[Effect of isoptin chlorhydrate on the sino-auriculo-ventricular conduction in the heart of the dog].

The effects of Isoptin chlorhidrate (Verapamil) on sino-auriculo-ventricular conduction and automatism were studied on the heart in situ of 13 dogs. In three of them the drug was associated with intermittent intravenous drip of succinylcholine infusión (2 ml in 500 ml 5% dextrose solution). The drug was administered intravenously in 2 minutes (10 mg). In a first step, the action was followed during 45 minutes. In a second step, a second dosis (10 mgr) was administered 45 minutes after the first one. Proximal bipolar leads in the sinoauricular node, His bundle and Purkinje nets as well as distant bipolars leads between the ostium of the superior vena cava and left atrium or lead II, were recorded. Grass's preamplifiers and a Dumont Dual beam oscilloscope with two electronic switches were used for recording. Automatism of the sinus as well as of the His-Purkinje specific pathway was depressed. A significant prolongation of conduction time in A--V node was manifested by increased duration of P--R and A--H intervals. The sinoauricular as well as the Purkinje-muscle conduction were also slightly prolonged. An accumulation of the drug was demonstrated (a second dosis administered 45 minutes after the first one) by an accentuation of A--V block (second degree) and accentuated bradycardia. No escape rhythms were observed and circulation was maintained by mechanical stimulation of the ventricles. The latter effects were more accentuated in dogs in which an intermittent succinylcholine solution drip was administered.