Isolated rat hearts were perfused with blood from a support animal for 15 minutes (flow rate, 2.5 mL/min; perfusion pressure, 60.1 +/- 1.3 mm Hg). Control left ventricular developed pressure (LVDP) was measured, and the hearts (six per group) were subjected to 10, 20, 30, 40, 50, 60, 70, or 80 minutes of global
ischemia (37 degrees C) and 60 minutes of reperfusion. Pacing (320 beats per minute) was instituted before and after
ischemia. In all groups, transient arrhythmias occurred at the onset of reperfusion, to be followed by an early phase of recovery that peaked after 2 to 3 minutes of reperfusion. The relation between the extent of this initial recovery and the duration of preceding
ischemia was described by a bell-shaped curve. Thus, the maximum initial mean recovery after 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 LVDP. Possibly indicative of reperfusion-induced injury, LVDP then declined in all groups so that after 20 minutes of reperfusion, the mean recovery was 63%, 53%, 48%, 50%, 56%, 12%, 9%, and 5%, respectively. In the 10-, 20-, 30-, and 40-minute
ischemia groups, there then was a secondary 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
ischemia. To define the early phase of recovery that had been obscured by reperfusion-induced arrhythmias, we repeated the experiments with the inclusion of a cardioplegic infusion (St
Thomas' solution for 2 minutes before
ischemia). This significantly reduced the incidence of
ventricular fibrillation during early reperfusion. The extent of the initial postischemic recovery of LVDP was similar to that observed without
cardioplegia; however, the mean secondary recovery was greater in all groups. Again, the relation of early transient (2 to 5 minutes) recovery to the duration of
ischemia was represented by a bell-shaped curve, whereas the secondary recovery was inversely related.
CONCLUSIONS: