Hypoplastic Left Heart Syndrome
Hypoplastic left heart syndrome is a serious heart condition that babies are born with, where the left side of the heart doesn’t develop properly and is too small to pump blood effectively to the body.
Table of contents
- What is hypoplastic left heart syndrome?
- Structures affected by the condition
- How the heart works with this condition
- How common is this condition
- Signs and symptoms
- Causes and risk factors
- Diagnosis
- Treatment options
- Living with the condition
What is hypoplastic left heart syndrome?
Hypoplastic left heart syndrome, also called HLHS, is a rare and complex heart condition that a baby is born with. The term “congenital” means the condition is present at birth[1]. In this condition, the left side of the heart doesn’t form correctly during the first eight weeks of pregnancy[4].
HLHS is considered a critical congenital heart defect, which means it is one of the most serious types of heart problems that require urgent care[3]. It is also classified as a single-ventricle heart defect because one side of the baby’s heart didn’t develop correctly[2].
Without treatment, hypoplastic left heart syndrome is fatal within the first hours or days of life[5]. However, advances in medical care over the past several decades have dramatically improved outcomes for children with this condition[13].
Structures affected by the condition
In babies with hypoplastic left heart syndrome, several structures on the left side of the heart are underdeveloped or too small[3]. These include:
- Left ventricle: This is the lower left chamber of the heart, which normally pumps oxygen-rich blood to the body. In HLHS, it is very small and cannot pump effectively[2].
- Mitral valve: This valve separates the upper and lower left chambers of the heart. It may be too small or completely closed[4].
- Aortic valve: This valve controls blood flow from the left ventricle to the aorta. It can be too small or completely closed[4].
- Aorta: This is the large blood vessel that carries blood from the heart to the rest of the body. In HLHS, the ascending portion of the aorta is often underdeveloped or too small[3].
Many babies with HLHS also have an opening between the two upper chambers of the heart, called an atrial septal defect. Normally, there would be a solid wall of tissue separating these chambers[2].
How the heart works with this condition
In a normal heart, each side has a specific job. The right side pumps oxygen-poor blood to the lungs to pick up oxygen, while the left side pumps oxygen-rich blood to the body[2].
In a baby with hypoplastic left heart syndrome, the heart’s left side is too small to pump enough blood to the body. Instead, the right ventricle must take over and pump blood to both the lungs and the entire body[2]. This happens through a blood vessel called the ductus arteriosus, which all babies have before birth[3].
During pregnancy, a baby has two small openings between the left and right sides of the heart: the ductus arteriosus and the foramen ovale. These openings usually close within a few days after birth[3]. In babies with HLHS, oxygen-rich blood bypasses the left side of the heart through these openings. When they begin to close, it becomes much harder for oxygen-rich blood to reach the rest of the body, which can lead to serious problems[3].
How common is this condition
Hypoplastic left heart syndrome affects about 1 out of every 3,800 to 3,955 babies born in the United States[3][2]. This means approximately 929 to 1,025 babies are born with HLHS each year in the United States[3][8].
This condition accounts for about 2% to 3% of all congenital heart diseases[2][8]. Although rare, HLHS is responsible for 23% of all cardiac-related deaths in the first week of life[6]. The condition affects more male babies than female babies[2][8].
Signs and symptoms
Babies with hypoplastic left heart syndrome may appear healthy right after birth[7]. However, symptoms usually develop within the first few hours or days of life as the ductus arteriosus begins to close[1][2].
Common symptoms include[1][2][3]:
- Cyanosis: A blue or gray color to the skin, lips, and fingernails. The color changes may be easier or harder to see depending on skin color.
- Rapid or difficult breathing
- Fast heart rate
- Poor feeding or trouble feeding
- Lack of energy or being unusually sleepy
- Cold hands and feet
- Weak pulse
- Sweaty, clammy, or cool skin
Without treatment, a baby with this condition may go into shock, which is a life-threatening emergency. Signs of shock include cool, clammy skin, a weak and rapid pulse, breathing that may be slow and shallow or very rapid, and dull eyes[1].
If your baby shows any of these symptoms, especially changes in skin color, trouble breathing, or weak pulse, get emergency medical help immediately[1].
Causes and risk factors
Hypoplastic left heart syndrome results from underdevelopment of sections of the heart during the first eight weeks of pregnancy[7]. Most of the time, there is no known cause for the condition[2]. However, the cause is believed to be complex and likely involves multiple factors[8].
In some cases, the cause may be genetic. Babies with changes in specific genes known as GJA1 or NKX2-5 may have a higher risk of developing HLHS[2]. Some babies with genetic disorders such as Turner syndrome or trisomy 18 may also have hypoplastic left heart syndrome[2].
In some families, there is a genetic tendency toward developing HLHS, but most families have no prior history of congenital heart disease[7]. The causes of HLHS among most babies are unknown[3]. Some babies have heart defects because of changes in their genes or chromosomes. A combination of genes and other risk factors may increase the risk for HLHS[3].
Diagnosis
Diagnosis before birth
In many cases, hypoplastic left heart syndrome can be diagnosed before a baby is born[5]. During pregnancy, routine ultrasound exams are performed. If a basic ultrasound shows the possibility of heart problems, a more detailed test called a fetal echocardiogram can be done[7][3].
A fetal echocardiogram is a detailed ultrasound of the baby’s heart. This test can show problems with the structure of the heart and how the heart is working[3]. A routine ultrasound during the second trimester of pregnancy usually can detect if the baby has HLHS[10].
Diagnosis after birth
If the condition was not found during pregnancy, doctors may notice symptoms soon after birth[3]. A healthcare provider will examine the baby and listen to the baby’s heart. The provider may hear a sound called a heart murmur, which is caused by rushing blood flow[10][3].
After birth, several tests may be used to diagnose HLHS[2]:
- Echocardiogram: This test uses sound waves to create pictures of the heart. It shows how blood flows through the heart and can reveal that the lower left heart chamber and heart valves are small, and that the aorta may be small[10].
- Physical examination: The doctor will check for symptoms such as blue skin color, difficulty breathing, and weak pulses[5].
If HLHS is found before birth, healthcare professionals usually recommend giving birth at a hospital with a cardiac surgery center[10].
Treatment options
A baby born with hypoplastic left heart syndrome needs urgent treatment[10]. Treatment includes medicines to manage symptoms and a series of surgeries or, in some cases, a heart transplant[1][10].
Initial medical treatment
Before surgery can be performed, medicine is used to keep the ductus arteriosus open. The medication alprostadil is used for this purpose[10]. This blood vessel normally closes in all babies soon after birth, but babies with HLHS need this connection to remain open so that blood can reach the body[10].
Surgical treatment
Most babies with HLHS undergo a three-stage surgical approach over the first few years of life[6][13]. Each surgery is designed to help the heart work better by allowing the right side of the heart to pump blood to the body:
- Norwood procedure: This is typically the first surgery, performed within a few days of birth[10]. This complex operation reconstructs the heart so that the right ventricle can pump blood to both the lungs and the body.
- Glenn procedure: This second surgery is typically performed when the baby is three to six months old[8][10]. This operation connects one of the major veins from the upper body directly to the lung arteries.
- Fontan procedure: This final surgery is usually done when the child is between two and five years of age[8][10]. This operation completes the process by connecting the remaining major veins from the lower body to the lung arteries.
Alternative approaches
In some cases, particularly for very high-risk babies with additional medical problems such as low birth weight or shock, doctors may use a less invasive approach called the hybrid strategy[16]. This involves placing small bands on both lung vessels, with or without placing a stent in the ductus arteriosus. This gives the baby extra time to grow and allows doctors to treat other conditions before performing more traditional open-heart surgery[16].
Heart transplant
Some babies may need a heart transplant instead of the three-stage surgical approach[1][10]. The decision about which treatment path to follow depends on many factors and should be discussed with your child’s healthcare team.
Living with the condition
Over the past two decades, survival and life expectancy for children with hypoplastic left heart syndrome have improved dramatically[18]. Today, about 70% of children who undergo the three-stage surgical approach reach adulthood[8].
Children with HLHS require ongoing medical care throughout their lives. They will need regular checkups with a heart doctor to monitor their heart function and watch for potential complications[3]. Surgical repairs for HLHS are not a cure, and people with this condition need routine follow-up care to stay as healthy as possible[3].
Children with HLHS may experience some developmental challenges. They typically experience delays in both brain development and motor skills[8]. They also have an increased risk of heart failure as adults[8]. Despite these challenges, advances in medical technologies, surgical techniques, and growing experience in managing HLHS have made survival into adulthood a reality for many children with this condition[13].
Families caring for a child with HLHS face ongoing challenges and may experience anxiety about their child’s future health[22]. Support from healthcare teams, education about the condition, and connection with other families can help parents navigate these challenges[22].
