[Comparative effects of inhalation anesthetics on atrioventricular conduction with and without calcium entry blockers].
Calcium entry blockers have been used during general anesthesia in order to control hypertension and tachyarrhythmias. It is well known that both calcium entry blockers (CEBs) and inhalation anesthetics have depressant effects on atrioventricular (AV) conduction and sinus automaticity. Therefore, this study was designed to evaluate combined effects of either halothane, enflurane, isoflurane, or sevoflurane and CEBs (verapamil, diltiazem, or nifedipine) on AV conduction. The following 3 sets of experiments were performed using 90 mongrel dogs anesthetized with ketamine 100-150 mg im, thiamylal 25 mg/kg iv and nitrous-oxide with 50% oxygen. Experiment 1: to evaluate the effects of ketamine and thiamylal on AV conduction. Experiment 2: to evaluate drug interactions of halothane with CEBs. Experiment 3: to evaluate the combined effects of four different inhalation anesthetics at equipotent concentrations (0.8% halothane, 1.6% enflurane, 1.2% isoflurane, and 1.7% sevoflurane) and verapamil. The following variables were measured utilizing His bundle electrocardiogram: Sinus cycle length (SCL), AV conduction time (AH interval), His Purkinje conduction time (HV interval), effective and functional refractory period of AV node (ERP and FRP). It was confirmed that ketamine im and thiamylal iv used for induction of anesthesia did not change AV conduction time from experiment 1. The combined effects of either verapamil (0.1 mg/kg) or diltiazem (0.15 mg/kg) and 0.8% halothane were additive on AV conduction. Although nifedipine (0.01 mg/kg) did not affect AV conduction, there was the significant prolongation of SCL with halothane compared to without halothane. In experiment 3, 0.8% halothane and 1.6% enflurane were stronger than 1.2% isoflurane and 1.7% sevoflurane concerning inhibitory effects on AV conduction. Verapamil had some deleterious effects in 1.6% halothane or 3.2% enflurane anesthesia because of extreme inhibitory effects on AV conduction and sinus automaticity. In conclusion, caution must be exercised in usage of CEBs if inhalation anesthetics are used in higher concentrations.
Yokota
S
S
Department of Anesthesiology, Hokkaido University School of Medicine, Sapporo, Japan.
D000769:Anesthesia, Inhalation; D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004562:Electrocardiography; D006221:Halothane / Q000494:pharmacology; D006329:Heart Conduction System / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology
D000777:Anesthetics; D002121:Calcium Channel Blockers; D014700:Verapamil; D006221:Halothane