Attenuation of ST-segment elevation by ischemic preconditioning: Reflection of cardioprotection in Gottingen but not in Ossabaw minipigs

Background: Ischemic preconditioning (IPC; brief cycles of coronary occlusion/ reperfusion) reduces myocardial infarct size. The ST-segment elevation during coronary occlusion is progressively attenuated with increasing number of IPC cycles. Progressive attenuation of ST-segment elevation is considered a result of sarcolemmal K-ATP channel activation and has been considered to reflect and predict IPC's cardioprotection. We have recently demonstrated that IPC failed to reduce infarct size in minipigs of a particular strain (Ossabaw), which had a genetic predisposition to develop, but not yet established a metabolic syndrome. To determine whether or not Ossabaw minipigs nevertheless had attenuated ST-segment elevation over repetitive IPC cycles, we compared Gottingen vs. Ossabaw minipigs in which IPC reduces infarct size. Methods and results: We analyzed surface chest electrocardiographic (ECG) recordings of anesthetized open-chest contemporary Gottingen (n = 43) and Ossabaw minipigs (n = 53). Both minipig strains were subjected to 60 min coronary occlusion and 180 min reperfusion without or with IPC (3 x 5 min/ 10 min coronary occlusion/ reperfusion). ST-segment elevations during the repetitive coronary occlusions were analyzed. In both minipig strains, IPC attenuated ST-segment elevation with increasing number of coronary occlusions. IPC reduced infarct size in Gottingen minipigs (45 +/- 10% without vs. 25 +/- 13% of area at risk with IPC), whereas such cardioprotection was absent in Ossabaw minipigs (54 +/- 11% vs. 50 +/- 11%). Conclusion: Apparently, the block of signal transduction of IPC in Ossabaw minipigs occurs distal to the sarcolemma, where K-ATP channel activation still attenuates ST-segment elevation as it does in Gottingen minipigs.

Automated summary

This study compared the attenuated ST-segment elevation over repetitive ischemic preconditioning (IPC) cycles in Gottingen and Ossabaw minipigs. The results showed that while IPC still attenuated ST-segment elevation in Ossabaw minipigs, it failed to reduce infarct size compared to Gottingen minipigs. This suggests that the block of IPC signal transduction in Ossabaw minipigs occurs distal to the sarcolemma.