LIDOCAINE CONVERTS INDUCIBLE VENTRICULAR-FIBRILLATION INTO SUSTAINED VENTRICULAR-TACHYCARDIA IN CONSCIOUS DOGS WITH RECENT MYOCARDIAL-INFARCTION

The aim of the present study was to investigate the effect of lidocain e (L) on ventricular tachyarrhythmias with special reference to ventri cular fibrillation (VF). Myocardial infarction (MI) was created in 39 dogs by doubly ligating the left anterior descending (LAD) coronary ar tery. Ah animals surviving the infarction (n = 33) were subjected to p rogrammed ventricular stimulation 7.6 +/- 3.2 days later. Local electr ical activity was recorded from the subepicardium of the left ventricu lar wall by means of a specially designed composite electrode. L (2 an d 4 mg/kg i.v.) facilitated the induction of sustained monomorphic ven tricular tachycardia (sVT) in 8 dogs with nonsustained polymorphic ven tricular tachycardia (nsVT) in the control. In 13 dogs developing sVT during control stimulation, L slowed the rate of tachycardia in 8 anim als (first-dose effect), while it abolished arrhythmia induction in 5 animals (second-dose effect). It was interesting that L (2 mg/kg) abol ished reproduction of control VF in 12 animals by converting it into s VT. L significantly depressed conduction and prolonged ventricular ref ractoriness in the infarction zone. The results suggest that L facilit ates induction of sVT in conscious dogs with recent MI, thereby decrea sing susceptibility of infarcted myocardium to aggressive polymorphic nsVT or VF. The capability of L to exacerbate slow conduction in the i nfarction zone seems not to favor the development of VF during this st age of MI.