeon will create a new aorta and attach it to the right side of the heart. The right side of the heart can now pump blood to both the lungs and the body without the ductus arteriosus staying open. The surgeon will direct blood to the lungs with a Blalock-Taussig or Sano shun.
- Bi-directional Glenn Shunt procedure: When your infant is between four to six months old, the surgeon will connect the large vein returning blood from the top part of the body to the artery bringing blood to the lungs, allowing blood to go directly to the lungs without entering the right side of the heart. This procedure will reduce the pressure and workload on the right side of the heart.
- Fontan procedure: When your child is 18 months to three years old, a surgeon will connect the large vein returning blood from the lower part of the body directly to the artery bringing blood to the lungs. The right side of the heart will now only pump oxygen-filled blood to the body; all the blood returning from the body bypasses the heart and goes directly to the lungs, and blood does not mix.
Your child may need more than these three surgeries, depending on the severity of the defect and how well past surgeries worked, or your doctor may recommend a heart transplant.
A heart transplant will fix all the problems of blood flow but will add issues related to organ transplants that your child will need to deal with throughout their lifetime.
Talk to your doctor about what is suitable for your child.
Prognosis and complications
Hypoplastic left heart syndrome is usually fatal within the first few days to months of life if not treated. And after the surgeries are complete, your child will still need to see a cardiologist regularly to monitor their heart.
Some complications your child may develop later in life include:
- Decreased activity tolerance
- Heart rhythm abnormalities
- Higher risk of infections
- High-risk pregnancies
- Varicose veins
- Fluid retention
- Heart failure
- Blood clots
Hypoplastic left heart syndrome is a heart defect that can be detected prior to your child’s birth, or which may become evident within days after their birth. It is usually fatal if not treated. Treatment requires surgery and life-long monitoring by a cardiologist.
Call your doctor if your newborn has symptoms of a heart defect or if you have had surgery to repair a hypoplastic left heart and are pregnant or plan to become pregnant.
Hypoplastic left heart syndrome is a congenital heart defect affecting how the blood moves through the heart.
Treatment will differ based on how severe the heart defect is and whether other heart defects are present.
If your child requires surgery, afterwards your child will need to see a cardiologist regularly to monitor their heart.
American Heart Association. (2022). Single Ventricle Defects.
CDC. (2022). Facts about Hypoplastic Left Heart Syndrome.
GARD. (2021). Hypoplastic left heart syndrome.
Rychik, J. (2014). Hypoplastic Left Heart Syndrome: Can We Change the Rules of the Game? AHA Journals.