Congenital Heart Defect: Hypoplastic Left Heart Syndrome (HLHS)

A congenital heart defect is one of the most common types of birth defects [1]. It is an abnormality in the heart that develops before birth [1]. Hypoplastic Left Heart Syndrome (HLHS) is a relatively common complex congenital heart defect, which is a clinically useful description of a constellation of cardiac malformations, all characterized by underdevelopment or absence of the left ventricle [1,2]. As the baby develops during pregnancy, the left side of the heart does not form correctly [1]. Features of HLHS include varying degrees of hypoplasia of the left ventricle, mitral valve and aortic valve atresia or stenosis, and hypoplasia of the ascending aorta [2]. Coarctation of the aorta occurs in 67% to 80% of these cases [2]. Hence, it affects normal blood flow through the heart [1].

The causes of heart defects such as hypoplastic left heart syndrome among most babies are unknown [1]. Some babies have heart defects because of changes in their genes or chromosomes [1, 2]. These types of heart defects also are thought to be caused by risk factors such as the things the mother comes in contact with within the environment or what the mother eats or drinks or the medications the mother takes [1,2].

In most cases, children with HLHS appear healthy [3]. The typical baby with HLHS initially may be nearly indistinguishable from a baby without it [3]. Untreated, the prognosis for the infant is certain death [3]. When a baby is not diagnosed during pregnancy, symptoms may develop within the first few hours or days of life. It includes; [3]

• Rapid breathing or shortness of breath

• Rapid heartbeat or pounding heart

• Poor suckling and feeding

• Cold extremities (poor perfusion)

• The blue colour of the skin, lips, and nailbeds (cyanosis)

• Weakness

Treatments for some health problems associated with hypoplastic left heart syndrome include: [1]

• Medicines: Some babies and children will need medicines to help strengthen the heart muscle, lower their blood pressure, and help the body get rid of extra fluid.

• Nutrition: Some babies with hypoplastic left heart syndrome become tired while feeding and do not eat enough to gain weight. To make sure babies have a healthy weight gain, a special high-calorie formula might be prescribed. Some babies become extremely tired while feeding and might need to be fed through a feeding tube.

• Surgery: Soon after a baby with hypoplastic left heart syndrome is born, multiple surgeries done in a particular order are needed to increase blood flow to the body and bypass the poorly functioning left side of the heart. The right ventricle becomes the main pumping chamber to the body. These surgeries do not cure hypoplastic left heart syndrome, but help restore heart function. Sometimes medicines are given to help treat symptoms of the defect before or after surgery. Surgery for hypoplastic left heart syndrome is known as staged reconstruction and is usually done in three separate stages.

I. Stage 1: Norwood Procedure

This surgery usually is done within the first 2 weeks of a baby’s life. Surgeons create a “new” aorta and connect it to the right ventricle [4]. They also place a tube from either the aorta or the right ventricle to the vessels supplying the lungs (pulmonary arteries) [4]. Thus, the right ventricle can pump blood to both the lungs and the rest of the body. This can be a very challenging surgery [4]. After this procedure, an infant’s skin still might look bluish because oxygen-rich and oxygen-poor blood still mix in the heart [4].

Babies who have the Norwood procedure usually spend 3 to 4 weeks in the hospital to recover [2, 4]. They get-around-the-clock care and monitoring. They also get medicines to help the heart and improve blood flow. During this time, the care team teaches parents how to care for their baby at home. Babies usually can go home when they are feeding well, growing well, and gaining weight [4].

At home, the baby needs to be watched closely. Parents will be in close contact with the care team and should keep an eye on: [4]

• weight gain and growth

• oxygen levels

Parents should call the care team right away if their baby: [4]

• has feeding problems

• has breathing problems

• seems very irritable

• just doesn't seem quite right

II. Stage 2: Bi-directional Glenn Shunt Procedure

This usually is performed when an infant is 4 to 6 months of age [5]. This procedure creates a direct connection between the pulmonary artery and the vessel (the superior vena cava) returning oxygen-poor blood from the upper part of the body to the heart [5]. This reduces the work the right ventricle has to do by allowing blood returning from the body to flow directly to the lungs [5].

III. Stage 3: Fontan Procedure

This procedure usually is done sometime during the period when an infant is 18 months to 3 years of age [6]. Doctors connect the pulmonary artery and the vessel (the inferior vena cava) returning oxygen-poor blood from the lower part of the body to the heart, allowing the rest of the blood coming back from the body to go to the lungs [6]. Once this procedure is complete, oxygen-rich, and oxygen-poor blood no longer mixes in the heart and an infant’s skin will no longer look bluish [6].

Many children thrive and do well after heart surgery [1]. However, infants who have these surgeries are not cured and may have lifelong complications [1,2, 6]. They will need regular follow-up visits with a cardiologist (a heart doctor) to monitor their progress. If the hypoplastic left heart syndrome defect is very complex, or the heart becomes weak after the surgeries, a heart transplant may be needed [2]. Infants who receive a heart transplant will need to take medicines for the rest of their lives to prevent their body from rejecting the new heart [2].

To summarize, in hypoplastic left heart syndrome the heart’s left side is underdeveloped. If not treated, HLHS is fatal within the first few days or weeks of life. While treatment is difficult, surgical and medical interventions have improved chances of survival. Treatment may include a series of surgeries to restore function to the left side of the heart (stage reconstruction), or a heart transplant. However, even with treatment, lifelong complications are possible and life expectancy may be reduced.

Reference:

1. Congenital Heart Defects - Facts about Hypoplastic Left Heart Syndrome | CDC. Available on https://www.cdc.gov/ncbddd/heartdefects/hlhs.html

2. Hypoplastic left heart syndrome: Prognosis and management options. Available on https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817797/

3. Hypoplastic Left Heart Syndrome (HLHS) | Symptoms & Causes | Boston Children's Hospital. Available on https://www.childrenshospital.org/conditions-and-treatments/conditions/h/hypoplastic-left-heart-syndrome/symptoms-and-causes

4. Hypoplastic Left Heart Syndrome Surgery: The Norwood Procedure (for Parents) - Nemours KidsHealth. Available on https://kidshealth.org/en/parents/norwood.html

5. Hypoplastic Left Heart Syndrome Surgery: The Glenn Procedure (for Parents) – Nemours KidsHealth. Available on https://kidshealth.org/en/parents/glenn.html

6. Hypoplastic Left Heart Syndrome Surgery: The Fontan Procedure (for Parents) - Nemours KidsHealth. Available on https://kidshealth.org/en/parents/fontan.html