Early experimental myocardial infarction. Evaluation of histologic criteria and comparison with biochemical and electrocardiographic measurements.

Light microscopical criteria of early experimental myocardial infarction were compared with biochemical changes in glycogen content and the tissue K+/Na+ ratio in 19 mongrel dogs. Five sham-operated dogs served as controls, and seven of the 14 dogs with experimentally induced infarcts received infusions of glucose, insulin, and potassium (GIK). Infarcts were diagnosed by a scoring system based on edema formation, congestion, waviness of myofibers, myofibrillar degeneration, polymorphonucleosis, glycogen depletion, and fuchsinorrhagia. Significant histologic scores were associated with tissue K+/Na+ ratios of less than 1.2, with 30% depletion of biochemical glycogen, and with epicardial ST-segment elevation. Progression of the infarction zone to involve the surrounding border zone was prevented by GIK infusions. Routine light microscopy used in conjunction with tissue K+/Na+ ratios enabled early infarction to be diagnosed with a high degree of accuracy.