Impact of Hybrid Stage 1 Palliation for Hypoplastic Left Heart Syndrome: Histopathological Findings

The purpose of the study is to analyze the impact of hybrid stage 1 palliation on right ventricular myocardial pathology in hypoplastic left heart syndrome. Sufficient amount of right ventricular biopsies could be obtained from 16 of 32 patients who underwent Norwood operation between 2007 and 2013. Histopathological findings of right ventricle in patients who underwent primary Norwood operation (primary group, n = 5), patients with aortic atresia (HS1P AA group, n = 6) or aortic stenosis (HS1P AS group, n = 5) who underwent staged Norwood palliation following hybrid stage 1 palliation were compared. To eliminate the influence of right ventricular pressure afterload, right ventricular biopsies were obtained from patients with truncus arteriosus communis (TAC group, n = 6) at total correction. The percentage of myocardial fibrosis was significantly higher in both HS1P groups than in TAC group; moreover, it was significantly higher in HS1P AA group than in primary group. Capillary vascular density was significantly lower in all hypoplastic left heart syndrome groups than in TAC group. At the sub-endocardial layer, collagen type I/III ratios were higher in HS1P AA group than in other hypoplastic left heart syndrome groups. The proportions of N-cadherin immunolocalized to myocyte termini were lower in all hypoplastic left heart syndrome groups than in TAC group. Right ventricle in hypoplastic left heart syndrome showed more significant ischemic change and myocardial immaturity than that in truncus arteriosus communis. Hybrid stage 1 palliation for aortic atresia would be a risk factor for further right ventricular myocardial ischemia.