Hypoplastic Left Heart Syndrome
Hypoplastic left heart syndrome describes a defect where the left ventricle is too small to support systemic circulation. In addition, the aortic itself has a decreased diameter and the aortic and mitral valves are often underdeveloped or atretic.
- In the absence of a fully functional left ventricle and/or aortic valve, preservation of systemic circulation and survival is dependent on a patent ductus arteriosus. In this case, the right ventricle takes over for the left to supply the pulmonary and systemic circuits as well as the coronary arteries and brachiocephalic veins (in a retrograde direction).
- The amount of blood flow to the pulmonary and systemic circulation is a function of their vascular resistance which, in turn, is influenced by the size of the interartial orifice. Arterial defects that restrict movement cause pressure in the left atrium and pulmonary circuit to increase and thus, restrict pulmonary blood flow. Arterial openings that do not restrict movement do have this effect.
- Increased pulmonary blood flow brings a larger volume of oxygenated blood back to the left atrium which then mixes with the systemic venous return in the right via the foramen ovale.
- Hypoplastic left heart syndrome is the most lethal congenital heart defect that still supports normal uterine growth. During the prenatal period, all blood, aside from a small amount volume of pulmonary venous return, passes through the right heart. Return from the superior and inferior vena cava, pulmonary venous system, and oxygenated blood from the placenta combine in the right atrium. The right ventricle receives this blood and, taking over for the left ventricle, distributes it to the body and coronary arteries making use of the connection between the ductus arteriosus and aorta.
- Clinical manifestation
- The newborn with hypoplastic left heart syndrome may appear normal after birth while the ductus arteriosus is patent and pulmonary vascular resistance is relatively high.
- When the ductus closes, however, systemic circulation and perfusion of the coronary arteries becomes restricted and the infant may begin to appear cyanotic or pale with decreased peripheral pulses. The decrease in pulmonary resistance that occurs with expansion of the lungs allows pulmonary blood flow to increase and can cause tachypnea. Eventually, these infants develop cardiogenic shock, acidosis, and renal failure and typically die quickly without intervention.
- Management of hypoplastic left heart syndrome begins with administration of prostaglandin E1 to maintain a patent ductus arteriosus and thus, pulmonary and systemic blood flow. The goal of pre-surgical interventions is to maintain systemic circulation, increase pulmonary vascular resistance, and reduce the right ventricular volume load.
- Three goals have been established for initial, successful, palliation by surgical intervention.
- Establishment of a permanent unobstructed communication between the right ventricle and aorta while preserving right ventricular function
- Limit pulmonary blood flow while preserving pulmonary artery architecture
- Relieve pulmonary venous obstruction
- Initial palliative surgery carries the risk of numerous potential complications that can be related to the anatomy of the defect itself or surgical manipulation. These must be monitored and may require additional surgeries.
- Cardiac transplantation is a treatment option that may be available depending on donor availability and probability of rejection.