Preclinical evaluation of implantable cardioverter-defibrillator developed for magnetic resonance imaging use

doi:10.1016/j.hrthm.2014.12.012

Heart Rhythm

Volume 12, Issue 3, March 2015, Pages 631-638

https://doi.org/10.1016/j.hrthm.2014.12.012 Get rights and content

Background

Many patients with an implantable cardioverter-defibrillator (ICD) have indications for magnetic resonance imaging (MRI). However, MRI is generally contraindicated in ICD patients because of potential risks from hazardous interactions between the MRI and ICD system.

Objective

The purpose of this study was to use preclinical computer modeling, animal studies, and bench and scanner testing to demonstrate the safety of an ICD system developed for 1.5-T whole-body MRI.

Methods

MRI hazards were assessed and mitigated using multiple approaches: design decisions to increase safety and reliability, modeling and simulation to quantify clinical MRI exposure levels, animal studies to quantify the physiologic effects of MRI exposure, and bench testing to evaluate safety margin.

Results

Modeling estimated the incidence of a chronic change in pacing capture threshold >0.5V and 1.0V to be less than 1 in 160,000 and less than 1 in 1,000,000 cases, respectively. Modeling also estimated the incidence of unintended cardiac stimulation to occur in less than 1 in 1,000,000 cases. Animal studies demonstrated no delay in ventricular fibrillation detection and no reduction in ventricular fibrillation amplitude at clinical MRI exposure levels, even with multiple exposures. Bench and scanner testing demonstrated performance and safety against all other MRI-induced hazards.

Conclusion

A preclinical strategy that includes comprehensive computer modeling, animal studies, and bench and scanner testing predicts that an ICD system developed for the magnetic resonance environment is safe and poses very low risks when exposed to 1.5-T normal operating mode whole-body MRI.

Introduction

In recent years, magnetic resonance imaging (MRI) has become the fastest growing technique in diagnostic imaging,¹ and it is the modality of choice for many clinical indications.² However, MRI is contraindicated in certain populations because of potential adverse interactions with foreign bodies implanted in patients. One such common contraindication is cardiac implantable electronic devices (CIEDs), including both pacemakers and implantable cardioverter-defibrillators (ICDs). The overlapping demographic resulting from expanding clinical indications for both CIEDs and MRI make safe access to MRI an increasingly common concern. It is estimated that up to 75% of CIED patients are expected to develop an indication for MRI over the life of their device.³

This growing interest in MRI compatibility has fostered advancements in design and testing to allow safe access to MRI for patients implanted with select pacemakers under carefully monitored conditions.4, 5 These advancements mitigate the risk of potential adverse interactions between the pacemaker system and MR fields (Table 1). However, MRI is generally contraindicated for ICD patients because of limited safety evidence.⁶ ICD patients present additional MR safety concerns compared to pacemaker patients because ICD patients have a history of ventricular arrhythmias and the devices have additional features for arrhythmia detection and treatment. Given the number of variables that impact the safety of MRI scanning in ICD patients (eg, scanner, scan sequence, patient, patient position, lead), a practical clinical trial that leads to valid meaningful conclusions is not feasible. Thus, quantifying and assessing patient risks to minimize these hazards requires a more comprehensive approach.

To address safety concerns and patient need for MRI, an MR conditionally safe ICD system was developed specifically for the purpose of allowing patient access to whole-body MRI under monitored conditions. Development included extensive preclinical testing to ensure patient safety and creation of a programming mode for operation in the MRI environment. The development and preclinical testing, including computer modeling and simulation, animal studies, as well as bench and scanner testing, are presented in this study.

Section snippets

Methods

Preclinical mitigation of MRI hazards included both design decisions during development and experiments during evaluation of the Evera MRI SureScan ICD system (Medtronic Inc, Minneapolis, MN) for whole-body MR scanning at 1.5 T under normal operating mode conditions (maximum whole-body specific absorption rate value of 2 W/kg) and maximum gradient slew rate of 200 T/m/s per axis. The Evera MRI SureScan ICD system is composed of an Evera MRI dual-chamber (DR) or single-chamber (VR) SureScan ICD,

Pacing capture threshold

Clinically relevant dissipated power levels for normal operating mode (2 W/kg whole-body specific absorption rate) at the lead tip electrode–tissue interface of defibrillation leads were predicted by simulation to be <130 mW. The effect of dissipated power on PCT is shown in Figure 2. During canine studies, correlation was observed between change in PCT (ΔPCT) and dissipated power at the lead tip–tissue interface, and ΔPCT increased gradually with increasing power. Variation in PCT response at

Discussion

In contrast to pacemakers, there is much less published experience on the use of ICDs in the MRI environment. The current case report literature on off-label use of non-MR conditional ICDs describes a variety of clinical outcomes ranging from loss of ICD functionality to successful MR scans with no adverse events.16, 17, 18, 19 More recently, published single-center experiences with ICDs have noted issues such as unexpected depletion of battery voltage and electrical resets,20, 21 with an

Conclusion

This study used a preclinical strategy consisting of comprehensive computer modeling, animal studies, and bench and clinical scanner testing to demonstrate an ICD system designed for the MR environment is safe with very low risks when exposed to 1.5-T normal operating mode whole-body imaging. The MRI considerations presented in this study should form the minimum requirements necessary for proving safety of MR-conditionally safe ICD systems, and the results will be confirmed by a human clinical

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Cited by (16)

Utilization and programming of an automatic MRI recognition feature for cardiac rhythm management devices
2021, Heart Rhythm O2
Cardiac implantable electronic devices (CIED)—ie, pacemakers, implantable cardioverter-defibrillators, and cardiac resynchronization therapy devices—have recently been designed to allow for patients to safely undergo magnetic resonance imaging (MRI) when specific programming is implemented. MRI AutoDetect is a feature that automatically switches CIED’s programming into and out of an MR safe mode when exposed to an MRI environment.
The purpose was to analyze de-identified daily remote transmission data to characterize the utilization of the MRI AutoDetect feature.
Home Monitoring transmission data collected from MRI AutoDetect–capable devices were retrospectively analyzed to determine the workflow and usage in patients experiencing an MRI using the MRI AutoDetect feature.
Among 48,756 capable systems, 2197 devices underwent an MRI using the MRI AutoDetect feature. In these 2197 devices, the MRI AutoDetect feature was used a total of 2806 times with an average MRI exposure of 40.83 minutes. The majority (88.9%) of MRI exposures occurred on the same day as the MRI AutoDetect programming. A same day post-MRI exposure follow-up device interrogation was performed 8.6% of the time. A device-related complaint occurred within 30 days of the MRI exposure in 0.25% of MRI exposures using MRI AutoDetect but with no adverse clinical outcome.
As a result of automation in device programming, the MRI AutoDetect feature eliminated post-MRI device reprogramming in 91.4% of MRI exposures and, while less frequent, allowed for pre-MRI interrogations prior to the day of the MRI exposure—reducing resource utilization and creating workflow flexibility.
Safety of thoracic magnetic resonance imaging for patients with pacemakers and defibrillators
2019, Heart Rhythm
Citation Excerpt :
More importantly, focused radiofrequency fields may generate heat at the tip of leads implanted in myocardium, resulting in tissue damage and potential increases in capture thresholds. Research experience with animal, phantom, and computer models for these device setting values is the mainstay of the recommendation to avoid routine thoracic MRI in patients with nonconditional CIEDs.9–13 A recent registry review of MRI for patients with nonconditional CIEDs excluded thoracic MRIs.14
During magnetic resonance imaging (MRI), cardiac implantable electronic device (CIED) leads can be antennae to focus energy onto myocardium, leading to heating and arrhythmias. Clinical data on thoracic MRI safety for patients with legacy devices are limited.
The purpose of this study was to identify patients undergoing thoracic MRI with legacy devices, compare the incidence of adverse events of those patients with control patients undergoing brain MRI with legacy devices, and compare paired cardiac troponin T (cTnT) values.
In this single-center study, we reviewed a prospectively collected database of patients with CIED undergoing MRI from January 25, 2008, through February 28, 2017.
Of 952 patients (1290 scans), 120 patients (12.6%) underwent 134 thoracic MRI scans with legacy CIEDs (median [range] age 61.98 [21.24–86.96] years; male 71.1%). Median (range; interquartile range [IQR]) age of leads across devices was 3.5 (1.6–7.1; 5.5) years; implantable cardioverter-defibrillators (ICDs) were oldest (median [range; IQR], 3.7 [1.1–8.0; 6.9] years). No difference was observed in incidence of adverse events between groups. Paired cTnT values were compared for 19 patients (19 scans) with no difference between pre- and postimaging values. No significant difference was present in device setting values before and after MRI (mean follow-up 72.5 days). Incidence of adverse events was no different after adjustment for ICD coil number.
Thoracic MRI is relatively safe in an institutional multidisciplinary program. It does not represent greater risk than brain MRI for patients with legacy CIEDs.
2017 HRS expert consensus statement on magnetic resonance imaging and radiation exposure in patients with cardiovascular implantable electronic devices
2017, Heart Rhythm
Citation Excerpt :
There are significant practical and logistical limitations to the conduct of human trials because they cannot address the millions of potential variables present during MR scanning of a patient with a CIED. Computer modeling is valuable and is an accurate method of assessing millions of combinations in variables affecting PM and ICD lead heating and the probability of PCT change.29,30 Lead electrode heating can be affected by many factors, including patient size, patient position within the scanner, scan sequence, lead route, and lead design.29,34
The Safety of Cardiac and Thoracic Magnetic Resonance Imaging in Patients with Cardiac Implantable Electronic Devices
2016, Academic Radiology
Studies reporting the safety of magnetic resonance imaging (MRI) in patients with a cardiac implantable electronic device (CIED) have mostly excluded examinations with the device in the magnet isocenter. The purpose of this study was to describe the safety of cardiac and thoracic spine MRI in patients with a CIED.
The medical records of patients with a CIED who underwent a cardiac or thoracic spine MRI between January 2011 and December 2014 were reviewed. Devices were interrogated before and after imaging with reprogramming to asynchronous pacing in pacemaker-dependent patients. The clinical interpretability of the MRI and peak and average specific absorption rates (SARs, W/kg) achieved were determined.
Fifty-eight patients underwent 51 cardiac and 11 thoracic spine MRI exams. Twenty-nine patients had a pacemaker and 29 had an implantable cardioverter defibrillator. Seventeen percent (n = 10) were pacemaker dependent. Fifty-one patients (89%) had non-MRI-conditional devices. There were no clinically significant changes in atrial and ventricular sensing, impedance, and threshold measurements. There were no episodes of device mode changes, arrhythmias, therapies delivered, electrical reset, or battery depletion. One study was prematurely discontinued due to a patient complaint of chest pain of which the etiology was not determined. Across all examinations, the average peak SAR was 2.0 ± 0.85 W/kg with an average SAR of 0.35 ± 0.37 W/kg. Artifact significantly limiting the clinical interpretation of the study was present in 33% of cardiac MRI studies.
When a comprehensive CIED magnetic resonance safety protocol is followed, the risk of performing 1.5-T magnetic resonance studies with the device in the magnet isocenter, including in patients who are pacemaker dependent, is low.
Impact of magnetic resonance imaging on ventricular tachyarrhythmia sensing: Results of the Evera MRI Study
2016, Heart Rhythm
Citation Excerpt :
The right ventricular lead was positioned in the apex in a majority of patients (72%). The MR-ICD has specific design and material modifications to reduce interaction with the MRI environment, as described previously.11 Briefly, the ferromagnetic material was reduced, a Hall effect sensor replaced the mechanical reed switch, battery circuitry protection was added, and filters to prevent gradient and radiofrequency energy coupling were added.
Studies have shown that magnetic resonance imaging (MRI) conditional pacemakers experience no significant effect from MRI on device function, sensing, or pacing. More recently, similar safety outcomes were demonstrated with MRI conditional defibrillators (implantable cardioverter-defibrillator [ICD]), but the impact on ventricular arrhythmias has not been assessed.
The purpose of this study was to assess the effect of MRI on ICD sensing and treatment of ventricular tachyarrhythmias.
The Evera MRI Study was a worldwide trial of 156 patients implanted with an ICD designed to be MRI conditional. Device-detected spontaneous and induced ventricular tachycardia/ventricular fibrillation (VT/VF) episodes occurring before and after whole body MRI were evaluated by a blinded episode review committee. Detection delay was computed as the sum of RR intervals of undersensed beats. A ≥5-second delay in detection due to undersensing was prospectively defined as clinically significant.
Post-MRI, there were 22 polymorphic VT/VF episodes in 21 patients, with 16 of these patients having 17 VT/VF episodes pre-MRI. Therapy was successful for all episodes, with no failures to treat or terminate arrhythmias. The mean detection delay due to undersensing pre- and post-MRI was 0.60 ± 0.59 and 0.33 ± 0.63 seconds, respectively (P = .17). The maximum detection delay was 2.19 seconds pre-MRI and 2.87 seconds post-MRI. Of the 17 pre-MRI episodes, 14 (82%) had some detection delay as compared with 11 of 22 (50%) post-MRI episodes (P = .03); no detection delay was clinically significant.
Detection and treatment of VT/VF was excellent, with no detection delays or significant impact of MRI observed.
Clinical safety of the Iforia implantable cardioverter-defibrillator system in patients subjected to thoracic spine and cardiac 1.5-T magnetic resonance imaging scanning conditions
2015, Heart Rhythm
Citation Excerpt :
This study is unique for using remote monitoring to assess device function post-MRI, which is FDA approved for daily monitoring of ICD system performance. Unlike pacemakers, there are far fewer data on the safety of ICDs in MRI environment.10,11,13 Moreover, studies of off-label scans typically are mixed with pacemaker data, have a relatively small number of subjects with ICDs, and are limited to certain ICD models and MRI scanners.
Implantable cardioverter-defibrillators (ICDs) are generally considered a contraindication to magnetic resonance imaging (MRI).
The purpose of the ProMRI Phase C study, a multicenter, prospective, single-arm, nonrandomized study, was to evaluate the clinical safety of the Biotronik ProMRI Iforia ICD system during MRI.
Patients were enrolled after ICD implantation, with either a dual-chamber DR-T or single-lead VR-T DX system. Study-defined, nondiagnostic cardiac or thoracic spine MRI was performed at least 1 week after enrollment. ICDs were placed into MRI mode with ventricular fibrillation (VF) detection/therapy programmed “off” before scan and restored to non-MRI mode after scan. Interrogation was performed before, immediately after, and 1 month post-MRI. The primary end-points were (1) ventricular pacing threshold increase >0.5 V from pre-MRI to 1 month post-MRI; (2) R-wave amplitude decrease >50% from pre-MRI to 1 month post-MRI or R-wave amplitude <5 mV at 1 month post-MRI; and (3) MRI and ICD system-related serious adverse device effects.
One hundred seventy patients were enrolled at 39 US centers. One hundred fifty-three patients underwent MRI (25.7% cardiac, 74.3% thoracic spine) and completed follow-up. Freedom from the primary end-points was met in all but 1 subject, in whom reduced R-wave amplitude was detected 1 month post-MRI. No serious adverse device effects occurred during the course of the study.
These results demonstrate the clinical safety and efficacy of the ProMRI ICD system in patients subjected to thoracic spine and cardiac MRI imaging in 1.5-T scanners.

View all citing articles on Scopus

: This study was funded by Medtronic, Inc. Dr. Gold is a consultant to, and receives clinical trials funds from, Medtronic, Boston Scientific, and St. Jude Medical. Dr. Kanal is a consultant to Medtronic, Boston Scientific, and St. Jude Medical. Drs. Schwitter and Sommer are consultants to Medtronic. T. Bratten, Dr. Yoon, Dr. Ellingson, and L. Landborg are employees of Medtronic, Inc.

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Preclinical evaluation of implantable cardioverter-defibrillator developed for magnetic resonance imaging use

Background

Objective

Methods

Results

Conclusion

Introduction

Section snippets

Methods

Pacing capture threshold

Discussion

Conclusion

Heart Rhythm

Heart Rhythm

Am J Cardiol

Current clinical issues for MRI scanning of pacemaker and defibrillator patients

Pacing Clin Electrophysiol

Randomized trial of pacemaker and lead system for safe scanning at 1.5 Tesla

Heart Rhythm

ACR guidance document on safe MR practices

J Magn Reson Imaging

Pacemaker reed switch behavior in 0.5, 1.5, and 3.0 Tesla magnetic resonance imaging units: are reed switches always closed in strong magnetic fields?

Pacing Clin Electrophysioj

Swine as models in biomedical research and toxicology testing

Vet Pathol