Preclinical evaluation of implantable cardioverter-defibrillator developed for magnetic resonance imaging use
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
References (22)
- et al.
Magnetic resonance imaging in patients with a pacemaker system designed for the magnetic resonance environment
Heart Rhythm
(2011) - et al.
Safe magnetic resonance imaging scanning of patients with cardiac rhythm devices: a role for computer modeling
Heart Rhythm
(2013) - et al.
1.5 Tesla for patients with pacemakers and implantable cardiac defibrillators
Am J Cardiol
(2012) - 2012 MR Benchmark Report. IMV Medical Information Division,...
- Kaiser CP. Soaring MRI use draws scrutiny. Diagnostic Imaging Online January 4, 2002. Available at:...
- et al.
Current clinical issues for MRI scanning of pacemaker and defibrillator patients
Pacing Clin Electrophysiol
(2005) - et al.
Randomized trial of pacemaker and lead system for safe scanning at 1.5 Tesla
Heart Rhythm
(2013) - et al.
ACR guidance document on safe MR practices
J Magn Reson Imaging
(2013) - et al.
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
(2002) - Assessment of the safety of magnetic resonance imaging for patients with an active implantable medical device....
Swine as models in biomedical research and toxicology testing
Vet Pathol
Cited by (16)
Safety of thoracic magnetic resonance imaging for patients with pacemakers and defibrillators
2019, Heart RhythmCitation 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
2017 HRS expert consensus statement on magnetic resonance imaging and radiation exposure in patients with cardiovascular implantable electronic devices
2017, Heart RhythmCitation 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
Impact of magnetic resonance imaging on ventricular tachyarrhythmia sensing: Results of the Evera MRI Study
2016, Heart RhythmCitation 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.
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 RhythmCitation 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.
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.