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otential interference of small neodymium magnets withardiac pacemakers and implantable cardioverter-defibrillatorshomas Wolber, MD,* Salome Ryf, PhD,†‡ Christian Binggeli, MD,* Johannes Holzmeister, MD,*orinna Brunckhorst, MD,* Roger Luechinger, PhD,† Firat Duru, MD*

rom the *Cardiovascular Center, Cardiology, University Hospital, Zurich, †Institute for Biomedical Engineering,‡

niversity and ETH, Zurich, and Federal Office of Public Health, Berne, Switzerland.

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ACKGROUND Magnetic fields may interfere with the functionf cardiac pacemakers and implantable cardioverter-defibrilla-ors (ICDs). Neodymium-iron-boron (NdFeB) magnets, whichre small in size but produce strong magnetic fields, haveecome widely available in recent years. Therefore, NdFeB mag-ets may be associated with an emerging risk of device inter-erence.

BJECTIVE We conducted a clinical study to evaluate the poten-ial of small NdFeB magnets to interfere with cardiac pacemakersnd ICDs.

ETHODS The effect of four NdFeB magnets (two spherical mag-ets 8 and 10 mm in diameter, a necklace made of 45 sphericalagnets, and a magnetic name tag) was tested in forty-one

MCpfUNisoa

ppnawrudneiacfisz.ch. (Received August 31, 2006; accepted September 8, 2006.)

547-5271/$ -see front matter © 2007 Heart Rhythm Society. All rights reserved

CD. The maximum distance at which the magnetic switch of aevice was influenced was observed.

ESULTS Magnetic interference was observed in all patients. Theaximum distance resulting in device interference was 3 cm. No

ignificant differences were found with respect to device manu-acturer and device types.

ONCLUSION Small NdFeB magnets may cause interferenceith cardiac pacemakers and ICDs. Patients should be cau-ioned about the interference risk associated with NdFeB mag-ets during daily life.

EYWORDS Magnet; Pacemaker; Implantable cardioverter-defibril-ator; Electromagnetic interference; Neodymium

Heart Rhythm 2007;4:1–4) © 2007 Heart Rhythm Society. All

mbulatory patients with a pacemaker and 29 patients with an rights reserved.

Interference of environmental factors with cardiac pace-akers and implantable cardioverter-defibrillators (ICDs)ay cause temporary or permanent changes of device func-

ion. The vast majority of interactions in clinical practiceay be attributed to electromagnetic interference, whichay result from a wide spectrum of sources in everyday life

nd at the workplace.1 Common permanent magnets forousehold or office use are generally associated with lowisk due to low magnetic field strength. However, verytrong magnets made from neodymium-iron-boronNd2Fe14B) have recently become available. Because ofigh magnetic field strength and low production costs,dFeB magnets are increasingly being incorporated intoarious articles for household and office use, for example, inoys, jewelry, and even clothes. The aim of this study was toetermine the risk of magnetic interference caused by smallommercially available NdFeB magnets in patients withardiac pacemakers and ICDs.

ddress reprint requests and correspondence: Thomas Wolber, M.D.,ardiovascular Center, Cardiology, University Hospital Zurich, Raemistr.00, CH-8091 Zurich, Switzerland. E-mail address: thomas.wolber@

ethodsonsecutive patients with pectorally implanted cardiacacemakers or ICDs were recruited during regular deviceollow-up visits at the outpatient pacemaker service at theniversity Hospital of Zurich. Tests were performed usingdFeB magnets of different sizes and configurations, which

ncluded a single small (8 mm) and a larger (12 mm)pherical magnet, a necklace made of 45 spherical magnetsf three different sizes, and a magnetic name tag (Figures 1nd 2).

After initial device interrogation, NdFeB magnets werelaced in direct skin contact over the implanted device. Magnetosition and orientation were varied systematically until mag-et interference was noted. Then, starting from the center of therea of magnet interference during direct skin contact, magnetsere elevated from the skin in 1-cm increments. The occur-

ence of magnet interference was evaluated at each distancentil cessation of interference was observed. The same proce-ure was repeated using four different kinds of NdFeB mag-ets. In pacemakers, magnet effect documented by continuouslectrocardiogram monitoring was used to evaluate magnetnterference. In ICDs, interference was defined as emission ofudible tones or annotation of magnet detection during marker-hannel recording. Recording of marker channels was used in

ve devices, which could not be programmed to emit acoustic

. doi:10.1016/j.hrthm.2006.09.012

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2 Heart Rhythm, Vol 4, No 1, January 2007

ignals. In these devices, programmer heads, which did notontain built-in magnets, were placed eccentrically to allowontinuous telemetry during the test. No special programmingf the device was performed before the test. After comple-ion of all measurements, devices were reinterrogated toheck for inadvertent programming during the test proce-ure, and regular testing and programming were performed

igure 1 NdFeB magnets used for evaluation of magnetic interferenceith cardiac devices. A: Small and large sphere. B: Small spheres firmly

ticking to both sides of a thumb. C: Magnetic name tag.

s indicated clinically. p

Data were analyzed with SPSS for Windows, version3 (SPSS, Chicago, IL). Categorical data are presented asrequencies (%), continuous variables are presented asean � standard deviation (SD). Fisher’s exact test was

sed to compare rates. Continuous variables were com-ared using Student’s t-test or analysis of variance withost hoc analysis. Two-sided P-values �.05 were con-idered significant.

The study was conducted according to specific institu-ional and regional ethics guidelines. All participants pro-ided written informed consent.

esultstotal of 280 measurements were performed in 70 consec-

tive patients. Baseline characteristics of the study patientsnd devices are listed in Table 1. The NdFeB magnets usedor the tests are depicted in Figure 1, and physical charac-eristics are presented in Table 2. The necklace was made of0 small, 20 medium-sized, and five larger spheres. Mag-etic interference was observed in all patients. Occurrenceates of magnetic interference at various distances arehown in Figure 3. The maximum distance of interferenceas 3 cm. Pacemakers were affected at greater distances

mean distance (SD), 2.1 (0.6) cm] compared with ICDs1.7 (0.6) cm; P � .007]. There was no significant differ-nce between single-chamber [1.9 (0.7) cm] and dual-cham-er devices [2.0 (0.6) cm; P � .6] or between manufacturersP � .4). Magnetic interference was dependent on the size,onfiguration, and shape of the magnets (Table 3). Whilehe larger sphere and the chain of spheres caused magneticnterference with virtually all devices, the name tag inter-ered with 57% of the devices. No patient experienced anyymptoms during magnet testing. All devices resumed reg-lar function immediately after magnet removal.

iscussionhe findings of this study suggest that small, commerciallyvailable NdFeB magnets may cause interference with mod-rn cardiac pacemakers and ICDs. All devices were suscep-ible to interference within a distance of up to 3 cm. Nota-ly, only small magnets weighing up to 8 g were tested.arger NdFeB magnets are likely to cause interference atreater distances, but no such magnets were investigatedecause those magnets have to be handled with care onccount of their strong adhesive force.

Interference may occur if the magnetic switch of anmplanted device is affected by an external magnetic field.eed switches incorporated in many pacemakers and ICDsre typically closed by a 0.9 mT magnetic field and reopent 0.7 mT.2 In recent years, Hall sensors or semiconductor-ased magnetic switches are increasingly being used, inhich opening and closure occur at the same field strength.agnet switch closure results in temporary asynchronous

acing in pacemakers and in temporary suspension of tachy-rrhythmia detection in most ICDs, whereas bradycardia

acing functions remain unaffected in most ICDs.

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3Wolber et al Magnets and Pacemaker Interference

During daily life, transient magnet reversion has beeneported to occur at a rate of 11% per patient per year.3 Mostatients with cardiac devices are unlikely to recognizehort-lasting magnetic interference. Many individuals withn implanted pacemaker remain asymptomatic during asyn-hronous pacing, and brief episodes of asynchronous pacingeem to be associated with very low clinical risk, althoughompetitive pacing during spontaneous rhythm may resultn stimulation of the ventricle during its vulnerable periodnd may induce ventricular arrhythmias, especially in high-isk patients, such as those with ischemia.4 Initiation of

igure 2 NdFeB magnets forming a necklace (A), a triangle (B), and af multiple magnets are demonstrated with iron powder.

able 1 Baseline characteristics of 70 study patients andevices.

ge (years) 65 (17)ale sex 50 (71%)ody mass index (kg/m2) 27 (4)acemakers 41- Single chamber 7- Dual chamber 34

CDs 29- Single chamber 15- Dual chamber 14

evice manufacturer- Guidant 25- St. Jude Medical 22- Pacesetter 3- Medtronic 19- Vitatron 1

ime since implantation (months) 27 (28)

Numbers are counts or mean (SD).

able 2 Physical characteristics of tested magnets.

Size/Diameter(mm)

Weight(g)

AdhesiveForce (kg)

Remanence(T)

mall sphere 8 2.1 0.9 1.22–1.26edium sphere 10 4.0 1.5 1.26–1.29arge sphere 12 8.1 2.9 1.29–1.32ame tag 40 � 11 � 4 8.3 NA NA

Adhesive force and remance values were obtained from the distributor

f the magnets. NA � information not available e

eentrant pacemaker tachycardia, atrial flutter, or fibrillationy magnet application to a pacemaker has also been de-cribed.5–7 Some ICDs emit alarm tones during the occur-ence of magnet interference. If this function is unavailabler deactivated, magnet effects may be identified by use of arogrammer and recording of the marker channel, but thisill not be recognized by the patient.All devices tested in the current study resumed normal

unction after removal of the magnetic field. However, per-anent or recurring magnetic influence might be caused by

rolonged exposure to magnetic name tags, brooches, orther jewelry or apparel with magnetic closures. In Guidantevices, ICD functions may be permanently disabled by aagnet applied for 30 seconds if the “change tachy modeith magnet” feature is programmed “on.” Unintentional

). Shape and extension of the magnetic field resulting from the assembly

igure 3 Percentage of devices exhibiting magnetic interference during

row (C

xposure to NdFeB magnets at various distances.

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4 Heart Rhythm, Vol 4, No 1, January 2007

CD deactivation with potentially fatal consequences haseen reported.8–10 In newer devices, magnet application iseing used to trigger specific functions, including storage ofvent markers and electrograms. Thus, in these devices,agnet interference may lead to eccentric, although innoc-

ous, device behavior.11

Because of higher magnetic field strength, NdFeB magnetsre much smaller in size than conventional permanent mag-ets. The field strength of a specific magnet, as well as thextension and shape of the magnetic field of multiple magnetshat have been put together, may not be easily predicted with-ut performing B-field measurements. Our measurementsemonstrated that the necklace, which was made of 25 spheres,id not cause interference at greater distance than the onebserved with a single sphere. However, changes in the con-guration of the magnets result in very different shape andxtension of the magnetic field (Figure 2). Furthermore, vari-us coatings or incorporation into pieces of jewelry or apparelay make these magnets less recognizable, and the risk of

nterference may be underestimated by patients. Althoughagnet interference may only cause fixed-rate pacing in pace-aker patients, such interference may suspend tachycardia

etection in ICDs with potentially life-threatening conse-uences. Therefore, the use of name tags, jewelry, or readinglasses containing NdFeB magnets should generally be con-idered to be contraindicated. Magnetic toys and NdFeBagnets for home and office use should be handled with

aution in patients with pacemakers and ICDs.

onclusionmall NdFeB magnets may cause interference with modern

able 3 Frequencies of interference of various NdFeB magnets

Single-chamberpacemaker(n � 7)

Dual-chambepacemaker(n � 34)

hain of spheres 7 (100%) 33 (97%)arge sphere 7 (100%) 33 (97%)mall sphere 4 (57%) 28 (82%)ame tag 3 (43%) 24 (71%)

acemakers and ICDs. Patients should be cautioned about

he interference risk associated with NdFeB magnets duringveryday life, and product declarations should include in-ormation on the potential hazard that may be associatedith the use of these magnets.

eferences1. Pinski SL, Trohman RG. Interference in implanted cardiac devices. Part II.

Pacing. Clin Electrophysiol 2002;25:1496–1509.2. 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 resonanceimaging units: are reed switches always closed in strong magnetic fields? PacingClin Electrophysiol 2002;25:1419–1423.

3. Kolb C, Deisenhofer I, Weyerbrock S, Schmieder S, Plewan A, Zrenner B, SchmittC. Incidence of antitachycardia therapy suspension due to magnet reversion inimplantable cardioverter defibrillators. Pacing Clin Electrophysiol 2004;27:221–223.

4. Bilitch M, Cosby RS, Cafferky EA. Ventricular fibrillation and competitivepacing. N Engl J Med 1967;276:598–604.

5. Barold SS, Falkoff MD, Ong LS, Heinle RA. Paradoxical induction of endlessloop tachycardia by magnet application over a DDD pacemaker. Pacing ClinElectrophysiol 1986;9:503–510.

6. van Gelder LM, El Gamal MI. Magnet application, a cause of persistent ar-rhythmias in physiological pacemakers. Report of 2 cases. Pacing Clin Electro-physiol 1982;5:710–714.

7. Furman S, Cooper JA. Atrial fibrillation during A-V sequential pacing. PacingClin Electrophysiol 1982;5:133–135.

8. Bonnet CA, Elson JJ, Fogoros RN. Accidental deactivation of the auto-matic implantable cardioverter defibrillator. Am Heart J 1990;120:696 –697.

9. Rasmussen MJ, Friedman PA, Hammill SC, Rea RF. Unintentional deactivationof implantable cardioverter-defibrillators in health care settings. Mayo Clin Proc2002;77:855–859.

0. Ferrick KJ, Johnston D, Kim SG, Roth J, Brodman R, Zimmerman J, Fisher JD.Inadvertent AICD inactivation while playing bingo. Am Heart J 1991;121:206–207.

1. Levine PA, Moran MJ. Device eccentricity: postmagnet behavior of DDDRpacemakers with automatic threshold tracking. Pacing Clin Electrophysiol 2000;

ngle- and dual- chamber pacemakers and ICDs

Single-chamberICD (n � 15)

Dual-chamberICD (n � 14)

Total(n � 70)

15 (100%) 13 (93%) 68 (97%)15 (100%) 14 (100%) 69 (99%)11 (73%) 7 (50%) 50 (71%)7 (47%) 6 (43%) 40 (57%)

with si

r

23:1570–1572.

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Noedymium magnets are very strong

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Last Updated: Friday, 1 December 2006, 01:01 GMT E-mail this to a friend Printable version

Fridge magnets 'can be a killer'

Fridge magnets and decorative jewellery could be a killer if you have a weak heart, experts warn.

A strong type of magnet used in many new commercial products can interfere with pacemakers and implanted heart devices with deadly consequences.

Close contact - within about 3cm - with a neodymium magnet is enough to destabilise these life-saving heart devices, Heart Rhythm journal reports.

The authors suggest manufacturers include a health warning on products.

Ordinary iron or ferrite magnets, which are a dull grey colour with a low magnetic strength, are of little concern.

Very strong magnets made from neodymium-iron-boron, which are shiny and silver in colour, have only recently become available.

But because of their high magnetic field strength and low production costs, they are being used in computer hard drives, headphones and hi-fi speakers, as well as toys, jewellery and even clothes.

Swiss researchers at the University Hospital of Zurich tested the effect of neodymium magnets in 70 heart patients - 41 with pacemakers and 29 with implantable cardioverter defibrillators.

Magnetism

The small 8g magnets tested interfered with all of the patients' devices, regardless of their make or type, when they were in a maximum range of 3cm.

The researchers said largerneodymium magnets would be likely to cause interference at greater distances than this.

Although the devices worked normally again once the magnet was removed, the authors warned permanent damage might occur with prolonged exposure - if someone were to wear a magnetic name badge, for example.

Lead researcher Thomas Wolber said: "Physicians should caution patients about the risks associated with these

SEE ALSOScientists seek biologicalpacemaker 10 Nov 04 | Science/Nature'Intelligent' pacemaker on trial 28 May 04 | Southern CountiesMagnet mattresses 'could switchoff pacemakers' 18 May 00 | Health

RELATED INTERNET LINKSHeart Rhythm journalBritish Heart FoundationNeodymium Magnets UK

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magnets.

"We also recommend that the packaging includes information on the potential risks."

Warnings

Ian Asquith, director of Neodymium Magnets UK, a supplier of neodymium magnets to product manufacturers, said his company was aware of the risks and sends warnings out with every magnet.

But consumers were generally unaware, he said, and manufacturers had a responsibility to warn consumers of any risks.

"There is a real danger. These magnets are everywhere. They are in lots of badges, fridge magnets and mobile phones. If you were on a busy bus and someone you are squashed up against had a magnet in their top pocket you could easily come within 3cm of it.

June Davison, of the British Heart Foundation, said anyone with concerns should contact their pacemaker clinic.

"Pacemakers are manufactured to the highest standards, are rigorously tested, and most have a protective case to shield them from outside interference. Problems are rare."

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Livsfarligekøleskabsmagneter

Køleskabsmagneter kan kostemenneskeliv, lyder advarslen fra schweiziske forskere

Michael Winther-Rasmussen - 16:29 - 02. dec. 2006

En meget stærk type magnet, der blandt andet kanbruges i køleskabsmagneter, kan have fatalekonsekvenser for personer med pacemaker. Kort afstand - hvilket vil sige op til tre centimeter - mellem magnet og pacemaker kan få det livsvigtige apparat til at svigte.

Sådan lyder advarslen fra en gruppe forskere veduniversitetshospitalet i Zürich i Schweiz. Det skriver BBCmed baggrund i en artikel i fagbladet 'Heart Rhythm'.

Forskere har undersøgt en ny kraftig type magnet, der erved at finde indpas i computere, telefoner, højtalere,legetøj og smykker. De gennemførte forsøg med en lillemagnet på otte gram på 70 hjertepatienter. I samtligeforsøg havde magneten en negativ effekt på depacemakere og indopererede defibrillatorer patienterne var udstyret med. Forskerne vurderer, at større magneterkan have effekt på større afstande.

Alle de livsvigtige apparater fungerede normalt igen, såsnart magneten blev fjernet, men det er forskernes opfattelse at længevarende påvirkning kan forårsagepermanente skader.

- Læger bør advarer patienter om de risisci, der erforbundet med disse magneter, siger forskerholdets leder, Thomas Wolber, der også opfordrer til, at derplaceres advarsler på produkter, der indeholdermagneterne.

Det er ikke alle magneter, der er farlige. Forskerne har alene fundet en negativ effekt ved de nye kraftfulde neodym-magneter.

ForsideNyhederSportUnderholdning112LæserbladetDøgnets nyheder ErhvervForbrug / kup!Sex & samlivSpørg Joan ØrtingVerden på vrangenBilerFerie Side 9 pigenGallerierWeb-tvTV-guidenKonkurrencerSuDoku/KakuroVejret PokerMeetic datingMassage & escort EBblogAbonnementeAvisenAnnoncerWeb-shopDialogSkoleSkolefodboldOm Ekstra Bladet

Det er kun de nye kraftige magnter, der blandt andet indeholder neodym, der er farlige. De er billige at lave og derfor oplagte til blandt andetkøleskabsmagneter. (Foto:Colourbox.com)

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Magnets 'threat to heart patients'By PA

Magnets used in toys, jewellery and office equipment may pose a serious risk to patients fitted with pacemakers and other heart implants, according to researchers.

A study has found they can interfere with the operation of devices such as pacemakers and implantable cardioverter defibrillators (ICDs).

Ordinary iron or ferrite magnets, like those used to stick messages and badges on fridges, are of little concern.

But researchers found that more powerful magnets made from neodymium-iron-boron (NdFeB) may present a real problem.

NdFeB magnets are increasingly being used in homes and offices. They can be found in the hard drives of computers, "in-ear" headphones, and certain hi-fi speakers, as well as toys, jewellery and even clothing.

Scientists in Switzerland tested two spherical NdFeB magnets of 8mm and 10mm diameter, and a necklace made from 45 magnetic beads, on 70 heart patients. Forty-one of the volunteers were fitted with pacemakers and 29 with ICDs.

In all cases, being close to the magnets caused interference which disrupted the

functioning of the devices. Normal operation was resumed as soon as the magnets were removed.

Dr Thomas Wolber of the University Hospital of Zürich, who led the study, said: "Physiciansshould caution patients about the risks associated with these magnets. We also recommend that packaging include information on the potential risks that may be associated with these types of magnets."

The findings were reported in the journal Heart Rhythm.

In an accompanying commentary, Dr Huagui Li, a US cardiologist at the Minnesota Heart Clinic in Edina, Minneapolis, wrote: "This study is timely and important to attract the attention of both the public and the medical profession about the potentially serious health consequences of magnets used in decoration productions ... for an ICD patient, the magnetic interference can be fatal."

He said manufacturers who used magnets should be required to place warning labels on their products.

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