Glibenclamide attenuates peaked T wave in early phase of myocardial ischemia.

OBJECTIVES

ECG peaked T wave appears during the early phase of myocardial ischemia, but the underlying mechanisms remain unknown. The purpose of this study was to elucidate the role of ATP-sensitive K+ channel (KATP) in this ECG change.

METHODS

In 12 anesthetized, open-chest dogs, the sinus node was crushed and the right atrium was paced at a cycle length of 400 ms. The left anterior descending coronary artery was abruptly occluded for 60 s before (control) and 15 min after an intravenous infusion of vehicle (n = 6) or glibenclamide (1 mg/kg, n = 6), a blocker of KATP. Forty-eight epicardial electrograms were simultaneously recorded from the anterior surface of the left ventricle. The potentials at 40, 80 and 120 ms from the J point were measured, and these points corresponded to the early, middle and late phases of the T wave, respectively.

RESULTS

During the control occlusion, T wave increased time-dependently and the maximal T-wave change was noted at the end of 60 s of coronary occlusion. The extents of T-wave elevation at the early, mid and late T phases were 5.5 +/- 0.5, 7.3 +/- 0.8 and 11.7 +/- 1.8 mV, respectively, and these T-wave elevations were significantly reduced by 33 +/- 21%, 59 +/- 12% and 63 +/- 13%, respectively, after the pretreatment with glibenclamide but not with its vehicle. The % reductions of mid and late T by glibenclamide were significantly larger than that of early T wave (P < 0.05).

CONCLUSIONS

An abrupt coronary occlusion accompanied peaked T wave as an early ECG wave change. As the extent of this T-wave elevation was attenuated by glibenclamide, the ischemia-induced alteration of ventricular repolarization can partly (60%) be explained by the modification of KATP activation.