Different effects of acute ischemia and anoxia on the canine myocardium.

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Abstract
Differences between ischemic and anoxic myocardium with respect to early mechanical and metabolic changes were investigated. Ischemia and anoxia were induced in the area perfused by the distal left anterior descending artery in 32 mongrel dogs. Since both the ischemia and the anoxia in this preparation resulted in very little change in global cardiac hemodynamics, indirect mechanical and metabolic effects on the involved myocardium were minimal. However, regional anoxia caused a later development of a myocardial systolic bulge than did regional ischemia (44.8 .+-. 13.6 vs. 26.8 .+-. 9.9 s). Myocardial ATP content was reduced to the same level 5 min after the onset of ischemia and anoxia. Anoxia with high K+ did not result in an earlier myocardial systolic bulge time, but myocardial ATP was maintained at a higher level than during ischemia. Anoxia with low pH also did not affect the time for development of a myocardial systolic bulge. Neither acidosis nor hyperpotassemia are more causally related to the earlier development of a myocardial systolic bulge during regional ischemia than during regional anoxia. Also the absolute value of myocardial ATP content is unlikely to be causally related to the determination of myocardial contraction, as reflected by the development of a myocardial systolic bulge.