Which Phenotypes Should We Include in the Hypoplastic Left Heart Syndrome?

The recent special issue of the World Journal for Pediatric and Congenital Heart Surgery devoted to hypoplastic left heart syndrome, and its related anomalies, contained significant information of great clinical relevance. Very little attention, however, was devoted to the integrity of ventricular septum as providing a criterion to distinguish between the phenotypes to be included within the syndrome, as opposed to the related anomalies. In this commentary, we summarize the evidence in support of the notion that the phenotypes to be included within the syndrome can be interpreted on the basis of an acquired disease of fetal life. We suggest that it is the integrity of the ventricular septum that provided the major criterion for the distinction between the lesions making up the syndrome and the related anomalies. The subsets of lesions to be included within the syndrome can then be recognized in terms of the time, subsequent to the closure of the embryonic interventricular communication, at which the left ventricle ceased its growth relative to the remainder of the cardiac components. On this basis, it is possible to recognize the combinations of aortic and mitral atresia, mitral stenosis with aortic atresia, combined mitral and aortic stenosis, and hypoplasia of the left ventricle with commensurate hypoplasia of the aortic and mitral valves; the latter combination now recognized as the hypoplastic left heart complex.