Paradoxical induction of endless loop tachycardia by magnet application over a DDD pacemaker.

It is well known that removal of a testing magnet from a DDD pulse generator may cause endless loop tachycardia in patients with retrograde ventriculoatrial conduction; application of the magnet then terminates the tachycardia. We have observed the opposite response to the magnet and in this report we describe the paradoxical induction of endless loop tachycardia by magnet application over a DDD pulse generator and its persistence despite repeated removal and reapplication of the magnet. This unusual behavior occurred only in the "magnet off" function and is due to magnet-induced signals sensed by the atrial channel circuitry.