ATTENUATION OF S-T SEGMENT ELEVATION DURING REPETITIVE CORONARY OCCLUSIONS TRULY REFLECTS THE PROTECTION OF ISCHEMIC PRECONDITIONING AND ISNOT AN EPIPHENOMENON

Attenuation of S-T segment elevation between the first and subsequent balloon inflations of a coronary angioplasty procedure has been assume d to indicate a transition to a preconditioned state, but there has be en no validation of this assumption. Open-chest rabbits were instrumen ted with a coronary snare and epicardial electrode. The coronary arter y 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 w as quantitated as the voltage-time integral. For the first coronary oc clusion total S-T segment elevation averaged 40.8 +/- 5.4 mV.min, sign ificantly 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 ischemi c preconditioning was blacked by intravenous infusion of 8-(p-sulfophe nyl)theophylline, an adenosine receptor antagonist, attenuation of S-T segment elevation was no longer apparent. When preconditioning was ph armacologically triggered by tyramine rather than ischemia, there also was no alteration in S-T segment elevation among the 3 occlusions. Th erefore, S-T elevation was diminished during the second episode of isc hemia only when a transition occurred fl om non-preconditioned to prec onditioned state between occlusions. An attenuated S-T segment is a va lid marker for the presence of the preconditioned state.