Attenuation of S-T segment elevation during repetitive coronary occlusions truly reflects the protection of ischemic preconditioning and is not an epiphenomenon

Attenuation of S-T segment elevation between the first and subsequent balloon inflations of a coronary angioplasty procedure has been assumed to indicate a transition to a preconditioned state, but there has been no validation of this assumption. Open-chest rabbits were instrumented with a coronary snare and epicardial electrode. The coronary artery was occluded twice for 5 min with each occlusion followed by 10 min of reflow before a final 30 min occlusion. The evolving S-Televation was quantitated as the voltage-time integral. For the first coronary occlusion total S-T segment elevation averaged 40.8 +/- 5.4 mV.min, significantly greater than 26.2 +/- 4.6 mV.min for the second occlusion (p < 0.001). There was no further change during the initial 5 min of the third occlusion (24.5 +/- 1.5 mV.min). When the protection of ischemic preconditioning was blacked by intravenous infusion of 8-(p-sulfophenyl)theophylline, an adenosine receptor antagonist, attenuation of S-T segment elevation was no longer apparent. When preconditioning was pharmacologically triggered by tyramine rather than ischemia, there also was no alteration in S-T segment elevation among the 3 occlusions. Therefore, S-T elevation was diminished during the second episode of ischemia only when a transition occurred fl om non-preconditioned to preconditioned state between occlusions. An attenuated S-T segment is a valid marker for the presence of the preconditioned state.