The effect of ischaemic injury on the fine structure of canine atrial myocardium

An experimental model for producing a uniformly and maximally ischaemic segment of atrial myocardium has been devised and used in 23 dogs to investigate the effects of severe ischaemia of up to 6 h duration on the fine structure of atrial myocardial cells. Throughout the first 30 min of ischaemia the cells maintained a fine structure comparable with that of control tissue. In the subsequent 2 h they developed morphological alteration at differing rates, despite their uniform deprivation of blood supply. Even at 90 min the ischaemic tissue showed discontinuous change, with many areas differing little from control, and it was only after 3 h that all cells showed well developed and similar alterations. These included glycogen depletion, marked clumping and margination of nuclear chromatin, and the mitochondrial degeneration typically seen in ischaemically injured ventricle. The changes were very severe after 4 and 6 h of ischaemia, when disruption of cellular membrane systems was also evident. At these times the tissue closely resembled ventricular myocardium made ischaemic for similar intervals, except for the persistence of well-preserved ‘specific atrial granules’. Atrial muscle cells therefore develop the fine structural changes associated with ischaemia more slowly than ventricular muscle cells and have a more variable response to the initiation of ischaemic injury.