Hypoplastic Left Heart Syndrome (HLHS)

What HLHS is

In a normal heart, the right side pumps blood to the lungs and the left side pumps oxygen-rich blood to the body. In HLHS:

• the left ventricle is very small or missing
• the mitral and aortic valves are narrowed or closed
• the ascending aorta is very small

Before birth, this is tolerated because the fetus gets oxygen from the placenta, and the right ventricle pumps blood to the body through the ductus arteriosus. After birth, this vessel normally closes within days. When it closes, blood flow to the body drops sharply, causing shock. A small opening between the upper heart chambers (atrial septum) is also needed for oxygen-rich blood to mix.

Causes and risk factors

The cause is usually unknown. Factors associated with HLHS include:

• genetic changes, including chromosome conditions such as Turner syndrome
• a family history of congenital heart defects
• maternal diabetes

HLHS is slightly more common in boys.

Signs and symptoms

Many babies seem well for the first hours or days. As the ductus closes:

• gray, pale or bluish color (cyanosis)
• rapid, difficult breathing
• poor feeding and sleepiness
• cold hands and feet
• weak or absent pulses
• low urine output
• shock and collapse if untreated

Diagnosis

• Prenatal ultrasound: many cases are detected at the 18 to 22 week anatomy scan, followed by a fetal echocardiogram. Prenatal diagnosis allows delivery at a hospital with a pediatric cardiac surgery center.
• Newborn pulse oximetry screening: a painless test of oxygen levels in the hand and foot, done before discharge, detects many critical heart defects.
• Echocardiogram: confirms the diagnosis after birth.
• Chest x-ray, ECG and blood tests for assessment.

Treatment

Immediately after birth

• Prostaglandin E1 infusion keeps the ductus arteriosus open.
• Breathing support and careful management of oxygen and blood flow.
• Sometimes a catheter procedure to enlarge the opening between the atria.

Staged surgical repair

The goal is to make the right ventricle the single pumping chamber for the body, while blood from the body flows passively to the lungs.

The period between the Norwood and Glenn operations carries the highest risk. Many centers use home monitoring programs during this time, with daily weights and oxygen readings.

Heart transplant

A transplant is an alternative for some infants, or later if the single-ventricle circulation fails. Donor hearts for infants are scarce.

Fetal intervention

In selected cases, procedures before birth (such as opening a narrowed aortic valve or atrial septum) are offered at specialist centers.

Long-term issues

Children and adults with Fontan circulation need lifelong follow-up. Possible problems include:

• reduced exercise capacity
• heart rhythm problems
• heart failure as the single ventricle weakens
• blood clots
• liver disease (Fontan-associated liver disease)
• protein-losing enteropathy and plastic bronchitis (rare)
• developmental delays and learning difficulties, which benefit from early intervention
• need for further surgery or transplant

Outlook

Survival has improved greatly. Most babies who survive the first year and complete the Fontan stage live into adulthood, and many go to school, work and live active lives. Life expectancy remains reduced compared with the general population, and long-term outcomes continue to be studied as the first generations of survivors reach adulthood.

Frequently asked questions

What is hypoplastic left heart syndrome?

HLHS is a rare, serious heart defect present at birth in which the left side of the heart is too small to pump blood to the body. Babies depend on a temporary blood vessel that closes after birth, so they need emergency treatment and a series of surgeries.

How is HLHS treated?

Treatment begins with medicine to keep a fetal blood vessel open, followed by three operations: the Norwood procedure in the first weeks, the Glenn at about 4 to 6 months, and the Fontan between 18 months and 4 years. A heart transplant is an alternative for some.

What is the life expectancy for HLHS?

Survival has improved substantially. Most children who complete all three surgical stages survive into adulthood, though life expectancy is still lower than average and complications can develop over time. Lifelong specialist care is essential.

Can HLHS be detected before birth?

Yes. HLHS is often detected on the routine anatomy ultrasound at 18 to 22 weeks of pregnancy and confirmed with a fetal echocardiogram. Prenatal diagnosis lets families plan delivery at a center with pediatric heart surgery.

What causes HLHS?

In most cases the cause is unknown. It may involve genetic factors, and it is more common in some chromosomal conditions. A family history of congenital heart disease increases the chance. It is not caused by anything parents did during pregnancy.