Hypoplastic left heart syndrome (HLHS) is a severe form of congenital heart disease which is always fatal without treatment. Though it has a wide spectrum of structural variations, it usually presents with symptoms in the first to third days of life. At birth and shortly thereafter the baby appears to be normal and well.
Once the physiological right-to-left shunts close down, during the first few days of life, the effects of not having a functioning left ventricle and aorta manifest dramatically as a very sick baby. The clinical signs include breathing problems with tachypnea, a grayish-blue tinge to the skin, especially of the lips and around the mouth, and vascular shock.
The outlook for HLHS was uniformly dismal before the 1980s. Most infants succumbed to the lethal effects of a minimal systemic circulation, mostly within the first two weeks of life. The mean age at which infants died was 4.5 days. In a few rare cases, the infant develops pulmonary hypertension and thus achieves a kind of balance between the systemic and pulmonary circulation.
Initial treatment is aimed at keeping the ductus arteriosus and the interatrial septal opening (the foramen ovale) open and enlarging the latter, if required. In addition, the cardiac failure and the metabolic effects of hypoxemia must be carefully countered by diuretics, inotropics to increase ventricular contractility, bicarbonate infusion and ventilator support where required.
With the development of palliation staged surgeries (the Norwood surgery), the prognosis has improved dramatically for these infants. The surgery consists of:
- An immediate procedure consists of opening the atretic aorta longitudinally and joining it to the pulmonary trunk to make a new aorta. The pulmonary arteries are separated from the trunk and joined by a new shunt to the aorta or to the right ventricle directly, to provide blood supply to the lungs.
- At about 4-6 months, the bidirectional Glenn procedure is performed. Here a cavopulmonary shunt is created by fusing the superior vena cava with the right pulmonary artery, separating it from the right atrium. This removes the upper part of the venous inflow from the body to the pulmonary circulation instead of allowing it to mix with the oxygenated blood from the left atrium.
At 18-36 months, the Fontan procedure is performed. This is a total cavopulmonary shunt created by joining the inferior vena cava to the right pulmonary trunk. From this point the venous return is totally separated from the right ventricle, and cyanosis is no longer present.
The Norwood surgery is constantly being refined and diagnosis is becoming more precise. Survival rates following this staged procedure are above 70% at 5 years at present. Mortality may be as high as 90% in centers which handle few cases, however, and specialized multi-disciplinary care centers are, therefore, the preferred location for treatment of these children.
Unfavorable risk factors
The following factors are known to reduce the chances of a favorable outcome following palliation surgery:
- A higher partial pressure of oxygen in arterial blood above 60 mm Hg
- A narrow interatrial opening of less than 3 mm diameter
- Mitral valve atresia
- Aortic atresia
- Other major anomalies outside the heart
It is obvious that when the interatrial opening is too narrow, it causes reduced mingling of oxygenated and desaturated blood, and therefore severely compromises the systemic availability of oxygen. On the other hand, a wide opening results in pulmonary overcirculation and congestive failure, worsening cardiac status and systemic circulation. The presence of aortic atresia could lead to less blood reaching the coronary arteries leading to myocardial insufficiency. A high arterial oxygen partial pressure is a sign that too much blood is reaching the pulmonary circulation, which results in volume overload and poor perfusion of the systemic circulation.
In some cases the infant who has undergone early stage 1 surgery is not fit for further reconstruction, or has significant mitral and aortic valve lesions which make the procedure unsuitable. For this reason, cardiac transplantation may be a best practice in such patients. The limitations include:
- Lack of enough donors
- Matching donor and recipient hearts for size
- Significant mortality during the waiting period due to deterioration of multiple organs and cardiac failure, as well as the increasing risk of post-operative pulmonary hypertension as the waiting period increases
65% of all babies who are put on a transplant list are alive at 5 years. Of those who receive a transplant, more than three out of four survived at 5 years. Rejection is the main cause of mortality in the post-transplant group.
Other complications include:
- Post-transplantation accelerated coronary vessel disease
- Sequelae of long-term immunosuppressive therapy such as renal disease (11%), or an increased risk of marrow malignancies (10%). This may be reduced by avoiding the use of corticosteroids over the long term in these children and using as low doses of immunosuppressive medication as is required to prevent rejection
Children who have undergone the reconstructive procedure have a higher rate of delayed development, and about 6% had either central nervous system conditions or underdeveloped neurological staging. About 8 of every 100 children have mental retardation.
The most important factor in predicting the ultimate outcome is the initial status of the infant.
Caring for the infant till inevitable death without resort to palliation or transplantation surgery is a third option often recommended to and followed by parents. This may be because of the highly uncertain outcome, especially in the early days of surgical treatment. With increasingly successful outcomes of surgery, this may become less common in the coming years.
Reviewed by Yolanda Smith, BPharm