Hypoplastic left heart syndrome (HLHS) symptoms & causes

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Hypoplastic left heart syndrome (HLHS) is one of the most challenging congenital heart defects to care for. But Boston Children's Hospital is a world pioneer in innovative HLHS care—including fetal cardiac intervention—and our team is well-qualified to care for your child.

We are known for our science-driven approach. We’re home to the world’s most extensive pediatric hospital research enterprise and we partner with elite health care and biotech organizations around the globe. But as specialists in innovative, family-centered care, our physicians never forget that your baby is precious, and not just a patient.

What characterizes HLHS?

Hypoplastic left heart syndrome is one of several congenital (present at birth) heart defects in which the heart has only one fully functioning ventricle. Learn about single ventricle defect.

In HLHS, most of the structures on the left side of the heart are too small and underdeveloped (hypoplastic) to provide enough red blood flow for the body’s needs. The most critical defect in HLHS is the small left ventricle, which needs to be large enough and strong enough to pump blood out to the body. If it’s too small, it simply can’t function effectively.

Other left heart structures can also be underdeveloped in varying degrees, including:

  • the mitral valve, which controls blood flow between the left atrium and left ventricle in the heart
  • the aortic valve, which regulates blood flow from the left ventricle or main pumping chamber into the aorta
  • the aorta, the largest artery in the body, which supplies oxygen-rich blood to the body and is one of the two great arteries in the heart

In HLHS, despite the severity of the heart defect, the fetus or newborn is able to survive because of two naturally occurring “holes in the heart,” which allow for the communication of blood between the left and right sides of the heart. These are the:

  • patent ductus arteriosus (PDA)a blood vessel (the ductus arteriosus) that connects the two great arteries (the aorta and the pulmonary artery) and usually closes soon after birth. As long as the ductus remains open (patent), blood can pass from the right ventricle and pulmonary artery to the aorta and body, allowing some oxygen-rich blood to circulate.
     
  • patent foramen ovale (PFO): The foramen ovale is a small opening between the right and left atria, normally present in utero, but which usually closes shortly after birth. With HLHS, it’s important that the foramen ovale stay open (patent) as this allows blood returning from the lungs to cross from the left atrium to the right atrium and out to the body via the right ventricle and pulmonary artery.

In HLHS, blood returning to the right atrium from the lungs must pass through the PFO to reach the right side of the heart. The right ventricle must then do “double duty”—pumping blood to the lungs through the pulmonary artery and to the body through the PDA.

Once the PDA begins to close (a natural occurrence), the baby will become extremely sick (go into “shock”) due to lack of blood supply to the body. At this point, treatment is necessary for the baby to survive.

How is HLHS diagnosed?

  • prenatal, or fetal, diagnosis: made by fetal ultrasound. When you go for your routine fetal ultrasound, your doctor should be able to identify:
    • a four-chamber heart
    • two valves entering the heart
    • two valves and blood vessels exiting the heart

HLHS can be diagnosed on fetal ultrasound when the person performing the ultrasound notices that the left heart structures are small. If HLHS is suspected, you should be referred to a fetal pediatric cardiologist for a fetal echocardiogram (a specialized fetal cardiac ultrasound).

  • postnatal diagnosis: If HLHS wasn’t diagnosed prenatally, HLHS is usually diagnosed after the newborn baby shows signs of distress.

What is the value of diagnosing HLHS prenatally?

A diagnosis of HLHS through prenatal cardiac ultrasound enables us to plan to treat your newborn immediately after delivery. The family and medical team should plan for delivery at, or next to, a cardiac center that’s equipped to care for the newborn, such as:

  • a children’s hospital with an adult or obstetric hospital attached or very near
  • a medical center that has adult/obstetric care, as well as neonatal and pediatric cardiac services

What are the symptoms of HLHS?

At first, a newborn with HLHS may appear normal. But symptoms usually develop in the first few hours or days of life. Lack of vital blood flow causes the baby to go into profound shock, endangering the brain, liver, kidneys and other vital organs. Symptoms may include:

  • rapid breathing or shortness of breath
  • rapid heartbeat or pounding heart
  • poor suckling and feeding
  • cold extremities (poor perfusion)
  • blue color of the skin, lips and nailbeds (cyanosis)
  • lethargy

How do you treat HLHS?

  • fetal cardiac intervention: A small number of prenatally diagnosed fetuses with HLHS may benefit from fetal intervention.
  • stabilization and intervention of the newborn: If the diagnosis of HLHS is known before birth, the neonatal and cardiac teams will begin caring for the newborn with HLHS immediately after birth. A few newborns will need to have a procedure to open up a too-small foramen ovale immediately after birth (performed in the cardiac catheterization laboratory), but most will be stable and require mostly close observation in the cardiac intensive care unit.

An intravenous medication called prostaglandin (PGE), to keep the ductus arteriosus from closing, will be started and administered until the surgery.

  • staged surgical interventions: All children with HLHS will undergo at least three surgeries within the first three years of life.

    There are three variations of the first surgery (“Stage I”). Which variation is used will depend on the surgeon’s preference, the baby’s size, and the exact anatomic features of the heart. These surgical options are:
  • the Norwood operation
  • the Sano modification
  • the hybrid procedure

The second surgery is called the bidirectional-Glenn shunt, and the third is called the Fontan. Together, they make up a series of surgeries called the Fontan Sequence. The goals of these surgeries are to:

  • enable the fully-functioning right ventricle to do the work normally done by two ventricles
  • separate the blue (low-oxygen-content) blood (pulmonary circulation) from the red (well-oxygenated) blood (systemic circulation)

Will my child be OK?

Open heart surgery at Boston Children’s has the one of the highest success rates in the United States among large pediatric cardiac centers. However, your child will need at least three staged surgeries in his first few years of life.

Note: Infants who’ve had initial surgery for a single ventricle defect are typically enrolled in Boston Children’s Home Monitoring Program between the baby’s Stage I and Stage II operations in the Fontan sequence. For more, see “Boston Children’s Home Monitoring Program for your child” in Treatment & care.

What about later in life?

Children with hypoplastic left heart syndrome will need follow-up care throughout their lives to ensure that their hearts continue to function adequately. Most children will also need heart medication(s). Complications going forward can include arrhythmias (abnormal heart rhythms), heart failure, blood clots, and a few other rare problems.

Your cardiologist will help you create a long-term care program as your baby grows into childhood and his teen years. Families with a child with HLHS will have an ongoing relationship with their cardiologist. We will treat your child if complications arise, and we’ll advise on daily-life issues such as exercise, activity levels, nutrition and pregnancy precautions.

Causes of Hypoplastic Left Heart Syndrome

It’s important to understand that as parents, you’ve done nothing to cause HLHS and its associated defects. Nothing you have ingested or have been exposed to environmentally has been linked to having a child with HLHS. Familial cases have been reported, but the genetic link has yet to be clarified.

HLHS is the result of underdevelopment of sections of the fetal heart during the first eight weeks of pregnancy. But it’s not understood why some babies’ hearts don’t develop normally. Congenital heart defects usually occur sporadically (by chance), with no clear reason for their development.

When to seek medical advice

Call your health care provider immediately if your baby or child is having difficulty breathing or is breathing rapidly, has a bluish color, tires easily, has cold hands and feet, is drowsy or unresponsive and is uninterested in eating.

Who’s at risk

Congenital heart defects usually occur sporadically (by chance), with no clear reason for their development. So, it’s difficult to predict who’s at risk. Familial cases have been reported, but the genetic link has yet to be clarified.

Complications

Children who have had HLHS reconstruction surgeries can be susceptible to arrhythmias, heart failure and blood clots as they go forward. And the potential does exist for needing a heart transplant in early or mid-childhood.

Long-term outlook

In many cases, the Fontan reconstructive surgeries now can palliate (not cure) HLHS, so the outlook for your child is positive. Children who have undergone HLHS reconstruction can be susceptible to arrhythmias, heart failure, blood clots and a few other complications. And the potential does exist for needing a heart transplant in early or mid-childhood.

Your cardiologist will help create a long-term care plan as your baby grows into childhood and his teen years. Most people who have had congenital heart disease repair have an ongoing relationship with their cardiologist; we will consult and treat your child if complications arise, and we’ll advise on daily-life issues such as exercise, activity levels, nutrition and pregnancy precautions.

For teens

As a teen with a congenital heart defect, you have a lot to cope with. Besides the typical issues any teenager faces—from social acceptance to body changes and more—you also have to deal with medical appointments and procedures, some delay of your natural wish for independence, the consciousness of feeling different and personal responsibility for maintaining your good health.

If you as a teen (or as the parent of a teen) feel overwhelmed, depressed or anxious through this time, speak to your doctor to get help.

What you can do at home

Consult your child’s cardiologist for guidance on specific steps for follow-up care at home. And as your baby recovers and grows, be sure to follow a regular program of well-baby/well-child checkups.

Prevention

It’s important to understand that as parents, you’ve done nothing to cause HLHS and its accompanying defects, and there are no precautions you could have taken to prevent it. Congenital heart defects usually occur sporadically (by chance), with no clear reason for their development.

HLHS Glossary

Advanced Fetal Care Center (AFCC) at Boston Children’s
the only comprehensive fetal care center in New England, and one of just a few in the United States. The AFCC is the first and most experienced center performing fetal cardiac interventions—treating abnormalities such as HLHS in utero to reduce potentially fatal concerns after delivery.

aorta
one of the heart’s two great arteries. In a normal heart, the aorta arises from the left ventricle and pumps oxygen-rich blood out to the body. In HLHS, the aorta can be too undersized to function adequately.

cardiac catheterization
provides detailed visual information and measurements about the structures inside the heart, cardiac catheterization is a procedure that can be performed on a fetus, a baby, a child or an adult. Catheterization can be diagnostic-only, diagnostic and therapeutic, or diagnostic and interventional.

cardiac/cardio
pertaining to the heart

cardiac intervention
a minimally invasive procedure, such as cardiac catheterization or angioplasty, to diagnose and treat heart disease

cardiac magnetic resonance imaging (MRI)
a non-invasive diagnostic tool using 3-D imaging technology produced by magnets to accurately determine the blood flow and functioning of your child's heart


cardiac surgery
surgical procedure performed on the heart

cardiac surgeon
doctor who performs surgery on the heart. A pediatric cardiac surgeon performs surgery on the hearts of infants and children.   
         
cardiologist
doctor who diagnoses and treats heart problems non-surgically. A pediatric cardiologist treats infants and children with heart problems.

The Center for Families at Boston Children’s
dedicated to helping families find the information, services and resources they need to understand their child’s medical condition and take part in their care


cyanosis (cyanotic)
blue color of skin, lips and nailbeds caused by lack of oxygen-rich (red) blood circulating in baby’s bloodstream—a major symptom of HLHS

congenital heart defect
heart defect present at birth. The heart usually forms in the first eight weeks of fetal development. It's thought that most congenital heart defects develop during this period.

diagnosis
medical determination of illness or disease based on physical examinations and advanced technology diagnostic testing tools

echocardiogram (echo, cardiac ultrasound)
a diagnostic tool that evaluates the structure and function of the heart using electronically recorded sound waves that produce a moving picture of your child’s heart and heart valves. The ultrasound can detect an HLHS defect.

electrocardiogram (ECG, EKG)
a diagnostic tool that evaluates the electrical activity of your child’s heart. An EKG is usually the initial test for evaluating the causes of symptoms and detecting heart abnormalities, including HLHS.

fetal cardiac intervention
Advanced catheterization treatment of the baby’s heart while still in utero.


fetal echocardiogram (fetal ultrasound)
a diagnostic tool that uses sound waves to evaluate the structure and function of the baby’s heart while still in utero. The ultrasound can detect an HLHS defect in the fetus.

fetal magnetic imaging (MRI)
a non-invasive diagnostic tool that uses 3-D imaging technology produced by magnets to accurately determine the blood flow and functioning of your child’s heart in utero. Drawing on our expertise in pediatric imaging, Boston Children’s is setting a new standard in fetal MRI.

Fontan sequence
a series of three palliative operations performed on children whose congenital heart defect results in just one full-sized functioning ventricle (single ventricle defect), including HLHS.  They are the Norwood (and its alternatives), the bi-directional-Glenn Shunt and the Fontan Operation. The Fontan surgeries are usually performed at intervals starting at a few months and ending at a few years of age.

heart valves
valves (tricuspid, pulmonary, mitral and aortic) that regulate uni-directional blood flow into and out of the heart chambers. In HLHS, the mitral and aortic valves are undersized 

hypoplastic left heart syndrome (HLHS)
a congenital (present at birth) heart defect in which most of the structures on the left side of the heart—and especially the left ventricle—are too small and underdeveloped to provide enough red blood flow for the body’s needs

interventional cardiologist
a doctor who specializes in performing minimally invasive procedures, such as cardiac catheterization or angioplasty, to diagnose and treat heart disease

symptoms
the presenting reasons why a child needs medical attention. A symptom’s characteristics—including but not limited to onset, quality, triggers and severity—help diagnosticians to determine an illness or disease, or to determine what further testing is needed to determine the illness or disease.

palliative
aiming to reduce the severity and impact of a disease, rather than cure it

patent ductus arteriosus (PDA)  a blood vessel (the ductus arteriosus) that connects the two great arteries (the aorta and the pulmonary artery) and usually closes soon after birth. As long as the PDA remains open (patent), blood can pass from the right ventricle and pulmonary artery to the aorta and body, allowing some oxygen-rich blood to circulate.

patent foramen ovale (PFO)
The foramen ovale is a small opening between the right and left atria, normally present in utero, but which usually closes shortly after birth. With HLHS, it’s important that the foramen ovale stay open (patent), as this allows blood returning from the lungs to cross from the left atrium to the right atrium and out to the body via the right ventricle and pulmonary artery.

pulmonary artery  one of the heart’s two great arteries. In a normal heart, the pulmonary artery arises from the right ventricle and carries oxygen-poor blood to the lungs, where it receives oxygen.

pulmonary artery banding
a repair in which a band is secured around the pulmonary artery to limit blood flow to the lungs. Pulmonary banding is an aspect of the hybrid procedure, one of the surgical options for treating HLHS.

shunt  an artificial connection of blood vessels in order to redirect blood or other fluids. In pediatric cardiology and cardiac surgery, this usually refers to a Gore-Tex (a synthetic material) tube connected between the aorta or one of its branches and the pulmonary artery.

single ventricle defect (SVD)
one of several congenital (present at birth) heart defects in which the heart has only one fully functioning ventricle. Hypoplastic left heart syndrome (HLHS) is a single ventricle defect.

sporadic
occurring by chance, occasionally, not inherited


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