Hypoplastic Left Heart Syndrome

Hypoplastic Left Heart Syndrome (HLHS) is a rare and serious heart defect present at birth (congenital heart defect) where the left side of the heart is severely underdeveloped. This condition prevents the heart from effectively pumping oxygen-rich blood to the body, requiring immediate and complex medical care, often involving multiple surgeries or a heart transplant.

What is Hypoplastic Left Heart Syndrome?

Hypoplastic Left Heart Syndrome (HLHS) is a rare, complex congenital heart defect where the left side of the heart, including its main pumping chamber (left ventricle) and major blood vessels, is severely underdeveloped. This condition is present at birth and prevents the heart from effectively pumping oxygen-rich blood to the body.

Normally, your heart has two distinct pumping systems. The right side pumps blood to your lungs to pick up oxygen, and the left side pumps that oxygen-rich blood out to the rest of your body. In babies with HLHS, the structures on the left side of the heart are too small or not fully formed. This includes the main pumping chamber (left ventricle), the valve between the upper and lower left chambers (mitral valve), the valve that controls blood flow out of the heart (aortic valve), and the body's main artery (aorta). Because the left side cannot pump blood effectively, the right side of the heart must do all the work. It pumps blood to both the lungs and the body. This is possible only because of two temporary connections that are normally present in a fetus but usually close shortly after birth: the patent ductus arteriosus (PDA) and the patent foramen ovale (PFO). These connections allow blood to bypass the underdeveloped left side and reach the body.

Symptoms

Symptoms of Hypoplastic Left Heart Syndrome (HLHS) usually appear within hours or days after birth and are caused by the body not getting enough oxygen-rich blood. These signs can include bluish or grayish skin, rapid or difficult breathing, poor feeding, and unusual sleepiness or lethargy.

Babies with HLHS often appear healthy at birth. However, as the temporary connections (patent ductus arteriosus and patent foramen ovale) that help blood flow begin to close, symptoms quickly become noticeable. One of the most common signs is a bluish or grayish tint to the skin, lips, fingers, and toes. This is called cyanosis and happens because the blood circulating through the body does not have enough oxygen. Babies may also breathe very rapidly or have difficulty breathing, sometimes grunting with each breath. Other important symptoms include poor feeding, which means the baby may not suck well or may tire quickly during feedings. They might also seem unusually sleepy (lethargic), be less active than expected, or have cold hands and feet. These symptoms indicate that the baby's body is struggling to get enough oxygen and nutrients.

Causes & risk factors

The exact cause of Hypoplastic Left Heart Syndrome (HLHS) is often unknown, but it is a congenital heart defect, meaning it develops before birth. While it is not usually linked to anything parents did or did not do, genetic factors may play a role in some cases.

HLHS occurs during fetal development when the baby's heart is forming. It is not caused by anything the mother did or did not do during pregnancy. In most cases, doctors do not know why the left side of the heart fails to develop properly. Sometimes, HLHS is associated with certain genetic conditions, such as Turner syndrome or trisomy 18. This suggests that genetic factors can contribute to the development of the condition in some babies. However, many babies with HLHS do not have any known genetic syndromes. Because the specific cause is often unknown and it develops early in pregnancy, HLHS cannot be prevented. Researchers continue to study the genetic and environmental factors that might contribute to its development.

How it's diagnosed

Hypoplastic Left Heart Syndrome (HLHS) can sometimes be diagnosed before birth through a routine fetal ultrasound. After birth, doctors diagnose it using a physical exam, pulse oximetry to check oxygen levels, and an echocardiogram, which is a special ultrasound of the baby's heart.

A prenatal diagnosis of HLHS can occur during a routine fetal ultrasound, often around the middle of pregnancy. This allows doctors to see the developing heart and identify any structural abnormalities. If HLHS is suspected, further specialized ultrasounds may be performed. After birth, if a baby shows symptoms of HLHS, doctors will perform a physical exam, listening to the heart for murmurs and checking pulses. They will also use a pulse oximeter, a small device placed on the baby's hand or foot, to measure the oxygen level in the blood. Low oxygen levels can be a sign of a serious heart problem. The most definitive diagnostic test is an echocardiogram. This is a non-invasive ultrasound of the heart that creates detailed images of its chambers, valves, and blood vessels. An echocardiogram allows doctors to clearly see the underdeveloped left side of the heart and confirm the diagnosis of HLHS.

Treatment options

Treatment for Hypoplastic Left Heart Syndrome (HLHS) typically involves a series of complex surgeries performed in stages, or a heart transplant. Before surgery, medications like prostaglandin are used to keep vital blood vessels open, ensuring blood flow to the body and lungs.

Immediately after birth, babies with HLHS need urgent medical care. A medication called prostaglandin is often given intravenously (through a vein) to keep the patent ductus arteriosus (PDA) open. This temporary connection is crucial for blood flow to the body until surgery can be performed. The most common treatment approach is a series of three staged surgeries. The first surgery, called the Norwood procedure, is performed within the first few days of life. It reconstructs the aorta and ensures blood flow to the body. The second surgery, the Glenn procedure, is typically done when the baby is 4 to 6 months old. It reroutes blood from the upper body directly to the lungs. The third and final surgery, the Fontan procedure, is usually performed when the child is 2 to 3 years old. This procedure completes the rerouting of blood, allowing all oxygen-poor blood to flow directly to the lungs without passing through the heart's pumping chambers. In some cases, a heart transplant may be considered as an alternative treatment option, either initially or if the staged surgeries are not successful long-term.

Recovery & outlook

Recovery from Hypoplastic Left Heart Syndrome (HLHS) treatment is a lifelong journey requiring ongoing specialized medical care. While survival rates have significantly improved, individuals with HLHS may face long-term health challenges, including heart failure, irregular heart rhythms, and developmental delays.

Children and adults who have undergone treatment for HLHS require lifelong follow-up care with a heart specialist (cardiologist) who specializes in congenital heart disease. Regular check-ups, tests, and sometimes medications are necessary to monitor heart function and manage any complications. Despite the significant advancements in surgical techniques and medical care, individuals with HLHS may still experience various long-term health issues. These can include heart failure, which means the heart cannot pump enough blood to meet the body's needs, and irregular heart rhythms (arrhythmias). Some individuals may also experience developmental delays or learning challenges. The outlook for babies born with HLHS has improved dramatically over the past few decades. Many individuals now survive into adulthood and can lead fulfilling lives. However, it remains a serious condition that requires continuous medical attention and support from a dedicated healthcare team.

When to see a doctor

If a baby with Hypoplastic Left Heart Syndrome (HLHS) shows signs of worsening symptoms, such as increased bluish skin color, severe difficulty breathing, extreme lethargy, or very poor feeding, seek immediate emergency medical attention. These could indicate a serious complication.

It is crucial for parents and caregivers to be aware of emergency signs that require immediate medical attention for a baby with HLHS. These symptoms suggest that the heart is struggling to provide enough oxygen to the body. Call 911 or go to the nearest emergency room if your baby's skin, lips, or nail beds become more noticeably blue or grayish (worsening cyanosis). Also, seek immediate help if your baby is having severe difficulty breathing, such as gasping for air, flaring nostrils, or grunting loudly. Other critical signs include extreme lethargy, where the baby is unusually unresponsive or difficult to wake up, or if they are refusing to feed or are unable to keep down fluids. Cold, clammy skin can also be a sign of a medical emergency. Always contact your child's cardiologist or seek emergency care if you are concerned about any sudden changes in your baby's condition.

Frequently asked questions

Can Hypoplastic Left Heart Syndrome be cured?

No, Hypoplastic Left Heart Syndrome is a lifelong condition. Treatments aim to improve heart function and blood flow, but the heart's structure remains altered. Individuals require ongoing specialized medical care throughout their lives.

What is the life expectancy for someone with HLHS?

Survival rates for individuals with HLHS have greatly improved due to advancements in medical and surgical care. Many individuals now live into adulthood, but life expectancy can vary depending on the severity of the condition and the presence of complications. Lifelong specialized care is essential.

Are there long-term complications after HLHS surgery?

Yes, common long-term complications after HLHS surgery can include heart failure, irregular heart rhythms (arrhythmias), and developmental delays. Individuals require regular follow-up with a cardiologist to monitor for and manage these potential issues.

Can Hypoplastic Left Heart Syndrome be prevented?

No, HLHS is a congenital heart defect that develops during early fetal growth, and its exact cause is often unknown. Therefore, it cannot be prevented. It is not caused by anything parents did or did not do during pregnancy.

What is the purpose of the Norwood procedure?

The Norwood procedure is the first of three staged surgeries for HLHS, typically performed within the first few days of life. Its purpose is to reconstruct the aorta, the body's main artery, and ensure that the right side of the heart can effectively pump blood to the body.

How common is Hypoplastic Left Heart Syndrome?

Hypoplastic Left Heart Syndrome is considered a rare congenital heart defect. While specific numbers can vary, it affects a small percentage of babies born with heart conditions, making it one of the more uncommon and complex heart defects.

Sources

• MedlinePlus — Hypoplastic Left Heart Syndrome
• Mayo Clinic — Hypoplastic Left Heart Syndrome
• Cochrane Library — Hypoplastic Left Heart Syndrome