What Is the Hypoplastic Left Heart Syndrome?

As yet, there is no agreed definition for the so-called “hypoplastic left heart syndrome”. Even its origin remains contentious. Noonan and Nadas, who as far as we can establish first grouped together patients as belonging to a “syndrome” in 1958, suggested that Lev had named the entity. Lev, however, when writing in 1952, had described “hypoplasia of the aortic outflow tract complex”. In his initial description, as with Noonan and Nadas, he included cases with ventricular septal defects. In a subsequent account, he suggested that only those with an intact ventricular septum be included within the syndrome. There is much to commend this later approach. When assessed on the basis of the integrity of the ventricular septum, the hearts to be included can be interpreted as showing an acquired disease of fetal life. Recognition of this fact is important to those seeking to establish the genetic background of left ventricular hypoplasia. Flow is also of importance, with septal integrity then influencing its effect on the structure of the hypoplastic ventricle. In our review, we summarise the evidence supporting the notion that an intact ventricular septum should now be part of the definition of the hypoplastic left heart syndrome.