Hypoplastic Left Heart Syndrome – HLHS
The “Hypoplastic Left Heart Syndrome” – or more conveniently, “HLHS” – is a unique defect of the heart in many ways. Until a decade ago, the diagnosis was a virtual death sentence. Today, the revolution in cardiac surgical thinking and technique has changed the situation radically.
Whereas survival beyond the first few months of life was previously unheard of, many centers are today reporting encouraging results. And it is bound to improve further as more knowledge is gained from the early experience.
What is the HLHS ?
The heart has two upper and two lower chambers – one of each is right sided and the other left sided. The left sided chambers, with their blood vessels and valves are sometimes referred to as the LEFT HEART. ( This does not mean that the person has TWO hearts! )
The structures included by the term “left heart” are the left atrium, left ventricle, mitral valve, aortic valve and the aorta.
Sometimes, due to abnormal development, the left heart structures may be small – or hypoplastic. The defect may affect any combination of left heart structures, or rarely even all of them. This condition is called Hypoplastic Left Heart Syndrome or (HLHS). Some surgeons recognize sub-types of HLHS which have different outcomes. The actual measurements below which we can categorize a small “left heart” as HLHS have been described.
Why is HLHS such a dangerous condition ?
The left ventricle is the main pumping chamber of the heart. By its action, the left ventricle delivers “pure” blood to all parts of the body. This blood contains oxygen and energy-giving nutrients, which are required by different organs to function normally.
In HLHS, there is a reduction in the flow of “pure” blood from the left ventricle. This is because the ventricle itself is small, or the pathway of blood flow into it (the left atrium and mitral valve) or out of it (the aortic valve, and aorta) is small. So all parts of the body – the kidneys, liver, muscles, brain and the heart itself – get less energy, and cannot work normally.
What then are Nature’s compensatory methods in HLHS ?
HLHS is caused by altered blood flow patterns even as the child is developing within the mother’s body. At birth, the left sided heart structures are severely under-developed and are very small. So they are not able to pump blood to the remaining parts of the body.
If such a condition continues, life is not possible. To help correct it, the right ventricle assists the left ventricle in its work. The situation becomes a functional type of Single Ventricle – that is, there is only one working ventricle – the right.
Also, the ductus arteriosus remains patent after birth for some time, and this helps blood flow as well. The blood pumped by the right ventricle first enters the pulmonary artery. Here, it is divided into two portions. One portion of this blood crosses the Patent Ductus Arteriosus and flows into the aorta. From here it is distributed to all the other parts of the body, just as in a normal person.
The remaining portion of blood in the pulmonary artery enters the lungs for purification. In this way, the right ventricle supports blood flow into the lungs as well as the aorta.
However, when the ductus arteriosus closes – as it normally does soon after birth – there is a sudden worsening. With the left heart being too small, all of a sudden there is no blood flow into the aorta. If left untreated, survival is impossible.
Should HLHS be surgically treated ?
This is, in my opinion, the most difficult question to answer about HLHS. Various issues – emotional, scientific, economic and ethical – arise, confusing the whole affair and making it very complex. Rather than stating my personal opinions, I will attempt to discuss the options available.
When detected early enough in pregnancy, Medical Termination of Pregnancy (MTP) – also called “therapeutic abortion” – may be offered to the family. The argument in favor of MTP is that the outcome of surgery for HLHS is still uncertain, particularly in the long run. Also, the surgical process is emotionally traumatic to the entire family, and the expense is considerable. Another theoretic reason to prefer MTP is that it does not pass on the genetic defect of HLHS patients to future generations.
Against this choice stand witness the increasingly large number of survivors of surgery for HLHS. Support groups made up of parents of these “tough kids” are living evidence that it is possible to face and overcome the difficulties in caring for such children. And the results of surgery are rapidly improving. Very soon, these may be good enough to make MTP an ethically unacceptable option for HLHS. Also, many people have religious and moral objections to MTP.
A sympathetic approach to discussing these problems with the parents is essential. No parent should be made to feel guilty about choosing MTP after a diagnosis of HLHS is made. At the same time, a easily understandable and considerate explanation of all the surgical options, the “state-of-the-art” results, the potential risks and problems, and long term outcome should be given to all parents who wish to consider surgery for their children.
What can the surgeon actually do ?
Just around 10 years ago, all that specialists could do for HLHS kids was to pray ! Things changed with the innovative effort of a brilliant cardiac surgeon, Dr.William Norwood. While Dr.Norwood was working with one of the greatest paediatric cardiac surgeons of our times – Dr.Aldo Castaneda – he conceived the operation for HLHS that bears his name. Rapid strides in treating HLHS have taken place ever since then, and results are improving.
Early diagnosis and stabilization
The first step in treating HLHS is recognizing the condition early. It is now possible to reliably detect HLHS even as early as 16 to 20 weeks into a pregnancy, by ultrasonography. Such pregnancies need close monitoring and co-ordinated management by many medical specialists. These children must preferably be delivered in a hospital which is equipped to manage HLHS cases, or transported to such a center immediately after birth.
As I have explained earlier, the patent ductus arteriosus (PDA) is what keeps the HLHS child alive. This PDA has a tendency to close after birth, and must be kept open. It is possible to do so by using a drug called Prostaglandin (Prostacyclin). This is truly the “miracle drug” of pediatric cardiology. Many birth defects of the heart that need a PDA for survival can be treated initially with prostaglandin.
A “prostaglandin drip” is started soon after the child is born. This must only be done in a well equipped hospital, under the guidance of qualified physicians. Children treated with prostaglandin may need artificial respiration if their breathing effort becomes weak.
Once the child’s condition has improved, surgery is possible with lesser risk. This may take a day or two of intensive therapy. It must not however be unduly delayed.
What are the surgical options ?
There are two major lines of treatment for HLHS. The first is a series of operations called the Norwood Procedure. The other alternative is Heart Transplantation. Both are formidable procedures, and carry some risks. But the good news is that results are steadily improving. Let me first describe what these operations are.
What is the Norwood operation ?
This is a multi-stage procedure to treat HLHS. The first stage is usually performed within the first week of life. It is an “open-heart” operation, done using the heart-lung machine to support the circulation. The aorta, which is very small in HLHS, is entirely reconstructed by an ingenious technique.
The initial portion of the pulmonary artery, the small aorta, and an Aortic Homograft are stitched together in such a way that an almost normal-sized new aorta – called a “neo-aorta” is built. This neo-aorta has a connection with the right ventricle through the pulmonary artery. So the right ventricle now acts as the chamber pumping blood to the whole body.
At this time, the wall between the two upper chambers (atrium) – the inter-atrial septum – is also cut away. This is done so that there is no obstruction to blood returning from the lungs into the left atrium and flowing into the right ventricle. To provide blood flow into the lungs, a new channel is created by making a modified Blalock Taussig Shunt using a 3.5 to 4 millimeter sized PTFE (Gore-tex) tube graft.
(I have described in detail elsewhere the aortic homograft and Blalock-Taussig shunt)
At the second stage of the Norwood procedure, the modified BT shunt is closed, and a Bidirectional Glenn Shunt (BDG) constructed, just as in Tricuspid Atresia and other Single Ventricle conditions. At the same time, if the pulmonary arteries are found to be deformed, they are repaired. This procedure is called Pulmonary Arterioplasty.
At the third stage, a complete Fontan circulation is established. The details of the Fontan operation are just as in Tricuspid Atresia.
What are the problems with a Norwood staged operation ?
Each of the three stages has its own risks and complications.
Norwood operation – Stage 1
The first stage is the most critical. The operation is only palliative – that is, it does not correct the defect entirely, but only provides partial relief. At the end of the operation, the heart is provided with a single pumping chamber – the right ventricle – which must provide the entire body and the lungs with blood flow.
The average patient spends a week or 10 days in the intensive care unit, and around 20 days in hospital. Numbers do not mean much in a condition like HLHS where most hospitals have not operated on many children, but around 40% do not survive the first stage.
In centers which are more experienced with such operations, the results are better. And they are improving every day, and soon will hopefully be good enough to allow more confident and encouraging projections of outcome.
After a first stage Norwood operation, the follow up care of children is similar to that of a patient being considered for a Fontan operation. The important issues are to
- preserve ventricular function
- ensure good and symmetric growth of pulmonary arteries
- keep lung blood vessel resistance low
- prevent any obstruction to blood flow at the inter-atrial septum.
Most centers follow a fixed protocol of doing a cardiac catheterization test after six months. At this time, the future course of treatment is decided upon.
In the meantime, if there are any added complications, the protocol may be modified. Problems that may occur include an increase in severity of cyanosis – bluish discoloration – or a failure of the child to feed well or grow and develop normally. Heart failure may set in too. In all of these conditions, an earlier catheterization study may be required.
Norwood operation – Stage 2
The second stage of the Norwood operation is usually performed at 6 to 9 months of age. It is a much safer operation than the first stage. Post operative care is routine, and follow up is the same as for patients who have had a Bidirectional Glenn shunt for other single ventricle conditions.
One complication that may arise is an increase in severity of cyanosis due to the development of abnormal vein connections – called veno-venous collaterals. This can be treated by a method called Trans-catheter Embolization.
In this method, small pellets of teflon or metal wire are delivered into the abnormal veins through a catheter. These cause blood to clot inside the abnormal collateral veins, and block them.
At around 9 to 12 months after the second stage, a cardiac catheterization test is repeated. If the situation is suitable for a Fontan type operation, the third stage is carried out. This is often possible at an age of 18 to 24 months.
The evaluation and technique of the Fontan operation are the same as for Tricuspid Atresia, which I have discussed in another section.
Norwood operation – Stage 3
This is in effect a complete Fontan operation. Risks, complications, and long term outcome are likely to be similar to Fontan operations performed for other diseases.
Research is currently in progress to find out what factors are peculiar to HLHS in determining outcome.
What is Heart Transplantation ?
Sometimes the heart may be so severely hypoplastic (small), or other conditions may co-exist that make a Norwood type operation more risky and likely to fail. The only choice then is to replace the heart with another healthy one – Heart Transplantation.
Adult heart transplantation is currently quite successful. But in a newborn infant it is a formidable operation. A heart transplant for HLHS was first performed successfully in 1985 by Drs. Bailey and Gundry at Loma Linda in California, USA – still the center with the most experience in neonatal heart transplantation.
The philosophy behind transplanting a child with severe HLHS is that when reconstruction by a Norwood operation is attempted
- the right ventricle may fail after many years
- the tricuspid valve may become leaky later
- the pulmonary valve may become leaky due to the high pressures that it needs to withstand
- the operation itself is very difficult technically.
However, transplantation too carries its price tag. There is an indefinite waiting period till a donor organ becomes available. Some patients will die before a donor becomes available.
Also, since the operation is new, and is still limited to very few institutions world-wide, long term results are uncertain. Early development of coronary artery disease in the donated heart may limit late survival. Complications of the medicines used to prevent graft rejection include development of a form of cancer called lymphoma. And heart transplantation is also an expensive affair.
Maybe in the future, transplantation will be better reserved for the more severe forms of HLHS who are unsuited for reconstruction. In the others, repair techniques must be preferred. With improvement in technology and experience, most of these patients should be correctable successfully.
For some time to come, however, HLHS will remain a troublesome challenge to those of us who are concerned with treating congenital heart disease.