Defining the Spectrum of Hypoplastic Left Heart Syndrome (HLHS)

Abstract

The 2021 International Paediatric and Congenital Cardiac Code and the Eleventh Revision of the International Classification of Diseases provide the following definition for hypoplastic left heart syndrome (HLHS): “Hypoplastic left heart syndrome (HLHS) is defined as a spectrum of congenital cardiovascular malformations with normally aligned great arteries without a common atrioventricular junction, characterized by underdevelopment of the left heart with significant hypoplasia of the left ventricle including atresia, stenosis, or hypoplasia of the aortic or mitral valve, or both valves, and hypoplasia of the ascending aorta and aortic arch.” Although HLHS with intact ventricular septum (HLHS + IVS) and HLHS with ventricular septal defect (HLHS + VSD) are different cardiac phenotypes, both of these lesions are part of the spectrum of HLHS.

What Is the Hypoplastic Left Heart Syndrome?

“…Our colleagues then suggest that division of the syndrome on the basis of ventricular septation is already “described and reported in the majority of the medical literature.” 1 It is surprising, therefore, to find that the manuscript authored by several of our colleagues, describing their experience in Gainesville, provided no details on the presence or absence of ventricular septal defects. 5 Nor was the significance of the ventricular septum included in the review providing an overview of classification and morphology of the syndrome.…”

“…The alternative view is strong on opinion but short in terms of evidence. We read that the authors “strongly believe that the subtype of HLHS with ventricular septal defect in the setting of mitral atresia and aortic stenosis (or mitral stenosis and aortic stenosis) fits within the extant IPCCC and ICD-11 definition of HLHS.” 1 This is hardly surprising when extant definitions offer no details regarding the integrity of the ventricular septum. We had anticipated that, in their counterpoint, the authors would provide the evidence as to why cases with deficient ventricular septation should be included.…”

“…7 The latter lesion, however, is excluded by our colleagues from inclusion in the syndrome. 1 Since they place such emphasis on spectrums, this does not seem logical.…”

“…The emphasis placed on mitral atresia, nonetheless, is pertinent when questions are raised as to whether the syndrome is, indeed, an acquired disease of fetal life. Specifically “this argument cannot be true for all variants of HLHS, because, in some cases, mitral atresia occurs early in development, with a nearly absent left ventricular chamber.” 1 The type of atresia that occurs early in life is due to absence of the atrioventricular connection. When found in the setting of the intact ventricular septum, the atresia was shown to be due to obliteration of the initially patent left atrioventricular connection.…”

“…And as we have emphasized, the evidence now exists to show that reduction of flow through the mitral valve can induce the spectrum in the setting of an intact ventricular septum. 2,3 A reason for including mitral atresia with patent aortic root, however, according to our colleagues, is because the lesion “is treated with the same interventions as other subtypes of HLHS.” 1 We would direct them to the statement made by Tchervenkov and colleagues that “one cannot define anatomy, morphology, and nomenclature of a cardiac phenotype by the type of treatment used, as treatment may evolve over time.” 4 There is, of course, nothing wrong with changing one's mind. When confronted with the evidence substantiating the need for change, we have changed our own opinions on several occasions.…”