DYNAMICS OF EARLY POSTISCHEMIC MYOCARDIAL FUNCTIONAL RECOVERY - EVIDENCE OF REPERFUSION-INDUCED INJURY

Background The present study was designed to explore the relation betw een the duration of ischemia and the rate and extent of myocardial fun ctional recovery after reperfusion. Methods and Results Isolated rat h earts were perfused with blood from a support animal for 15 minutes (h ow rate, 2.5 mL/min; perfusion pressure, 60.1+/-1.3 mm Hg). Control le ft ventricular developed pressure (LVDP) was measured, and the hearts (six per group) were subjected to 10, 20, 30, 40, 50, 60, 70, or 80 mi nutes of global ischemia (37 degrees C) and 60 minutes of reperfusion. Pacing (320 beats per minute) was instituted before and after ischemi a. In all groups, transient arrhythmias occurred at the onset of reper fusion, to be followed by an early phase of recovery that peaked after 2 to 3 minutes of reperfusion. The relation between the extent of thi s initial recovery and the duration of preceding ischemia was describe d by a bell-shaped curve. Thus, the maximum initial mean recovery afte r 10, 20, 30, 40, 50, 60, 70, or 80 minutes of ischemia was 97%, 108%, 145%, 154%, 118%, 34%, 41%, and 24%, respectively, of preischemic LVD P. Possibly indicative of reperfusion-induced injury, LVDP then declin ed in all groups so that after 20 minutes of reperfusion, the mean rec overy was 63%, 53%, 48%, 50%, 56%, 12%, 9%, and 5%, respectively. In t he 10-, 20-, 30-, and 40-minute ischemia groups, there then was a seco ndary increase in LVDP, possibly indicating the start of recovery from stunning. After 60 minutes of reperfusion, the mean recovery of LVDP was 82%, 65%, 59%, 54%, 47%, 9%, 7%, and 4%, respectively; this second phase of recovery was inversely proportional to the duration of ische mia. To define the early phase of recovery that had been obscured by r eperfusion-induced arrhythmias, we repeated the experiments with the i nclusion of a cardioplegic infusion (St Thomas' solution for 2 minutes before ischemia). This significantly reduced the incidence of ventric ular fibrillation during early reperfusion. The extent of the initial postischemic recovery of LVDP was similar to that observed without car dioplegia; however, the mean secondary recovery was greater in all gro ups. Again, the relation of early transient (2 to 5 minutes) recovery to the duration of ischemia was represented by a bell-shaped curve, wh ereas the secondary recovery was inversely related. Conclusions Althou gh the results of the present study confirm the protective properties of cardioplegia, they also shed some light on the nature of reperfusio n-induced injury and myocardial stunning and their complex relation to the severity of the preceding ischemia.