doi: 10.1161/CIRCULATIONAHA.104.497545
(Circulation. 2005;111:e390-e392.)
© 2005 American Heart Association, Inc.
Correspondence |
Letters Regarding Article by Roguin et al, "Modern Pacemaker and Implantable Cardioverter/Defibrillator Systems Can Be Magnetic Resonance Imaging Safe: In Vitro and In Vivo Assessment of Safety and Function at 1.5 T"
VA Ann Arbor Healthcare System, Cardiology Section, Ann Arbor, Mich, carol.chen-scarabelli{at}med.va.gov
St. John Hospital & Medical Center, Wayne State University School of Medicine, Detroit, Mich
In a recent study by Roguin et al, the authors reported safety and compatibility of MRI at 1.5 T in dogs implanted with modern pacemakers and implantable cardioverter/defibrillator (ICD) systems, with transient capture failure reported in only 1 animal.1 Another recent study, including cardiac, vascular, and general MRI studies, documented safety of MRI (at 1.5 T) in humans with pacemakers.2
The clinical advantages of MRI over other imaging studies include the ability to evaluate soft tissue without the use of potentially nephrotoxic agents, and avoidance of radiation exposure; however, the safety of MRI in patients with cardiac implantable electronic devices remains uncertain as the effect of magnet application/exposure on ICDs will vary according to the manufacturer and the device programming.
Magnet application or exposure to a constant magnetic field of sufficient strength will result in reed switch closure in St. Jude ICDs3 and Medtronic ICDs, causing temporary interruption of tachyarrhythmia detection capability, without affecting bradycardia pacing function (unlike asynchronous pacing, which occurs in pacemakers when exposed to a magnet).4,5 Furthermore, the magnet response in ICDs can be programmed to ignore the magnet and therefore continue to deliver therapy.4 Significant electromagnetic interference (EMI) may cause reset or damage the ICD, or it may be interpreted as a tachyarrhythmia.5
In Guidant ICDs, magnet response may be programmed on or off. Magnet application/exposure for >30 seconds may cause deactivation of the ICD, even though bradycardia pacing is unaffected. Therefore, for procedures in which EMI may occur, it is important to ensure that the ICD is programmed to enable magnet use ("on") and that "change tachy mode with magnet" is "off" to allow magnet application for temporary suspension of tachyarrhythmia therapy, with resumption of normal operation after magnet removal.5
The inability of the ICD to detect tachyarrhythmias (ie, ventricular tachycardia/fibrillaton) and, therefore, to treat such arrhythmias should they occur during magnet application/exposure is a serious concern. In addition, pacemaker-dependent patients who have a combination permanent pacemaker/ICD require reprogramming of the pacemaker component to asynchronous pacing (to reduce the risk of pacing inhibition resulting from EMI in pacemaker- dependent patients) because magnet application/exposure in these combination permanent pacemaker/ICD devices will not cause asynchronous pacing. Finally, the risk of loss of capture, whether transient or not, is dangerous for pacemaker-dependent patients. Consequently, serious consideration of these concerns is imperative before using MRI in this patient population.
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1. Roguin A, Zviman MM, Meininger GR, Rodrigues ER, Dickfeld TM, Bluemke DA, Lardo A, Berger RD, Calkins H, Halperin HR. Modern pacemaker and implantable cardioverter/defibrillator systems can be magnetic resonance imaging safe: in vitro and in vivo assessment of safety and function at 1.5 T. Circulation. 2004; 110: 475–482.
2. Martin ET, Coman JA, Shellock FG, Pulling CC, Fair R, Jenkins K. Magnetic resonance imaging and cardiac pacemaker safety at 1.5-Tesla. J Am Coll Cardiol. 2004; 43: 1315–1324.
3. Magnet use for SJM implanted cardioverter-defibrillators. St. Paul, Minn: St. Jude Medical Cardiac Rhythm Management Division; 2004.
4. Options for suspending Medtronic ICD detection, Revision A. Minneapolis, Minn: Medtronic; 2004.
5. Magnet use with Guidant ICD implantable cardioverter defibrillator systems. Indianapolis, Ind: Guidant; 2004.
Letters Regarding Article by Roguin et al, "Modern Pacemaker and Implantable Cardioverter/Defibrillator Systems Can Be Magnetic Resonance Imaging Safe: In Vitro and In Vivo Assessment of Safety and Function at 1.5 T"
Department of Cardiology, Hospital of the University of Münster, Münster, Germany
To the Editor:
In their carefully performed study, Roguin and coworkers simulate possible hazardous effects of MRI on pacemaker- and implantable cardioverter-defibrillator (ICD) systems.1 Based on their in vivo findings in a chronically instrumented canine model using 3 different ICDs and on their in vitro findings (ICD: n=17, ICD lead: n=10, pacemaker: n=9, pacemaker lead: n=33), they have not made specific recommendations about the safety of specific devices and leads, but they state that further studies are needed before any recommendations can be made.
The authors rightly state that experimental results obtained in vitro or in healthy laboratory animals exposed to MRI cannot be automatically extrapolated to predict thermal changes in human subjects.1 Because of differences in chest anatomy, every animal study will have its limitations with respect to the radius of the semicircle lead configuration in the coronal plane. Heating is considered to be especially problematic when objects are configured in a loop or coil because conducting loops are known to provide a high current density in low-impedance, metallic, conductive materials.2 The fact that in 1 animal a temporary deterioration of pacing threshold occurred confirms that relevant thermal injury took place at the lead tip.1 Temporary deterioration of pacing threshold has also been observed in a patient who underwent MRI by mistake.3 In our phantom studies with 0.5 T, we observed temperature increases in some leads of up to 23°C at radiofrequency exposures of 1.3 W/kg.4 This increase in temperature occurs in a range that is used for temperature-controlled radiofrequency catheter ablation of cardiac accessory pathways and is probably capable of inducing tissue injury at the lead tips.5
It is also true that in patient studies, the increase in temperature is expected to be smaller than that of a static no-flow phantom because of heat convection resulting from intravascular blood flow and myocardial perfusion. Power deposition into the pacemaker leads during an MRI procedure is a complex function of numerous variables, including Larmor frequency, which in turn is determined by the main magnetic field strength. The main magnetic field strength is even higher than 0.5 T in the majority of clinically used MRI scanners. Therefore, in the clinical setting, power deposition can be critical, and it has been recommended that before patients undergo MRI, an in vitro testing of electrodes identical in type must be performed. Although Roguin and colleagues measured a tissue temperature increase of 2.8°C with the Medtronic M5024 lead,1 the Medtronic M5024 lead reproducibly increased myocardial tissue temperature 2 mm subendocardially by >20°C (SAR 1.3 W/kg) in our study.4 The question of which model best reflects reality—the one used by Roguin and colleagues1 or ours4—is debatable. What is really important is to notice that there are conflicting data, at least for the Medtronic M5024 lead. It is true that in vitro testing of electrodes is mandatory before a pacemaker or an ICD patient undergoes MRI, but such in vitro testing does not completely rule out critical temperature increases of identical leads in different settings.
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TopReferencesReferences References References |
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1. Roguin A, Zviman MM, Meininger GR, Rodrigues ER, Dickfeld TM, Bluemke DA, Lardo A, Berger RD, Calkins H, Halperin HR. Modern pacemaker and implantable cardioverter/defibrillator systems can be magnetic resonance imaging safe: in vitro and in vivo assessment of safety and function at 1.5 T. Circulation. 2004; 110: 475–482.
2. Lemieux L, Allen PJ, Franconi F, Symms MR, Fish DR. Recording of EEG during fMRI experiments: patient safety. Magn Reson Med. 1997; 38: 943–952.[Medline] [Order article via Infotrieve]
3. Anfinsen OG, Berntsen RF, Aass H, Kongsgaard E, Amlie JP. Implantable cardioverter defibrillator dysfunction during and after magnetic resonance imaging. Pacing Clin Electrophysiol. 2002; 25: 1400–1402.[CrossRef][Medline] [Order article via Infotrieve]
4. Sommer T, Vahlhaus C, Lauck G, von Smekal A, Reinke M, Hofer U, Block W, Traber F, Schneider C, Gieseke J, Jung W, Schild H. MR imaging and cardiac pacemakers: in-vitro evaluation and in-vivo studies in 51 patients at 0.5 T. Radiology. 2000; 215: 869–879.
5. Langberg JJ, Calkins H, el-Atassi R, Borganelli M, Leon A, Kalbfleisch SJ, Morady F. Temperature monitoring during radiofrequency catheter ablation of accessory pathways. Circulation. 1992; 86: 1469–1474.
Letters Regarding Article by Roguin et al, "Modern Pacemaker and Implantable Cardioverter/Defibrillator Systems Can Be Magnetic Resonance Imaging Safe: In Vitro and In Vivo Assessment of Safety and Function at 1.5 T"
Department of Radiology, University of Bonn, Bonn, Germany, t.sommer{at}uni-bonn.de
To the Editor:
We have read the article by Roguin and coworkers1 with great interest. In patients with ICDs, inadequate shock therapies may be induced by the pulsed electromagnetic MRI fields (gradient and/or radiofrequency fields). This risk can be reduced, as has been suggested by the authors, by deactivating the therapy functions of the ICD and programming the device into a "monitor-only" mode. It is possible, however, that the electromagnetic interference caused by the MRI system may cause an electrical reset or "power on reset," putting the ICD back to the factory settings with therapy options activated. In this case, the patient would be at risk for inadequate shock therapies during MRI.
We feel that it is important that evaluation of the risks of MRI in ICD patients include the following points. Our own experience (data not yet published) clearly indicates that exposure of the ICD to the static magnetic field alone may be enough to cause an electrical reset, and the fact that a specific ICD model did not undergo an electrical reset during MRI once does not necessarily rule out the possibility that it could happen under slightly different geometrical (eg, another position and/or orientation of the device inside the MR bore) or electrical (eg, different battery state) conditions.
Furthermore, we would like to clarify the authors’ points regarding reed switch behavior during MRI. Despite the strong static magnetic fields of MR systems, the reed switch remains open in up to 50% of all orientations of the pacemaker device with respect to the static magnetic field.2,3 These data further strengthen the need for inactivation of the sensing function during MRI because potentially harmful inhibition or false triggering of the pacemaker may occur if the reed switch is open.
The complex interactions between ICDs and MRI have not yet been fully evaluated. Although the article by Roguin et al provides valuable and important information, we feel that it is too early to give recommendations about MRI in ICD patients or to declare certain ICD models as MRI safe.
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TopReferencesReferences References References |
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1. Roguin A, Zviman MM, Meininger GR, Rodrigues ER, Dickfeld TM, Bluemke DA, Lardo A, Berger RD, Calkins H, Halperin HR. Modern pacemaker and implantable cardioverter/defibrillator systems can be magnetic resonance imaging safe: in vitro and in vivo assessment of safety and function at 1.5 T. Circulation. 2004; 110: 475–482.
2. Luechinger R, Duru F, Zeijlemaker VA, Scheidegger MB, Boesiger P, Candinas R. 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 Electrophysiol. 2002; 25: 1419–1423.[CrossRef][Medline] [Order article via Infotrieve]
3. Sommer T, Vahlhaus C, Lauck G, von Smekal A, Reinke M, Hofer U, Block W, Traber F, Schneider C, Gieseke J, Jung W, Schild H. MR imaging and cardiac pacemakers: in-vitro evaluation and in-vivo studies in 51 patients at 0.5 T. Radiology. 2000; 215: 869–879.
Department of Medicine, Division of Cardiology, Johns Hopkins Medical Institutions, Baltimore, Md
Department of Pathology, Johns Hopkins Medical Institutions, Baltimore, Md
Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, Md
Response
We agree with Vahlhaus et al that carefully monitored patient studies are needed before firm recommendations can be made. The risk-benefit ratio must be individually evaluated in each patient, with an understanding that, as with many other medical procedures, the performance of an MRI examination poses the potential for harm. We acknowledged in our paper that "experimental results obtained in vitro or in healthy laboratory animals exposed to radiofrequency-induced heating during MR procedures cannot be automatically extrapolated to predict thermal or other physiological changes in human subjects."
We tested heating in vitro in a container filled with 0.45% NaCl, which provides electric conductance similar to tissue and permits conductive fluid to surround the device. A semicircle configuration of the leads in the coronal plane was chosen to achieve a maximal magnetic induction area. We agree that the in vitro testing settings may influence the heat measurements. Sommer et al1 used, similar to us, a static no-flow phantom; however, the lead length was not described. Our in vitro results are similar to those reported by Sommer et al1 for certain leads (5068 or 4033), and different for others (5024); thus, lead length may play a role in the different results.
In our study, we also tested temperature changes in vivo and examined the heart tissue surrounding the lead tip for any (heat) damage. An open-chest canine model was used to measure heating in vivo, applying the maximal energy as well as clinically relevant MRI protocols. The leads did not heat up, likely because of the cooling effect of blood flow through the heart tissue and around the lead tip–tissue interface.
The tissue of the chronic studies in animals exposed to prolonged MRI scans confirmed no signs of thermal injury. In 1 animal, a temporary deterioration in pacing capture threshold occurred immediately after the scan. The capture threshold returned to baseline after 12 hours, and 4 weeks later, the tissue surrounding the lead was normal histologically. We presume that some edema, and not thermal injury, occurred at the lead tip–tissue interface, which subsequently resolved.
The fact that several large series, with nearly 250 device patients reporting the safety of MRI in patients with pacemakers,2–7 and almost no major changes in pacing thresholds, is encouraging and implies that in vivo the blood flow in the heart chambers has an important cooling effect.
During MRI scan, all implantable cardioverter-defibrillators (ICDs) should be set to "therapy off" because the devices interpret the scan noise as ventricular fibrillation, and they may attempt to deliver a shock. A shock will not be delivered, however, because the ferromagnetic transformer that is used to step up the battery voltage to the shocking voltage will be saturated by the magnetic field of the MRI scanner. The efficiency of the transformer will, thereby, be compromised, preventing it from delivering high voltage to the capacitor.
All patients should be carefully monitored with the option of rapid external delivery of direct current shock if needed. The Guidant and Medtronic devices offer the option to program differently the detection and therapy functions. We recommend that all functions be programmed to "off." Chen-Scarabelli and Scarabelli raise the concern regarding the reed switch during the scan. The reed switch in ICDs influences only the tachyarryhthmia functions of the device. The device during the MR scan should have therapy programmed to "off." Thus, the inability of the ICD to detect tachyarrhythmias and therefore to treat such arrhythmias, should they occur during magnet application/exposure, should not be a concern. External means of defibrillation and resuscitation should be immediately available.
We agree with Chen-Scarabelli and Scarabelli that the risk of loss of capture, whether transient or not, is dangerous for pacemaker-dependent patients. Consequently, serious consideration of these concerns is imperative before embarking on the use of MRI in this patient population.8
Among the ICDs tested, only 1 model, Medtronic 7271(GEM-1), had electrical reset. This occurred in 3 different devices from the same model. After the reset, the device changed its default programming to "therapy on." We recommend not scanning patients with this ICD model. Although we tested several devices from different models, we did not observe a similar reset phenomenon, although this could occur. As noted above, therapy would not be delivered, however, even if the ICD had therapy on, and MRI-induced noise was detected as ventricular fibrillation.
For a contemporary patient with an ICD or pacemaker to undergo an MRI, a strong clinical need for diagnostic information and the absence of an acceptable imaging alternative are required.
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TopReferencesReferences References References |
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1. Roguin A, Zviman MM, Meininger GR, Rodrigues ER, Dickfeld TM, Bluemke DA, Lardo A, Berger RD, Calkins H, Halperin HR. Modern pacemaker and implantable cardioverter/defibrillator systems can be magnetic resonance imaging safe: in vitro and in vivo assessment of safety and function at 1.5 T. Circulation. 2004; 110: 475–482.
2. Sommer T, Vahlhaus C, Lauck G, von Smekal A, Reinke M, Hofer U, Block W, Traber F, Schneider C, Gieseke J, Jung W, Schild H. MR imaging and cardiac pacemakers: in-vitro evaluation and in-vivo studies in 51 patients at 0.5 T. Radiology. 2000; 215: 869–879.
3. Yang A, Sommer T, Skowasch D et al, Long term effect of MRI of the brain at 1.5 Tesla on pacemaker function in patients with antibradicardia pacing [abstract]. Circulation. 2002; 106: II-690.
4. Martin ET, Coman JA, Shellock FG, Pulling CC, Fair R, Jenkins K. Magnetic resonance imaging and cardiac pacemaker safety at 1.5-Tesla. J Am Coll Cardiol. 2004; 43: 1315–1324.
5. Duru F, Luechinger R, Candinas R. MRI in patients with cardiac pacemakers. Radiology. 2001; 219: 856–858.
6. Vahlhaus C, Sommer T, Lewalter T, Schimpf R, Schumacher B, Jung W, Luderitz B. Interference with cardiac pacemakers by magnetic resonance imaging: are there irreversible changes at 0.5 Tesla? Pacing Clin Electrophysiol. 2001; 24: 489–495.[CrossRef][Medline] [Order article via Infotrieve]
7. Juralti NM, Sparker J, Gimbel JR, Wilkoff BL. Strategies for the safe performance of magnetic resonance imaging in selected pacemaker patients [abstract]. Circulation. 2001; 104: II-638.
8. Gimbel JR, Kanal E. Can patients with implantable pacemakers safely undergo magnetic resonance imaging? J Am Coll Cardiol. 2004; 43: 1325–1327.
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