Hypoplastic Left Heart Syndrome – Symptoms and Causes

ByJanis Updated

Overview

Hypoplastic Left Heart Syndrome (HLHS) is a rare but serious birth defect that affects the development of the heart. This condition occurs when parts of the left side of the heart don’t develop properly during pregnancy.

Babies born with HLHS have an underdeveloped left ventricle, aorta, aortic valve, and mitral valve. Without immediate treatment, this condition can be life-threatening. The heart cannot pump enough oxygen-rich blood to meet the body’s needs.

Prenatal testing can often detect HLHS before birth, allowing parents and medical teams to prepare for immediate treatment after delivery. Treatment typically involves a series of surgeries, medication, and ongoing cardiac care.

Symptoms

Hypoplastic left heart syndrome (HLHS) is a serious heart defect present at birth. In babies with HLHS, the left side of the heart doesn’t develop correctly while the baby is in the womb.

The main symptoms of HLHS typically appear shortly after birth. Babies may develop a bluish-gray skin color (cyanosis) when the oxygen levels in their blood drop. This often happens within the first few hours or days of life.

Other common signs include:

  • Rapid, difficult breathing
  • Poor feeding
  • Cold hands and feet
  • Unusual drowsiness or inactivity
  • Fast heart rate
  • Weak pulse
  • Excessive sleepiness or unusual fussiness

Some babies might show symptoms right away, while others develop problems when a natural connection between the heart chambers (called the ductus arteriosus) starts to close.

Doctors can often detect HLHS before birth through prenatal ultrasound. For babies diagnosed after birth, physical exams and tests like echocardiograms help confirm the condition.

When to Get Medical Help Right Away

Seek emergency medical care if your baby shows any of these warning signs:

  • Bluish or gray skin color
  • Rapid or difficult breathing
  • Poor feeding or excessive sleepiness
  • Excessive sweating, especially during feeding

Contact your doctor if you notice:

  • Slow weight gain
  • Difficulty feeding
  • Less energy than normal
  • More fussiness than usual

Remember that symptoms may appear within hours or days after birth as the ductus arteriosus closes. Early detection and prompt treatment greatly improve outcomes for children with this heart condition.

Causes

Hypoplastic left heart syndrome (HLHS) develops during pregnancy when the baby’s heart forms incorrectly. The left side of the heart doesn’t grow properly, making it too small to pump blood effectively.

This creates significant problems after birth when the baby needs to circulate blood throughout their body.

Several factors may contribute to this condition. Genetic factors play an important role, with some cases showing family patterns.

Some babies with HLHS have changes in certain genes that affect heart development. These genetic changes can sometimes be part of larger genetic syndromes.

The exact cause of HLHS remains unknown. However, research suggests several possible factors:

  • Some cases are linked to genetic abnormalities.
  • Blood flow problems during early heart development.
  • Complex interactions between genetic and environmental factors.

HLHS occurs during the first 8 weeks of pregnancy when the baby’s heart develops. The exact mechanism remains unclear, but researchers believe it involves complex interactions between genetic and environmental factors.

Some studies suggest that blood flow problems during early heart development might contribute to HLHS. When blood doesn’t flow properly through the developing heart, the left side may not grow properly.

Risk Factors

Several factors might increase the chance of a baby developing hypoplastic left heart syndrome (HLHS). While doctors don’t fully understand all causes, certain patterns have emerged in research.

Genetic factors play an important role. Children with certain genetic conditions face higher risks, and HLHS sometimes runs in families. About 10% of babies with HLHS have a relative with a similar heart problem.

Maternal health conditions during pregnancy can affect heart development. Diabetes, obesity, and smoking may increase the risk of congenital heart defects, including HLHS.

Environmental exposures during early pregnancy might contribute to the risk. These include certain medications, chemicals, and infections.

Poor maternal nutrition may also play a role.

Previous pregnancy history matters too. Parents who have had one child with HLHS have a slightly higher chance (2–4%) of having another baby with the condition.

Gender differences exist, with boys slightly more likely than girls to develop HLHS.

Complications

Hypoplastic left heart syndrome (HLHS) can lead to several serious health problems if not treated promptly. Babies with this condition often develop complications soon after birth when the natural connection between the heart’s chambers (ductus arteriosus) begins to close.

Without treatment, HLHS typically leads to heart failure within the first few days or weeks of life. The heart cannot pump enough blood to meet the body’s needs, causing organs to function poorly.

Even with surgical treatment, children with HLHS may face long-term issues such as:

  • Developmental delays
  • Growth problems
  • Heart rhythm abnormalities
  • Blood clots
  • Increased risk of infection
  • The potential need for a heart transplant later in life

Regular follow-up care with heart specialists is essential throughout life to monitor for these complications.


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Health Writer

Janis's areas of expertise include nutrition, exercise, stress management, and mental health. She is passionate about educating and empowering people to take control of their health and make positive changes that can last a lifetime. Janis believes that small, sustainable changes are the key to long-term success, and she works with her clients to develop personalized plans that fit their individual needs and lifestyles.