Abstract
Ninety-three dogs were studied with normothermic or hypothermic ischemia for 60 or 90 minutes, with or without potassium cardioplegia. Radioactive-labeled microspheres (9 ± 1) were injected into the aortic perfusion cannula just prior to aortic cross-clamping and at 2, 6, and 10 minutes after the clamp was released. Left ventricular (LV) function was analyzed with a right heart bypass model before and 45 minutes after the ischemia period. Changes in LV function were defined as the arithmetic difference in the center of mass between preischemia and postischemia computer-drawn Sarnoff curves. Regardless of technique of myocardial protection, increased subendocardial flow 2 minutes after ischemia correlated strongly with preservation of LV function ( p < 0.01). Well-preserved hearts showed a rapid return to normal levels of coronary blood flow ( p < 0.01). In contrast, a delay in the peaking of subendocardial flow to 10 minutes was associated with poor function ( p < 0.01). There was a high correlation between ultrastructural morphology and LV function. While well-preserved hearts show early preferential subendocardial perfusion, the poorly protected myocardium is unable to restore adequate subendocardial flow early in the reperfusion period.
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