Hypoplastic Left Heart Syndrome

What is Hypoplastic left heart syndrome?

Hypoplastic left heart syndrome (HLHS) is a rare congenital heart defect where left part of the heart and its structures-left ventricle, mitral valve, aortic valve, aorta- are underdeveloped. It is more commonly seen in males. Left part of the heart is responsible for pumping oxygenated blood to the rest of the body. In HLHS this function is severely impaired [1].

hypoplastic left heart syndrome


Like for many other congenital defects, the exact cause of HLHS is unknown. There have been some cases reported with familial inheritance with autosomal recessive pattern- both parents should have to be carriers of the recessive gene and their offspring inherits both of these genes. It is believed that HLHS has a multifactorial inheritance (also see caudal regression syndrome).

Abnormality is believed to occur early on in embryonal development, when the mitral and aortic valve develops. In order for the heart to develop, it needs sufficient blood flow. When the blood flow is impaired, the heart structures cannot develop properly. If the mitral and aortic valve is underdeveloped, it causes disturbance in development of left ventricle. Since there is no blood output from left ventricle, the aorta also does not develop.

Another possible cause for HLHS is believed to be premature closure of the foramen ovale- an opening in the heart wall that allows blood flow from the right to the left atrium during fetal period. Normally this opening closes right after birth. In case this shunt is closed, the blood cannot flow to the left atrium.

Recent genetic studies have shown that HLHS is genetically related to bicuspid aortic valve [2].


Usually children born with HLHS get very sick soon after birth. The symptoms include:

  • Cyanosis- blue, grey-blue colour of skin
  • Rapid breathing
  • Cold hands, feet
  • Inactivity
  • Refusing feeding
  • A doctor can hear a heart murmur

If no action is taken, the child can quickly go into cardiac shock which is characterised by:

  • Cool, pale or grey-coloured skin
  • Weak, rapid pulse
  • Slow, shallow breathing
  • Pupils dilate
  • Loss of consciousness[3]


Prenatal diagnostics

HLHS can be diagnosed during pregnancy by using ultrasound and fetal echocardiography. Usually during routine ultrasonography some signs of HLHS can be found, but the diagnosis can be confirmed after performing fetal echocardiography.

Laboratory studies

There are several laboratory tests that should be performed in order to exclude other conditions as well as to monitor the condition of the patient.

  • Complete blood cell count
    • In HLHS haemoglobin levels are normal
    • Neonatal anemia (low haemoglobin levels) can cause congestive heart failure that mimics symptoms of HLHS
    • White blood cell count is normal; sepsis can also cause similar symptoms as HLHS (see acute respiratory distress syndrome)
  • Electrolyte levels
    • Electrolyte disbalance can be caused by poor oral intake
    • In HLHS electrolyte levels are usually normal, but carbon dioxide levels can rise when respiratory failure sets in
  • Creatinine
    • When systemic blood flow is reduced, renal failure might set in
  • Liver function tests
    • Elevation of liver enzymes is a sign of liver cell damage, that can be caused by the lack of blood flow to the organ
  • Karyotype analysis

Imaging studies

  • Chest X-ray- typical findings in chest X-ray are increased size of the heart and increased markings of the lung vessels. Signs of lung edema can also be present.
  • Echocardiography- method of choice for HLHS. The two dimensional image can clearly show the extent of the hypoplasia. Usually Doppler imaging is also used to evaluate the blood flow.

This echocardiographic still frame shows a 4-chamb

  • Examination of other organs

If the infant experienced prolonged state of cardiac shock, other organs can be impaired. Ultrasound imaging of abdominal organs and the brain is usually used to assess the damage [4].

Other tests

  • Electrocardiography- ECG will show signs of enlarged right atrium and ventricle, as well as sinus tachycardia, and deviation of the cardiac axis. In some patients signs of myocardial ischemia are present.
  • Heart catheterization- usually this procedure is not done as a routine intervention. Cardiac catheterisation can resolve some issues present in ECG, which is beneficial for further surgical treatment of the patient [4].


If the fetus is diagnosed with HLHS during pregnancy, delivery should be planned in an institution where appropriate cardiac care can be ensured. Studies have shown that there are no benefits to performing a caesarean section to deliver the baby [6].


  • Opening of ductus arteriosus- keeping this fetal blood vessel open will ensure blood circulation to vital organs. Ductus arteriosus is keep open by using prostaglandin E1 infusion.
  • Metabolic acidosis correction- when the cardiac output is not sufficient to support the tissue requirements of oxygen, metabolic acidosis can occur. Correction is done with sodium bicarbonate infusion.
  • Pulmonary vascular resistance- decreased pulmonary vascular resistance causes decreased systemic blood flow. Oxygen should only be administered if there is severe lack of oxygen.
  • Intropics- this type of medication is used for severely ill patients with sepsis, shock and acidosis. Intropics ensure the balance between pulmonary and systemic vascular resistance
  • Diuretics- used to manage overcirculation of the blood in the lungs before surgery
  • Antibiotics- indicated if the infant is at risk for infection [4,5]


The aim of the surgical treatment is to ensure appropriate blood supply to the body. Multiple surgeries need to be performed in a specific order. The right ventricle becomes the main pump that ensures the circulation to the organs. The stages and procedures usually performed are:

Norwood Procedure

This procedure “creates” a new aorta which is than connected to the right ventricle. This procedure is usually done in the first two weeks of life. Oxygen rich and oxygen poor blood will still continue to mix in the heart therefore the infants skin might look blueish.

Bi-directional Glenn Shunt procedure

This procedure is usually performed at 4 to 6 months of age. In this procedure a direct connection between pulmonary artery and superior vena cava is made. This procedure decreases the work of right ventricle by allowing the returning blood from the body to flow to the lungs.

Fontan procedure

This procedure is usually done until the baby is 3 years old. The pulmonary artery is connected with inferior vena cava. After this procedure the blood will no longer mix in the heart and the skin colour becomes normal [5,6]. Also read about velocardiofacial syndrome.

hypoplastic left heart syndrome surgery

Life expectancy & Survival Rate

If the HLHS is not diagnosed during pregnancy or straight after birth this condition is fatal. After surgery the survival rate is more than 75%, but it largely depends on the function of right ventricle. Patients often suffer from complications due to surgeries. In some cases heart transplantation is used. There are also various other conditions that HLHS can complicate with, for example Short bowel syndrome after bowel resection in case of necrotizing enterocolitis [1].

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  1. General information for patients: https://medlineplus.gov/ency/article/001106.htm
  2. Causes: http://emedicine.medscape.com/article/890196-overview#a7
  3. Symptoms: http://www.mayoclinic.org/diseases-conditions/hypoplastic-left-heart-syndrome/symptoms-causes/dxc-20164182
  4. Diagnostics: http://emedicine.medscape.com/article/890196-workup#c5
  5. Surgical treatment: http://pediatricct.surgery.ucsf.edu/conditions–procedures/hypoplastic-left-heart-syndrome.aspx
  6. Treatment: https://www.cdc.gov/ncbddd/heartdefects/hlhs.html

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