Vagally-mediated atrial fibrillation in dogs: conversion with bretylium tosylate

We developed a stable, reproducible model of acute atrial fibrillation (sustained for up to 90 min) in open-chest, anesthetized dogs utilizing continuous bilateral stimulation of the cervical vagi and transient rapid atrial pacing. This model was then used to study the defibrillatory effects of bretylium tosylate. In five dogs, sequential runs of atrial fibrillation lasting 1-60 minutes were induced. A single, rapid, intravenous bolus of bretylium caused conversion of all episodes of atrial fibrillation (n = 31) after a mean of 33 seconds (range 15-151 sec). In 28 of 31 episodes (90%) conversion occurred within 40 seconds. The dose of bretylium was 2.5 mg/kg in all but one episode in which 5.0 mg/kg was given. We conclude that bilateral vagal stimulation produces a stable canine model of acute atrial fibrillation and that the arrhythmia is rapidly converted with intravenous bretylium.