Hypoplastic left heart syndrome (HLHS) is a serious congenital heart defect in which the structures on the left side of the heart do not develop normally. The left ventricle, mitral valve, aortic valve, aorta and aortic arch may be smaller or less developed than usual, making it difficult for the heart to pump oxygen-rich blood to the body.
Symptoms usually appear soon after birth, particularly as a normal fetal blood vessel called the ductus arteriosus begins to close. Babies may develop breathing problems, poor feeding, weakness, cool or bluish skin and signs that the body is not receiving enough blood.
Hypoplastic left heart syndrome requires urgent medical treatment. Management usually involves medicines to stabilize blood flow followed by a series of heart operations, while heart transplantation may be considered in selected cases. Lifelong follow-up with a cardiology team is necessary.
Main symptoms
Symptoms of hypoplastic left heart syndrome usually develop during the first hours or days after birth as blood flow through the ductus arteriosus decreases.
Common symptoms can include:
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Rapid or difficult breathing
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Poor feeding
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Unusual tiredness or lethargy
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Weak pulses
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Cool skin
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Gray or bluish skin
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Poor blood flow to the body's tissues
These symptoms can indicate that the body is not receiving enough oxygen-rich blood. HLHS in a newborn is a medical emergency and requires immediate hospital care.
Possible causes
The exact cause of hypoplastic left heart syndrome is not known in most cases. HLHS develops during pregnancy when the structures on the left side of the fetal heart do not grow normally.
Research suggests that the condition probably results from several interacting factors rather than one single cause. Genetic changes, abnormal heart development and changes in blood flow within the fetal heart may all contribute.
Some cases have been associated with genetic variants, including changes involving genes such as MYH6. However, currently identified genetic changes explain only a proportion of HLHS cases, and the condition does not usually follow a simple pattern of inheritance.
HLHS is a congenital structural heart condition and is not contagious. It cannot be transmitted from one person to another.
Confirming a diagnosis
Hypoplastic left heart syndrome can sometimes be detected during pregnancy on a routine ultrasound. When a congenital heart problem is suspected, fetal echocardiography can provide a more detailed view of the baby's heart and blood flow.
Doctors look for underdevelopment of structures on the left side of the heart, particularly the left ventricle, mitral valve, aortic valve, ascending aorta and aortic arch. Fetal echocardiography can also help assess blood flow patterns and the function of the right ventricle.
If HLHS is not diagnosed before birth, it may be suspected when a newborn develops poor circulation, breathing problems, weak pulses or bluish or gray skin. Echocardiography after birth is used to examine the heart's anatomy and confirm the diagnosis.
Treatment options
Treatment for hypoplastic left heart syndrome focuses on maintaining blood flow to the body and lungs because the left side of the heart cannot pump effectively. After birth, medicines and intensive monitoring are used to keep the ductus arteriosus open and stabilize breathing, circulation and organ function before surgery.
Most babies undergo a series of staged operations. These usually include the Norwood procedure during the newborn period, followed by the Glenn or hemi-Fontan procedure and later the Fontan procedure, which gradually redirect blood flow so the right side of the heart can support circulation more effectively.
These procedures improve blood flow but do not cure hypoplastic left heart syndrome or create a normal two-ventricle heart. Heart transplantation may be considered in selected cases, and lifelong follow-up with a congenital heart specialist is necessary because complications can develop over time.
Long-term care
Children with hypoplastic left heart syndrome require ongoing follow-up with specialists in congenital heart disease. Regular monitoring is needed after each stage of surgery and throughout childhood because circulation and heart function can change over time.
Long-term complications can include abnormal heart rhythms, blood clots and progressive heart problems that may eventually require additional procedures or transplantation. Adults who underwent Fontan palliation also continue to require specialized congenital cardiology care.