TIME COURSE OF CHANGES IN VENTRICULAR EXCITABILITY AND CONDUCTION DURING MYOCARDIAL ISCHEMIA AND REPERFUSION IN THE DOG - EFFECT OF LIDOCAINE

Strength-interval curves and conduction times were determined in anesthetized dogs during and after myocardial ischemia using a computerized system capable of determining a 5 point strength-interval curve with conduction times within 20 s. At the peak incidence of ligation arrhythmias (5 min of ischemia) the falling limb of the strength-interval curve was shifted to the left and conduction time was prolonged while at 15 min of ischemia the strength-interval was shifted upward and conduction times had returned toward control. Lidocaine enhanced the upward shift of the strength-interval curve contributing to the electrical stability of the myocardium during this phase of ischemia. During the 1st minute after abrupt reperfusion of the ischemic zone there was a slight downward shift of the early part of the strength-interval curve and conduction times tended to be shorter than control. Lidocaine enhanced the electrophysiological changes after abrupt reperfusion reducing excitation thresholds and increasing the tendency to superconductivity. Lidocaine enhanced electrical stability during acute ischemia but tended to exaggerate electrophysiologic defects seen during abrupt reperfusion.