Abnormal hemodynamic loading during heart development leads to myocardial hypoxia, stimulating collagen production in the subendocardium. Therefore, EFE in this chick embryonic model of HLHS appears to be a secondary effect of abnormal hemodynamics. Developmental Dynamics 247:509-520, 2018. © 2017 Wiley Periodicals, Inc.

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The heart grows in response to circulatory demands and this growth is governed by genetic programs but may be modified by hemodynamic alterations. Hypoxic regions are present in the developing myocardium. Conotruncal banding (CTB) is a well‐established model of embryonic pressure overload. The aim of this study was to elucidate how the extent of hypoxic regions in myocardium is changed under pressure overload.Conotruncal banding was performed in the chick model at embryonic day (ED) 4.The marker for hypoxia Hypoxyprobe 1, was injected into the vitelline vein at ED 6 and ED 8. The embryos were reincubated for 1h and then fixed in 4% PFA. The reaction product was detected on paraffin sections with Hypoxyprobe‐1 antibody.Examination of control hearts showed isolated regions of hypoxia in the left ventricular wall and interventricular septum. In pressure‐overloaded hearts we found ventricular dilatation, thickening of the compact myocardium and trabeculae. The hypoxic regions were significantly more extensive in the compact layer of both ventricles, septum, and the outflow tract.We conclude that the thickening of the embryonic myocardium induced by pressure overload results in its increased hypoxia. This finding can explain previous observations of matching capillary growth in this model, as well as accelerated maturation of the conduction system.Supported by project UNCE 204013 and PRVOUK P35/LF1/5.

Endocardial fibroelastosis (EFE) is a diffuse thickening of the ventricular endocardium, causing myocardial dysfunction and presenting as unexplained heart failure in infants and children. It is believed to be caused by persistent and increased wall tension in the ventricles. . Its frequent association with hypoplastic left heart syndrome (HLHS) lead us to hypothesize abnormal hemodynamic loading is an important factor in its pathogenesis. We have tested this theory in a chick model of HLHS induced by left atrial ligation (LAL). At ED8 and 12 modifications of myocardial architecture and fibrosis were studied by histology and immunoconfocal microscopy, and the amount of collagen was quantified by image analysis.Histology with H&E / Alcian Blue staining did not reveal any significant fibrosis in the LAL hearts with the exception of cardiac skeleton and valves. Immunohistochemistry with collagen I antibody clearly showed a thickening of the layer of subendocardial fibrous tissue. Quantification of staining area normalized by endocardial circumference showed a significant increase at ED12, but not ED8 in the LAL group. We conclude that abnormal hemodynamic loading stimulates fibrous production in the subendocardium of the hypoplastic left ventricle. Therefore, EFE in HLHS clearly appears to be a secondary effect of abnormal hemodynamics.Grant Funding Source: Supported by Ministry of Education, Youth and Sports PRVOUK‐P35/LF1/5, Academy of Sciences RVO: 67985823, and Grant Agency of the Czech Republic P302/11/1308