Hypoplastic left heart syndrome

Hypoplastic left heart syndrome (also known as HLHS), is a rare congenital heart defect in which the left ventricle of the heart is severely underdeveloped.

Causes
If part of the endocardial tube gets pinched shut in a region that becomes the future ventricle, hypoplastic heart syndrome will occur. If the pinched part of the endocardial tube is the bulbus-cordis region of the developing heart, hypoplastic RIGHT syndrome will occur. If it is in the ventricle region it will be the LEFT side that is hypoplastic.

There is evidence associating it with Gap junction protein, alpha 1.

Colleagues at Cincinnati Children’s Hospital in Ohio studied 1,500 newborns from 38 children’s hospitals in the United States from the 1990s to 2006. They found that babies born between April and July were more likely to have this defect, establishing strong evidence that seasonality and environmental factors play a significant role in causation. PMID: 20817208

Presentation
In babies with HLHS, the aorta and left ventricle are very small, and the aortic and mitral valves are either too small to allow sufficient blood flow or are atretic (closed) altogether. As blood returns from the lungs to the left atrium, it must pass through an atrial septal defect to the right side of the heart.

In a healthy human, the left side of the heart receives oxygen-rich blood from the lungs and pumps it out to the rest of the body; with these structures underdeveloped, they cannot circulate blood to other organs, and the right ventricle must pump blood to both the lungs, as it would normally, and to the rest of the body, a situation which cannot be sustained for long.

In cases of HLHS, the right side of the heart often must pump blood to the body through a patent ductus arteriosus. As the ductus arteriosus usually closes within eleven days after birth, blood flow is severely restricted and eventually cutoff, leading to dangerously low circulation and eventually to shock.

Treatment
Without life-prolonging interventions, HLHS is fatal, but with intervention, an infant may survive. A pediatric cardiothoracic surgeon may perform a series of operations or a full heart transplant. In the meantime, the ductus may be kept open to allow blood-flow using medication containing prostaglandin. Because these operations are complex and need to be individualized for each patient, a cardiologist must assess all medical and surgical options on a case-by-case basis.

Currently, infants who undergo either the staged reconstructive surgery (Norwood procedure almost immediately after birth, Glenn procedure at 3 to 6 months of age, and the Fontan procedure at 3 to 5 years of age) or who undergo cardiac transplantation have a 5-year survival of approximately 50-60% as a group. However, it is becoming clear that there are higher risk subsets where 5 year survival is lower (including those with lower birth weight,additional congenital anomalies, a genetic syndrome or those with a highly restrictive atrial septum. For patients without these additional risk factors, 5 year survival now approaches 80%. Further, studies show that about 50% of those children who survived surgery in the early development of staged reconstruction have developmental delay or need special education; about 25% of these surgical survivors have severe disabilities. There is growing evidence that while the incidence of developmental and behavioral disabilities continues to be higher than that in the general population, children operated upon in the more current era have shown significantly better neurological outcomes. An alternative to the traditional Norwood is the Hybrid procedure.

Some parents choose an option referred to as compassionate care, and these infants receive treatment aimed at relieving suffering without extending life. Compassionate care is overseen by a physician, and may be carried out either in the hospital or at home. Studies show that when presented with all options, about half of parents choose life-prolonging interventions and half choose compassionate care. A study in 2003 concluded that a selection of physicians who are experts in the care of children with HLHS were evenly split when asked what they would do if their own children were born with HLHS, with 1/3 stating that they would choose surgery, 1/3 stating that they would choose palliative (compassionate) treatment without surgery, and 1/3 stating that they are uncertain which choice they would make.

The three-stage procedure is a palliative procedure (not a cure), as the child's circulation is made to work with only two of the heart's four chambers.

Step 1: Norwood procedure
The first step is the Norwood procedure. In this procedure, the right ventricle is used to pump blood into the systemic circulation. Since the right ventricle is no longer directly pumping blood to the lungs, a shunt is required in order to pass deoxygenated blood through the lungs. Either the subclavian artery can be connected to the pulmonary circulation (Blalock-Taussig shunt), or a shunt is made directly from the right ventricle to the pulmonary circulation (Sano shunt). The narrow aorta is enlarged using a patch to improve blood flow to the body.

During this time the baby may be medically fragile and have feeding problems because the heart is working very hard. There is a considerable degree of venous mixing in the right ventricle, leading to lower oxygenation saturation. In addition, the Blalock-Taussig shunt and the Sano shunt both expose the lungs to systemic arterial pressures, leading in the long term to pulmonary hypertension and eventually to heart failure.

The Hybrid procedure is used in place of the Norwood. The Hybrid procedure does not necessitate the use of heart-lung bypass or performing a sternotomy. Instead of a six-hour surgery, the Hybrid typically takes one to two hours. In the procedure, a stent is placed in the Ductus Arteriosis to maintain its patency, and the Pulmonary Artery has a band placed over it to limit over-circulation to the lungs. Outcomes with the Hybrid approach are comparable with the Norwood.
 * Hybrid (Sano) procedure

Step 2: Glenn procedure
The second stage, the bi-directional Glenn procedure or Hemi-Fontan (see also Kawashima procedure) relieves some of the above problems. In this operation, the superior vena cava is ligated from the heart and connected to the pulmonary circulation. At this time, the Blalock-Taussig or Sano shunt is taken down. At this point, the lungs are no longer exposed to systemic arterial pressures, but much lower venous pressures. Although venous blood from the upper half of the body is no longer mixing with oxygenated blood in the right ventricle, there is still venous mixing from the lower half of the body, leading to some degree of oxygen desaturation.

During this time the child may have improved quality of life as the heart does not have to work as hard.

Step 3: Fontan procedure
The final procedure, the Fontan (Fontan procedure) completes the repair of the hypoplastic left heart. Although there are several variations, the functional effect is to redirect venous blood from the lower body (through the inferior vena cava) away from the right atrium to the pulmonary artery. Now, there should not be any mixing of oxygenated and deoxygenated blood in the right ventricle. The right ventricle performs the traditional job of the left, supplying the body with oxygenated blood, while the passive systemic venous pressure performs the traditional job of the right, passing deoxygenated blood to the lungs.

The Norwood Procedure is generally performed within a week of birth, the second stage at 3–6 months of age, and the Fontan at 18 months to four years of age. There are two types of Fontan: the Lateral Tunnel Fontan, and the Extracardiac Fontan. When the Fontan Procedure was first being done for children with HLHS, the only Fontan was the Lateral Tunnel Fontan. This requires actual cutting in the heart itself to create a "tunnel" by which the blood can travel passively to the lungs. Within the last decade, doctors have created an Extracardiac Fontan. This operation creates a tunnel outside the heart itself which reduces the chances of Fontan patients developing scar tissue on the heart which might later cause arrhythmias.

Prognosis
While infants successfully treated for HLHS have a good chance of survival, they may experience chronic health problems for the rest of their lives. The 3-stage surgeries were developed in the early 1980s with no survivors prior to that time. Therefore, the earliest survivors are in their mid 20s and the long term prognosis is unknown. However, the advances in surgical and medical techniques have helped increase the survival rate dramatically since the surgeries were first developed.

As is true for patients with other types of heart defects involving malformed valves, HLHS patients run a high risk of endocarditis, and must be monitored by a cardiologist for the rest of their lives to check on their heart function.

The three stage Norwood procedure only increases the life of the heart as HLHS cannot be cured. The child may need a heart transplant at some point in the child's lifetime.

There is an extensive network of parents and children who have experienced this problem, and a number of targeted small press publications and websites.

Patients receiving the Fontan Procedure have an increased incidence of "Plastic Bronchitis."