Hypoplastic Left Heart Syndrome (HLHS): Information on Causes, Diagnosis & Treatments

Left Side Heart Not Developed Hypoplastic left heart syndrome (HLHS) is a rare heart birth defect, which means that the child was born with the condition involving a critically underdeveloped left side of the heart. The syndrome limits the heart’s ability to pump blood throughout the body, causing the right side of the heart to overwork when pumping blood to the lungs and eventually out to the body.

Upon observation of the newborn, the child often appears healthy even though they are suffering from hypoplastic left heart syndrome. However, the condition is often identified through early diagnosis during pregnancy. Other times, the symptoms develop quickly in the first hours or days of the child’s new life.

Scientists have yet to understand why the hearts of many babies do not develop normally. The underdevelopment on the left side of the heart typically occurs in the first two months of pregnancy. According to statistics maintained by the American Heart Association, approximately 16 out of every 10,000 babies are born with the hypoplastic left heart syndrome birth defect, where boys tend to be more at risk for developing the syndrome than girls. Additionally, most infants with the condition were born with other n

eurologic or cardiovascular organ defects.

Who Is at Risk for Hypoplastic Left Heart Syndrome?

Medical science has yet to determine exactly why the condition develops within the first eight weeks of pregnancy. However, the single known risk factor associated with the condition involves mothers who have birth a previous child born with hypoplastic left heart syndrome who are most likely to have another baby with HLHS or another health defect.

The symptom is the result of an undeveloped heart during the first two months of pregnancy. The syndrome causes the heart’s left side to restrict proper blood flow, usually, because the left ventricle (lower left chamber) does not exist or developed at too small a size. Additionally, the mitral valve or aortic valve on the left side of the heart might not work properly or the aorta (the heart’s main artery) developed at too small a size.

Complications

If the defect is not surgically repaired, the condition is fatal and will usually claim the child’s life within the first few weeks after their birth. However, many babies survived with treatment but will often suffer serious complications as they mature. Some of these complications involve:

  • Arrhythmia (abnormal heart rhythm)

  • Tiring easily especially when exercising or participating in sports activities

  • Nervous system and brain developmental problems

  • The buildup of fluid (edema) in the feet, legs, abdomen, or lungs

  • Blood clot formations that could result in a stroke or pulmonary embolism

  • Other complications that require a heart transplantation or additional heart surgeries

Because babies are born with the ductus arteriosus and foreman ovale that are necessary for survival in the womb, the newborn’s body can still receive sufficient levels of oxygen in the first few hours or days after birth. However, it is during this time that the ductus arteriosus and foreman ovale will naturally close and restrict the flow of blood unless the doctor diagnoses the condition and performs the first of three surgical procedures to repair the problem.

Common Symptoms

Newborns who have developed HLHS usually become seriously ill within the first few hours or days after birth. The most common hypoplastic left heart syndrome symptoms include:

  • Cyanosis where the color of the skin takes on a grayish-blue tint

  • Poor feeding

  • Difficult, rapid breathing

  • Cold feet and hands

  • Inactivity

  • Drowsiness

  • Overall weakness

If the doctor does not diagnose the child’s HLHS condition before the ductus arteriosus and foreman ovale closes, the newborn symptoms can lead to quick death. This is because the ductus arteriosus and foreman ovale can begin to close in a few hours after birth causing the child to go to shock and produce symptoms that include:

  • Clammy cool skin

  • Cyanosis where the color the skin, nail beds and lips take on a grayish-blue tint

  • Dilated pupils

  • Pounding heart (rapid heartbeat)

  • Abnormally rapid or shallow breathing

  • Poor perfusion (cold extremities)

  • Staring eyes

Any person in shock can appear conscious or unconscious. However, without immediate medical attention, the condition can be fatal.

Diagnosing Hypoplastic Left Heart Syndrome

Doctors can often diagnosis hypoplastic left heart syndrome while the child is still in the womb. The condition can be identified using routine ultrasound equipment as early as the second trimester of the mother’s pregnancy.

However, if the heart defect is not detected in the womb, the doctor may be suspicious of the condition if the baby has trouble breathing or the newborn’s skin appears with a grayish-blue tint. Listening to the child’s heart can also identify a defect if the doctor hears a heart murmur produced by turbulent blood flow that produces an irregular whooshing sound.

To confirm the diagnosis, the doctor will usually perform an echocardiogram using high-pitched sound waves that produce images of the heart and motion that can be seen on a video screen. A positive diagnosis of hypoplastic left heart syndrome will usually reveal itself in an echocardiogram as an abnormally small left ventricle and aorta. It is usually at this time that the echocardiogram reveals other congenital heart defects including hypoplastic right heart syndrome or an atrial septal defect.

Other diagnostic tests might include:

  • Chest x-ray to reveal the shape and size of the lungs and heart

  • Doppler ultrasound that measures the flow of blood moving through the heart’s valves

  • Echocardiogram (ECG) to record the heart’s changes through each heartbeat to identify heart muscle stress or an arrhythmia (abnormal heart rhythm)

Treating the Condition

Without treatment in a timely manner, the baby can easily die within hours or days. However, repair of the condition is not easy. The newborn will likely undergo a series of operations to ensure the function of the heart’s left side is rerouted properly. In some cases, a heart transplantation is the only effective option, which often requires the child to take numerous medications for life to prevent the rejection of the transplanted organ.

The type of treatment the doctor recommends is usually based on the overall health of the baby, the expert surgeon, the extent of the syndrome, the parent’s preferences, and the expectation of how the condition might worsen over time. Recommended treatment for hypoplastic left heart syndrome include:

  • The Norwood Procedure to reroute the flow of blood after the child was born

  • Bidirectional Glenn Operation to install a shunt in the baby’s heart 3 to 6 months after their birth.

  • Fontan Operation to connect the body’s major blood vessel (inferior vena cava) to the heart and the first 18 to 36 months after the completion of the Glenn operation.

There are two different approaches that can treat hypoplastic left heart syndrome while the fetus is still in the womb including a fetal balloon atrial septectomy to open the hole in the heart or an aortic valve surgical procedure that opens the valve before the left ventricle has time to shrink.

The prognosis of treating the condition is highly dependent on the baby’s health, the severity of the defect and any associated complications.

Back to the Top

Sources:

https://www.cdc.gov/ncbddd/birthdefects/stories/hlhs.html

https://rarediseases.info.nih.gov/diseases/6739/hypoplastic-left-heart-syndrome

https://www.cdc.gov/ncbddd/heartdefects/hlhs.html

http://www.mayoclinic.org/diseases-conditions/hypoplastic-left-heart-syndrome/home/ovc-20164178

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