The effects of lidocaine on intracellular and extracellular potentials, activation, and ventricular arrhythmias during acute regional ischemia in the isolated porcine heart.

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Abstract
The effects of were studied of lidocaine, 1 and 5 .mu.g/ml, on subepicardial transmembrane and DC extracellular potentials and on spontaneous ventricular arrhythmias during occlusion of the left anterior descending coronary artery in the Langendorff-perfused porcine heart. In the minutes after coronary occlusion, the resting membrane potential and action potential amplitude of cells in the ischemic zone were reduced and the extracellular complexes displayed TQ depression and ST elevation. The magnitude of the depression in action potential amplitude and of the ST elevation was exaggerated, and their time course was accelerated during occlusion in the presence of lidocaine. Diastolic potentials were little affected by the drug. The activation delay and the number of sites that failed to be activated in the ischemic zone were increased by lidocaine. The effect of drug on normal tissue was to decrease the action potential duration. These drug effects were concentration-dependent. Lidocaine did not prevent ventricular tachycardia from occurring during occlusion. The high concentration prevented its degeneration into fibrillation. Patterns of activation characteristic of a focal mechanism, possibly due to the injury current flow and present at the onset of tachycardia, were not affected by lidocaine. The drug did not entirely prevent but greatly decreased the incidence of large circus movements (diameter 1-2 cm) taking place in the ischemic zone and responsible for continuation of tachycardia. The high concentration prevented the fractionation of wavefronts into multiple wavelets and micro-reentrant circuits (diameter: 0.5 cm) which is characteristic of fibrillation. The effectiveness of lidocaine against fibrillation during coronary occlusion is due to conversion of areas of unidirectional block and slow conduction in the ischemic zone into areas of total block.