Hypoplastic left heart syndrome
Overview
Hypoplastic left heart syndrome (also known as HLHS), is a rare congenital heart defect in which the left side of the heart is severely underdeveloped
Symptoms
Initially, a newborn with hypoplastic left heart may appear normal. Symptoms usually occur in the first few hours of life, although it may take up to a few days to develop symptoms. These symptoms may include: Lethargy Poor suckling and feeding Shortness of breath Rapid breathing Cold extremities Enlarged liver Poor pulse Pounding heart Bluish (cyanosis) or poor skin color Sudden death In healthy newborns, bluish color occurs in hands and feet as a response to cold (this reaction is called peripheral cyanosis). However, a bluish color observed in the chest or abdomen, lips, and tongue is abnormal (called central cyanosis) because it reflects lack of adequate levels of oxygen in the blood. This is secondary to the heart malformation and circulatory malfunction. Central cyanosis often increases with crying.
Causes
Hypoplastic left heart is a rare type of congenital heart disease. It is more common in males than in females. The problem develops before birth when there is not enough growth of the left ventricle and other structures (aortic and mitral valves that guard the exit and entrance of the ventricle and the aorta, the blood vessel that carries oxygenated blood from the left ventricle to the entire body). In patients with this condition, the left side of the heart is unable to send enough blood to the body. As a result, the right side of the heart must maintain the circulation for both the lungs and the body. This extra workload eventually causes the heart to fail. The only possibility of survival is a connection between the right and the left side of the heart its blood vessels, through which blood may pass. This is called a shunt. Babies are normally born with two of these connections (the foramen ovale and the ductus arteriosus), which normally close on their own a few days after birth. If ductus arteriosus is allowed to close in a baby with hypoplastic left heart syndrome, however, the patient will quickly die because no blood will be pumped to the body. As with most congenital heart defects, there is no known cause. Around 10% of patients with hypoplastic left heart syndrome will have other birth defects.
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 early 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.
Treatment
The two methods for treatment of HLHS are transplantation and a three-stage surgical procedure. Each of these are open heart surgeries (meaning the chest is open and the sternum has to be separated), requiring the child to be on a heart bypass machine for at least five hours. The heart is stopped and the heart bypass machine pumps blood to the body. After successful surgery is performed there can be added complications of restarting the heart and getting the child off the heart bypass machine. 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.
- 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 bloodflow 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 saturations. 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 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.
- 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 arrythmias.