Opposite effects of lidocaine and diltiazem on electrophysiologic alterations in acutely ischemic porcine myocardium

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Abstract
To investigate the actions of lidocaine and diltiazem on the ischemic alterations associated with the onset of acute ischemic arrhythmias, the left anterior descending coronary artery was occluded for 6-min periods separated by 30 min of reperfusion, under control conditions and after injection of lidocaine (2.4–3.8 μg/mL of plasma) or diltiazem (390–510 ng/mL) in open–chest anesthetized pigs. Sixty-one unipolar electrograms were continuously recorded in the ischemic zone. Isochronal maps and isopotential maps were determined by computer analysis. The magnitude of beat-to-beat alternation of unipolar waveforms was described by the difference between the time integrals subtended by electrograms of consecutive beats. Activation times were prolonged by ischemia and the ST segment became elevated. Delay and ST elevation developed at a faster rate in the presence of lidocaine than under control conditions, but were reduced by diltiazem. ST-T alternation was not significantly different between control and lidocaine occlusions, but the incidence of negative T waves and that of ventricular tachycardia degenerating to fibrillation were higher in lidocaine occlusions than in control occlusions. In contrast, unipolar waveform alternation and negative T waves were virtually abolished by diltiazem, even at fast pacing rates (180–210 beats/min) at which diltiazem did not reduce ST elevation. Ventricular arrhythmias also were abolished by diltiazem. Thus, lidocaine and diltiazem produce opposite effects on the ischemic alterations most closely associated with the initiating mechanism of tachycardia. This could be related to differences between these drugs with regard to their actions on transmembrane currents during repolarization.Key words: acute myocardial ischemia, lidocaine, diltiazem, ventricular arrhythmias, electrical alternans.

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