MEXILETINE HAS NO EFFECT ON DEFIBRILLATION ENERGY-REQUIREMENTS IN DOGS

Many of the antiarrhythmic drugs produce a rise in the ventricular def ibrillation threshold (DFT). Although mexiletine has also been reporte d as the probable cause of a significant elevation of DFT, there has b een no previous study; therefore, the effect of mexiletine on DFT was investigated in the present study. The experiments were performed on t en mongrel dogs in the open-chest state using general anesthesia. Mexi letine 1, 2, 4, 6, or 8 mg/kg was administered as the loading dose, fo llowed by the same dose/kg per hour. In these five groups, fibrillatio n/defibrillation (F/D) trials were performed repeatedly every 10 minut es, until 60 minutes after starting the maintenance dose. F/D trials w ere also performed at. 30, 45, and 60 minutes after the completion of mexiletine infusion. The heart was allowed to fibrillate for a total o f 30 seconds. Applying internal paddles to the heart, energies of 2, 3 , 5, 7, 10, 20, and 30 J maximum were used. The minimal energy shock t hat caused defibrillation was defined as the DFT. The mexiletine conce ntration in each group changed from 0 to 6.11 mu g/mL, DFT ranged from 2-10 J, and no statistical correlation was found between mexiletine c oncentration and DFT. We conclude that mexiletine does not induce an i ncrease in DFT in dogs.