Hypoplastic Left Heart Syndrome (HLHS) is a severe congenital heart defect characterized by the underdevelopment of the entire left side of the heart, which pumps oxygenated blood to the body. This life-threatening condition requires immediate, complex medical intervention shortly after birth to reroute circulation and sustain life. The prognosis for a child born with HLHS has dramatically improved over the last few decades due to advancements in surgical techniques and specialized care. Life expectancy associated with HLHS depends on the anatomy of the defect, the demanding three-stage surgical palliation, and the unique challenges of long-term survival with a single functioning heart ventricle.
Defining Hypoplastic Left Heart Syndrome
Hypoplastic Left Heart Syndrome is a complex anatomical defect where several left-sided cardiac structures fail to develop adequately during gestation. Affected structures typically include the left ventricle, the mitral and aortic valves, and often the ascending aorta. Without a functional left ventricle, the heart cannot support systemic circulation, meaning blood cannot be effectively pumped to the rest of the body.
Survival outside the womb depends entirely on the right side of the heart taking over the function of pumping blood to both the lungs and the body. This is possible only through two temporary fetal connections: the patent foramen ovale and the patent ductus arteriosus (PDA). The right ventricle pumps a mixture of oxygenated and deoxygenated blood through the PDA to the body. Since the PDA naturally begins to close shortly after birth, a continuous infusion of medication is immediately needed to keep this vessel open, preventing circulatory collapse.
The Essential Three-Stage Treatment Plan
The treatment for HLHS is a palliative strategy that reconfigures the heart to function with a single ventricle (the right ventricle). This staged reconstruction is completed over several years through three procedures, each managing a different phase of circulatory adaptation.
The first procedure, the Norwood operation, is performed within the first few days of life. Its goal is to create a new, large main artery, or “neo-aorta,” from the pulmonary artery and the small native aorta, allowing the right ventricle to pump blood to the entire body.
The second stage, the Glenn procedure (or Hemi-Fontan), is typically performed when the child is four to six months old. The superior vena cava, which returns deoxygenated blood from the upper body, is attached directly to the pulmonary artery. This rerouting allows blood from the upper body to flow passively to the lungs, reducing the workload on the single ventricle.
The third and final stage is the Fontan procedure, performed between two and four years of age. This operation connects the inferior vena cava, returning deoxygenated blood from the lower body, directly to the pulmonary artery. After this, all deoxygenated blood flows passively through the lungs before returning to the single pumping ventricle. The single ventricle is then solely responsible for pumping oxygenated blood to the body, establishing Fontan circulation.
Current Survival Rates and Life Expectancy
Survival for children with HLHS has improved significantly since the introduction of the staged palliation approach in the 1980s. With modern surgical and medical care, survival rates have increased markedly, although the risk remains substantial, particularly in the initial stages.
The highest mortality risk occurs during the first year of life, primarily associated with the Norwood procedure and the “interstage” period between the first and second surgeries. Recent data indicate that the overall survival rate to one year of age is approximately 63.5% to 73.7%.
For children who survive the initial year and successfully complete the first two stages, the long-term prognosis improves considerably. Current survival estimates show that children born between the late 1990s and early 2010s have a 5-year survival rate of approximately 58.6% and a 10-year survival rate of around 54.6%. For those surviving to one year of age, the probability of reaching adolescence is high, with long-term survival estimated to be around 90% in some specialized centers. The median life expectancy for individuals with Fontan circulation is now estimated to extend well into the 20s and 30s, with a growing number of patients reaching middle age.
Long-Term Outlook and Ongoing Care Needs
Individuals who have completed the Fontan procedure live with a unique physiological state where blood flows passively to the lungs. This passive flow results in chronically elevated central venous pressure. This sustained high pressure in the veins and lymphatic system is the underlying cause for many specific long-term complications that develop years after surgery.
One concerning complication is Fontan-associated liver disease (FALD), characterized by liver congestion and progressive fibrosis due to chronic venous hypertension. While mild liver changes are common in nearly all Fontan patients, FALD can progress to cirrhosis and, in rare cases, hepatocellular carcinoma. Other protein-losing syndromes are linked to lymphatic dysfunction.
These long-term complications include:
- Protein-losing enteropathy (PLE): Affecting 4% to 13% of patients, this involves the loss of proteins and immunoglobulins into the gastrointestinal tract, leading to swelling and increased risk of infection.
- Plastic bronchitis (PB): Occurring in about 4% of patients, this life-threatening condition involves a proteinaceous cast forming and being expectorated from the airways.
- Chronic risks of heart failure, electrical abnormalities like arrhythmias, and thromboembolic events due to altered blood flow.
Many individuals with Fontan circulation will eventually require a heart transplant. Lifelong, specialized cardiology follow-up is necessary to proactively manage these complex, multi-system issues and optimize long-term health.