The Effect of Power Frequency High Intensity Electric Fields on Implanted Cardiac Pacemakers

Thirty‐five patients fitted with 16 different pacemaker models (from 6 manufacturers) were exposed to 50 Hz electric fields up to a maximum of 20 kV/m. Four different response patterns were encountered: (1) normal sensing and pacing in all Medtronic and some Vitatron units; (2) reversion to the fixed (interference) rale in ail Telectronics. all Pacesetter, some Vitatron and CPI units; (3) slowand irregtilarpacing in one CPI and in all Cordis units; (4) mixed behaviorovera critical range of field strengths in which slow and irregular pacing preceded reversion to fixed‐rate, in some Telectromics and Pacesetter units. The field strengths required to induce such behavior varied from unit to unit and from model to model, with Telectronics being the most sensitive. In general, the interference threshold depended on the magnitude and distribution of induced body current relative to the pacemaker as well as field strength and thus varied with patient height, build and posture. While only a small proportion of pacemaker patients are likely lo encounter electric fields strong enough to interim.1 with pacemaker behavior, this possible hazard should be recognized.