Quantification of hyperaemia bordering ischaemic myocardium in experimental myocardial infarction

To quantify and determine the time course of hyperaemia adjacent to acutely ischaemic myocardium, 19 dogs underwent open-chest coronary-artery occlusion and 4 had sham-occlusion. At 15 min (19 animals) and 45 min (9 animals) post-occlusion regional myocardial blood flow (RMBF) was measured by the radionuclide-labelled microsphere technique. The dogs were sacrificed after 24 hours, the hearts were excised, sectioned into four segments from apex to base, and stained with triphenyl tetrazolium chloride (TTC). Transmural samples were taken from necrotic areas, normal areas, and the zone bordering the infarct. Each sample was divided into an endocardial and epicardial layer. At 15 min post-occlusion RMBF in the border zone was 16% greater than in the normal myocardium (116+/-16 vs 100+/-12 cm3xmin(-1)x100g(-1);P<0.05). In addition, the ratio of endocardial to epicardial flow was lower in the border zone (0.87+/-0.05) compared with normal myocardium (1.01+/-0.02; P<0.05) indicating that the hyperaemia observed was predominantly epicardial. From 15 to 45 min hyperaemic endocardial flow tended to decline: 126 to 108 cm3xmin(-1)x100g(-1) (P<0.05). In four sham-occlusion dogs there were no differences (P>0.05) in RMBF between sites equivalent to those sampled in occluded animals. These studies document a hyperaemic border zone persisting at least 45 min post-occlusion. Hyperaemia appears to be more prominent and of longer duration in the epicardium than endocardium.