Pacing in magnetic resonance imaging environment: clinical and technical considerations on compatibility.

Magnetic resonance imaging is a widely accepted tool for the diagnosis of a variety of disease states. However, the presence of an implanted pacemaker is considered to be a strict contraindication to magnetic resonance imaging in the vast majority of medical centres, precluding a substantial and growing number of patients from the diagnostic advantages of this imaging modality. The potential effects of magnetic resonance imaging on cardiac pacemakers are multiple (Table 1). The static magnetic field may close the reed switch, resulting in asynchronous pacing. The radiofrequency field may induce an undesirable fast pacing rate. The time-varying magnetic gradient fields may induce currents in the pacemaker system of sufficient magnitude to pace the heart. There are other theoretical concerns, including potential thermal injury at the lead tip. However, the most influential factor that supports the current practice is the reported lethal consequences of magnetic resonance imaging in patients with implanted pacemakers. Despite the above-mentioned concerns, the effects of magnetic resonance imaging on cardiac pacemakers remain controversial. Most of the previous studies that prohibit magnetic resonance imaging in pacemaker patients were based on in vitro and animal model data from the 1980’s using older pacemaker and lead technology. More recent anecdotal reports describe a small series of pacemaker patients who have safely