[Time course of the myocardial infarction in the rabbit]

The histopathologic evolution of myocardial infarct and of areas distant from infarct in rabbit hearts was studied. The left coronary artery of 55 rabbits was ligated, and rabbits were sacrificed at 2, 4, 6, 8, 12, 14, 16, 18, 26, 35 and 56 days post-ligature (n = 5 per group). Two rabbits were used as control and two were sham operated. The hearts were excised, cut in slices and stained with hematoxilin-eosin, Masson's trichrome and picrosirius red. Histological evaluation was semi-quantitative (scale: 0 to +++). At day 2, presence of neutrophils was +++, disappearing completely at day 6. Fibroblast proliferation increased from day 4 to day 14 post-occlusion. Coagulation necrosis in medial myocardium during the first week was +++. Subendocardic myocytolysis was evident from day 2 up to day 56 post-infarction. During the second week, proliferation of lymphocytes and macrophages (+++), granulation tissue formation (+++), and incipient traces of fibrosis that peaked at day 35 were observed. Cicatrization was complete at day 56 (+++). In areas far from infarction (right ventricle and septum), proliferation of fibroblasts was observed at day 2, and perivascular, interstitial and endocardic fibrosis at day 16. In conclusion, myocardial infarction in rabbits, unlike myocardial infarction in human beings, is characterized by early presence of fibroblasts and subendocardic fibrosis, and quick increase and precocious disappearance of neutrophils. An interesting finding was the early proliferation of fibroblasts in normal areas far from infarct.