Interference with cardiac pacemakers by magnetic resonance imaging: Are there irreversible changes at 0.5 Tesla?

The safety and feasibility of magnetic resonance imaging (MRI) in patients with cardiac pacemakers is an issue of gaining significance. The effect of MRI on patients' pacemaker systems has only been analyzed retrospectively i n some case reports. Therefore, this study prospectively investigated if MR I causes irreversible changes in patients' pacemaker systems. The effect of MRI at 0.5 Tesla on sensing and stimulation thresholds, lead impedance and battery voltage, current, and impedance was estimated during 34 MRI examin ations in 32 patients with implanted pacemakers. After measurements at base line and with documentation of intrinsic rhythm and modification of the pac ing mode, patients underwent MRI. The rest of the function time of the pace maker was calculated. Measurements were again performed after 99.5 +/- 29.6 minutes (mean +/- SD), immediately after MRI examination, and 3 months lat er. Lead impedance and sensing and stimulation thresholds did not change af ter MRI. Battery voltage decreased immediately after MRI and recovered 3 mo nths later. Battery current and impedance tended to increase. The calculate d rest of function time did not change immediately after MRI. MRI affected neither pacemaker programmed data, nor the ability to interrogate, program, or use telemetry. Surprisingly, in the gantry of the scanner, temporary de activation of the reed switch occurred in 12 of 32 patients when positioned in the center of the magnetic field. Missing activation of the reed switch through the static magnetic field at 0.5 Tesla is not unusual, MRI at 0.5 Tesla does not cause irreversible changes in patients' pacemaker systems.