76: Hypoplastic Left Heart Syndrome

Epidemiology

• Hypoplastic left heart syndrome (HLHS) accounts for 5 percent of all congenital heart anomalies and is responsible for 25 percent of cardiac deaths in the first week of life. Its incidence is 1.8 in 10,000 live births, with 25 percent of cases showing associated noncardiac malformations and 5 percent associated with chromosomal abnormalities.

Morphology

• HLHS includes a wide spectrum of anatomic abnormalities with the common feature of hypoplasia of the left ventricle (LV) and the ascending aorta. At one end of the spectrum there may be some mild LV hypoplasia, mild aortic stenosis, and aortic coarctation. At the other end there is complete absence of the LV, aortic atresia, and aortic arch interruption.

Pathophysiology

• Systemic venous return is channeled via an interatrial communication to the right ventricle (RV) and, through the pulmonary artery (PA) and patent ductus arteriosus (PDA), to the systemic and pulmonary circulations. Balanced physiology ensues, with Q_P:Q_S varying according to systemic and pulmonary vascular resistance (PVR) as well as with the unrestrictive nature of the atrial septal defect (ASD).

Clinical features

• As a result of ductal closure in the postnatal period, HLHS is uniformly fatal if not treated. Evidence of pulmonary overcirculation is evident on clinical examination once PVR diminishes in early post-natal life.

Diagnosis

• Prenatal echocardiography can be used to detect unbalanced ventricles as early as 20 weeks of gestational age. Postnatal echocardiography readily establishes the diagnosis and guides medical and surgical decision-making.

Treatment

• Prostaglandin E₁ (PGE₁) infusion is the cornerstone of early resuscitation, coupled with balloon atrial septostomy in case of a restrictive ASD. A three-stage single-ventricle palliation approach has been adopted by most centers. The first stage involves aortic arch reconstruction and establishment of a reliable source of pulmonary blood flow, and the second and third stages consist of sequential partitioning of the systemic and pulmonary circulations. Transplantation has been used as the initial approach or, more commonly, for those who fail palliative strategy. In high-risk neonates, initial palliation with a hybrid approach (stenting of coarctation and PA banding) should be considered.

Outcomes

• Operative survival of stage I Norwood palliation depends on several variables, including anatomic factors (diameter of ascending aorta, operative weight, restrictive ASD, associated anomalies), and nears 80 percent in several series. Operative mortality between 5 and 10 percent has been observed for second- and third-stage palliation. Long-term complications [ventricular failure, atrioventricular (AV) valve regurgitation, arrhythmias, and protein-losing enteropathy, among others] dictate late prognosis and the need for reintervention or transplantation.