Early pathologic detection of acute myocardial infarction.

The use of tetrazolium stains for identifying myocardial infarction during the early stages of ischemic injury has become increasingly popular in both experimental and clinical studies. However, the accuracy of these stains in delineating infarctions prior to the onset of well-defined histologic necrosis is unknown. Therefore, eight open-chested, anesthesized dogs were subjected to high left anterior descending coronary artery occlusions for six hours. The hearts were then excised and "breadloafed' into 5mm-thick transverse slices that were incubated in triphenyltetrazolium chloride (TTC) for ten minutes. Three to five tissue samples were obtained from each of three areas of two transverse ventricular slices: from TTC-unstained areas (infarction) and TTC-stained areas, both close to the infarct and remote from the infarct, for electron microscopy. All eight dogs had well-defined areas of unstained tissue that appeared pale gray next to the brick-red TTC-stained tissue. Ultrastructure of the TTC-stained tissue both close to and remote from the infarct showed only modest loss of glycogen and relaxation of myofibers. Ultrastructure of the TTC-unstained tissue in all eight dogs showed numerous mitochondrial amorphous dense bodies, intracellular edema, nuclear chromatin clumping and margination, sarcolemmal disruption, and interstitial edema. Therefore, TTC is a reliable stain for localizing myocardial cells that ultrastructurally appear irreversibly injured by ischemia.