Hypoplastic Left Heart Syndrome (HLHS) is one of the most complex cardiac defects seen in the newborn and remains probably the most challenging to manage of all congenital heart defects. It is one of a group of cardiac anomalies that can be grouped together under the description "single ventricle" defects.
Example of a normal heart
Example of Hypoplastic Left
2. Hypoplastic left ventricle.
3. Large patent ductus arteriosus supplying the only source of blood flow to the body.
4. Atrial septal defect allowing blood returning from lungs to reach the single ventricle.
The mitral and aortic valves are either completely "atretic" (closed), or they are very small. The left ventricle itself is tiny, and the first part of the aorta is very small, often only a few millimeters in diameter.
This results in a situation where the left side of the heart is completely unable to support the circulation needed by the body's organs, though the right side of the heart (the side that delivers blood to the lungs) is typically normally developed.
Blood returning from the lungs to the left atrium must pass through an atrial septal defect (ASD) to the right side of the heart.
The right ventricle must then do a "double duty" of pumping blood both to the lungs (via the pulmonary artery) and out to the body (via a patent ductus arteriosus (PDA)). The patent ductus arteriosus, a normal structure in the fetus, is often the only pathway through which blood can reach the body from the heart. When the ductus arteriosus begins to close, as it typically does in the first days of life, the blood flow to the body will severely diminish resulting in dangerously low blood flow to vital organs and leading to shock. Without treatment, Hypoplastic Left Heart Syndrome is uniformly fatal, often within the first hours or days of life.
Signs and Symptoms of Hypoplastic Left Heart Syndrome
As mentioned above, infants with Hypoplastic Left Heart Syndrome can develop life-threatening shock when the ducutus arteriosus begins to close. In most cases, however, the ductus arteriosus is widely open at the time of birth, supplying the blood flow to the body and babies may not be diagnosed right away. As the ductus arteriosus closes, which it typically will in most infants in the first hours or days of life, the perfusion to the body is seriously diminished and shock rapidly ensues.
Newborns with Hypoplastic Left Heart Syndrome will typically have lower-than-normal oxygen saturations. This is because all of the blood from the lungs (the oxygenated "red" blood) mixes together in the single right ventricle before being pumped out of the lungs and body. Cyanosis, therefore, may be the first clue to the presence of a serious underlying cardiac condition. Respiratory distress (difficult or fast breathing) is often present because the lungs will tend to receive an excessively large amount of blood flow. There is often no or just a faint murmur present in newborns with Hypoplastic Left Heart Syndrome.
The pulses may be very weak in all extremities on examination depending on flow through the ductus arteriosus. Lethargy, poor feeding, and worsening respiratory distress may be seen as the ducturs arteriosus closes. Ultimately, severe shock resulting in seizures, renal failure, liver failure, and worsening cardiac function may develop. Whether these problems are reversible depends on both the severity and the duration of shock.
Diagnosis of Hypoplastic Left Heart Syndrome
This heart defect is one of the most readily diagnosed on fetal echocardiograms and is one of the most common cardiac defects picked up on screening obstetrical ultrasounds. Such early diagnosis of the anomaly allows for prompt intervention for stabilization at the time of birth so that severe shock may be avoided.
Planning to deliver such an infant at a hospital capable of aggressive newborn resuscitation is important in improving the chances for a good outcome.
Echocardiography is the principal method of diagnosing Hypoplastic Left Heart Syndrome. It can give detailed information of the anatomy of the various cardiac structures affected in Hypoplastic Left Heart Syndrome, as well as important information about the function of the right ventricle, the heart valves, the size of the atrial septal defect (important for blood mixing) and the size of the patent ductus arteriosus.
Cardiac catheterization is rarely used as part of the initial evaluation, with this heart defect due to the high risks in an often unstable newborn. Catheterization, though, does play an important role in the evaluation of the cardiopulmonary function and anatomy in older children with Hypoplastic Left Heart Syndrome while planning for later stages in the treatment.
Treatment of Hypoplastic Left Heart Syndrome
The management of the newborn with Hypoplastic Left Heart Syndrome can be divided into the initial stabilization period and the operative / post-operative period.
If the fetus has been diagnosed before delivery, stabilization measures are started immediately so the newborn does not become unstable. In newborns that are delivered and then suspected of having Hypoplastic Left Heart Syndrome, stabilization begins even while diagnostic tests are going on. The rapid stabilization of these infants must begin as soon as the diagnosis is suspected.
Catheters are placed, usually in the umbilical blood vessels, which allow medications to be given and blood to be obtained for testing. An infusion of prostaglandin, a medication that prevents the patent ductus arteriosus from closing, is begun, thus maintaining the pathway for blood to reach the body from the right ventricle.
Even though the infant may have low oxygen saturations, supplemental oxygen is avoided since it tends to promote more blood flow to the lungs which may steal blood flow from the body and place excessive demands on the already stressed single right ventricle.
Manipulations of medications and respiratory treatments (including possible mechanical ventilation) are performed to optimally balance the flow of blood to the body and the flow of blood to the lungs.
Close monitoring is essential to detect any organ dysfunction and maintain cardiopulmonary stability because infants with this anomaly may be very unpredictable and undergo quite sudden changes.
There are essentially three treatment options that have been proposed for children with Hypoplastic Left Heart Syndrome.
In the past, due to poor outcomes with available treatments at that time, no treatment was often recommended. Today it is rare that a family may choose not to treat a child with Hypoplastic Left Heart Syndrome, though in cases when the infant is unable to be satisfactorily stabilized no treatment may be advised.
Cardiac transplantation in the newborn period is performed as primary treatment for Hypoplastic Left Heart Syndrome at some centers in this country. While transplantation has the advantage of replacing the very abnormal heart of a child with Hypoplastic Left Heart Syndrome with one of normal structure, this treatment is limited by the scarcity of newborn organs available for transplantation and the life-long need for anti-rejection therapy. Additionally, although outcomes for transplantation continue to improve, and the incidence of rejection is lowest in patients transplanted as newborns, the average life span of the transplanted heart is limited (currently less than 15 years).
The most commonly pursued treatment for Hypoplastic Left Heart Syndrome is "staged reconstruction" in which a series of operations, usually three, are performed to reconfigure the child's cardiovascular system to be as efficient as possible despite the lack of an adequate left ventricle. These surgeries do not correct the lesion, and are instead considered "palliative".
The first operation in the staged approach is known as the Norwood 1 operation and is typically performed in the first week of life. With the Norwood operation, the right ventricle become the systemic or main ventricle pumping to the body. A "new" or "neo" aorta is made from part of the pulmonary artery and the original, tiny aorta, which is reconstructed / enlarged to provide blood flow to the body. Finally, to provide blood flow to the lungs, a small tube graft is placed either from an artery to the lung vessels (called a modified Blalock-Taussig shunt) or from the right ventricle to the lung vessels (called a Sano modification). Because of the extensive reconstruction of the aorta that must be done, this operation is one of the most challenging heart surgeries in pediatrics.
The subsequent operations in the staged reconstruction plan are the bi-directional Glenn procedure, typically done at 3 to 6 months of age, and the Fontan operation, typically done in children older than 2 or 3 years. These operations are described in more detail in the Heart Encyclopedia chapter on "Single Ventricle Cardiac Anomalies."
Hypoplastic Left Heart Syndrome / Norwood Surgery
Results with staged reconstruction for children with The Norwood operation is the most complex and highest risk procedure in the sequence of staged reconstruction for Hypoplastic Left Heart Syndrome. Current management at major pediatric heart centers has resulted in survival rates of 75 percent or better.
The recovery period in the hospital following the Norwood operation is often unpredictable and complicated, averaging about 3 to 4 weeks. A small percentage of patients who leave the hospital may continue to experience significant problems in the first months of life.
Occasionally, the right ventricle does not function well following the Norwood operation and in some case, cardiac transplantation may need to be considered.
If a child with Hypoplastic Left Heart Syndrome reaches the time for the second stage (about 4 to 6 months of age) without major complications, the survival through the Glenn and Fontan operations are much better, exceeding 90 percent with current methods.
Almost all children with Hypoplastic Left Heart Syndrome will continue to need some cardiac medications to maximize the efficient function of their heart, and all will require regular periodic follow-up visits with their cardiologist to evaluate their cardiac function and detect late complications such as arrhythmias.
How the Norwood operation works
The right ventricle is now the main (only) pumping chamber for the body.
It pumps blood into the Main Pulmonary Artery, then the left and right pulmonary arteries (LPA and RPA) and then to the lungs (to oxygenate the blood).
The Norwood operation SEPARATES the main pulmonary artery from its two major branches (see above), and connects it instead directly to the Aorta.
So far so good, the main pumping chamber is supplying the body with blood.
HOWEVER we have now cut off the lungs from the circulation, so no oxygen is being added to the blood – not good. So we need to connect the new Aorta to the lungs – through an Aortic to Pulmonary artery shunt (actually not the aorta, a branch of it called the subclavian artery, connected to the RPA). This shunt (see diagram ) is called a modified Blalock-Taussig shunt, after its inventors.
This allows some of the blood to travel to the lungs and get oxygen. This blood returns to the left atrium and through the atrial septal defect (or the atrial septum may have been completely removed) and mixes with the deoxygenated (blue) blood returning to the right atrium from the body – so the mixture is partially oxygenated and then goes to the right ventricle and is pumped to the rest of the body.
Not an ideal situation. but better than no oxygen at all getting to the body, obviously.
Second Stage Operation
The second stage of repairing a hypoplastic heart is the Bidirectional Glenn shunt.
Bidirectional Glenn Shunt
The bidirectional shunt is performed by connecting the superior vena cava (SVC) to the right branch of the pulmonary artery using fine sutures, and dividing or tying up the pulmonary artery. Now, venous blood from the head and upper limbs will pass directly to the lungs, bypassing the right ventricle. The venous blood from the lower half of the body however will continue to enter the heart.
The bidirectional Glenn shunt is preferred in very small babies - below 2 years of age - in whom the lung vessel resistance is still quite high, and in borderline cases with abnormal pulmonary arteries.
Third Stage Operation
Fontan Procedure Summary
The Fontan is an open-heart surgery in which a passageway is created for oxygen-poor blood to bypass the right ventricle and travel directly to the lungs for fresh oxygen. It is used to treat a variety of different congenital heart defects. There are two stages to the Fontan, which are usually performed at two different stages in a young patient’s life. Each stage will require about ten days to three weeks of recovery time in the hospital.
Francis Fontan performed the Fontan operation first in 1968. The Fontan operation is a heart operation used to treat complex congenital heart defects (birth defects of the heart) like tricuspid atresia, hypoplastic left heart syndrome (HLHS), pulmonary atresia and single ventricle.
The aims of the "ideal" Fontan operation are
· To achieve a smooth stream-lined blood flow from veins to the lungs
· To retain growth potential as the child becomes older
· To avoid use of artificial materials
· To be adaptable to patients of any age group
The Fontan Principle
What is a Fontan-type circulation ?
It is an integral part of the entire operation for conditions like tricuspid atresia, pulmonary atresia, hypoplastic left heart syndrome ( HLHS ) and other single ventricle pathology.
We - you, me, cardiologists, surgeons, and everyone else - have been accustomed to thinking of the heart as having four chambers - two atria and two ventricles. These four chambers acting in unison maintain the circulation of blood.
To understand the Fontan circulation, you must make a "leap of imagination". In your mind, eliminate the right ventricle from the heart ! Tough isn't it ? And how can the heart possibly work without a right ventricle ?
Illogical as it may seem, this however was exactly what Dr.Fontan proved with his operation. In his original repair, he connected the right atrium directly to the pulmonary artery, and closed the ASD. Blood entering the right atrium from the veins passed across this surgical connection into the pulmonary artery and to the lungs. It completely bypassed the right ventricle.
There must be a flaw in this somewhere! How can the blood enter the lungs if it is not PUMPED IN by the right ventricle ? Well, that really is what makes this procedure unique. Normally the right ventricle will do the pumping. But in tricuspid atresia - and many other conditions in which a Fontan operation is performed - there is NO right ventricle. So blood flows PASSIVELY into the lungs - without being propelled into them by a right ventricle.
Why is lung blood flow so important ?
Because it is the only place in the body that blood can be purified by the addition of oxygen. So when lung blood flow is very low, oxygen supply is reduced to the entire body. This has many harmful effects, since no organ can perform its work normally without oxygen for energy.
So where does the energy for blood flow to the lungs come from ?
First, you must understand that any fluid flowing in a tube will continue to move, becoming slower and slower, until the resistance offered by the tube makes it stop. In a Fontan type circulation, the left ventricle pumps blood into the aorta and arteries. This blood flows at first rapidly into the different organs. The very same force pushes the blood across capillaries, and through the veins, but with lesser force. Slowly, blood enters the right atrium, and then passes across the surgical connection into the lungs - all the while unaided by a right ventricle.
But by its very nature, this flow depends on many factors. For instance, if the blood vessels in the lung are thick walled and narrow before surgery, they will offer very high resistance to passive blood flow. In such a state, the Fontan operation cannot be performed, or will have a high risk of failure, since the extra energy needed to maintain lung blood flow is not available.
Even normally a small amount of resistance will exist across the lung blood vessels. After a Fontan operation, the pressure in the veins will therefore be higher than normal, in order to overcome this resistance and maintain lung blood flow. The elevated pressure in the veins has a few ill effects.
How to interpret the survival funnel plots
These graphs show the national average survival after specific procedures for treating congenital heart disease. The national average is shown as a horizontal grey line. Two control limits are shown; a warning limit (Green line, 98%) and an alert limit ( Red line 99.5%). Unit performances are shown as identifiable coloured symbols. If a unit's symbol is above the green line then the performance is no different from the national average. If a unit’s survival rate is below the warning limit, their performance will be closely monitored in subsequent years. If a unit’s survival rate is below the alert limit, an investigation into possible reasons and remedial actions will be launched by the appropriate professional and regulatory bodies.