EFFECTS OF LIDOCAINE AND DILTIAZEM ON RECOVERY OF ELECTROPHYSIOLOGIC ACTIVITY DURING PARTIAL REPERFUSION FOLLOWING SEVERE MYOCARDIAL-ISCHEMIA IN CANINE HEARTS

The effects of lidocaine and diltiazem on recovery of electrophysiolog ic activity during partial reperfusion following severe myocardial isc hemia were investigated in 28 dogs. The left anterior descending arter y was ligated, and the distal end was connected to the carotid artery. Myocardial ischemia was induced by retrograde blood flow for 10 minut es, after which flow-limited reperfusion (30-60% of the coronary flow before ischemia) was performed. The dogs were divided according to the agent administered before ischemia into the following three groups: s aline (group S, n = 11); lidocaine (group L, n = 8, 0.07 mg/kg/min by intravenous drip infusion following 2 mg/kg intravenous injection); an d diltiazem (group D, n = 9, 0.02 mg/kg/min by intravenous drip infusi on. There were no significant differences among the three groups in th e incidence of ventricular tachyarrhythmia, which occurred as Ventricu lar tachycardia (VT) or ventricular fibrillation (VF). Ln each group, the occurrence of VT was frequently preceded by delayed potential whic h was initiated after reperfusion, with depressed conduction in the ep icardium, suggesting reentry (82%, 96%, and 87%, not significant). The determining factors for VT with degeneration into VF were long durati on of VT in groups S and L (VT with degeneration into VF vs VT without , 1.2 +/- 0.2 seconds vs 0.6 +/- 0.1 seconds, P < .05, in group S and 11.6 +/- 2.5 seconds vs 2.2 +/- 0.4 seconds, P < .05, in group L), and decrease in average R-R interval during VT in groups L and D (195 +/- 8 ms vs 313 +/- 17 ms, P < .01, in group L and 201 +/- 11 ms vs 327 /- 28 ms, P < 0.01, in group D). In addition, occurrence of epicardial electrophysiologic activity with reduced time from onset of the QRS c omplex in the surface electrocardiogram to the onset of the activity d uring VT preceded VF in group L (VT with degeneration into VF vs VT wi thout, 130.0 +/- 15.1 ms vs 185.8 +/- 21.4ms, P < .05), while that wit h prolongation of the time had this effect in group D (116.0 +/- 15.7 ms vs 69.0 +/- 10.7 ms, P < .05). It is concluded that, even when part ial reperfusion is applied, neither lidocaine nor diltiazem suppresses VT because-neither drug decreases delayed potential acting as a trigg ering factor or suppresses-VF, since the alteration of the epicardial conductivity during VT can change the VT circuit to a smaller one.