Subcellular structure of the atrial myocardium of children in cases of atrial septal defect

In order to study the initial development of myocardial ultrastructural changes owing to right atrium volume overload, myocytes have been studied in specimens taken from the right atrial wall and auricle of four children aged 1 to 6 years with ostium secundum atrial septal defect undergoing cardiac surgery. The younger patients (1 to 4-year-old children) we observed did not show diffuse and significant myocardial ultrastructural damages. The most significant myocardial changes were observed in the 2 older patients (six years old) as we found subcellular signs of myocardial hypertrophy such as an increased number of mitochondria, increased glycogen inclusions, areas of new sarcomerogenesis and nuclei lobulated and variably shaped. Focal degenerative changes, such as rupture of mitochondrial cristae and intercellular fibrosis were also noted. These changes may be considered as the initial features of myocardial hypertrophy because they were not as severe and diffuse as those usually seen in a marked functional failur

Scanning electron microscopy study of endocardial regeneration in bovine pericardial patch-grafts implanted in the canine heart

The pattern of endocardial regeneration was studied in bovine parietal pericardial patch-grafts implanted in canine hearts. The grafts consisted of fibrous tissue without a cellular lining. They were implanted with either the thoracic or the cardiac surface facing the lumen of the canine ventricle to evaluate the effect on endocardial regeneration. The grafts were retrieved 7, 21, 45 and 60 days after implantation and were examined using scanning electron microscopy. At 7 days, both the thoracic and the cardiac aspect exhibited connective tissue fibers, focally covered by fibrin, platelets and blood cells. The cardiac aspect showed finer and more highly intermingled filamentous fibers than the thoracic aspect. At 21-60 days, the thoracic surface displayed a continuous network of connective fibers with a few blood cells and isolated groups of spindle-shaped cells resembling fibroblasts. At 21-60 days, the cardiac surface showed a diffuse growth of cells on the connective fiber substratum. Regenerating cells first lined the periphery of the grafts (21 days) and then proliferated towards the centrum (45-60 days). These cells varied in size and shape, were mostly closely packed, exhibited numerous microvilli or longer cytoplasmic projections, and resembled regenerating endothelial cells and mature endocardial cells. The topographic arrangement of the new lining cells suggests that they were the result of a per continuitatem regeneration (endothelial re-endothelialization) and that they they originated from the healthy endocardium of the host surrounding the implantation site. The arrangement of the connective fibers, finer on the cardiac than on the thoracic aspect, probably facilitated the development of a cellular lining.(ABSTRACT TRUNCATED AT 250 WORDS