Arrhythmogenic activity of cardiac muscle in pulmonary veins of the dog: implication for the genesis of atrial fibrillation

Objective: Pulmonary veins are important foci of ectopic beats to initiate paroxysmal atrial fibrillation. The purpose of this study were to investiga te the electrophysiological characteristics of excitable cells in canine pu lmonary veins obtained from healthy and chronic rapid atrial pacing dogs an d their responses to cardioactive agents. Methods: Transmembrane action pot entials (APs) were recorded from multiple sites of pulmonary veins isolated from 17 healthy dogs and 14 dogs with chronic (6-8 weeks) rapid atrial pac ing (780 bpm). Results: In normal superfusate, several types of electrical activities were identified, including silent electrical activity, fast resp onse APs driven by electrical stimulation, and spontaneous fast or slow res ponse APs (with or without early afterdepolarizations). The incidences of A P with an early afterdepolarization (93% versus 41%) was greater in chronic pacing dogs. The spontaneous activities were depressed by beta-adrenocepto r blocker, calcium channel blocker, adenosine and acetylcholine. High frequ ency (>8 Hz) irregular rhythms occurred spontaneously or were induced by ca rdioactive agents or electrical stimuli. The incidence of spontaneously occ urring tachyarrhythmias was much higher in preparations from chronic pacing dogs (93%) than from control (12%). The tachyarrhythmias were suppressed b y sodium channel blocker, potassium channel blocker or magnesium. Conclusio ns: Pulmonary veins have arrhythmogenic ability through spontaneous activit ies or high-frequency irregular rhythms. The higher incidence of spontaneou sly occurring high-frequency irregular rhythms in chronic rapid atrial paci ng dogs may account for the increased risk of atrial fibrillation in these dogs. (C) 2000 Elsevier Science B.V. All rights reserved.