Elsevier

Heart Rhythm

Volume 12, Issue 3, March 2015, Pages 540-544
Heart Rhythm

“Power-on resets” in cardiac implantable electronic devices during magnetic resonance imaging

https://doi.org/10.1016/j.hrthm.2014.10.039Get rights and content

Background

Magnetic resonance imaging (MRI) has been safely performed in some patients with cardiac implantable electronic devices (CIEDs) under careful monitoring and prespecified conditions. Pacemaker-dependent patients are often excluded, partly because of the potential for “power-on reset” (PoR), which can lead to a change from asynchronous to inhibited pacing with consequent inhibition of pacing due to electromagnetic interference during MRI.

Objective

The purpose of this study was to review risk factors for PoR during MRI.

Methods

A prospective study was performed between January 2008 and May 2013 in patients with CIEDs undergoing clinically indicated MRI. Eligible patients were not pacemaker dependent. Devices were interrogated before and after MRI, programmed to an asynchronous mode or an inhibition mode with tachyarrhythmia therapies turned off, and reprogrammed to their original settings after MRI.

Results

MRI scans (n = 256) were performed in 198 patients with non–MRI-conditional CIEDs between 2008 and 2013 (median age 66 years; interquartile range 57–77 years; 59% men). PoR occurred during 9 MRI scans (3.5%) in 8 patients. PoR was more frequent with Medtronic devices than with other generator brands (n = 9/139 vs 0/117 [6% vs 0%]; P = .005). Devices with PoR were all released before 2002 and were implanted from 1999 to 2004. Effects of PoR included a decrease in heart rate during MRI (n = 4) and transient anomalous battery life indication (n = 1). All devices functioned normally after MRI.

Conclusion

PoR occurs infrequently but can cause deleterious changes in pacing mode and heart rate. MRI should not be performed in pacemaker-dependent patients with older at-risk generators. Continuous monitoring during MRI is essential because unrecognized PoR may inhibit pacing or accelerate battery depletion due to high pacing output.

Introduction

Magnetic resonance imaging (MRI) is the imaging modality of choice for many disorders of the brain, spine, and musculoskeletal system. With an aging population and increased use of cardiac implantable electronic devices (CIEDs), it is increasingly likely that patients with CIEDs will need an MRI during their life span.1 MRI in patients with CIEDs, however, is “discouraged” or “should not be performed.”2 It should only be considered in situations when there is a clear clinical indication and the benefits outweigh the risks.3

In the past few years, several studies have demonstrated the safety of MRI in select patients with non–MRI-conditional CIEDs under close clinical supervision.4, 5, 6, 7, 8 Patients who are pacemaker dependent have been excluded from many protocols, partly because of the potential for power-on reset (PoR). A PoR may cause the CIED to revert to its factory default settings. Instead of programmed asynchronous pacing used during MRI in a pacemaker-dependent patient, the device may be reset to an inhibited mode. Electromagnetic interference (EMI) during MRI could cause inappropriate inhibition of pacing, resulting in asystole.9, 10, 11 Because MRI may at times be required in pacemaker-dependent patients, a better understanding of the risk factors for PoR is needed. Accordingly, our aim was to review our experience performing MRI in patients with CIEDs to determine the incidence of and risk factors for PoR.

Section snippets

Methods

A prospective study was performed at Mayo Clinic, Rochester, MN, between January 2008 and May 2013 in patients with non–MRI-conditional CIEDs undergoing clinically indicated MRI with the approval of the institutional review board. In consultation with the referring physician, the radiologist decided whether alternative imaging modalities could provide similar information at less risk to the patient. If it was determined that MRI was the preferred imaging modality, the referring clinician

Results

MRI scans (N = 279) were performed in 219 patients with CIEDs. Twenty-three scans in 21 patients were excluded because patients had MRI-conditional devices. This yielded 256 MRI scans performed in 198 patients. The median age was 66 years (IQR 55–77 years), and 59.4% of patients were men (Table 1). Overall, devices were implanted a median of 30.2 months (IQR 12.8–53.6 months) before MRI. A majority of CIEDs (54.3%) were manufactured by Medtronic (Minneapolis, MN), with Boston Scientific

Discussion

PoR is a safety feature meant to ensure minimal pacemaker functionality in situations in which the generator may not function properly. The typical factory default mode is VVI (inhibited pacing mode) in pacemakers and activated tachyarrhythmia therapies in ICDs.9, 10 PoR can occur when a CIED is exposed to strong electromagnetic fields during MRI. Patients who are pacemaker dependent or who have a slow intrinsic rate are at particular danger of complications from PoR, which could result in

Conclusion

PoR occurs infrequently but can cause deleterious changes in CIED function. MRI should not be performed in pacemaker-dependent patients with older at-risk generators (market release 2002 or before). Continuous monitoring during MRI is essential, as unrecognized PoR may inhibit pacing or accelerate battery depletion due to high pacing output.

In this article, we demonstrated that certain older cardiac pacemakers are more susceptible to “power-on reset” (PoR) when exposed to magnetic resonance

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    This work was funded entirely by Mayo Clinic.

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