Hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect in which the structures on the left side of the heart are critically underdeveloped. This includes the left ventricle, mitral valve, aortic valve, and ascending aorta, which are too small or malformed to support normal systemic blood circulation. As a result, the right ventricle must pump blood to both the lungs and the rest of the body. HLHS is one of the most serious forms of congenital heart disease and is uniformly fatal without intervention. Affected newborns typically appear normal at birth but rapidly develop signs of cardiovascular collapse as the ductus arteriosus closes within the first days of life. Symptoms include cyanosis (bluish skin discoloration), rapid or labored breathing, poor feeding, lethargy, weak pulses, and cool extremities. HLHS accounts for approximately 2–3% of all congenital heart defects. The condition is slightly more common in males than females. Diagnosis is often made prenatally by fetal echocardiography or shortly after birth. Initial stabilization requires prostaglandin E1 infusion to maintain ductal patency. Definitive treatment involves a series of three staged open-heart surgical procedures: the Norwood procedure (performed in the neonatal period), the Glenn or hemi-Fontan procedure (at approximately 4–6 months), and the Fontan procedure (at 2–4 years of age). These surgeries reconfigure the circulation so that the right ventricle serves as the systemic ventricle. Cardiac transplantation is an alternative in some centers. Despite significant advances in surgical outcomes, HLHS remains associated with long-term complications including heart failure, arrhythmias, neurodevelopmental delays, and the need for lifelong cardiac follow-up. Survival has improved dramatically over recent decades, with many patients now reaching adulthood.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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