Hypoplastic Left Heart Syndrome (HLHS) is a severe congenital heart defect affecting the left side of a baby’s heart. This side, including structures like the left ventricle, mitral valve, and aorta, is underdeveloped and cannot effectively pump blood to the body. Babies with HLHS require complex, specialized medical care from birth.
Understanding Hypoplastic Left Heart Syndrome
HLHS is a rare congenital heart defect, accounting for approximately 2-3% of all congenital heart disease cases. In this condition, several structures on the left side of the heart are severely underdeveloped. These include the left ventricle, the main pumping chamber, which is too small or non-functional, along with the mitral valve and the aortic valve, which may be too small or completely closed. The aorta, the large artery that carries oxygenated blood to the body, is also often very small and blocked.
Because the left side of the heart cannot effectively pump blood to the body, the right side of the heart must compensate. The right ventricle, normally responsible for pumping blood to the lungs, takes on the additional role of pumping blood to both the lungs and the rest of the body. This redirection of blood flow relies on two temporary fetal connections: an atrial septal defect (a hole between the upper chambers of the heart) and a patent ductus arteriosus (a blood vessel connecting the pulmonary artery and the aorta). Without these connections, which typically close shortly after birth, survival would not be possible.
Current Survival Rates and Influencing Factors
Survival rates for babies born with HLHS have significantly improved over the past few decades due to advancements in medical and surgical interventions. Without treatment, an infant with HLHS typically survives only a few days to a few weeks. With modern surgical treatment, survival rates to age 5 have been reported to be around 72%, with approximately 90% of those children reaching age 18.
Several factors influence the survival of infants with HLHS. Early diagnosis, often occurring prenatally through ultrasound or fetal echocardiogram, allows for planned delivery at a specialized medical center and prompt initiation of care, including medication to keep the ductus arteriosus open. Access to specialized medical centers with experienced surgical teams and comprehensive post-operative care plays a large role in positive outcomes.
Challenges that can negatively influence survival include the presence of other congenital anomalies, which can complicate the overall health picture. Complications during or after surgery, such as infection, heart failure, neurological issues, or pulmonary hypertension, can also impact the outcome. Low birth weight and preterm birth have also been associated with higher mortality rates.
Surgical and Medical Management for Survival
The primary treatment for HLHS involves a staged surgical approach, often referred to as palliative repair, which aims to reconfigure the heart’s circulation to function with a single ventricle. This series of three operations is performed over the first few years of life. The goal is to enable the right ventricle to effectively pump blood to both the body and the lungs.
The first stage, known as the Norwood procedure, is usually performed within the first few days of a baby’s life. This operation involves creating a new, larger aorta by connecting the main pulmonary artery to the existing aorta, allowing the right ventricle to pump blood to the body. A shunt is also created to provide controlled blood flow to the lungs. Before this surgery, and between stages, medications like prostaglandin E1 are administered intravenously to keep the ductus arteriosus open, which is necessary for maintaining blood flow to the body.
The second stage, the Glenn shunt (or bidirectional Glenn procedure), is typically performed when the child is around 4 to 6 months old. During this procedure, the superior vena cava, which carries oxygen-poor blood from the upper body, is connected directly to the pulmonary artery. This allows blood from the upper body to flow passively to the lungs for oxygenation, reducing the workload on the single ventricle. The temporary shunt from the Norwood procedure is removed at this time.
The third and final stage, the Fontan procedure, is usually performed when the child is between 2 and 5 years of age. This operation completes the single-ventricle circulation by connecting the inferior vena cava, which carries oxygen-poor blood from the lower body, directly to the pulmonary artery. After the Fontan, all deoxygenated blood bypasses the heart and flows directly to the lungs, allowing the single ventricle to focus solely on pumping oxygenated blood to the body. Medical management throughout these stages includes medications to support heart function and nutritional support.
Long-Term Outlook for Survivors
Many individuals who undergo the staged surgical palliation for HLHS are now surviving into adulthood, with some reaching their 30s and 40s. This population of adult survivors requires ongoing specialized medical care. Regular cardiology follow-ups are a lifelong requirement, often transitioning from pediatric to adult congenital heart disease centers to ensure continuous monitoring and management.
Despite the success of the staged surgeries, survivors of HLHS may experience ongoing medical needs and potential complications. These can include heart failure, abnormal heart rhythms (arrhythmias), protein-losing enteropathy (a condition affecting protein absorption), and liver complications due to altered blood flow dynamics.
Some individuals may also experience neurodevelopmental or motor delays. While many survivors lead active lives, they may have some physical limitations and might need to adapt their activities, such as avoiding competitive sports. The long-term prognosis continues to be studied as this population ages, with a focus on mitigating potential morbidities and enhancing quality of life.