Boesiger, Peter

Duru, Firat

Luechinger, Roger

Zeijlemaker, Volkert A.

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References1. Kragelund C, Snorgaard O, Kober L,Bengtsson B, Ottesen M, Hojberg S, OlesenC, Kjaergaard JJ, Carlsen J, Torp-PetersenC; TRACE Study Group. Hyperinsulinaemia isassociated with increased long-term mor-tality following acute myocardial infarctionin non-diabetic patients. Eur Heart J 2004;25:1891–1897.2. Berton G, Cordiano R, Palmieri R, Cucchini F,De Toni R, Palatini P. Microalbuminuriaduring acute myocardial infarction; a strongpredictor for 1-year mortality. Eur Heart J2001;22:1466–1475.Charlotte KragelundDepartment of Cardiology andEndocrinologyFrederiksberg University HospitalDK-2000 FrederiksbergDenmarkE-mail address: kragelund@dadlnet.dkOle SnorgaardDepartment of EndocrinologyHillerød University HospitalDK-3400 HillerødDenmarkLars KøberDepartment of CardiologyRigshospitalet,DK-2100 CopenhagenDenmarkChristian Torp-PedersenDepartment of CardiologyBispebjerg University HospitalDK-2400 CopenhagenDenmarkdoi:10.1093/eurheartj/ehi298Online publish-ahead-of-print 4 May 2005Heating of pacemaker leads duringmagnetic resonance imagingIs MRI contraindicated in PM-patients? Intheir carefully performed study, Luechingeret al.1 convincingly show the possibleheating of pacemaker leads by measuringheating at the lead tip together with thepacing parameters. Heating, comparablewith in vitro data, occurred in the presenceof blood ﬂow. Therefore, protection by thecooling effect of myocardial blood ﬂow inany in vivo or clinical setting is small andmust no longer be overestimated.They speculate about the clinical signiﬁ-cance and state that there is a lack offollow-up data with respect to signiﬁcantthreshold changes. Our follow-up datashowed that battery current and impe-dance only tended to increase. The calcu-lated rest of function time did not changenor was any signiﬁcant threshold altera-tion with the need to modify programmeddata observed.2The heating problem may be even morepronounced in the clinical setting. Thechest anatomy of swine, even if weighing60–65 kg, does not resemble that inhumans. The difference in radius ofthe semicircle lead conﬁguration in thecoronal plane may lead to heating effectsof greater extent in humans. Heating isconsidered to be especially problematicwhen objects are conﬁgured in a loop orcoil, as conducting loops are known toprovide a high current density in low impe-dance, metallic, conductive materials.3It is up to the reader to decide whetherit is beside the point to present an edi-torial comment in an animal study paperthat could be understood as a recommen-dation for clinicians planning to performMRI scans in pacemaker patients. In aclinical setting, our recommendation isdifferent. If the referring physician, theradiologist, and the cardiologist agreethat MRI is an urgent diagnostic necessitywithout an acceptable imaging alternativein a patient with cardiac pacemaker,certain requirements have to be met.Written informed consent of the patientis needed. To reduce the risk of thermalinjury during MRI, RF-exposure andsequence time have to be minimized.Like monitoring of systemic haemody-namics and cardiac rhythm with MRI com-patible devices, cardiological standby foronline analysis of cardiac rhythm andstandby for immediate cardiopulmonaryresuscitation belong to the minimal pre-cautions. A complete pacemaker checkincluding interrogation, evaluation ofintrinsic rhythm, sensing thresholds,stimulation thresholds, lead impedance,and battery voltage is mandatory beforeand immediately after MRI. Additionalassessments, i.e. 4 weeks following MRI,are recommended.References1. Luechinger R, Zeijlemaker VA, Pedersen EM,Mortensen P, Falk E, Duru F, Candinas R, Boe-siger P. In vivo heating of pacemaker leadsduring magnetic resonance imaging. EurHeart J 2005;26:376–383.2. Vahlhaus C, Sommer T, Lewalter T, Schimpf R,Schumacher B, Jung W, Luderitz B.Interference with cardiac pacemakers bymagnetic resonance imaging: are there irre-versible changes at 0.5 Tesla? Pacing ClinElectrophysiol 2001;24:489–495.3. Lemieux L, Allen PJ, Franconi F, Symms MR,Fish DR. Recording of EEG during fMRI experi-ments: patient safety. Magn Reson Med 1997;38:943–952.Christian VahlhausDepartment of CardiologyHospital of the University of Mu¨nsterGermanyE-mail address:vahlhaus@uni-muenster.dedoi:10.1093/eurheartj/ehi299Online publish-ahead-of-print 4 May 2005Heating of pacemaker leads duringmagnetic resonance imaging: replyWe appreciate Dr Vahlhaus’ interest in ourpaper.1 We agree that heating at the leadtip–myocardium interface may not signiﬁ-cantly decrease due to the cooling effect.However, this is only valid for the chroni-cally implanted leads. In the acute setting,scar formation is not prominent and thecooling effects may be more pronounced.In addition, in our study, we did notintend to make a direct comparisonbetween the in vitro and in vivo settings,as lead conﬁgurations and positions werenot identical.We absolutely agree with Dr Vahlhaus’comments concerning the anatomicaldifferences between pigs and humans,as mentioned in our study limitations.However, the pig model is much morerepresentative of the human anatomy,when compared with canines with asmaller torso, as used in the recently pub-lished paper by Roguin et al.2 In our study,the pacemaker leads were implementedwith loops comparable with those seen inthe humans. Therefore, we do not expectany systematic underestimation of theheating problem. Nevertheless, we agreethat special lead conﬁgurations may resultin higher heating effects. In addition,other positions in the bore may result inhigher temperatures as shown in Figure 2in our paper.Our paper does not serve the purpose ofan overall recommendation for safe MRIprocedures in pacemaker recipients, butto show the realistic temperature excur-sion in vivo to allow interpretation byphysiologic accepted temperature limitsused by safety requirements. We fullyagree with Dr Vahlhaus that this studyLetters to the Editor 1243and the editorial should not be inter-preted as a recommendation for cliniciansto perform MRI in pacemaker patients.The diagnostic need for an MRI has to beevaluated individually for each patient,and if there is an urgent necessity and inthe absence of an alternative imagingmodality, MRI may be considered withthe precautions and follow-up measuresas recommended by Dr Vahlhaus, inaccordance with our paper.References1. Luechinger R, Zeijlemaker VA, Pedersen EM,Mortensen P, Falk E, Duru F, Candinas R,Boesiger P. In vivo heating of pacemakerleads during magnetic resonance imaging.Eur Heart J 2005;26:376–383.2. Roguin A, Zviman MM, Meininger GR,Rodrigues ER, Dickfeld TM, Bluemke DA,Lardo A, Berger RD, Calkins H, Halperin HR.Modern pacemaker and implantablecardioverter/deﬁbrillator systems can bemagnetic resonance imaging safe: in vitroand in vivo assessment of safety and functionat 1.5 T. Circulation 2004;110:475–482.Roger LuechingerInstitute for Biomedical EngineeringUniversity and ETH ZurichGloriastrasse 35CH 8092 ZurichSwitzerlandTel: þ41 44 255 30 64Fax: þ41 44 255 45 06E-mail address:luechinger@biomed.ee.ethz.chVolkert A. ZeijlemakerBakken Research CenterMedtronic, Inc.Maastricht, The NetherlandsFirat DuruDivision of CardiologyUniversity Hospital of ZurichZurich, SwitzerlandPeter BoesigerInstitute for Biomedical EngineeringUniversity and ETH ZurichZurich, Switzerland1244 Letters to the Editor

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