Effects of "duration" of reperfusate administration versus reperfusate "dose" on regional functional, biochemical, and histochemical recovery.

This study tests the hypothesis that improved myocardial salvage following regional ischemia occurs when attention is directed toward the duration of blood cardioplegic reperfusion rather than the reperfusate "dose". Pilot studies after global ischemia established the postischemic oxygen use pattern consistent with normal and impaired recovery; the best recovery occurred when postischemic muscle consumed oxygen in excess of basal demands. Experimental studies were then performed on 22 dogs undergoing 2 hours of left anterior descending coronary occlusion. Nine dogs received normal blood reperfusion, with the heart allowed to remain in the beating, working state. In 13 dogs, cardiac O2 demands were kept low during reperfusion by delivering a dose of 150 to 250 mumol/L Ca2++ aspartate-glutamate-enriched blood cardioplegic solution containing 250 to 350 micrograms/kg body weight diltiazem during total vented bypass. This same reperfusate dose with diltiazem was given over 10 minutes in five dogs and over 20 minutes in eight others. Persistent systolic bulging (ultrasonic crystals) of -27% (p less than 0.05) of systolic shortening followed normal blood reperfusion without bypass. During blood cardioplegic reperfusion, regional O2 uptake exceeded basal demands by 24 ml/100 gm/min at 10 minutes (p less than 0.05) and did not return to baseline until 20 minutes had elapsed. Hearts reperfused with blood cardioplegia for 20 minutes had better recovery of systolic shortening (58% versus 30%, p less than 0.05), less edema (79.8% versus 80.9% water content, p less than 0.05), and less triphenyltetrazolium chloride nonstaining (12% versus 21%, p less than 0.05) than those reperfused for 10 minutes with the same solution containing the same diltiazem dose. Continuing blood cardioplegic reperfusion until myocardial oxygen uptake reaches control levels enhances regional functional recovery after acute coronary occlusion. These results indicate that attention should be directed toward the duration of reperfusion, as well as the "dose" of cardioplegic reperfusate.