Induction of atrial fibrillation and flutter in dogs using methacholine

Systemic infusion of methacholine has been used to facilitate induction of atrial fibrillation. However, the dose-response relationship, reproducibili ty and effect of anesthetic agents on induction are not well understood. Th e use of methacholine to facilitate electrical induction of sustained (> 10 minutes duration) atrial fibrillation or flutter was examined. In 25 dogs induction of atrial arrhythmias was attempted using a series of ten 50 Hz t rains of 10 seconds duration delivered via an endocardial catheter in the b aseline anaesthetized state and subsequently in the presence of graded dose s of intravenous methacholine (maximum 5 mu g/kg/min). Studies were repeate d in 13 dogs to assess reproducibility. Twelve dogs (48%) had inducible sus tained atrial flutter or fibrillation lasting greater than 10 minutes in th e baseline state. During infusion of methacholine the remaining 13 (52%) do gs also had inducible sustained atrial flutter or fibrillation (mean infusi on rate 1.6 +/- 1.9 mu g/kg/min). Induction of sustained atrial flutter or fibrillation was reproducible in all but one dog. The type of anesthetic di d not significantly affect inducibility. Induction of prolonged atrial fibr illation or flutter is possible in the baseline anaesthetized state in appr oximately half of dogs using high frequency programmed electrical stimulati on. The yield of inducible sustained atrial fibrillation or flutter with pr ogrammed stimulation during intravenous infusion of methacholine was increa sed to 100%. Induction of sustained atrial fibrillation or flutter was high ly reproducible.