Time course and zonal variations of ischemia-induced myocardial cationic electrolyte derangements

Myocardial cationic electrolytes were determined at regular time intervals up to 24 hours after coronary artery ligation in the dog. Replicate electrolyte ratios were computed for different areas of the heart at each time interval. For purposes of statistical analysis, ratios from two border areas and four areas remote from the infarct were pooled as values for ZONE B and ZONE N, respectively, and compared with those from the infarct proper, ZONE I. Ischemia-induced tissue Mg++/Ca++ changes paralleled those of K+/Na+ with respect to time course and zonal variations. In ZONE I, both K+/Na+ and Mg++/Ca++ fell precipitously during the first hour, and the falls became more gradual thereafter, approac hing those of extracellular fluid at 24 hours. Changes in ZONE B, which appeared normal histologically, followed a similar downward trend but differed in magnitude from those in ZONE I (P smaller than 0.01). Changes in ZONE N were small but did not always overlap values in sham-operated dogs. It was concluded that lowered tissue K+/Na+ and Mg++/Ca++ were sensitive, but not specific, indices of myocardial ishemia, and multiple samplings of ionic ratios were essential for proper interpretation of ischemia-induced myocardial electrolyte derangements.