Ultrasound Obstet Gynecol 2000; 15: 271±278. Editorial Hypoplastic left heart syndrome J.M. SIMPSON INTRODUCTION Hypoplastic left heart syndrome HLHS) is the term used to describe a group of congenital heart lesions character- ized by severe underdevelopment of left heart structures. Up to the early 1980s this condition was untreatable and was uniformly fatal in early infancy. The initial reports of Norwood and colleagues provided the impetus for active intervention for this condition 1 . Advances in surgical techniques mean that intervention is now possible for this condition, with better results in recent years 2 . Hypoplastic left heart syndrome may be diagnosed during fetal life, thus a knowledge of this condition is highly relevant to those involved in prenatal diagnosis. This Editorial aims to describe the antenatal sonographic features of HLHS and to address issues regarding prenatal and postnatal management. DEFINITION Hypoplastic left heart syndrome is not a single entity but is rather a spectrum of congenital heart malformations characterized by severe hypoplasia of the left ventricle and left ventricular outflow tract. In `classical' HLHS the aortic valve is atretic, with either atresia or severe hypoplasia of the mitral valve. In some instances, the term has been applied to other lesions including critical aortic stenosis with severe hypoplasia of the left ventricle, unbalanced atrioventricular septal defects with hypoplasia of the left ventricle and aorta, and severe coarctation of the aorta. In this Editorial, unless stated otherwise, the term HLHS will be applied to cases of `classical' HLHS. Where relevant, reference will be made to the other variants of HLHS. INCIDENCE The birth incidence of HLHS has been estimated to be 0.1± 0.25/1000 livebirths 3,4 . These birth estimates will certainly underestimate the incidence during fetal life, because they do not include cases of spontaneous intrauterine death which occur with increased frequency in fetuses with congenital heart disease. One large study described a 5% rate of spontaneous intrauterine death in a series of 161 cases of HLHS diagnosed prenatally 5 . SONOGRAPHIC FEATURES The sonographic features of some of the more common forms of HLHS are described below. `Classical' hypoplastic left heart syndrome Mitral and aortic atresia There is no communication between the left atrium and left ventricle. This may be due to a complete absence of the left atrioventricular connection or an imperforate mitral valve. Typically, the left ventricle is slit-like and there may be no demonstrable left ventricular cavity at all Figure 1). Aortic atresia mitral valve patent) The left ventricle is echogenic, hypoplastic and globular, contrasting with the slit-like ventricle observed in mitral atresia Figure 2). Other variants of HLHS Critical aortic stenosis with hypoplastic left ventricle In this condition, the left ventricle typically appears EDITORIAL 271
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