Hypoplastic Left Heart Syndrome
The left side of the heart is severely underdeveloped
Quick Facts
- Type: Critical congenital heart defect
- What it is: Underdeveloped left side of the heart
- Appears: In the first days of life
- Treatment: Staged surgery or heart transplant
Overview
Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect in which the structures on the left side of the heart, including the main pumping chamber and key valves, are too small or poorly formed. Because the left heart normally pumps oxygen-rich blood to the body, this underdevelopment leaves the heart unable to supply the body adequately.
HLHS is one of the most serious heart defects and is considered a critical condition that becomes apparent in the first days of life. It requires specialized treatment, typically a series of operations or, in some cases, a heart transplant. Outcomes have improved significantly with modern care.
Symptoms
A baby with HLHS may appear well at first but usually becomes ill within the first hours to days of life as a fetal blood vessel begins to close.
- Bluish or grayish skin color
- Rapid or difficult breathing
- Poor feeding and lack of energy
- Weak pulses
- Cold hands and feet
- Increasing sleepiness or unresponsiveness
HLHS is a medical emergency. A newborn who becomes blue, gray, very sleepy, or who is breathing with difficulty needs immediate medical care. Because a baby with HLHS may look healthy for the first day or two before deteriorating, newborn pulse oximetry screening is valuable for catching the problem early. Any rapid change in a newborn's color, breathing, or alertness should be treated as urgent.
Causes
HLHS develops during early fetal heart formation, when the left-sided structures fail to grow properly. The exact cause is usually unknown.
- Abnormal fetal development: The left heart chambers and valves do not form normally.
- Genetic factors: It can occur with certain genetic and chromosomal conditions and sometimes runs in families.
In most cases there is no clear single cause, and it is not the result of anything the parents did. Genetic counseling can help families understand recurrence risk.
Risk Factors
- A family history of congenital heart defects, especially left-sided defects
- Certain genetic or chromosomal conditions
- Having a sibling with HLHS, which modestly raises the risk
Diagnosis
HLHS is increasingly found before birth, allowing families and doctors to plan ahead.
- Prenatal ultrasound and fetal echocardiogram: Can identify the underdeveloped left heart during pregnancy.
- Echocardiogram after birth: The main test to confirm the diagnosis and detail the heart's structure.
- Pulse oximetry: Newborn screening may detect low blood oxygen.
- Chest X-ray and ECG: Provide supporting information about heart size and rhythm.
- Blood tests: Help assess oxygen levels and overall condition in the newborn period.
Treatment
HLHS requires specialized treatment soon after birth and an individualized long-term plan.
- Stabilizing medication: A medicine is often given to keep a fetal blood vessel open, maintaining blood flow until surgery.
- Staged surgery: A series of operations, usually three over the first years of life, reroutes blood flow so the right side of the heart pumps to the body.
- Heart transplant: Considered in some children as an alternative or later option.
Children with HLHS need lifelong follow-up with a heart specialist. Care is complex and individualized, and decisions are made together with the family and a specialized heart team. The staged surgical approach reroutes blood so that the stronger right chamber pumps blood to the body, while blood reaches the lungs through other connections; each stage builds on the last. Between operations, babies are watched closely because this is a vulnerable time. As children grow, the team monitors heart function, oxygen levels, growth, and development, and some children eventually need a heart transplant if the heart cannot keep up. While HLHS remains one of the most serious heart conditions, survival and quality of life have improved with advances in surgery and intensive care. Families benefit from support services and counseling as part of comprehensive care, given the demands of this lifelong condition.
When to See a Doctor
HLHS is a newborn emergency. Seek immediate care or call emergency services if a baby:
- Develops bluish or grayish skin
- Breathes rapidly or with difficulty
- Feeds very poorly or becomes limp and unresponsive
- Has cold limbs and weak pulses
If HLHS is diagnosed before birth, delivery should be planned at a center with specialized newborn heart care.
Frequently Asked Questions
What is hypoplastic left heart syndrome?
It is a severe congenital heart defect in which the left side of the heart, which normally pumps blood to the body, is underdeveloped. As a result, the heart cannot supply the body with enough oxygen-rich blood, and the condition is critical from the newborn period.
Is HLHS detected before birth?
Often yes. A detailed prenatal ultrasound and fetal echocardiogram can identify HLHS during pregnancy. Diagnosing it early allows the family and medical team to plan delivery at a center with specialized newborn heart care.
How is hypoplastic left heart syndrome treated?
Treatment usually involves stabilizing medication after birth followed by a series of staged operations that reroute blood flow, typically three surgeries over the first years of life. In some children a heart transplant is considered. Lifelong specialist follow-up is needed.
Is HLHS an emergency?
Yes. HLHS is a critical condition, and a newborn can become seriously ill within hours to days as a fetal blood vessel closes. A baby who turns blue or gray, feeds poorly, or is very sleepy needs immediate medical care.
What is the outlook for a child with HLHS?
HLHS is a complex condition, but outcomes have improved considerably with staged surgery and specialized care. Many children survive and grow, though they need lifelong heart follow-up. Each child's outlook depends on their individual heart anatomy and response to treatment.
References
- Centers for Disease Control and Prevention (CDC). Hypoplastic Left Heart Syndrome.
- Mayo Clinic. Hypoplastic left heart syndrome.
- MedlinePlus, U.S. National Library of Medicine. Hypoplastic left heart syndrome.