Background: The purpose of this study was to determine whether transient ischemic preconditioning protects human myocardium against normothermic ischemic injury.
Methods: Isolated human right atrial trabeculae were suspended in an organ bath with oxygenated Tyrode's solution at 37 degrees C and field stimulated at 1 Hz. Developed force was recorded. Trabeculae (Warm I/R) received normoxic perfusion before 45 minutes of normothermic simulated ischemia (hypoxic, substrate-free buffer with pacing at 3 Hz) and 120 minutes of reperfusion. Preconditioned trabeculae (Warm IPC) were subjected to 5 minutes of normothermic simulated ischemia and 10 minutes of perfusion before normothermic simulated ischemia-reperfusion injury. Trabeculae (Cold I/R) were subjected to hypothermic (4 degrees C) ischemia (hypoxic buffer) for 4 hours and 60 minutes of reperfusion (37 degrees C). Preconditioned trabeculae (Cold IPC) were pretreated with 5 minutes of normothermic simulated ischemia before hypothermic ischemia and 60 minutes of reperfusion. At the end of reperfusion, trabeculae were frozen at -70 degrees C and assayed for tissue creatine kinase activity.
Results: At the end of reperfusion, warm preconditioned trabeculae (Warm IPC) recovered 51% +/- 5% of baseline developed force, whereas warm I/R trabeculae recovered 24% +/- 3% (p < 0.05). Tissue creatine kinase levels reflecting preserved tissue viability were sustained in Warm IPC trabeculae (1,183 +/- 204 U/g), whereas nonpreconditioned control trabeculae (Warm I/R) exhibited lower levels of enzymatic activity (403 +/- 32 U/g) (p < 0.05). In contrast, Cold IPC trabeculae recovered 47% +/- 5% and Cold I/R, 56% +/- 8% of baseline developed force at the end of reperfusion (p > 0.05).
Conclusions: We conclude that transient ischemic preconditioning protects human myocardium against normothermic ischemic injury.