Atrial pacing failure following termination of atrial fibrillation by acute administration of disopyramide phosphate.

Atrial pacing failure occurred after termination of atrial fibrillation by acute administration of disopyramide phosphate in a 71-year-old woman implanted with an AAI pacemaker for sick sinus syndrome. The atrial pacing threshold showed an 810% increase; however, the serum concentration of disopyramide corresponded to therapeutic level. Infusion of the same dose of disopyramide phosphate used during the period of atrial pacing rhythm did not increase the atrial pacing threshold. In the present patient, we supposed that atrial pacing failure did not occur by the effect of disopyramide alone, but rather was a reciprocal action in response to atrial fibrillation.