The following are key points to remember about magnetic resonance (MR) imaging in patients with cardiac implantable electronic devices (CIEDs):

1. Historically, magnetic resonance (MR) scanning in patients with CIEDs was thought to be contraindicated due to the following concerns: a) damage to the device causing temporary or permanent modification of function, b) movement and/or vibration of the pulse generator or lead(s), c) excessive heating of the leads, d) induced currents in the leads, e) inappropriate sensing, triggering, or activation of the device, and f) electrical reset and reed switch malfunction.
2. MR scanning could potentially lead to inhibition of pacemaker output, asynchronous pacing, rapid paced rates, or induction of ventricular fibrillation. Many of the deleterious effects, seen in early reports, occurred in patients who underwent MR scanning without having their devices appropriately reprogrammed for the scanning procedure.
3. Recently, MR conditional CIEDs have been approved in Europe and the United States. Additionally, an increasing number of patients with non-MR conditional CEIDs have been shown not to have deleterious effects from MR scanning.
4. The MagnaSafe registry was a prospective multicenter study of nonthoracic MR scanning in patients with implanted non-MR conditional CIEDs. A total of 1,500 nonthoracic MR studies were performed with no reported deaths, device failure, generator or lead replacement, loss of capture, or ventricular arrhythmia. Importantly, pacemaker-dependent patients with non-MR conditional ICDs were excluded from the registry because not all tachycardia therapies could be disabled during pacing in this group.
5. For pacemaker-dependent patients with non-MR conditional ICDs, and those with non-MR conditional pacemakers implanted before 2002, the risks of inappropriate tachycardia therapies, or pacing inhibition during MR scanning are unacceptably high, and alternative imaging modalities must be sought.
6. For non-MR conditional devices, MR scanning should only be considered if there are no other means to obtain the diagnostic information, and the the information will materially change clinical management.
7. Most MR conditional devices allow whole body MR scanning, but some have a thoracic exclusion zone.
8. MR ‘safe’ activation reprograms the device to OOO for nonpacing-dependent patients or VOO pacing for dependent patients.
9. MR scanning is contraindicated in the presence of surgical epicardial leads, and ‘free floating’ superior vena cava (SVC) coils, retained leads or fractured leads, the presence of an abdominal system, and implantation <6 weeks prior.
10. The patient’s heart rhythm should be monitored using electrocardiography and/or pulse oximetry throughout the scanning process in patients both with MR conditional and non-MR conditional CIEDs. An external defibrillator with external pacing pads should be available within the MR suite. All pacing parameters must be checked and programming changes reversed following the MR scan.

Keywords: Arrhythmias, Cardiac, Defibrillators, Implantable, Diagnostic Imaging, Electrocardiography, Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy, Cardiac Resynchronization Therapy Devices, Tachycardia, Vena Cava, Superior, Ventricular Fibrillation

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