Hypoplastic Left Heart Syndrome

What is Hypoplastic left heart syndrome?
Hypoplastic left heart syndrome (HLHS) is a rare congenital heart defect which occurs in approximately 1 in 5000 babies. The term ‘hypoplastic’ refers to the underdevelopment of a tissue or an organ. Therefore HLHS involves the underdevelopment, or sometimes absence, of left-sided heart structures. For example, the left ventricle, left atrium, bicuspid valve or the aorta could potentially be really small.
This ultimately results in the left side of the heart not functioning properly. Furthermore, an atrial septal defect (a hole between the atria – the top two chambers of the heart) is normally present.
Oxygenated blood is normally pumped to the body via the contraction of the left ventricle. However, in HLHS the left ventricle may be so underdeveloped that it is incapable of pumping blood around the body.
The cause for HLHS is unknown, however, it is mostly down to genetic factors caused by mutations to genes in chromosomes. Environmental factors such as: what medication was taken by the mother, or what she ate or drank and what she came into contact with whilst pregnant may also play a significant part in the development of this condition.
Signs and Symptoms:

  • Cyanosis (blue skin colour)
  • Difficulty breathing and/or fast breathing
  • Heart Murmur
  • Tiredness
  • Poor feeding
  • Cold hands and feet
  • Pounding heart
  • Weak pulse

HLHS is commonly diagnosed before birth during an ultrasound. If the doctor believes that there is an issue associated with the heart then a foetal echocardiogram (an ultrasound of the heart) would be requested and this would lead to the discovery of HLHS.
However, it may not be diagnosed before birth and upon seeing the noticeable symptoms or upon hearing a heart murmur an echocardiogram would be carried out and this would show that it’s Hypoplastic Left Heart Syndrome (due to the small or non-existent left sided features.)
To treat HLHS the new-born would immediately need prostaglandin. This medication prevents the ductus arteriosus from closing. This is very important as the ductus arteriosus connects the pulmonary artery to the aorta which allows oxygenated blood to be sent to the rest of the body. If it closed in an infant with HLHS then it would die due to the body being unable to receive oxygenated blood as the only route to the aorta and thus the body is the ductus arteriosus, unless an atrial septal defect was present.
Surgery would be essential in order for the survival of the child. In fact, three surgeries would be needed:

  1. Norwood Procedure – This open heart operation is carried out straight after the diagnosis of HLHS and this is usually around the first few days of the child’s life. It involves stopping the heart and allowing a machine, called a heart-lung machine, to perform the role of the heart. The surgeon enlarges the aorta – using a patch – and disconnects the pulmonary artery from the right ventricle and connects the aorta to the right ventricle instead. This now allows the right ventricle to pump blood around the body instead of the hypoplastic left ventricle. To allow deoxygenated blood to reach the lungs a shunt (made of Gore-Tex) is created joining the new aorta to the pulmonary artery. Essentially, the right ventricle now performs the job of both ventricles as it pumps blood to both the body and lungs. Therefore, the heart is now relying on a single ventricle. This surgery is extremely challenging and very long. It can take approximately six hours to complete. The survival rate is about 80% and the child can normally go home after 3-4 weeks. However, in some cases (e.g in very small babies) the Norwood Procedure isn’t suitable and instead the Hybrid procedure is preferred. This consists of keeping the ductus arteriosus open using a stent and making the atrial septal defect larger (which would allow blood to enter the aorta and to be sent to the body) and finally placing small bands on the pulmonary arteries which reduces the amount of blood flowing in them and thus protecting the lungs. This operation is usually 1-2 hours long and doesn’t require a heart-lung bypass machine. Cyanosis would still occur after either of these surgeries due to the mixing of oxygenated and deoxygenated blood still taking place.
  2. Bi-directional Cavo-Pulmonary Shunt Procedure – This second operation is undertaken when the child is between three to twelve months of age. The aim of this operation is to reduce the workload of the right ventricle. This is done by connecting the superior vena cava directly to the pulmonary artery. This improves the quality of life for the patient as the heart doesn’t have to work as hard as deoxygenated blood returning from the upper part of the body goes straight to the lungs via the pulmonary artery. This also is better for the lungs as they now receive blood at lower venous pressures rather than much higher arterial pressures. The shunt added in the Norwood Procedure is then removed. The child will still have a blue appearance even though deoxygenated blood from the upper part of the body no longer mixes with oxygenated blood in the right ventricle. This is due to the mixing of deoxygenated blood from the lower part of the body and the oxygenated blood in the right ventricle.
  3. The Fontan Procedure – This is the final stage and it takes place when the infant is between 18 months and four years of age. The purpose is to finally stop the mixing of deoxygenated and oxygenated blood which leads to partially oxygenated blood and therefore cyanosis. This is achieved by connecting the inferior vena cava, which brings deoxygenated blood from the lower part of the body, to the pulmonary artery. The right ventricle no longer has to pump blood to both the lungs and the rest of the body. It only has to send it to the body which was meant to have been done by the left ventricle.

Future of the child:
Even with all of these surgeries the child will still not be cured of HLHS and a heart transplant may be necessary. However, infant hearts are rarely obtainable and so one may not be available for the child. If they are able to receive a donated infant heart then they will have to take anti-rejection medication for the rest of their lives and this will severely weaken their immune system.
Even if the surgeries go well complications may develop which include:

  • Fluid in the lungs (pleural effusion)
  • Heart failure
  • A fast and irregular heart rhythm (arrhythmia)
  • Stroke
  • Problems of the development of the brain and nervous system
  • Easily becoming tired and breathless during exercise
  • Endocarditis
  • Death

Every patient would also need to regularly visit a cardiologist who would look out for any  of these complications.

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