Palliation for Hypoplastic Left Heart Syndrome

Abstract

Hypoplastic left heart syndrome is a term used to describe varying degrees of underdevelopment of the left heart structures—most particularly, the left ventricle. Aortic valve atresia or stenosis, atresia or interruption of the aortic arch, and severe stenosis or atresia of the mitral valve in combination with severe hypoplasia of the left ventricle all compose a constellation of defects initially categorized as “hypoplasia of the aortic tract complexes” by Lev in 1952 [1] and later called “hypoplastic left heart syndrome” by Noonan and Nadas [2]. In its most complex and common form, the central anatomic feature is atresia of the aortic valve. As a result of the atresia, the ascending aorta generally measures between 1.5–3 mm in diameter as it carries only retrograde flow to the coronary circulation. In over 90% of patients with aortic atresia, there is coexisting atresia or severe hypoplasia of the mitral valve and a diminutive or absent left ventricle [3]. Therefore, perinatal survival is dependent on maintenance of the systemic circulation through the ductus arteriosus and on adequate pulmonary venous return to the right ventricle—most commonly through a patent foramen ovale. Neonatal death usually results from inadequate coronary and systemic perfusion secondary either to physiologic closure of the ductus arteriosus or to a high pulmonary to systemic flow ratio as the pulmonary vascular resistance physiologically decreases in the early neonatal period.