Pacing induced sustained atrial fibrillation in a pony.

A transvenous, screw-in electrode was implanted in the right atrium of a healthy pony and connected with an implantable pulse generator programmed to deliver bursts of electrical stimuli to the atrium. Initially, cessation of burst pacing resulted in short (less than 1 minute), self-terminating episodes of atrial fibrillation. As burst pacing continued, the episodes of induced atrial fibrillation became longer. After 3 weeks of continuous atrial pacing, atrial fibrillation became sustained (56 hours). This model of pacing induced atrial fibrillation can be used to study the mechanisms leading to atrial fibrillation, its perpetuation and therapy. Our preliminary observations support the concept that once atrial fibrillation starts, it sets up changes in the electrical characteristics of the atrium that favor its own perpetuation.