Brief overview
- What is hypoplastic left heart syndrome (HLHS)? A severe congenital heart defect in which the left ventricle and the part of the aorta branching off from it are underdeveloped. In addition, the heart valves of the left side of the heart are narrowed or closed. Sometimes other defects accompany hypoplastic left heart syndrome.
- Causes: several changes (mutations) in different genes
- Effects: Heart failure (cardiac insufficiency), as a result of which too little blood is pumped into the body. If left untreated, HLHS is fatal within a short time after birth.
- Symptoms: e.g. rapid breathing, shortness of breath, pale cool skin, weak pulse, bluish discolored skin and mucous membranes
- Diagnosis: by means of cardiac ultrasound; rarely a cardiac catheterization is also necessary
- Treatment: medication to bridge the time until a multi-stage operation or a heart transplant can enable longer-term survival.
What is hypoplastic left heart syndrome (HLHS)?
Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect. It mainly affects the left side of the heart and the aorta branching off from it. HLHS causes heart failure (cardiac insufficiency), the consequences of which can be fatal if not treated quickly.
In detail, hypoplastic left heart syndrome is characterized by a combination of the following malformations:
Underdevelopment of the left ventricle: The left ventricle is severely underdeveloped (hypoplastic), i.e. very small. As a result, it is hardly or not at all able to fulfill its task – namely to pump blood into the outgoing aorta and thus further into the body (abdominal organs, arms, legs, etc.).
Underdevelopment of the ascending aorta: The ascending aorta is the first section of the aorta that branches off from the left ventricle. It is also not properly developed in HLHS.
Underdevelopment of the aortic isthmus: The aortic isthmus is a natural narrowing in the aorta at the transition between the aortic arch (second section of the aorta) and the descending aorta (“descending” aorta; third section of the aorta).
Severe narrowing (stenosis) or closure (atresia) of heart valves: The mitral valve (between the left atrium and left ventricle) and the aortic valve (between the left ventricle and aorta) are affected. Depending on the type of heart valve defect, there are four subgroups of hypoplastic left heart syndrome, such as MA/AoA (mitral and aortic valve atresia) or MS/AoA (mitral valve stenosis and aortic valve atresia)
Hypoplastic left heart syndrome occurs in up to ten percent of cases in the context of genetic syndromes such as trisomy 21 (Down syndrome) or Turner syndrome.
Hypoplastic left heart syndrome: frequency
Hypoplastic left heart syndrome is rare: It is found in around one to three out of every 10,000 children born alive. Boys are more frequently affected than girls.
Of all congenital heart defects, hypoplastic left heart syndrome accounts for around one to two percent. However, it is one of the most common causes of heart failure in newborns. HLHS is also the most common cause of heart-related death in babies in the first week of life.
What happens in HLHS?
Hypoplastic left heart syndrome has serious consequences: The underdevelopment and malformations of the left side of the heart render it more or less non-functional. The right side of the heart must therefore take over its task: pumping blood into the body’s circulation. This is only possible without problems in children until shortly after birth because they have “short circuits” in their blood circulation:
Ductus arteriosus and foramen ovale
The baby’s lungs do not have to and cannot yet fulfill their function in the womb (i.e. load the blood with oxygen). Instead, the mother supplies the fetus with oxygen-enriched blood. It enters the child’s inferior vena cava via the umbilical cord and continues into the right atrium. From there it flows via the right ventricle into the pulmonary artery. Here, only a small part of the blood is directed into the still “immobilized” lungs. Instead, the majority is transported via the ductus arteriosus directly into the main artery (aorta) and thus further into the systemic circulation.
It is also possible to bypass the lungs via the foramen ovale, which only starts working after birth: this is a small natural opening in the atrial septum of the fetus (unborn child from the 9th week of pregnancy until birth). Through this opening, some of the oxygen-rich umbilical cord blood can flow directly from the right atrium into the left atrium and thus be supplied to the body’s circulation.
After birth, the “short circuits” disappear
The foramen ovale also normally closes on its own shortly after birth. Sometimes, however, it remains partially or completely open (open foramen ovale).
HLHS: “Short circuits” vital for survival after birth
An open ductus arteriosus and an open foramen ovale ensure the survival of newborns with HLHS: blood enriched with oxygen, which comes from the now unfolded lungs and flows into the left atrium, can reach the right atrium via the open foramen ovale. There it mixes with the deoxygenated blood from the body.
The heart pumps this “mixed blood” via the right ventricle into the pulmonary artery. From there, some of the blood flows via the still open ductus arteriosus into the systemic circulation and thus maintains the supply to the organs and other tissues.
Closure of the ductus arteriosus shortly after birth therefore has dramatic consequences if hypoplastic left heart syndrome is present. The underdeveloped left ventricle can hardly or not at all maintain the body’s circulation.
The closure of the foramen ovale also causes the blood in the left atrium to back up into the lungs because it can no longer drain into the right atrium. However, the right ventricle continues to pump blood into the lungs. The blood volume in the lungs increases rapidly and breathing deteriorates noticeably.
Hypoplastic left heart syndrome manifests itself with symptoms as soon as the ductus arteriosus begins to close after birth (HLHS babies therefore usually still appear healthy immediately after delivery). Affected babies quickly develop signs of cardiogenic shock (= shock originating in the heart):
- rapid breathing
- shortness of breath
- weak pulse
- pallor
- bluish discoloration of skin and mucous membranes (cyanosis)
- low body temperature (hypothermia)
- metabolic acidosis (metabolic acidosis)
- listlessness (lethargy)
- Reduced or absent urination (oliguria or anuria) – i.e. hardly any wet diapers
Due to the underdevelopment and malformations of the left side of the heart and the aorta, too little oxygen-rich blood ends up in the body’s circulation. In addition, the pulmonary blood flow continues to increase due to various mechanisms. This places an enormous strain on breathing.
If the circulatory situation continues to deteriorate, there is a risk of heart attack and cerebral infarction (stroke due to reduced blood flow). Damage to other organs (such as the liver and intestines) can also occur due to the undersupply of blood.
If the ductus arteriosus is not reopened immediately so that the right side of the heart can continue to pump blood into the body’s circulation via this “short circuit”, at least for the time being, the baby will die of cardiovascular failure!
Hypoplastic left heart syndrome: diagnosis
After every birth, pediatricians listen to the heart and measure the oxygen saturation in the blood (pulse oximetry). However, these examinations are often initially inconspicuous in HLHS.
Hypoplastic left heart syndrome can be reliably diagnosed using a cardiac ultrasound examination (echocardiography). This allows the doctor to assess how pronounced the underdevelopment and malformations of the left side of the heart and the aorta are and which subtype of HLHS is present. Only rarely is an examination using cardiac catheterization necessary for the diagnosis (read more about this procedure here).
Further examinations provide information on the effects and possible consequential damage of hypoplastic left heart syndrome. For example, various blood values indicate how pronounced the metabolic derailment (hyperacidity) is. The enlargement of the heart muscle (cardiomegaly) that usually occurs in hypoplastic left heart syndrome can be seen on chest X-rays (chest X-ray) – as well as an increased pulmonary vascular pattern. X-rays may also show an accumulation of fluid in the lungs (pulmonary edema).
How is hypoplastic left heart syndrome treated?
Doctors immediately transfer babies with hypoplastic left heart syndrome to a neonatal intensive care unit or an intensive care unit for children with heart disease. There they can not only be continuously monitored, but also stabilized until surgery is possible.
Until then, the main task is to keep the ductus arteriosus open: To do this, the baby is given an infusion of prostaglandin E1 (PEG1). This substance can prevent the short circuit between the pulmonary artery and the aorta from closing or can completely reopen the short circuit.
If doctors have already diagnosed the heart defect in the womb, the newborn is given the prostaglandin infusion immediately after birth.
In addition, babies with HLHS are stabilized and treated as required. Severely ill babies may need to be ventilated by machine to ensure the oxygen supply to their tiny bodies. Sometimes an HLHS baby also needs medication to improve cardiovascular function.
Three-stage surgical procedure
The “used”, deoxygenated blood flowing back from the organs flows directly into the lungs via a bypass without any pumping support from the heart. After the three interventions, the pulmonary and systemic blood circulation function practically separately from each other with only one ventricle as the “motor” (Fontan circulation).
The schedule of the three-stage surgical procedure:
- 1st stage (Norwood procedure/Norwood operation I, alternatively: hybrid therapy): in the first week of life
- 2nd stage (bidirectional Glenn or Hemi-Fontan procedure, also known as Norwood operation II): at the age of three to six months
- 3rd stage (Fontan procedure, also known as Norwood surgery III): at the age of 24 to 36 months
Heart transplantation
In particularly severe cases, a heart transplant is sometimes the better treatment choice for hypoplastic left heart syndrome than the three-stage heart and vascular remodeling. Until a suitable donor heart is available, doctors continue to keep the baby alive with prostaglandin infusions (and other necessary measures). Unfortunately, this is not always successful because the supply of donor hearts is limited. As a result, around 20 percent of babies with HLHS die while waiting for a transplant.
Living with HLHS
A hypoplastic left heart requires some patients to take long-term anticoagulant medication to prevent blood clots from forming. Many children also need one or more medications to support heart function.
Some children with HLHS need to take antibiotics before going to the dentist or undergoing certain operations (e.g. in the respiratory tract). This is to prevent bacterial inflammation of the inner lining of the heart (endocarditis), which can occur as a result of such operations.
Children who have received a donor heart transplant have to take immunosuppressants for the rest of their lives – i.e. medication that suppresses the immune system so that it does not reject the foreign organ. As a side effect, however, those affected are more susceptible to infections. In addition, the immunosuppressants cause pathological changes to the vessels supplying the heart (coronary arteries) in many children within the first five years. A new heart transplant then becomes necessary.
HLHS: Complications
One possible consequence of HLHS – even after a successful operation – is a weakening single-chamber heart. Medication can counteract this in mild forms. Sometimes, however, a heart transplant is necessary.
After HLHS surgery, the pressure conditions in the blood circulation change. For example, the pressure in the vena cava is increased. As a result, proteins leak from the blood into the intestines, for example, where they cause diarrhea (protein loss syndrome/enteropathy). Children with hypoplastic left heart syndrome can develop this complication with increasing age. As a result, some children only develop protein loss in adolescence.
The lungs, or more precisely the bronchi, can also be affected by this type of condition (bronchitis fibroplastica). Affected children suffer severe coughing fits due to the leaked protein and fibrin-containing fluid and sometimes develop severe breathing problems. Doctors then try to alleviate the symptoms with various examinations and measures. A high-protein diet can be helpful or necessary if too much protein is lost.
Hypoplastic left heart syndrome is often associated with developmental disorders. It is therefore important that the children receive long-term care from specialized paediatricians and targeted early support.
The general quality of life differs from case to case. Some HLHS children can live an almost normal life (play, kindergarten, school, light sporting activities). Others have recurring, sometimes severe, performance impairments. However, the physical performance of people with hypoplastic left heart syndrome is usually generally limited compared to healthy people.
HLHS: Life expectancy
The course and prognosis of hypoplastic left heart syndrome depend largely on the type and severity of the heart defects and the timing of treatment. However, HLHS is life-threatening in any case: if a baby is born with HLHS, its immediate survival depends on the ductus arteriosus being kept open or reopened with medication until the child is operated on (or receives a new heart). If left untreated, it will die within a few days to weeks.
The life expectancy and long-term prognosis of an operated hypoplastic left heart syndrome cannot be predicted exactly. According to various studies, 50 to 80 percent of affected children are still alive after five years. The 10-year survival rate is put at around 50 to 70 percent.
The 5-year survival rate after a heart transplant is similar to that after the multi-stage surgical procedure.
