Response of Myocardial Fine Structure to Cardiac Arrest and Hypothermia

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Abstract
The appearance of the myocardium from isolated hearts was observed in the electron microscope before, during, and after hypoxic cardiac arrest at 17[degree] and 30[degree] C, respectively, and compared to control preparations. Changes in fine structure consisted of condensation of the mitochondrial envelope along with clearing and subsequent general and focal condensation of the matrix accompanied by less pronounced changes in the cristae; nuclear condensation; and intracellular edema. The edema consistently and other changes occasionally were progressive but minimal with perfusion at 37[degree] C. Hypoxia greatly accentuated the damage, which was inhibited but not entirely circumvented by hypothermia (17[degree] C). Perfusion of the arrested heart at 17[degree] C resulted in no changes consistently different from those found when cororaries were occulded at the same temperature. The changes were reversible with recovery if not too far advanced, although evidence for persistence of damage was found 30 minutes following resumption of contraction when damage was more extensive. These morphologic findings imply metabolic derangement both of oxidative and inotropic mechanisms. Obser- vations on possible alterations in membranes, ion transport, and conduction are too rudimentary to warrant any speculation about their significance. Previous studies on losses in the supply of phosphate-bond energy under similar circumstances are consistent with these changes in morphology of myocardial organelles.

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