REVIEW URRENT C OPINION
MRI and implantable cardiac electronic devices Werner Jung, Sebastian Ja¨ckle, and Vlada Zvereva
Purpose of review To assess the current knowledge about the potential hazard from MRI in patients with devices such as pacemakers and implantable cardioverter defibrillators (ICDs). Recent findings Most data concern ‘MRI unsafe’ devices, with only a few studies on ‘MRI conditional’ devices. No ‘MRI safe’ cardiac devices are currently available. Studies on ‘MRI unsafe’ devices tend to be small scale and reflect the experience of individual centres; few provide long-term follow-up data. Many newer devices are approved as ‘MRI conditional’ based on technical simulations or postmarket surveillance studies. With adequate measures taken before performing an MRI scan, reported complication rates are generally low, but there is a nonnegligible residual risk for power-on reset and lead heating. The presence of abandoned, older leads may affect the propensity for lead heating during MRI with newer devices, including those designated ‘MRI conditional’. Very little research has been carried out on the hazard from MRI scans in patients with ICDs, but registry data indicate more events with ICDs than with pacemakers. Summary The limited available data indicate a manageable but not negligible MRI-associated hazard in patients with implantable cardiac devices. Further controlled studies and large, independent registries, particularly in Europe, are needed to provide important safety information. Keywords 3-T MRI, implantable cardiac defibrillators, pacemakers, retained leads, risk–benefit assessment
INTRODUCTION MRI and implantable cardiac electronic devices are two of the most important medical technologies today. They are often necessary with the same patients: an estimate in 2005 predicted that up to 75% of recipients of pacemakers and implantable cardioverter defibrillators (ICDs) will develop an indication for MRI examination over time [1,2]. A recent study indicated that physicians may request MRI procedures for 17% of their patients within 12 months of implant [3]. With new technologies such as magnetic resonance (MR) angiography emerging, these numbers may underestimate future use of MRI in cardiac patients. Thus, any potential hazard from MRI in patients with implantable devices needs to be taken seriously. Current classifications for implantable cardiac devices are ‘MR safe’, ‘MR conditional’, and ‘MR unsafe’ [4]. Most devices still belong in the ‘MR unsafe’ category. A small number of pacemakers, and still fewer ICD devices, are labelled as ‘MR conditional’. Fully ‘MRI safe’ devices remain to be developed. Major potential interactions between MRI and implantable cardiac devices are summarized in
Table 1. Not all risks may warrant the same concern; for example, modern devices contain even smaller amounts of ferromagnetic materials (none at all in lead tips) and are highly unlikely to move during an MRI scan. No risk should be dismissed without support from clinical data, however. Among other hazards are lead tip heating, which may result in loss of pacing capture or myocardial perforation [5–7], changes to programming, electrical reset or changes to pacing capture threshold (PCT). For ICDs, there is an additional risk that the rapidly changing magnetic gradients during MRI may trigger the delivery of inappropriate therapies [7]. Somewhat paradoxically, MRI-induced saturation of the charging
Department of Cardiology, Academic Teaching Hospital of the University of Freiburg, Schwarzwald-Baar Klinikum, Villingen-Schwenningen, Germany Correspondence to Werner Jung, MD, FHRS, FESC, Department of Cardiology, Academic Teaching Hospital of the University of Freiburg, Schwarzwald-Baar Klinikum, Klinikstrasse 11 D-78052 VillingenSchwenningen, Germany. Tel: +49 7721 933001; fax: +49 7721 9393099; e-mail: [email protected] Curr Opin Cardiol 2015, 30:65–73 DOI:10.1097/HCO.0000000000000132
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KEY POINTS Most data on the hazard from MRI in patients with implantable ‘MRI unsafe’ cardiac devices are from small, single-centre studies and few provide long-term follow-up data. With adequate measures taken before performing an MRI scan, reported complication rates are generally low, but there is a nonnegligible residual risk for power-on reset and lead heating. Very little research has been carried out in patients with ICDs, and registry data indicate there may be a greater risk than with pacemakers. There remains a need for MRI-conditional ICD devices as well as for devices designed to minimize the risk from 3-T scanning. Many newer devices are approved based on technical simulations or postmarket surveillance studies. Large, independent registries, particularly in Europe, would provide important safety information.
system may mitigate this risk by reducing the charge of the capacitor.
‘MAGNETIC RESONANCE UNSAFE’ DEVICES Patients with implantable devices occasionally underwent MRI scans before MRI-conditional pacemakers were available. Readers are referred to more extensive expositions in earlier reviews by, for instance, the present author [8,9 ] or other recent publications [10,11 ]. There is a continuum of risk and it is possible to reduce the risk from the MRI procedure through close monitoring, reprogramming of devices before scanning, and attempting to limit specific absorption rate (SAR) levels [12,13]. European Society of Cardiology (ESC) guidelines [14] give MRI scans in patients with MR-unsafe devices a low class of recommendation (IIb1; level of evidence B2). The guidelines include a number of measures to be taken before performing an MRI scan on patients with implantable cardiac devices (Fig. 1 [14]). Studies on MRI in patients with cardiac devices are summarized in Table 2 [5,13,15–31,32 ,33–36]. Most studies on MRI with ‘unsafe’ devices are small scale and reflect the experience of individual centres. Few provide long-term follow-up data. Although there are consistently low rates of &
&&
&&
1
Usefulness is less well established by evidence/opinion. Data derived from a single randomized clinical trial or large nonrandomized studies. 2
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complications, there appears to be a nonnegligible risk for clinically significant power-on resets. Increases in cardiac troponin levels, indicative of lead heating, also need to be taken seriously. Other events noted in a number of studies are changes in PCT, sensing threshold and lead impedance. Results from trials with earlier generations of cardiac devices may not be applicable to later products, which are typically smaller, with less magnetic material and improved electromagnetic interference protection. Nevertheless, guidelines stress that no device, unless appropriately tested and labelled, should be regarded as safe for MRI simply because it is ‘modern’ or recently manufactured [37]. Guidelines’ authors also express concern that there may be underreporting of adverse events, including deaths, in the available studies from MRI scans on device patients [37]. The most recent publication includes data from 12 months’ follow-up of 356 patients with single-chamber or dual-chamber pacemakers and urgent indication for a cranial MRI [30]. The investigators note that PCT, sensing threshold and lead impedance all remained more or less unchanged over the follow-up period. There are very few MRI-conditional ICDs available at the time of writing and all published work on MRI scans in patients with ICDs has been performed with ‘unsafe’ devices to date. Only a small number of procedures have been reported in the literature (Table 2). Most concerns mirror those with pacemakers: sensing errors and lead impedance changes. Decreased battery voltage was noted in two studies [23,29] and one study included an instance of power-on reset [27]. However, with a total of only 300 patients included in published studies, the database seems too small to draw reliable conclusions on the safety of MRI scanning in patients with ICDs. To provide prospective data from a multicentre environment, the MagnaSafe Registry (clinicaltrials. gov identification NCT00907361) was set up in 2009. The objective of the registry is to determine prospectively the adverse event rate and device parameter changes in patients with non-MRI-conditional cardiac devices (pacemakers or ICDs) implanted after 2001, undergoing clinically indicated nonthoracic MRI at 1.5 T. Devices are interrogated pre-MRI and post-MRI [38]. Target enrolment is 1500 patients. Analyses from the registry have so far only been presented in abstract form at scientific conferences. An analysis in 2012 of repeat MRI scans (two scans in 32 patients, three scans in six, four scans in three and six scans in one patient) found no association between the number of MRI scans and the rate of clinical events or device parameter changes [39]. A more recent abstract, from 2013, reported the results Volume 30 Number 1 January 2015
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MRI and implantable cardiac electronic devices Jung et al. Table 1. Potential effects of MRI fields on implantable cardiac devices Static field
ECG changes Mechanical force and torque on devices Reed switch closure ICD: Saturation of storage capacitor and loss of battery life
Radiofrequency field
Heating at the lead tip and at the lead–tissue interface Alteration of programming and potential damage to the pacemaker circuitry Electrical reset Rapid atrial pacing Pacing at multiples of the radiofrequency pulse and associated rapid ventricular pacing Asynchronous pacing Inhibition of pacing output
Time-varying magnetic gradient field
Induction of ventricular fibrillation Reed switch closure Heating at the lead tip and at the lead–tissue interface ICD: antitachycardia pacing or inappropriate shock therapy
ICD, implantable cardioverter defibrillator.
from 829 nonthoracic MRI studies in 617 pacemakers and 212 ICDs. Overall, more events were recorded with ICDs than with pacemakers. A decrease in battery voltage of at least 0.04 V occurred in 1% of pacemakers and 9% of ICDs. One or more clinically relevant device parameter changes occurred in 13% of pacemakers and 28% of ICD cases [40]. A second registry, NCT01999751, is a singlecentre, prospective, nonrandomized, unblinded case series of patients (500 planned) with permanent pacemakers or ICDs undergoing medically required MRI scanning, followed for a 12-month period. The registry has not yet published any findings and is scheduled to complete in 2017. These registries include only patients from the United States. As discussed below, most manufacturers gather postmarketing safety information on devices, but to the authors’ knowledge no public multinational European registry has been set up to follow MRI scans in patients with implantable cardiac devices.
‘MAGNETIC RESONANCE CONDITIONAL’ DEVICES Scans in patients with MR-conditional devices are currently recommended at an intermediate class of recommendation (IIa3; level of evidence B) [14]. All major device companies manufacture MRI-conditional pacemakers. The devices are approved for use in MRI scanners with a field strength of up to 1.5 T with appropriate safety measures taken. Available devices at the time of 3
Weight of evidence/opinion is in favour of usefulness.
writing are listed in Table 3. The list appears impressive, but there is a caveat: not all systems in the table have been fully tested under clinical conditions. The regulatory requirements have softened since the first MRI-conditional devices were approved, based on data from randomized studies. Authorities today may accept data from technical simulations and postmarket surveillance studies as proxies for MRI conditionality. This change, as well as increasing backwards compatibility with earlier devices or leads, has simplified and speeded up the approval process and reduced costs. The downside is a lack of data on many MRI-conditional devices in controlled clinical conditions and a corresponding need for independently managed studies and registries. To reduce the risk of influence from MRI scans, MRI-conditional devices introduce a number of design changes. Nonferromagnetic material is used as much as possible. The reed switches of conventional pacemakers (designed to avoid the effects of electromagnetic interactions by reverting to DOO or VOO pacing modes in the presence of a magnet) are replaced by solid-state Hall sensors, which have more predictable behaviour. The pacemaker leads are insulated and the winding pattern of the filaments in the inner lead coil is changed to minimize the interaction with radiofrequency fields. In addition, specific MRI programming modes have been developed to be used only during the procedure. The modes include system-integrity checks to prevent activation of the MRI mode unless the system is working flawlessly, increased pacing output during MRI scanning, and restoration of prescan programme states and values when the MRI mode is deactivated.
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Implanted PM/ICD
Conventional PM/ICD
MRI-compatible PM/ICD
Exclude patients with: • leads implanted 100% increase in ventricular PCT was measured, but this was maintained till the end of 15-month follow-up in only two patients.
Single-centre prospective
24
No abnormalities during 1.5-T MRI or 99 days’ follow-up.
MRI with MRI-conditional pacemakers Wilkoff et al. 2011 [31]
&&
MRI with ICD devices Nazarian et al. 2006 [19]
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Arrhythmias Table 2 (Continued) No. of patients
Publication
Design
Main findings
Mollerus et al. 2008 [21]
Single-centre prospective
5
Naehle et al. 2009 [23]
Single-centre prospective
18
Mollerus et al. 2009 [24]
Single-centre prospective
6
A small number of instances of increased ectopy during scans were observed.
Mollerus et al. 2010 [13]
Single-centre prospective
22
MRI at 1.5 T was associated with decreased sensing amplitudes and pace impedances.
Buendı´a et al. 2010 [25]
Single-centre prospective
5
Burke et al. 2010 [26]
Single-centre prospective
14
No abnormalities associated with 1.5-T MRI.
Halshtok et al. 2010 [35]
Single-centre prospective
9
No abnormalities associated with 1.5-T MRI.
Junttila et al. 2011 [36]
Single-centre prospective
10
Nazarian et al. 2011 [27]
Multicentre prospective
Cohen et al. 2012 [29]
Single-centre retrospective
MRI at 1.5 T was not associated with changes in troponin-I levels or PCTs. Battery voltage decreased significantly from pre to post-MRI. In two MRI examinations, oversensing of radiofrequency noise as ventricular fibrillation occurred but no attempt at therapy delivery was made.
Sensing errors during imaging in one case were noted.
No complications occurred during three serial cardiac MR scans prospectively performed at 1.5 T. During follow-up there were no occurrences of ICD dysfunction. Most patients had image artefacts but the studies were generally diagnostic regarding left ventricular function and wall motion. ICD artefacts often affected the imaging of anterior wall infarcts.
201
One power-on-reset event associated with 1.5-T MRI. Minor changes in lead parameters.
40
0.04 V decreases in battery voltage in 4%; pacing threshold increases 0.5 V in 3%; pacing lead impedance changes of 50 V in 6%. Minor, not clinically important differences in pacing lead impedance and left ventricular pacing threshold.
ICD, implantable cardioverter defibrillator; PCT, pacing capture threshold; SAR, specific absorption rate.
rises from 26 to 748C in guide wire tips within 30 s of scanning [43]. The degree of heating depends on the amplitude and phase of the electric field along the lead, as well as the lead length [44]. Animal studies demonstrated increases of up to 20.48C at 1.5 T and SAR 3.8 W/kg [7]. However, such data may not extrapolate to clinical conditions or, indeed, to newer pacemaker leads. Adequate selection of imaging landmarks and patient positioning can reduce the risk for MRI-related heating: Nordbeck et al. [45] found the greatest radio frequency-induced coupling with the torso centred along the superior– inferior direction of the transmit coil. Strach et al. [3] in 2010 included patients with abandoned leads in their study on the safety of 0.2-T MRI scanning in a varied cohort of pacemaker patients, with no reported adverse occurrences. Current ESC guidelines [14] recommend exclusion of patients with abandoned leads from MRI scanning. MRI-conditional devices are indicated for use only with their specific MRI-conditional leads and not in patients in whom abandoned leads are present. The ACR stresses that a retained MR-conditional lead should be considered as MR unsafe and the risk– benefit profile assessed correspondingly [37]. Two recent publications [46,47 ] have addressed the question of abandoned leads: the former in a situation that closely simulated clinical reality, &&
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and the latter in a single-centre retrospective analysis. Mattei et al. [46] used a human trunk simulator to host an MRI-conditional pacemaker implant (programmed in MRI mode) with or without an additional ‘abandoned’ lead placed beside the implant. Lead tip temperature was measured in the presence or absence of four different ‘abandoned’ leads: three conventional, commercially available leads and one from an MRI-conditional pacemaker system. The results showed a clear potential for interaction between leads, with temperature increases more than 308 C. The abandoned leads most susceptible to heating also had the greatest influence on the heating of the pacemaker lead. The investigators identified a number of factors that influence the interaction between the abandoned and newly implanted leads. The location and path of the abandoned lead and its position relative to the implant clearly matter: ipsilateral configurations of the two leads were associated with lower temperature increases than contralateral configurations. Capped lead tips were associated with a greater degree of heating than saline-exposed tips. Moreover, the structural characteristics of a lead (length, fixation modality, resistance, etc.) influenced the propensity for heating. In most clinical situations, the newly implanted lead will run more or less parallel to the abandoned Volume 30 Number 1 January 2015
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MRI and implantable cardiac electronic devices Jung et al. Table 3. Conditional MRI pacemakers and implantable cardioverter defibrillators available at the time of writing SAR (whole body)
Name
Medtronic, Minneapolis, MN, USA
EnRhythm/Revo MRI
Pacemaker
1.5 T
Full body
2 W/kg
2008
Ensura MRI
Pacemaker
1.5 T
Full body
2 W/kg
2011
Advisa MRI
Pacemaker
1.5 T
Full body
2 W/kg
2011
St Jude Medical, St Paul, MN, USA
Accent MRI
Pacemaker
1.5 T
Full body
4 W/kg
2011
Boston Scientific, Marlborough, MA, USA
Device type
Magnet strength
Manufacturer
Scan zone
Introduced
Assurity MRI
Pacemaker
1.5 T
Full body
4 W/kg
2014
Endurity MRI
Pacemaker
1.5 T
Full body
4 W/kg
2014
Endurity
Pacemaker
1.5 T
Scan restrictions
2 W/kg
2014
Endurity Core
Pacemaker
1.5 T
Scan restrictions
2 W/kg
2014
Fortify Assura
ICD
1.5 T
Full body
2 W/kg
2015
Ellipse
ICD
1.5 T
Full body
2 W/kg
2015
Quadra Assura
CRT-D
1.5 T
Full body
2 W/kg
2015
Quadra Assura MP
CRT-D
1.5 T
Full body
2 W/kg
2015
ImageReady MR Conditional Pacing Systems
Pacemaker
1.5 T
Full body
2 W/kg
2011
ACCOLADE
Pacemaker
3.0 T
Full body
2 W/kg
2014
Sorin, Milan, Italy
KORA 100
Pacemaker
1.5 T
Scan restrictions
2 W/kg
2013
Biotronik, Berlin, Germany
Evia
Pacemaker
1.5 T
Full body
2.0 W/kg
2009
Entovis
Pacemaker
1.5 T
Full body
2.0 W/kg
2009
Eluna
Pacemaker
1.5 T
Full body
2.0 W/kg
2014
Epyra
Pacemaker
1.5 T
Full body
2.0 W/kg
2014
Etrinsa
Pacemaker
1.5 T
Full body
2.0 W/kg
2014
Estella
Pacemaker
1.5 T
Full body
2.0 W/kg
2010
Ecuro
Pacemaker
1.5 T
Full body
2.0 W/kg
2010
Evia
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2009
Entovis
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2009
Eluna
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2014
Epyra
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2014
Etrinsa
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2014
Lumax
ICD
1.5 T
Scan restrictions
2.0 W/kg
2012
Ilesto
ICD
1.5 T
Full body
2.0 W/kg
2013
Iforia
ICD
1.5 T
Full body
2.0 W/kg
2013
Idova
ICD
1.5 T
Scan restrictions
2.0 W/kg
2013
Inventra
ICD
1.5 T
Full body
2.0 W/kg
2014
Iperia
ICD
1.5 T
Full body
2.0 W/kg
2014
Itrevia
ICD
1.5 T
Full body
2.0 W/kg
2014
Ilesto
ICD
3.0 T
Scan restrictions
2.0 W/kg
2013
Iforia
ICD
3.0 T
Scan restrictions
2.0 W/kg
2013
Inventra
ICD
3.0 T
Scan restrictions
2.0 W/kg
2014
Iperia
ICD
3.0 T
Scan restrictions
2.0 W/kg
2014
Itrevia
ICD
3.0 T
Scan restrictions
2.0 W/kg
2014
Lumax
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2012
Idova
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2013
Ilesto
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2013
Iforia
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2013
Inventra
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2014
Iperia
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2014
Itrevia
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2014
Note that after 2012–2013 not all systems in the table have been fully tested under clinical conditions, as elaborated in the text. CRT-D, cardiac resynchronization therapy-defibrillator; CRT-P, cardiac reynchronization therapy-pacemaker; ICD, implantable cardioverter defibrillator; SAR, specific absorption rate.
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lead, which, according to the findings by Mattei et al. [46], will minimize the potential for implant tip heating. This may be a reason why Higgins et al. [47 ] found no adverse effects in a small retrospective study in 19 patients, 16 with a pacemaker and three with an ICD, and a total of 35 MRI procedures using a 1.5-T magnet. All MRIs were performed following generator removal, with abandoned leads in place. Fifteen MRI studies imaged the head, 16 the spinal cord, and four the musculoskeletal system. For studies wherein SAR data were available, the SAR was never more than 1.5 W/kg. No complications were recorded either during the MRI examination or during the average 82 months’ follow-up. The small number of patients should be noted as a caveat when interpreting these results. &&
3-T MRI AND IMPLANTABLE DEVICES The use of 3-T MRI imaging technologies in clinical practice is increasing. The stronger magnetic field provides an improved signal-to-noise ratio over 1.5-T scans. This improves image quality (higher spatial and contrast resolution) and clinical efficiency (higher temporal resolution). The downside is the greater potential for adverse interactions with implantable devices from the stronger magnetic field, higher power radiofrequency pulses and higher frequency switching gradients in 3T scanners. Research on the hazard from 3-T fields is ongoing but, as noted by device guidelines, little or no information is available on MRI performed at 1.5 T or more, even for MRI-compatible devices [14]. It is unclear how far experiences with 1.5 T can be extrapolated to 3-T fields. At present, only insertable loop recorders (ILRs) and no pacemaker or ICD is approved for use with 3-T MRI systems. Naehle et al. [22] in 2008 took the precautions of using a transmit-receive head coil and an actively shielded 3-T MRI system and reported no incidents from 55 brain scans in 44 patients with a cardiac pacemaker. Haeusler et al. [48] found no safety risk in patients with an ILR during 62 MRI brain scans. A series of studies from Gimbel [49–51] between 2008 and 2011 describe single events from 3-T MRI scans in a small number of patients with pacemakers, ICDs and one implantable loop recorder. In two cases, inhibition of pacing during MRI scanning was observed. One event was a case of electromagnetic interference-induced output inhibition in a pacemaker patient, which is a risk with all magnetic fields [50]. It manifested as power-on-reset to the VVI, followed by asystole. The second event concerned an ICD, which was programmed to AAI with the defibrillation function turned off during scanning. In this case, pacing was inhibited before the 72
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start of the scan and was attributed to current induction between charged ions in blood within the aortic root and the motion of the MRI as the patient was moved into the bore of the scanner [51].
CONCLUSION Potential hazards from device–MR environment interaction are becoming an increasingly relevant issue in cardiac medicine. The development of MRIconditional pacemakers has improved the risk– benefit profile for patients undergoing MRI analysis. From available studies, the risk of complications appears to be fairly low, even with some MRI-unsafe devices. However, minor risks may have clinically significant effects when sufficiently large numbers of patients undergo MRI scans. The total investigated population to date remains too small to provide firm answers to many relevant questions, such as the potential hazard from abandoned leads or 3-T MRI scans. In addition, many newer devices are approved based on technical simulations or postmarket surveillance studies. Large, independent registries, particularly in Europe, would provide important safety information. Acknowledgements The authors gratefully acknowledge the assistance of Pelle Stolt PhD with drafting the manuscript. Financial support and sponsorship None. Conflicts of interest The authors have no conflicts of interest.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Kalin R, Stanton MS. Current clinical issues for MRI scanning of pacemaker and defibrillator patients. Pacing Clin Electrophysiol 2005; 28:326–328. 2. Levine GN, Gomes AS, Arai AE, et al. Safety of magnetic resonance imaging in patients with cardiovascular devices: an American Heart Association scientific statement from the Committee on Diagnostic and Interventional Cardiac Catheterization, Council on Clinical Cardiology, and the Council on Cardiovascular Radiology and Intervention. Circulation 2007; 116:2878– 2891. 3. Strach K, Naehle CP, Muhlsteffen A, et al. Low-field magnetic resonance imaging: increased safety for pacemaker patients? Europace 2010; 12:952– 960. 4. F04 Committee. Practice for marking medical devices and other items for safety in the magnetic resonance environment. ASTM International; 2013. http://www.astm.org/doiLink.cgi?F2503. [Accessed 1 September 2014] 5. Sommer T, Vahlhaus C, Lauck G, et al. MR imaging and cardiac pacemakers: in vitro evaluation and in vivo studies in 51 patients at 0.5 T 1. Radiology 2000; 215:869–879. 6. Achenbach S, Moshage W, Diem B, et al. Effects of magnetic resonance imaging on cardiac pacemakers and electrodes. Am Heart J 1997; 134:467– 473.
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MRI and implantable cardiac electronic devices Jung et al. 7. Lu¨chinger R. In vivo heating of pacemaker leads during magnetic resonance imaging. Eur Heart J 2005; 26:376–383. 8. Jung W, Zvereva V, Hajredini B, Ja¨ckle S. Initial experience with magnetic resonance imaging-safe pacemakers: a review. J Interv Card Electrophysiol 2011; 32:213–219. 9. Jung W, Zvereva V, Hajredini B, Ja¨ckle S. Safe magnetic resonance image & scanning of the pacemaker patient: current technologies and future directions. Europace 2012; 14:631–637. This is a review of the status of MRI with implantable cardiac devices in 2012 and protocols to minimize the hazard. 10. Van der Graaf AWM, Bhagirath P, Gotte MJW. MRI and cardiac implantable electronic devices; current status and required safety conditions. Neth Heart J 2014; 22:269–276. 11. Nazarian S, Beinart R, Halperin HR. Magnetic resonance imaging implantable && devices. Circ Arrhythm Electrophysiol 2013; 6:419–428. This is an exhaustive review by one of the major experts in the field of MRI and implantable cardiac devices. 12. Gimbel JR. The safety of MRI scanning of pacemakers and ICDs: what are the critical elements of safe scanning? Ask me again at 10 000. Europace 2010; 12:915–917. 13. Mollerus M, Albin G, Lipinski M, Lucca J. Magnetic resonance imaging of pacemakers and implantable cardioverter-defibrillators without specific absorption rate restrictions. Europace 2010; 12:947–951. 14. Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J 2013; 34:2281–2329. 15. Sommer T, Lauck G, Schimpf R, et al. MRI in patients with cardiac pacemakers: in vitro and in vivo evaluation at 0.5 tesla [in German]. Ro¨fo 1998; 168:36–43. 16. Vahlhaus C, Sommer T, Lewalter T, et al. Interference with cardiac pacemakers by magnetic resonance imaging: are there irreversible changes at 0.5 Tesla? Pacing Clin Electrophysiol 2001; 24:489–495. 17. Martin ET, Coman JA, Shellock FG, et al. Magnetic resonance imaging and cardiac pacemaker safety at 1.5-Tesla. J Am Coll Cardiol 2004; 43:1315– 1324. 18. Del Ojo JL, Moya F, Villalba J, et al. Is magnetic resonance imaging safe in cardiac pacemaker recipients? Pacing Clin Electrophysiol 2005; 28:274– 278. 19. Nazarian S, Roguin A, Zviman MM, 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. 20. Sommer T. Strategy for safe performance of extrathoracic magnetic resonance imaging at 1.5 tesla in the presence of cardiac pacemakers in nonpacemaker-dependent patients: a prospective study with 115 examinations. Circulation 2006; 114:1285–1292. 21. Mollerus M, Albin G, Lipinski M, Lucca J. Cardiac biomarkers in patients with permanent pacemakers and implantable cardioverter-defibrillators undergoing an MRI scan. Pacing Clin Electrophysiol 2008; 31:1241–1245. 22. Naehle CP, Meyer C, Thomas D, et al. Safety of brain 3-T MR imaging with transmit-receive head coil in patients with cardiac pacemakers: pilot prospective study with 51 examinations. Radiology 2008; 249:991–1001. 23. Naehle CP, Strach K, Thomas D, et al. Magnetic resonance imaging at 1.5-T in patients with implantable cardioverter-defibrillators. J Am Coll Cardiol 2009; 54:549–555. 24. Mollerus M, Albin G, Lipinski M, Lucca J. Ectopy in patients with permanent pacemakers and implantable cardioverter-defibrillators undergoing an MRI scan. Pacing Clin Electrophysiol 2009; 32:772–778. 25. Buendı´a F, Sa´nchez-Go´mez JM, Sancho-Tello MJ, et al. Nuclear magnetic resonance imaging in patients with cardiac pacing devices. Rev Esp Cardiol 2010; 63:735–739. 26. Burke PT, Ghanbari H, Alexander PB, et al. A protocol for patients with cardiovascular implantable devices undergoing magnetic resonance imaging (MRI): should defibrillation threshold testing be performed post(MRI). J Interv Card Electrophysiol 2010; 28:59–66. 27. Nazarian S, Hansford R, Roguin A, et al. A prospective evaluation of a protocol for magnetic resonance imaging of patients with implanted cardiac devices. Ann Intern Med 2011; 155:415–424. 28. Boilson BA, Wokhlu A, Acker NG, et al. Safety of magnetic resonance imaging in patients with permanent pacemakers: a collaborative clinical approach. J Interv Card Electrophysiol 2012; 33:59–67.
29. Cohen JD, Costa HS, Russo RJ. Determining the risks of magnetic resonance imaging at 1.5 Tesla for patients with pacemakers and implantable cardioverter defibrillators. Am J Cardiol 2012; 11:1631–1636. 30. Muehling OM, Wakili R, Greif M, et al. Immediate and 12 months follow up of function and lead integrity after cranial MRI in 356 patients with conventional cardiac pacemakers. J Cardiovasc Magn Reson 2014; 16:39. 31. Wilkoff BL, Bello D, Taborsky M, et al. Magnetic resonance imaging in patients with a pacemaker system designed for the magnetic resonance environment. Heart Rhythm 2011; 8:65–73. 32. Gimbel JR, Bello D, Schmitt M, et al. Randomized trial of pacemaker and lead && system for safe scanning at 1.5 Tesla. Heart Rhythm 2013; 10:685–691. This is a well-designed, randomized study of 1.5 T MRI scanning of MRI-conditional pacemakers showing safe performance without restrictions in positioning or body parts. 33. Wollmann CG, Steiner E, Vock P, et al. Monocenter feasibility study of the MRI compatibility of the Evia pacemaker in combination with Safio S pacemaker lead. J Cardiovasc Magn Reson 2012; 14:67. 34. Wollmann CG, Thudt K, Kaiser B, et al. Safe performance of magnetic resonance of the heart in patients with magnetic resonance conditional pacemaker systems: the safety issue of the ESTIMATE study. J Cardiovasc Magn Reson 2014; 16:30. 35. Halshtok O, Goitein O, Abu Sham’a R, et al. Pacemakers and magnetic resonance imaging: no longer an absolute contraindication when scanned correctly. Isr Med Assoc J 2010; 12:391–395. 36. Junttila MJ, Fishman JE, Lopera GA, et al. Safety of serial MRI in patients with implantable cardioverter defibrillators. Heart 2011; 97:1852–1856. 37. Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document on MR safe practices. J Magn Reson Imaging 2013; 37:501–530. 38. Russo RJ. Determining the risks of clinically indicated nonthoracic magnetic resonance imaging at 1.5 T for patients with pacemakers and implantable cardioverter-defibrillators: rationale and design of the MagnaSafe Registry. Am Heart J 2013; 165:266–272. 39. Russo RJ, Costa H, Doud D, et al. Repeat MRI for patients with implanted cardiac devices does not increase the risk of clinical events or parameter changes: preliminary results from the Magnasafe registry. J Am Coll Cardiol 2012; 59:E649–E1649. 40. Russo RJ, Costa H, Kabra A, et al. Determining the risks of magnetic resonance imaging at 1.5 Tesla for patients with pacemakers and implantable cardioverter defibrillators: the Magnasafe registry. J Am Coll Cardiol 2013; 61:10_S. 41. Irnich W. Risks to pacemaker patients undergoing magnetic resonance imaging examinations. Europace 2010; 12:918–920. 42. Langman DA, Goldberg IB, Finn JP, Ennis DB. Pacemaker lead tip heating in abandoned and pacemaker-attached leads at 1.5 Tesla MRI. J Magn Reson Imaging 2011; 33:426–431. 43. Konings MK, Bartels LW, Smits HF, Bakker CJ. Heating around intravascular guidewires by resonating RF waves. J Magn Reson Imaging 2000; 12:79–85. 44. Park S-M, Kamondetdacha R, Nyenhuis JA. Calculation of MRI-induced heating of an implanted medical lead wire with an electric field transfer function. J Magn Reson Imaging 2007; 26:1278–1285. 45. Nordbeck P, Ritter O, Weiss I, et al. Impact of imaging landmark on the risk of MRI-related heating near implanted medical devices like cardiac pacemaker leads. Magn Reson Med 2011; 65:44–50. 46. Mattei E, Gentili G, Censi F, et al. Impact of capped and uncapped abandoned leads on the heating of an MR-conditional pacemaker implant. Magn Reson Med 2014. [Epub ahead of print] 47. Higgins JV, Gard JJ, Sheldon SH, et al. Safety and outcomes of magnetic && resonance imaging in patients with abandoned pacemaker and defibrillator leads. Pacing Clin Electrophysiol 2014; 37:1284–1290. One of the very few studies on hazards from MRI in patients with abandoned leads. Although retrospective and small scale, the analysis includes follow-up data over 82 39 months after the scan. 48. Haeusler KG, Koch L, Ueberreiter J, et al. Safety and reliability of the insertable Reveal XT recorder in patients undergoing 3 Tesla brain magnetic resonance imaging. Heart Rhythm 2011; 8:373–376. 49. Gimbel JR. Magnetic resonance imaging of implantable cardiac rhythm devices at 3.0 tesla. Pacing Clin Electrophysiol 2008; 31:795–801. 50. Gimbel JR. Unexpected asystole during 3T magnetic resonance imaging of a pacemaker-dependent patient with a ‘modern’ pacemaker. Europace 2009; 11:1241–1242. 51. Gimbel JR. Unexpected pacing inhibition upon exposure to the 3T static magnetic field prior to imaging acquisition: what is the mechanism? Heart Rhythm 2011; 6:944–945.
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MRI and implantable cardiac electronic devices Werner Jung, Sebastian Ja¨ckle, and Vlada Zvereva
Purpose of review To assess the current knowledge about the potential hazard from MRI in patients with devices such as pacemakers and implantable cardioverter defibrillators (ICDs). Recent findings Most data concern ‘MRI unsafe’ devices, with only a few studies on ‘MRI conditional’ devices. No ‘MRI safe’ cardiac devices are currently available. Studies on ‘MRI unsafe’ devices tend to be small scale and reflect the experience of individual centres; few provide long-term follow-up data. Many newer devices are approved as ‘MRI conditional’ based on technical simulations or postmarket surveillance studies. With adequate measures taken before performing an MRI scan, reported complication rates are generally low, but there is a nonnegligible residual risk for power-on reset and lead heating. The presence of abandoned, older leads may affect the propensity for lead heating during MRI with newer devices, including those designated ‘MRI conditional’. Very little research has been carried out on the hazard from MRI scans in patients with ICDs, but registry data indicate more events with ICDs than with pacemakers. Summary The limited available data indicate a manageable but not negligible MRI-associated hazard in patients with implantable cardiac devices. Further controlled studies and large, independent registries, particularly in Europe, are needed to provide important safety information. Keywords 3-T MRI, implantable cardiac defibrillators, pacemakers, retained leads, risk–benefit assessment
INTRODUCTION MRI and implantable cardiac electronic devices are two of the most important medical technologies today. They are often necessary with the same patients: an estimate in 2005 predicted that up to 75% of recipients of pacemakers and implantable cardioverter defibrillators (ICDs) will develop an indication for MRI examination over time [1,2]. A recent study indicated that physicians may request MRI procedures for 17% of their patients within 12 months of implant [3]. With new technologies such as magnetic resonance (MR) angiography emerging, these numbers may underestimate future use of MRI in cardiac patients. Thus, any potential hazard from MRI in patients with implantable devices needs to be taken seriously. Current classifications for implantable cardiac devices are ‘MR safe’, ‘MR conditional’, and ‘MR unsafe’ [4]. Most devices still belong in the ‘MR unsafe’ category. A small number of pacemakers, and still fewer ICD devices, are labelled as ‘MR conditional’. Fully ‘MRI safe’ devices remain to be developed. Major potential interactions between MRI and implantable cardiac devices are summarized in
Table 1. Not all risks may warrant the same concern; for example, modern devices contain even smaller amounts of ferromagnetic materials (none at all in lead tips) and are highly unlikely to move during an MRI scan. No risk should be dismissed without support from clinical data, however. Among other hazards are lead tip heating, which may result in loss of pacing capture or myocardial perforation [5–7], changes to programming, electrical reset or changes to pacing capture threshold (PCT). For ICDs, there is an additional risk that the rapidly changing magnetic gradients during MRI may trigger the delivery of inappropriate therapies [7]. Somewhat paradoxically, MRI-induced saturation of the charging
Department of Cardiology, Academic Teaching Hospital of the University of Freiburg, Schwarzwald-Baar Klinikum, Villingen-Schwenningen, Germany Correspondence to Werner Jung, MD, FHRS, FESC, Department of Cardiology, Academic Teaching Hospital of the University of Freiburg, Schwarzwald-Baar Klinikum, Klinikstrasse 11 D-78052 VillingenSchwenningen, Germany. Tel: +49 7721 933001; fax: +49 7721 9393099; e-mail: [email protected] Curr Opin Cardiol 2015, 30:65–73 DOI:10.1097/HCO.0000000000000132
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Arrhythmias
KEY POINTS Most data on the hazard from MRI in patients with implantable ‘MRI unsafe’ cardiac devices are from small, single-centre studies and few provide long-term follow-up data. With adequate measures taken before performing an MRI scan, reported complication rates are generally low, but there is a nonnegligible residual risk for power-on reset and lead heating. Very little research has been carried out in patients with ICDs, and registry data indicate there may be a greater risk than with pacemakers. There remains a need for MRI-conditional ICD devices as well as for devices designed to minimize the risk from 3-T scanning. Many newer devices are approved based on technical simulations or postmarket surveillance studies. Large, independent registries, particularly in Europe, would provide important safety information.
system may mitigate this risk by reducing the charge of the capacitor.
‘MAGNETIC RESONANCE UNSAFE’ DEVICES Patients with implantable devices occasionally underwent MRI scans before MRI-conditional pacemakers were available. Readers are referred to more extensive expositions in earlier reviews by, for instance, the present author [8,9 ] or other recent publications [10,11 ]. There is a continuum of risk and it is possible to reduce the risk from the MRI procedure through close monitoring, reprogramming of devices before scanning, and attempting to limit specific absorption rate (SAR) levels [12,13]. European Society of Cardiology (ESC) guidelines [14] give MRI scans in patients with MR-unsafe devices a low class of recommendation (IIb1; level of evidence B2). The guidelines include a number of measures to be taken before performing an MRI scan on patients with implantable cardiac devices (Fig. 1 [14]). Studies on MRI in patients with cardiac devices are summarized in Table 2 [5,13,15–31,32 ,33–36]. Most studies on MRI with ‘unsafe’ devices are small scale and reflect the experience of individual centres. Few provide long-term follow-up data. Although there are consistently low rates of &
&&
&&
1
Usefulness is less well established by evidence/opinion. Data derived from a single randomized clinical trial or large nonrandomized studies. 2
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complications, there appears to be a nonnegligible risk for clinically significant power-on resets. Increases in cardiac troponin levels, indicative of lead heating, also need to be taken seriously. Other events noted in a number of studies are changes in PCT, sensing threshold and lead impedance. Results from trials with earlier generations of cardiac devices may not be applicable to later products, which are typically smaller, with less magnetic material and improved electromagnetic interference protection. Nevertheless, guidelines stress that no device, unless appropriately tested and labelled, should be regarded as safe for MRI simply because it is ‘modern’ or recently manufactured [37]. Guidelines’ authors also express concern that there may be underreporting of adverse events, including deaths, in the available studies from MRI scans on device patients [37]. The most recent publication includes data from 12 months’ follow-up of 356 patients with single-chamber or dual-chamber pacemakers and urgent indication for a cranial MRI [30]. The investigators note that PCT, sensing threshold and lead impedance all remained more or less unchanged over the follow-up period. There are very few MRI-conditional ICDs available at the time of writing and all published work on MRI scans in patients with ICDs has been performed with ‘unsafe’ devices to date. Only a small number of procedures have been reported in the literature (Table 2). Most concerns mirror those with pacemakers: sensing errors and lead impedance changes. Decreased battery voltage was noted in two studies [23,29] and one study included an instance of power-on reset [27]. However, with a total of only 300 patients included in published studies, the database seems too small to draw reliable conclusions on the safety of MRI scanning in patients with ICDs. To provide prospective data from a multicentre environment, the MagnaSafe Registry (clinicaltrials. gov identification NCT00907361) was set up in 2009. The objective of the registry is to determine prospectively the adverse event rate and device parameter changes in patients with non-MRI-conditional cardiac devices (pacemakers or ICDs) implanted after 2001, undergoing clinically indicated nonthoracic MRI at 1.5 T. Devices are interrogated pre-MRI and post-MRI [38]. Target enrolment is 1500 patients. Analyses from the registry have so far only been presented in abstract form at scientific conferences. An analysis in 2012 of repeat MRI scans (two scans in 32 patients, three scans in six, four scans in three and six scans in one patient) found no association between the number of MRI scans and the rate of clinical events or device parameter changes [39]. A more recent abstract, from 2013, reported the results Volume 30 Number 1 January 2015
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MRI and implantable cardiac electronic devices Jung et al. Table 1. Potential effects of MRI fields on implantable cardiac devices Static field
ECG changes Mechanical force and torque on devices Reed switch closure ICD: Saturation of storage capacitor and loss of battery life
Radiofrequency field
Heating at the lead tip and at the lead–tissue interface Alteration of programming and potential damage to the pacemaker circuitry Electrical reset Rapid atrial pacing Pacing at multiples of the radiofrequency pulse and associated rapid ventricular pacing Asynchronous pacing Inhibition of pacing output
Time-varying magnetic gradient field
Induction of ventricular fibrillation Reed switch closure Heating at the lead tip and at the lead–tissue interface ICD: antitachycardia pacing or inappropriate shock therapy
ICD, implantable cardioverter defibrillator.
from 829 nonthoracic MRI studies in 617 pacemakers and 212 ICDs. Overall, more events were recorded with ICDs than with pacemakers. A decrease in battery voltage of at least 0.04 V occurred in 1% of pacemakers and 9% of ICDs. One or more clinically relevant device parameter changes occurred in 13% of pacemakers and 28% of ICD cases [40]. A second registry, NCT01999751, is a singlecentre, prospective, nonrandomized, unblinded case series of patients (500 planned) with permanent pacemakers or ICDs undergoing medically required MRI scanning, followed for a 12-month period. The registry has not yet published any findings and is scheduled to complete in 2017. These registries include only patients from the United States. As discussed below, most manufacturers gather postmarketing safety information on devices, but to the authors’ knowledge no public multinational European registry has been set up to follow MRI scans in patients with implantable cardiac devices.
‘MAGNETIC RESONANCE CONDITIONAL’ DEVICES Scans in patients with MR-conditional devices are currently recommended at an intermediate class of recommendation (IIa3; level of evidence B) [14]. All major device companies manufacture MRI-conditional pacemakers. The devices are approved for use in MRI scanners with a field strength of up to 1.5 T with appropriate safety measures taken. Available devices at the time of 3
Weight of evidence/opinion is in favour of usefulness.
writing are listed in Table 3. The list appears impressive, but there is a caveat: not all systems in the table have been fully tested under clinical conditions. The regulatory requirements have softened since the first MRI-conditional devices were approved, based on data from randomized studies. Authorities today may accept data from technical simulations and postmarket surveillance studies as proxies for MRI conditionality. This change, as well as increasing backwards compatibility with earlier devices or leads, has simplified and speeded up the approval process and reduced costs. The downside is a lack of data on many MRI-conditional devices in controlled clinical conditions and a corresponding need for independently managed studies and registries. To reduce the risk of influence from MRI scans, MRI-conditional devices introduce a number of design changes. Nonferromagnetic material is used as much as possible. The reed switches of conventional pacemakers (designed to avoid the effects of electromagnetic interactions by reverting to DOO or VOO pacing modes in the presence of a magnet) are replaced by solid-state Hall sensors, which have more predictable behaviour. The pacemaker leads are insulated and the winding pattern of the filaments in the inner lead coil is changed to minimize the interaction with radiofrequency fields. In addition, specific MRI programming modes have been developed to be used only during the procedure. The modes include system-integrity checks to prevent activation of the MRI mode unless the system is working flawlessly, increased pacing output during MRI scanning, and restoration of prescan programme states and values when the MRI mode is deactivated.
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Arrhythmias
Implanted PM/ICD
Conventional PM/ICD
MRI-compatible PM/ICD
Exclude patients with: • leads implanted 100% increase in ventricular PCT was measured, but this was maintained till the end of 15-month follow-up in only two patients.
Single-centre prospective
24
No abnormalities during 1.5-T MRI or 99 days’ follow-up.
MRI with MRI-conditional pacemakers Wilkoff et al. 2011 [31]
&&
MRI with ICD devices Nazarian et al. 2006 [19]
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Arrhythmias Table 2 (Continued) No. of patients
Publication
Design
Main findings
Mollerus et al. 2008 [21]
Single-centre prospective
5
Naehle et al. 2009 [23]
Single-centre prospective
18
Mollerus et al. 2009 [24]
Single-centre prospective
6
A small number of instances of increased ectopy during scans were observed.
Mollerus et al. 2010 [13]
Single-centre prospective
22
MRI at 1.5 T was associated with decreased sensing amplitudes and pace impedances.
Buendı´a et al. 2010 [25]
Single-centre prospective
5
Burke et al. 2010 [26]
Single-centre prospective
14
No abnormalities associated with 1.5-T MRI.
Halshtok et al. 2010 [35]
Single-centre prospective
9
No abnormalities associated with 1.5-T MRI.
Junttila et al. 2011 [36]
Single-centre prospective
10
Nazarian et al. 2011 [27]
Multicentre prospective
Cohen et al. 2012 [29]
Single-centre retrospective
MRI at 1.5 T was not associated with changes in troponin-I levels or PCTs. Battery voltage decreased significantly from pre to post-MRI. In two MRI examinations, oversensing of radiofrequency noise as ventricular fibrillation occurred but no attempt at therapy delivery was made.
Sensing errors during imaging in one case were noted.
No complications occurred during three serial cardiac MR scans prospectively performed at 1.5 T. During follow-up there were no occurrences of ICD dysfunction. Most patients had image artefacts but the studies were generally diagnostic regarding left ventricular function and wall motion. ICD artefacts often affected the imaging of anterior wall infarcts.
201
One power-on-reset event associated with 1.5-T MRI. Minor changes in lead parameters.
40
0.04 V decreases in battery voltage in 4%; pacing threshold increases 0.5 V in 3%; pacing lead impedance changes of 50 V in 6%. Minor, not clinically important differences in pacing lead impedance and left ventricular pacing threshold.
ICD, implantable cardioverter defibrillator; PCT, pacing capture threshold; SAR, specific absorption rate.
rises from 26 to 748C in guide wire tips within 30 s of scanning [43]. The degree of heating depends on the amplitude and phase of the electric field along the lead, as well as the lead length [44]. Animal studies demonstrated increases of up to 20.48C at 1.5 T and SAR 3.8 W/kg [7]. However, such data may not extrapolate to clinical conditions or, indeed, to newer pacemaker leads. Adequate selection of imaging landmarks and patient positioning can reduce the risk for MRI-related heating: Nordbeck et al. [45] found the greatest radio frequency-induced coupling with the torso centred along the superior– inferior direction of the transmit coil. Strach et al. [3] in 2010 included patients with abandoned leads in their study on the safety of 0.2-T MRI scanning in a varied cohort of pacemaker patients, with no reported adverse occurrences. Current ESC guidelines [14] recommend exclusion of patients with abandoned leads from MRI scanning. MRI-conditional devices are indicated for use only with their specific MRI-conditional leads and not in patients in whom abandoned leads are present. The ACR stresses that a retained MR-conditional lead should be considered as MR unsafe and the risk– benefit profile assessed correspondingly [37]. Two recent publications [46,47 ] have addressed the question of abandoned leads: the former in a situation that closely simulated clinical reality, &&
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and the latter in a single-centre retrospective analysis. Mattei et al. [46] used a human trunk simulator to host an MRI-conditional pacemaker implant (programmed in MRI mode) with or without an additional ‘abandoned’ lead placed beside the implant. Lead tip temperature was measured in the presence or absence of four different ‘abandoned’ leads: three conventional, commercially available leads and one from an MRI-conditional pacemaker system. The results showed a clear potential for interaction between leads, with temperature increases more than 308 C. The abandoned leads most susceptible to heating also had the greatest influence on the heating of the pacemaker lead. The investigators identified a number of factors that influence the interaction between the abandoned and newly implanted leads. The location and path of the abandoned lead and its position relative to the implant clearly matter: ipsilateral configurations of the two leads were associated with lower temperature increases than contralateral configurations. Capped lead tips were associated with a greater degree of heating than saline-exposed tips. Moreover, the structural characteristics of a lead (length, fixation modality, resistance, etc.) influenced the propensity for heating. In most clinical situations, the newly implanted lead will run more or less parallel to the abandoned Volume 30 Number 1 January 2015
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MRI and implantable cardiac electronic devices Jung et al. Table 3. Conditional MRI pacemakers and implantable cardioverter defibrillators available at the time of writing SAR (whole body)
Name
Medtronic, Minneapolis, MN, USA
EnRhythm/Revo MRI
Pacemaker
1.5 T
Full body
2 W/kg
2008
Ensura MRI
Pacemaker
1.5 T
Full body
2 W/kg
2011
Advisa MRI
Pacemaker
1.5 T
Full body
2 W/kg
2011
St Jude Medical, St Paul, MN, USA
Accent MRI
Pacemaker
1.5 T
Full body
4 W/kg
2011
Boston Scientific, Marlborough, MA, USA
Device type
Magnet strength
Manufacturer
Scan zone
Introduced
Assurity MRI
Pacemaker
1.5 T
Full body
4 W/kg
2014
Endurity MRI
Pacemaker
1.5 T
Full body
4 W/kg
2014
Endurity
Pacemaker
1.5 T
Scan restrictions
2 W/kg
2014
Endurity Core
Pacemaker
1.5 T
Scan restrictions
2 W/kg
2014
Fortify Assura
ICD
1.5 T
Full body
2 W/kg
2015
Ellipse
ICD
1.5 T
Full body
2 W/kg
2015
Quadra Assura
CRT-D
1.5 T
Full body
2 W/kg
2015
Quadra Assura MP
CRT-D
1.5 T
Full body
2 W/kg
2015
ImageReady MR Conditional Pacing Systems
Pacemaker
1.5 T
Full body
2 W/kg
2011
ACCOLADE
Pacemaker
3.0 T
Full body
2 W/kg
2014
Sorin, Milan, Italy
KORA 100
Pacemaker
1.5 T
Scan restrictions
2 W/kg
2013
Biotronik, Berlin, Germany
Evia
Pacemaker
1.5 T
Full body
2.0 W/kg
2009
Entovis
Pacemaker
1.5 T
Full body
2.0 W/kg
2009
Eluna
Pacemaker
1.5 T
Full body
2.0 W/kg
2014
Epyra
Pacemaker
1.5 T
Full body
2.0 W/kg
2014
Etrinsa
Pacemaker
1.5 T
Full body
2.0 W/kg
2014
Estella
Pacemaker
1.5 T
Full body
2.0 W/kg
2010
Ecuro
Pacemaker
1.5 T
Full body
2.0 W/kg
2010
Evia
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2009
Entovis
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2009
Eluna
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2014
Epyra
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2014
Etrinsa
CRT-P
1.5 T
Scan restrictions
2.0 W/kg
2014
Lumax
ICD
1.5 T
Scan restrictions
2.0 W/kg
2012
Ilesto
ICD
1.5 T
Full body
2.0 W/kg
2013
Iforia
ICD
1.5 T
Full body
2.0 W/kg
2013
Idova
ICD
1.5 T
Scan restrictions
2.0 W/kg
2013
Inventra
ICD
1.5 T
Full body
2.0 W/kg
2014
Iperia
ICD
1.5 T
Full body
2.0 W/kg
2014
Itrevia
ICD
1.5 T
Full body
2.0 W/kg
2014
Ilesto
ICD
3.0 T
Scan restrictions
2.0 W/kg
2013
Iforia
ICD
3.0 T
Scan restrictions
2.0 W/kg
2013
Inventra
ICD
3.0 T
Scan restrictions
2.0 W/kg
2014
Iperia
ICD
3.0 T
Scan restrictions
2.0 W/kg
2014
Itrevia
ICD
3.0 T
Scan restrictions
2.0 W/kg
2014
Lumax
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2012
Idova
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2013
Ilesto
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2013
Iforia
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2013
Inventra
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2014
Iperia
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2014
Itrevia
CRT-D
1.5 T
Scan restrictions
2.0 W/kg
2014
Note that after 2012–2013 not all systems in the table have been fully tested under clinical conditions, as elaborated in the text. CRT-D, cardiac resynchronization therapy-defibrillator; CRT-P, cardiac reynchronization therapy-pacemaker; ICD, implantable cardioverter defibrillator; SAR, specific absorption rate.
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Arrhythmias
lead, which, according to the findings by Mattei et al. [46], will minimize the potential for implant tip heating. This may be a reason why Higgins et al. [47 ] found no adverse effects in a small retrospective study in 19 patients, 16 with a pacemaker and three with an ICD, and a total of 35 MRI procedures using a 1.5-T magnet. All MRIs were performed following generator removal, with abandoned leads in place. Fifteen MRI studies imaged the head, 16 the spinal cord, and four the musculoskeletal system. For studies wherein SAR data were available, the SAR was never more than 1.5 W/kg. No complications were recorded either during the MRI examination or during the average 82 months’ follow-up. The small number of patients should be noted as a caveat when interpreting these results. &&
3-T MRI AND IMPLANTABLE DEVICES The use of 3-T MRI imaging technologies in clinical practice is increasing. The stronger magnetic field provides an improved signal-to-noise ratio over 1.5-T scans. This improves image quality (higher spatial and contrast resolution) and clinical efficiency (higher temporal resolution). The downside is the greater potential for adverse interactions with implantable devices from the stronger magnetic field, higher power radiofrequency pulses and higher frequency switching gradients in 3T scanners. Research on the hazard from 3-T fields is ongoing but, as noted by device guidelines, little or no information is available on MRI performed at 1.5 T or more, even for MRI-compatible devices [14]. It is unclear how far experiences with 1.5 T can be extrapolated to 3-T fields. At present, only insertable loop recorders (ILRs) and no pacemaker or ICD is approved for use with 3-T MRI systems. Naehle et al. [22] in 2008 took the precautions of using a transmit-receive head coil and an actively shielded 3-T MRI system and reported no incidents from 55 brain scans in 44 patients with a cardiac pacemaker. Haeusler et al. [48] found no safety risk in patients with an ILR during 62 MRI brain scans. A series of studies from Gimbel [49–51] between 2008 and 2011 describe single events from 3-T MRI scans in a small number of patients with pacemakers, ICDs and one implantable loop recorder. In two cases, inhibition of pacing during MRI scanning was observed. One event was a case of electromagnetic interference-induced output inhibition in a pacemaker patient, which is a risk with all magnetic fields [50]. It manifested as power-on-reset to the VVI, followed by asystole. The second event concerned an ICD, which was programmed to AAI with the defibrillation function turned off during scanning. In this case, pacing was inhibited before the 72
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start of the scan and was attributed to current induction between charged ions in blood within the aortic root and the motion of the MRI as the patient was moved into the bore of the scanner [51].
CONCLUSION Potential hazards from device–MR environment interaction are becoming an increasingly relevant issue in cardiac medicine. The development of MRIconditional pacemakers has improved the risk– benefit profile for patients undergoing MRI analysis. From available studies, the risk of complications appears to be fairly low, even with some MRI-unsafe devices. However, minor risks may have clinically significant effects when sufficiently large numbers of patients undergo MRI scans. The total investigated population to date remains too small to provide firm answers to many relevant questions, such as the potential hazard from abandoned leads or 3-T MRI scans. In addition, many newer devices are approved based on technical simulations or postmarket surveillance studies. Large, independent registries, particularly in Europe, would provide important safety information. Acknowledgements The authors gratefully acknowledge the assistance of Pelle Stolt PhD with drafting the manuscript. Financial support and sponsorship None. Conflicts of interest The authors have no conflicts of interest.
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