Hypoplastic Left Heart Syndrome

Congenital heart disease characterized by underdevelopment of the left side of the heart. Lethal in 25% of infants during the first week of life.

Congenital disorder. Recurrence rate is 2% in siblings of an affected infant. Condition is fatal without palliative surgery.

0.1-0.27:1000 live births.

Multifactorial; a subgroup showing autosomal recessive inheritance may exist.

Range of abnormalities, including aortic atresia/stenosis, hypoplastic left ventricle, hypoplasia of the aortic arch, and mitral atresia or hypoplasia. The left ventricle is nonfunctional; systemic perfusion is maintained by the right ventricle through a patent ductus. Coronary perfusion occurs by retrograde flow through the aortic arch. Pulmonary venous blood usually mixes with systemic venous blood through an atrial septal defect or patent foramen ovale. Most neonates have a degree of interatrial mixing, allowing sufficient pulmonary blood flow with mild pulmonary venous hypertension. Unrestricted communications cause increased pulmonary flow, pulmonary hypertension, and systemic hypoperfusion. The absence of interatrial mixing results in pulmonary hypertension and congestion and marked hypoxia as a consequence of low pulmonary blood flow. The pulmonary and systemic circulations are supplied in parallel by the right ventricle. Systemic perfusion and oxygenation are dependent on maintaining a fine balance between pulmonary and systemic flow.

Neonatal cyanosis and symptoms and signs of right ventricular failure. Echocardiography is diagnostic.

Neonatal tachypnea, tachycardia, cyanosis, third heart sound, systolic murmur, and hepatomegaly. Chest radiograph may show cardiomegaly and increased pulmonary vasculature. Neonatal cardiovascular palliation is achieved by the Norwood procedure, which results in the right ventricle supplying systemic circulation. The pulmonary circulation is supplied by a systemic-to-pulmonary arterial shunt (e.g., Blalock-Taussig shunt). An atrial septectomy is performed to allow pulmonary venous blood to flow freely into the right atrium. At approximately 6 months, once pulmonary vascular resistance has fallen from the high neonatal level, a hemi-Fontan or bidirectional Glenn shunt is performed. This procedure results in the pulmonary circulation being supplied by the superior vena cava (passive process relies on superior vena cava pressure being greater than pulmonary venous pressure to maintain flow). The Fontan procedure is completed at least 6 months later to allow development of optimal right ventricular function. The completed procedure results in both superior vena cava and inferior vena cava blood being diverted to passively supply the pulmonary circulation. Heart transplantation may be required.

History and examination to elicit signs and symptoms of poor ventricular function. Poor ventricular function should be considered to represent greatly increased anesthetic risk. Define stage of palliation and hence physiologic requirements for anesthesia. Cardiac function/physiology. Review recent echocardiograms and cardiac catheterization data. Assess dependence on inotropes and the need for prostaglandin E1 in the neonatal period to maintain the patent ductus arteriosus. Measure normal SaO2, and consider measurement of blood gases. Assess for abnormal renal function, abnormal liver function, and the presence of a lactic acidosis suggestive of poor systemic perfusion.

In the neonate, systemic perfusion is dependent on the patent ductus arteriosus and maintenance of prostaglandin therapy. The pulmonary and systemic circulations are supplied in parallel, to maintain the ratio of pulmonary-to-systemic flow by maintaining a raised pulmonary vascular resistance [i.e., moderate acidosis, low fraction of inspired oxygen (FiO2), maintain preoperative PaCO2]. These measures will prevent an increase in pulmonary flow and a subsequent decrease in systemic perfusion. After the Norwood procedure, pulmonary and systemic circulations are still in parallel, so careful control of the ratio of pulmonary vascular resistance to systemic vascular resistance is still required. Following hemi-Fontan and completed Fontan procedures, the pulmonary perfusion is critically dependent on a maintained high venous pressure (preload pressure) and low pulmonary venous pressure. Spontaneous respiration or controlled ventilation with low inspiratory pressures will minimize any rise in intrathoracic pressure, which would impair flow to the pulmonary circuit. Aim to maintain a low pulmonary vascular resistance and avoid using positive end-expiratory pressure.

Careful consideration of the effect of anesthetic agent on systemic vascular resistance and pulmonary vascular resistance. Opiate-based anesthesia with low-dose volatile agents well tolerated. Caution with inotropes that may alter the ratio of systemic vascular resistance to pulmonary vascular resistance.