What Is Hypoplastic Left Heart Syndrome?

Hypoplastic left heart syndrome is a severe form of congenital heart disease in which the left side of the heart is malformed from birth. Without intervention, it leads to infant death in the first few weeks of life. It is found in about 3% of infants born with congenital heart disease and is slightly more common in boys than in girls.

Hypoplastic Left Heart Syndrome Symptoms

Some symptoms of hypoplastic left heart syndrome might include:

• Difficulty breathing
• Racing heartbeat
• Pale or bluish color
• Weak pulse

These symptoms might not start right away. Because of the anatomy of hypoplastic left heart syndrome and normal prenatal circulation, symptoms might only begin a few days after birth.

If surgery isn’t performed, hypoplastic left heart syndrome always leads to infant death, as the organs of the body don’t get enough blood. Just 45 years ago, the condition was universally fatal. With treatment, about 85% of infants surgically treated now are expected to be alive at age 30.

People with hypoplastic left heart syndrome are also at risk of certain problems even after they’ve had successful surgery. For example, such individuals are at a higher risk of abnormal heart rhythms, such as atrial fibrillation. They may also be limited in the amount that they can exercise. A minority of individuals have symptoms from malformations in other parts of the body as well.

Due to a variety of factors, children who survive their operations are also at higher risk for learning disorders, behavioral disorders (such as ADHD), and decreased academic achievement.

Causes

Anatomy

The left side of the heart pumps oxygenated blood coming from the lungs out to the rest of the body. This oxygen is needed by all your cells for basic life processes. Anything that impairs this pumping poses a life-threatening problem. Hypoplastic left heart syndrome is a congenital heart disease, which just means that it is a heart problem that is already present at birth.

In hypoplastic left heart syndrome, most of the parts of the left side of the heart are either underdeveloped or totally absent. This includes the left ventricle, the mitral valve, and the aorta. The wall of the left ventricle (the main pumping chamber) may be abnormally thick, making it unable to contain enough blood. In all cases, the left side of the heart doesn’t develop properly before birth. Some people with hypoplastic left heart syndrome have additional anatomical issues with their heart.

In an infant with hypoplastic left heart syndrome, the left side of the heart can’t pump enough blood to the body. Instead, the right side of the heart must do this work, receiving some oxygenated blood from the left side of the heart through an artery called the ductus arteriosus. Some oxygenated blood also flows in through an opening called the foramen ovale. The blood pumped out to the body is lower in oxygen than normal, leading the newborn to develop pale or blue skin (cyanosis).

Normally, the ductus arteriosus artery and the foramen ovale close within a few days after birth. This is a normal change in the way the blood should flow after birth compared to before. But because of the abnormal circulation in someone with hypoplastic left heart syndrome, this is a big problem. When these openings start to close, the infant develops signs of heart failure (which lead to death if not treated).

Genetic and Environmental Causes

The underlying causes leading to hypoplastic left heart syndrome are complex. Having mutations in certain genes might increase one’s risk of congenital heart disease. Certain environmental factors might increase risk as well, such as certain infections or exposures to toxins. However, these are complicated and not well understood, and many infants born with congenital heart disease don't have any risk factors.

A minority of infants with hypoplastic left heart syndrome have a recognized genetic syndrome that can cause other problems, like Turner syndrome.

Diagnosis

Hypoplastic left heart syndrome might be diagnosed during pregnancy or shortly after the baby is born. During pregnancy, a clinician might become concerned about hypoplastic left heart syndrome during fetal ultrasound. A fetal echocardiogram, (an ultrasound of the baby’s heart) can be used to confirm the diagnosis.

After birth, physical examination of the infant is an important part of the process and can point to a potential heart problem as a possible cause. Infants with this condition will often have low blood pressure. Diagnostic tests can also provide clues to eventually get the exact diagnosis. Some of these might include:

• Pulse oximetry screening
• Chest X-ray
• ECG (electrocardiogram)
• Basic laboratory blood tests, like a comprehensive metabolic panel and complete blood count

Echocardiogram, which provides visual information about the heart’s anatomy, is key. It’s important to get detailed information about the specific anatomical issues involved, which can vary somewhat.

Treatment

Initial Management

Because hypoplastic left heart syndrome is so serious, infants will initially need support to stabilize them before further treatment is a possibility. This may include medications like prostaglandin, which can help keep the ductus arteriosus open and increase blood flow. Other medications, like nitroprusside, may be needed to increase blood pressure. Some infants may need blood transfusions.

An infant who can’t breathe normally may also need ventilatory support. Some may need treatment with extracorporeal membrane oxidation (ECMO), which uses a machine to do some of the work that the heart and lungs normally do. Infants will need treatment in a neonatal intensive care unit, where they can receive in-depth medical monitoring and support.

These infants often have trouble feeding, and they may need nutritional support with high-calorie formulas. Some will eventually need surgical placement of a feeding tube to make sure they get enough nutrition.

Long-term Treatment Approaches

Three main treatment options exist for hypoplastic left heart syndrome: surgery, heart transplant, and compassionate care treatments. Patients and medical teams will make decisions about approach based on the infant’s overall medical picture, resource availability, and family preferences.

Surgery

Because the anatomical problem with hypoplastic heart syndrome is so severe, surgical treatment must be done in three different stages. These surgeries help rebuild part of the heart and redirect the way the blood flows.

The Norwood procedure, the first surgery, usually takes place when the infant is around one to two weeks old. This surgery creates a temporary shunt to get blood to the lungs.

More recently, a less invasive alternative to the Norwood has been developed, called the hybrid procedure. This procedure places a stent to help keep the ductus arteriosus open. Unlike the Norwood, it doesn’t require that the infant go on cardiopulmonary bypass. One advantage is that it delays complex reconstruction of the heart to when the infant is a little older and stronger. 

The second surgery, called the Glenn procedure, usually takes place when the infant is four to six weeks old, when the baby has outgrown the initial shunt. This procedure redirects blood flow from the upper body to the lungs. At this point, infants who had an initial hybrid procedure undergo a surgery that contains elements of both the Norwood surgery and the Glenn procedure.

The third surgery, called the Fontan procedure, usually takes place between 18 months and 4 years of age. Here, the surgeons ensure that blood from the lower part of the body goes directly to the lungs, without having to first go through the heart. After the procedure, low-oxygen blood and high oxygen blood are no longer mixing, the way they have from birth.

After each surgery, the child will need to spend a couple of weeks or so in the hospital being carefully monitored and supported. Sometimes, an infant requires additional unplanned heart surgeries as well, if they haven’t responded well enough to these interventions.

The individual’s heart will never be completely normal. Even after surgery, the blood doesn’t run through the heart in exactly the way as it does in someone without hypoplastic left heart syndrome. Infants run the risk of infection, bleeding, stroke, or other surgical complications, and not all infants survive all three surgeries.

Heart Transplant

Heart transplant is another potential treatment option. Here, a heart from a living donor is used to surgically replace the original heart. But suitable transplants are often not available. In general, transplant is seen as a potential option when other surgical approaches have been unsuccessful. It may also be the best choice if an infant has exceptionally difficult anatomy for surgical repair.

Organs transplant carries major risks such as organ rejection. Individuals must take medications their whole lives that help keep their body from attacking the donated heart.

Compassionate Care

A third approach is palliative care. In this case, no major surgery is performed, and the child can be taken home to live out their short life. The infant is made comfortable using treatments like pain medications and sedatives. Some families prefer this approach to the uncertainties and emotional and financial stress that come with surgical interventions. In some parts of the world, this is the only realistic approach.

Long-term Support

Children who survive the surgeries will require long-term support and care of a cardiologist. Often, follow-up surgeries or heart transplant are needed in adolescence or early adulthood. Individuals may need pacemaker placement if heart arrhythmias become a problem. Some people will also need support for neurodevelopmental problems. 

Coping

It’s very important for family members to get the psychological and practical support that they need. Feelings of grief, anxiety, and isolation are all normal. Don’t hesitate to seek counseling and additional social support from your friends and family. It can be incredibly challenging making all the difficult healthcare decisions required in caring for an infant with hypoplastic heart syndrome.

Many people find it helpful to network with other families who’ve cared for a child with congenital heart disease. Fortunately, this is easier than it has ever been. It’s also important to continue to receive support even after the situation stabilizes. The Adult Congenital Heart Association is a great resource for older individuals living with congenital heart disease.

A Word From Verywell

Receiving a diagnosis of hypoplastic left heart syndrome in a newborn is devastating. It will take time to get adjusted to the reality of the situation. Fortunately, many children can now survive to adulthood. However, many uncertainties are present, and even with successful surgeries, it is a long-term serious health condition. Take the time you need to talk with your healthcare team and your loved ones to make the best possible treatment decisions for you.