MR imaging and cardiac pacemakers: In vitro evaluation and in vivo studiesin 51 patients at 0.5 T

PURPOSE: To evaluate the safety and feasibility of magnetic resonance (MR) imaging at 0.5 T in patients with implanted cardiac pacemakers. MATERIALS AND METHODS: Twenty-one models of pacemakers and 44 pacemaker ele ctrodes were exposed to in vitro MR imaging with continuous registration of pacemaker output and temperature at the lead tip: Prior to MR imaging exam ination, pacemakers were programmed to an asynchronous mode (A00, V00, dr D 00). Pacemakers were examined before and after MR imaging. Forty-four patie nts with implanted pacemakers underwent 51 MR imaging examinations under ca rdiologic surveillance, continuous electrocardiography, pulse oximetry, and capnographic monitoring. RESULTS: MR imaging was safely performed in all patients. None of the pacem akers displayed a pacing dysfunction at MR imaging. No changes occurred in the programmed parameters in any device tested in vivo or in vitro. Maximum increases in the temperature at the lead tips were 8.90 degrees C at a spe cific absorption rate (SAR) of 0.6 W/kg and 23.50 degrees C under a worst-c ase radio-frequency (RF) heating condition with an SAR of 1.3 W/kg. CONCLUSION: MR imaging at 0.5 T can be safely performed in patients with im planted pacemakers in carefully selected clinical circumstances when approp riate strategies (programming to an asynchronous mode, adequate monitoring techniques, limited RF exposure) are used.