Safety of MRI Patients with Pacemakers and ICDs
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Synopsis: Given appropriate precautions, noncardiac and cardiac MRI can potentially be safely performed in patients with selected implantable pacemaker and defibrillator systems.
Source: Nazarian S, et al. Clinical utility and safety of a protocol for noncardiac and cardiac magnetic resonance imaging of patients with permanent pacemakers and implantable cardioverter defibrillators at 1.5 tesla. Circulation. 2006; 114:1277-1284.
Nazarian and colleagues from johns hopkins Hospital describe a protocol for magnetic resonance imaging (MRI) in patients with pacemakers and implanted defibrillators (ICDs). Candidates were entered into the study if they were referred to the investigators with a clinical indication for an MRI, had no acceptable imaging alternative, and had an implantable cardiac device. In addition, each patient's permanent pacemaker or ICD had previously been found to be safe by in vitro phantom and in vivo animal testing. Patients with a device implantation within 6 weeks and those with either nontransvenous epicardial leads, or active or passive fixation at the lead tip, or abandoned leads, were excluded. In 55 patients, a total of 68 MRI examinations were performed. Among these 55 patients, 31 (56%) had a permanent pacemaker, 24 (44%) had an ICD and 7 (13%) had a biventricular pacing system.
A radiologist and cardiac electrophysiologist were present during all scans, a standard protocol was followed, and all of the devices were interrogated before and immediately after MRI. Pacemaker dependence was assessed before MRI by transient programming of the pacer to ventricular inhibited pacing, at a back-up rate of 30 bpm. Pacing mode was programmed to an asynchronous mode (VOO/DOO) for patients without a hemodynamically stable escape rhythm. In patients who were not pacemaker dependent, an inhibited mode (VVI/DDI) was used. Magnet response, rate response, PVC response, noise response, ventricular sense response, conducted atrial fibrillation response, and all tachyarrhythmia functions were all disabled. After completion of the MRI study, device and lead parameters were re-interrogated and pacing and tachyarrhythmia functions were reprogrammed to the original settings. In all cases, imaging was performed with a 1.5 T scanner manufactured by General Electric Healthcare Technologies. During the scan, continuous ECG telemetry pulse oximetry and symptoms were monitored. The MRI imaging was performed according to institutional protocol for the region of interest. Efforts were made to limit the estimated whole-body average specific absorption rate to less than 2.0 W/kg, but 3 patients received slightly higher exposures.
No symptoms consistent with device movement or heating were reported during the MRI examinations. No inappropriate inhibition of pacing was observed during MRI. In patients in whom the magnet mode of their pace-maker could not be programmed off, lead switch activation led to transient asynchronous pacing at the specified magnet rate, but this was well-tolerated. No other unexpected or rapid activation of pacing was observed during MRI. All the devices functioned appropriately after MRI, and no changes in device programming were observed. Image quality was not affected when the pacemaker or ICD was located outside the field of view. When thoracic images were obtained, image distortion was present and extended to a maximum radius of 12 cm from the device generator. After the MRI, 4 patients had their devices removed and an additional 4 patients died of conditions unrelated to their pacemaker or ICD. Of the remaining 47 patients, 29 underwent chronic device interrogation, with a median time to follow-up of 99 days. No chronic abnormalities were observed.
Nazarian et al conclude that with a protocol that includes pretesting of similar devices and strict programming guidelines, cardiac MRI can be safely performed in patients with permanent pacemakers or ICD's.
Commentary
MRI has become an increasingly important imaging modality in many situations. Since strong magnetic fields can affect pacemakers and ICDs, MRI has usually been thought to be contraindicated. In this paper, and in a companion paper in the same journal, MRI was performed safely in patients with implanted rhythm devices, but caution must be exercised before MRI can be routinely recommended.
In this paper, similar model devices had been pretested and shown to be MRI resistant. Sophisticated changes in programming were made prior to the scan and then the devices were reprogrammed afterwards. Special monitoring was maintained during the procedure. Only a single type MRI scanner was used in each study. If these precautions are followed, MRI should be possible in most patients but few MRI suites could follow these procedures for routine cases. I agree with the authors recommendations that implantable device manufacturers continue their efforts to make implanted devices totally MRI tolerant.
Given appropriate precautions, noncardiac and cardiac MRI can potentially be safely performed in patients with selected implantable pacemaker and defibrillator systems.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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