EFFECTS OF NUCLEAR-MAGNETIC-RESONANCE IMAGING ON CARDIAC-PACEMAKERS

Patients with cardiac pacemakers are currently restricted from nuclear magnetic resonance imaging (MRI). The aim of the study was to analyze the influence of MRI on new generation pacemakers. Tests were perform ed using a phantom model with seven dual chamber and two single chambe r systems in a 0.5 Tesla MRI scanner. Monitoring by telemetry and osci llography were used during the standard clinical scan sequences as wel l as a pacemaker inquiry after each sequence. Spin echo, gradient echo , and fast field echo sequences were performed with the following stim ulation modes: VVI, VVIR, VOO, DDD, DDDR, and DOO. On entering the sta tic magnetic field, the reed switch was activated followed by asynchro nous stimulation. The subsequent scan showed no influence on the stimu lation function nor on the pacemaker program. Event counter function r emained intact. Pacemakers with automatic mode switching to demand pac ing or programmed inactivation of the reed switch were triggered in th e dual chamber mode and were inhibited in the one chamber mode during the scan. Alterations of pacemaker program or rapid pacing were not ob served. MRI scan could induce voltage as high as intracardiac signals, but the stimulation threshold of the heart was not reached. Thus, pac emakers should be programmed in the asynchronous mode during scan to a void inhibition and trigger mechanism.