Hypoplastic Left Heart Syndrome (HLHS)

At a glance

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

Nature

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

Incidence

0.1 to 0.27:1,000 live births.

Genetic inheritance

Multifactorial; a subgroup showing autosomal recessive inheritance may exist.

Pathophysiology

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, pulmonary congestion, and marked hypoxia because of the 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.

Diagnosis

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

Clinical aspects

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 (eg, 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.

Precautions before anesthesia

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. ...