Hypoplastic left heart syndrome

Overview

Hypoplastic left heart syndrome (HLHS) is a rare and serious congenital heart defect in which the left side of the heart is underdeveloped, including the left ventricle, mitral valve, aortic valve, and ascending aorta. Because the left side of the heart is responsible for pumping oxygen-rich blood to the body, this condition severely impairs systemic circulation. HLHS is typically diagnosed shortly after birth and requires immediate medical intervention to ensure survival.

Causes

The exact cause of hypoplastic left heart syndrome is not fully understood, but it results from abnormal development of the heart during early fetal life. It is thought to be influenced by a combination of genetic and environmental factors. While most cases are sporadic, some may be associated with genetic syndromes or chromosomal abnormalities, including:

• Turner syndrome

• Trisomy 18 or Trisomy 13

• Family history of congenital heart defects

Research is ongoing to identify specific gene mutations and developmental pathways involved in HLHS.

Symptoms

Symptoms of HLHS typically appear within the first hours or days after birth, especially as the ductus arteriosus begins to close. Common symptoms include:

• Gray or bluish skin color (cyanosis)

• Rapid or labored breathing

• Poor feeding

• Lethargy

• Cold extremities and weak pulses

• Signs of heart failure

Without treatment, HLHS is rapidly fatal due to the heart's inability to deliver oxygenated blood to the body.

Diagnosis

HLHS is often diagnosed during prenatal ultrasound screenings, particularly if a fetal echocardiogram is performed. Postnatal diagnosis involves:

• Physical examination: Identifying symptoms of poor circulation and heart failure

• Pulse oximetry: Measuring low blood oxygen levels

• Echocardiogram (ultrasound of the heart): Confirms structural defects and assesses heart function

• Chest X-ray: May show an enlarged heart and pulmonary congestion

• Electrocardiogram (ECG): To monitor heart rhythm and electrical activity

Early diagnosis, ideally before symptoms worsen, is crucial for planning immediate treatment.

Treatment

Treatment for HLHS is complex and typically requires a series of surgeries or, in some cases, heart transplantation. Initial stabilization involves:

• Prostaglandin E1 infusion: To keep the ductus arteriosus open and maintain blood flow to the body

• Oxygen and fluid management: To stabilize the infant until surgery

Surgical Options (Staged Palliation):

1. Norwood procedure: Performed within the first few days of life to reconstruct the aorta and connect it to the right ventricle

2. Glenn procedure: Typically done at 4–6 months of age to reduce the workload on the right ventricle by redirecting blood flow from the upper body directly to the lungs

3. Fontan procedure: Performed between 18 months and 3 years of age to direct lower body blood flow to the lungs, completing the separation of systemic and pulmonary circulation

Alternative:

• Heart transplantation: May be considered for some patients instead of or after staged surgeries

Ongoing medical management, including medications for heart function and rhythm, is essential after surgery.

Prognosis

The prognosis for infants with hypoplastic left heart syndrome has improved significantly due to advances in surgical techniques and neonatal care. Survival rates after the three-stage surgical approach have increased, with many children reaching adolescence and adulthood. However, long-term challenges remain, including:

• Exercise intolerance and fatigue

• Arrhythmias or heart failure

• Protein-losing enteropathy or liver complications in some cases

• Need for future heart transplantation

With close follow-up by a pediatric cardiology team and appropriate interventions, many individuals with HLHS can lead fulfilling lives, though lifelong cardiac care is essential.