BackgroundHypoplastic left heart syndrome (HLHS) covers a spectrum of rare congenital anomalies characterised by a non-apex forming left ventricle and stenosis/atresia of the mitral and aortic valves. Despite many studies, the causes of HLHS remain unclear and there are conflicting views regarding the role of flow, valvar or myocardial abnormalities in its pathogenesis, all of which were proposed prior to the description of the second heart field. Our aim was to re-evaluate the patterns of malformation in HLHS in relation to recognised cardiac progenitor populations, with a view to providing aetiologically useful sub-groupings for genomic studies.ResultsWe examined 78 hearts previously classified as HLHS, with subtypes based on valve patency, and re-categorised them based on their objective ventricular phenotype. Three distinct subgroups could be identified: slit-like left ventricle (24%); miniaturised left ventricle (6%); and thickened left ventricle with endocardial fibroelastosis (EFE; 70%). Slit-like ventricles were always found in combination with aortic atresia and mitral atresia. Miniaturised left ventricles all had normally formed, though smaller aortic and mitral valves. The remaining group were found to have a range of aortic valve malformations associated with thickened left ventricular walls despite being described as either atresia or stenosis. The degree of myocardial thickening was not correlated to the degree of valvar stenosis. Lineage tracing in mice to investigate the progenitor populations that form the parts of the heart disrupted by HLHS showed that whereas Nkx2–5-Cre labelled myocardial and endothelial cells within the left and right ventricles, Mef2c-AHF-Cre, which labels second heart field-derived cells only, was largely restricted to the endocardium and myocardium of the right ventricle. However, like Nkx2–5-Cre, Mef2c-AHF-Cre lineage cells made a significant contribution to the aortic and mitral valves. In contrast, Wnt1-Cre made a major contribution only to the aortic valve. This suggests that discrete cardiac progenitors might be responsible for the patterns of defects observed in the distinct ventricular sub-groups.ConclusionsOnly the slit-like ventricle grouping was found to map to the current nomenclature: the combination of mitral atresia with aortic atresia. It appears that slit-like and miniature ventricles also form discrete sub-groups. Thus, reclassification of HLHS into subgroups based on ventricular phenotype, might be useful in genetic and developmental studies in investigating the aetiology of this severe malformation syndrome.
Significant post-operative bleeding may occur following cardio-pulmonary bypass, sometimes necessitating early re-exploration. Two questions were asked by this study. Firstly, in children undergoing cardio-pulmonary bypass, can pre-operative, operative and immediately post-operative variables be used to predict post-operative blood loss? Secondly, in the same patient group, can the same variables be used to predict the surgical intervention of re-exploration for excessive bleeding within 12 h of surgery? In a prospective study of patients operated on in a 9-month period, bleeding fell rapidly in the first 3 h after surgery and early re-exploration for bleeding was necessary in 8 of the 206 patients. The only significant predictor of post-operative blood loss was minimum oesophageal temperature, low values being associated with greater blood loss (correlation r = -0.19 (P < 0.05)). With regard to re-exploration for bleeding, a long bypass time (P < 0.05) and abnormal pre-operative coagulation indices (P < 0.01) were significant and independent predictors. The data were also used to create a practical nomogram relating re-exploration for bleeding to hourly post-operative blood loss.
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