The response of implanted dual chamber pacemakers to 50 Hz extraneous electrical interference

Twenty-two patients with dual chamber pacemakers with interchangeable lead configuration were exposed to 50 Hz electromagnetic interference. Current, at corporeal levels from 0-600 microA, was applied between electrodes on shoulders and feet using a bedside injection unit. Pacemaker behavior was monitored with telemetered event markers and intracardiac electrograms. In bipolar mode, noise reversion mode was induced in all except two Medtronic units at high (> 170 microA) levels of corporeal current. In the Intermedics, Siemens Pacesetter, and Telectronics models, onset of noise reversion mode was preceded by a window of inappropriate function, characterized by rate acceleration due to atrial malsensing, or pacemaker inhibition due to ventricular malsensing. In unipolar mode, pacemaker malfunction occurred at much lower current levels. Inappropriate behavior preceded the onset of protective noise reversion mode. During current injection, all pacemakers could be interrogated and reprogrammed, and intracardiac telemetry was reliably obtained except in two Medtronic units at high current levels. No pacemaker was reset by the electrical interference, and no cross-talk was seen. Use of bipolar mode confers a high degree of protection from extraneous electrical interference, but in unipolar mode pacemakers may be inhibited by small amounts of corporeal current, potentially encountered in every day life. The current injection unit allows safe, controllable, and quantifiable investigation of the effects of the electric field induced by a current on implanted pacemakers. Telemetry of annotated intracardiac signals during electromagnetic interference clarifies observations of pacemaker acceleration and inhibition.