Different effects of increased volume and increased pressure on endocardial structure in hearts with atrial septal defect

Abstract

The nature and distribution of endocardial thickening associated with atrial septal defect of the fossa ovalis (secundum) type (ASD) were studied in seven hearts for which antemortem catheterization data were available. The cases included four with large shunt flow and relatively low pulmonary artery pressure ( flow group) and three with relatively small shunt flow and high pulmonary artery pressure ( pressure group). Two distinct and different patterns of endocardial change were evident in the right-sided chambers, one in hearts of the flow group, the other in those of the pressure group. Gross endocardial thickening, diffuse in the atrium and focal in the ventricle, was much more marked in the flow group. In hearts with high shunt flow and relatively low chamber pressure, endocardial fibroelastosis was marked and smooth muscle cells were few and atrophic; in hearts with small shunt flow but markedly elevated pressure, endocardial smooth muscle hyperplasia was a predominant and constant feature. Markedly increased diastolic mural tension and relatively low rates of change of mural tension corresponded to the fibroelastosis in the flow group; high rates of change of mural tension and increased levels of systolic mural tension corresponded to the smooth muscle hyperplasia in the pressure group. Focal superficial (subendothelial) fibroelastosis, more marked in the flow group, probably corresponded to local increases in velocity of blood flow or turbulence.