Interference in Implanted Cardiac Devices, Part II

1496 October 2002 PACE, Vol. 25, No. 10

Medical Sources of Electromagnetic Interference(EMI)

Patients with implanted cardiac devices (gen-erally of advanced age and with severe cardiovas-cular disease) often require diagnostic and thera-peutic procedures that involve strong sources ofEMI. It should be emphasized that with appropri-ate planning most of these procedures can be per-formed safely. Consultation regarding exposure toEMI in the medical environment constitutes a fre-quent clinical practice issue for physicians andnurses caring for patients with pacemakers andimplantable cardioverter defibrillators (ICDs). Theroutine use of prepocedural checklists to identifypatients with implanted cardiac devices in ad-vance is strongly recommended.1 Likewise, all in-stitutions (especially those with dedicated staffand clinics) should have written policies regard-ing evaluation and management of patients before,during, and after procedures involving sources ofEMI. Continuous education of patients and col-leagues in other specialties and avoidance of im-provisation will go a long way in preventing badoutcomes and reducing legal liability.

Magnetic Resonance Imaging (MRI)MRI has many advantages compared to X ray-

based diagnostic techniques, including its non-ionizing nature and the ability to discriminate dif-ferent soft tissues without contrast media. Inproperly operating MRI systems, the hazards asso-ciated with direct interactions between their elec-tromagnetic fields and the body are negligible.However, deleterious interactions between thesefields and implanted cardiac devices can occur.The Food and Drug Administration (FDA)database contains several reports of deaths inpacemaker patients during or immediately after

MRI.2 These reports are poorly characterized interms of type of pacemaker and programming, pa-tients’ pacemaker dependency, field strength ofthe MRI unit, imaging sequence, and cardiacrhythm at the time of the patient’s demise. Therisk of serious adverse events and the existence ofreasonable alternative imaging modalities havebeen obstacles to performance of large scale sys-tematic studies of MRI in patients with an im-plantable device. At most institutions, the pres-ence of an implantable device has constituted anabsolute contraindication to MRI, precluding asubstantial and growing number of patients fromthe advantages of this imaging modality. In a sur-vey of 1,567 Japanese pacemaker patients, 17%stated that they presented conditions for whichMRI would have been recommended if the devicehad not been present.3

Three types of electromagnetic fields are pre-sent in the MRI environment: an “always on”static magnetic field (with its spatial gradient), arapidly changing magnetic gradient field, and a ra-diofrequency field (Table I). The last two arepulsed during imaging.4 Exposure to the staticmagnetic field (0.2–2 T at the center of the magnetbore with current systems) occurs on entry intothe MRI suite. This results in activation of the reedswitch with asynchronous pacing in pacemakersand suspension of tachyarrhythmia detection inmost ICDs. Paradoxically, when the MRI staticfield is perpendicular to the reed switch axis (i.e.,patient inside the gantry of the scanner), the reedswitch may not be activated and demand pacing(as programmed) may persist.5 Even prolonged ex-posure to static magnetic fields (10 hours to 1.5 T)does not result in permanent damage to the reedswitch, telemetric coils, or pacemaker software.6

The static magnetic field can also impart transla-tional and rotational (torque) forces to a generatorcontaining sufficient ferromagnetic material thatcould result in pain and tissue damage. A mag-netic force exists only if the magnetic fieldchanges from place to place. Therefore, no mag-netic force is measured at the isocenter of the mag-net, but it increases rapidly towards the portal ofthe scanner. However, magnetic torque is highest

REVIEW

Interference in Implanted Cardiac Devices, Part IISERGIO L. PINSKI and RICHARD G. TROHMANFrom the Section of Cardiology, Rush Medical College and Rush-Presbyterian-St. Luke’s MedicalCenter, Chicago, Illinois

Address for reprints: Sergio L. Pinski, M.D., Cleveland ClinicFlorida, 2950 Cleveland Clinic Blvd., Weston, FL 33331. (954)659-5292.

Received June 23, 2001; revised October 15, 2001; accepted De-cember 31, 2001.

Reprinted with permission fromJOURNAL OF PACING AND CLINICAL ELECTROPHYSIOLOGY, Volume 25, No. 10, October 2002

Copyright © 2002 by Futura Publishing Company, Inc., Armonk, NY 10504-0418.

at the isocenter of the magnet. Shellock et al.7 ex-posed seven pacemakers and seven ICDs to a 0.2-T extremity MRI system and found that the mag-netic field attraction was relatively minor for alldevices. Luechinger et al.8 exposed 31 pacemakers(15 dual chamber and 16 single chamber) fromeight manufacturers and 13 ICDs from four manu-facturers to the static magnetic field of a 1.5-T MRIscanner while measuring magnetic force and ac-celeration measurements quantitatively andtorque qualitatively. For pacemakers, the mea-sured magnetic force was in the range of 0.05–3.60N. Pacemakers released after 1995 had lower mag-netic force values than older devices, with a mea-sured acceleration lower than the gravity of theearth (, 9.81 N/kg). Likewise, the torque levelswere significantly reduced in newer generationpacemakers (# 2 from a scale of 6). ICDs, exceptfor the more current GEM II 7273 (Medtronic Inc.,Minneapolis, MN, USA), showed higher force(1.03–5.85 N), acceleration (9.5–34.2 N/kg), andtorque (5–6 of 6) levels. The authors concludedthat modern pacemakers present no safety riskwith respect to magnetic force and torque inducedby the static magnetic field of a 1.5-T MRI scanner.On the contrary, ICDs, despite considerable re-duction in size and weight, may still pose prob-lems due to strong magnetic force and torque. Theeffects of the magnetic fields of 1.5-T MRI on othercontemporaneous ICDs have not been reported.The metallic parts of the leads are usually com-posed of MP35N. This alloy of nickel, cobalt,chromium, and molybdenum is nonferromag-netic; therefore, there is no concern that suchleads will move or dislodge due to magnetic at-traction.9

The radiofrequency fields can induce EMI inthe device circuitry with resulting inhibition orrapid pacing. Several mechanisms for rapid pac-

ing have been proposed. Rapid pacing up to theupper track limit can occur in dual chamber de-vices if EMI is sensed in the atrial channel. Inhibi-tion and tracking are avoided by programmingasynchronous modes.10 “Runaway” pacing syn-chronized to the radiofrequency pulses (attributedto interference with pacemaker electronics) is themost severe potential complication. Rates up to300 beats/min have been observed in animal stud-ies.11 In addition, the time-varying magnetic fieldspulsed during imaging can induce voltage in leads(up to 20 V in unipolar leads; much less in bipolarleads) that can pace the heart or interfere withsensing. This could occur with the device in theOOO mode or programmed to deliver subthresh-old pulses.12 The radiofrequency field in an MRIscanner has sufficient energy to cause local heat-ing of long conductive wires, like pacemakerleads, which could damage the adjacent myocar-dial tissue. Such thermal changes could result inincreased thresholds, myocardial perforation, orscar tissue formation and subsequent arrhythmo-genesis. In animal studies testing transesophagealpacing, MRI induced lead heating resulted in tis-sue necrosis.13 Bench studies have investigatedthe heating effects of MRI on endocardial pace-maker leads.14–16 Increases in lead tip temperatureof up to 10–20°C were common, depending on thelead model, the duration and type of the imagingsequence, and testing conditions. In one study, thechanges were similar when the leads were isolatedor connected to pulse generators,15 whereas in theother the effect was greatly attenuated when leadswere attached to the generator.14 For bipolar leadsconnected to a pacemaker and submerged insaline (the scenario that most closely resemblesclinical conditions), the mean increase in lead tiptemperature was 2.2°C (maximum observed 8.9°C)with a 1.5-T machine.14 Another study with a 0.5-T system found mean electrode maximum tem-perature raises of 1.8°C when used energies simi-lar to those used clinically.16 In vitro, heating wasless (especially when the lead was away from thefield isocenter) when imaging with a send/receivecoil than with a receive-only coil.17 The coolingeffect of circulating blood should also attenuatethe rise in temperature. The clinical significanceof electrode heating is unknown. The limitedavailable data do not suggest an increase in pacingthresholds after imaging. MRI has not been shownto reprogram or permanently damage pacemakersor ICDs. A single Reveal (Medtronic Inc.) im-plantable loop recorder exposed in vitro to a 1.5-TMRI scanner developed a nonreversible error.18

The body structure to be scanned also influ-ences the risk of interactions. With MRI of thebrain or an extremity, the device in the thorax isexposed to a weaker radiofrequency field. For ex-

INTERFERENCE IN ICDS

PACE, Vol. 25, No. 10 October 2002 1497

Table I.

Potential Effects of Magnetic Resonance Imaging onImplanted Cardiac Devices

1. Static magnetic fielda. Reed switch closureb. Generator displacement

2. Radiofrequency fielda. Alterations of pacing rate (inhibition or triggering)b. Spurious tachyarrhythmia detectionc. Heatingd. Electrical reset

3. Time-varying magnetic gradient fielda. Induction voltage (resulting in pacing)b. Heatingc. Reed switch closure

PINSKI, ET AL.


ample, in the bench study by Shellock et al.,7 the0.2-T extremity MRI system did not alter the func-tion of any device. They concluded that clinicaluse of these units (i.e., with the patient’s thoraxoutside the magnet bore) should be safe in patientswith implanted cardiac devices. However, duringbrain scanning the generator will be at the entry ofthe scanner and subject to a higher translationalmagnetic force. Cardiac MRI would expose the im-planted systems to the highest magnetic and ra-diofrequency fields.

Despite the risks, some investigators have per-formed carefully planned in vivo studies in an at-tempt to provide guidelines for safe MRI in devicepatients. Gimbel et al.19 described safe perfor-mance of MRI in five patients with permanentpacemakers. Unfortunately, the authors did notuse consistent safety strategies and studied onlyPacesetter (Siemens Pacesetter, Inc., Sylmar, CA,USA) devices. A 2-second pause of uncertainmechanism was observed in the only pacemakerdependent patient (programmed in DOO mode).Valhaus et al.5 performed 34 varied MRI examina-tions (including brain, neck, heart, abdomen, andextremities) with a 0.5-T superconducting systemin 32 patients with permanent pacemakers fromdifferent manufacturers. All pacemakers had beenimplanted for . 3 months and no patient waspacemaker dependent. Their protocol includedreprogramming of the pacemaker to an asyn-chronous mode (AOO, VOO, or DOO) at a rateabove the intrinsic one. Pacing and sensingthresholds, lead impedance, and battery voltagewere measured before the MRI, immediately after,and 3 months thereafter. The response of the reedswitch with the patient inside the gantry of thescanner was also carefully documented. No in-stance of rapid pacing was seen. Lead impedanceand pacing and sensing thresholds did not change.Battery voltage decreased immediately after MRIand recovered at 3 months. Battery current andimpedance tended to increase. The projectedlongevity did not change after MRI. Programmeddata and the ability to interrogate, program, or usetelemetry were not affected. In almost half of thepatients temporary deactivation of the reed switch(activated when entering the MRI suite) occurredwhen positioned in the gantry of the scanner at thecenter of the magnetic field. The authors con-cluded that MRI at 0.5 T is feasible in selectedpacemaker patients and that it does not affect thedevices irreversibly. Coman et al.20 reported pre-liminary results of clinically indicated 25 MRI ex-aminations at 1.5 T in 24 unselected patients withpacemakers. No specific programming was fol-lowed. They observed one instance of pacing in-hibition. Minor changes in capture threshold werecommon after the scan. Overall, 11% of the leads

required a change in output to accommodate thealtered threshold.

In view of the potential for catastrophic com-plications, the presence of a pacemaker shouldstill be considered a prima fascie contraindicationfor MRI. Although recent evidence suggests thatwith appropriate planning, selected patientscould undergo MRI without excessive risk,4 itshould be noted that obtaining detailed, informedconsent from the patient and performance of theprocedure under a research protocol approved bythe local human research or ethics committee maynot eliminate physician and institutional liabilityif a complication occurs. Therefore, alternativeimaging techniques should always be consideredfirst. The following recommendations should befollowed if MRI is deemed indispensable for pa-tient care. In nondependent patients, program-ming of the pacemaker to the OOO mode (whenavailable) or to subthreshold output will avoidmost interactions. It is important to note that rapidpacing secondary to induction voltage is still pos-sible in this mode. Alternatively, the pacemakercould be programmed asynchronously to overridethe intrinsic rate.5 Pacemaker dependent patientsshould be reprogrammed to asynchronous mode.Low field strengths (# 0.5 T) should be preferred.The patient must be monitored using electrocar-diography (ECG), pulse oxymetry, and directvoice contact during the scan. Imaging should bestarted with graded scanning sequences (singleslice, low resolution) and then eventually progressto more conventional sequences. Sequences witha high absorption rate (e.g., turbo spin-echo) aremore likely to induce EMI and lead heating andshould be avoided if possible. There is little infor-mation on ICDs and MRI. This combinationshould only be explored under investigational cir-cumstances. Tachyarrhythmia detection shouldbe disabled.

NeurostimulatorsSpinal cord stimulation has been used to treat

peripheral vascular disease, intractable pain, andrefractory angina pectoris. The few published re-ports on concomitant use of implanted cardiac de-vices and spinal cord stimulators have highlightedthe importance of testing to avoid interactions.21

Pacing inhibition or spurious tachyarrhythmia de-tection can occur secondary to oversensing of thespinal cord stimulator output. Bipolar spinal cordstimulation and bipolar pacemaker or ICD sensingminimize the risk of interaction.22 Testing at thehighest tolerated spinal stimulator output and atdifferent frequencies should be performed. Inhibi-tion can be output dependent, while noise rever-sion can be frequency dependent.23

Other implantable neurostimulators are being



introduced in clinical practice, including those forParkinson’s disease, epilepsy, fecal incontinence,and neurogenic bladder. There is little data on thecompatibility between these devices and pace-makers or ICDs. Testing protocols should explorethe possibility of interference before patient dis-charge, and the devices programmed accordingly.Tavernier et al.24 reported a patient with severeParkinson’s disease and two separate neurostimu-lators connected to quadripolar electrodes in thesubthalamic nuclei who received an ICD. An “in-tegrated bipolar” lead was used, and there was nooversensing of the neurostimulator signals even atmaximum output in unipolar configuration. Max-imum energy (34 J) shocks reproducibly reset bothneurostimulators (in right and left prepectoralpockets) to the off mode. Obwegeser et al.25 im-planted an ICD with a “dedicated bipolar” lead ina patient with essential tremor and a deep brainstimulator implanted into the left ventral interme-diate nucleus of thalamus. Testing during implan-tation did not disclose interactions. However,shocks . 20 J were not tested. It should be notedthat the programmer wand for Medtronic neu-rostimulators contains a magnet that will close thereed switch of a pacemaker or ICD if moved closeto the pocket.

Peripheral Nerve Stimulators

Peripheral nerve stimulators are used to as-sess the extent of neuromuscular blockade intra-operatively or in the intensive care unit26 and tolocalize nerves for blocks. O’Flaherty et al.27 re-ported a case of reproducible inhibition of aunipolar right-sided VVI pacemaker during intra-operative left facial nerve stimulation with thestandard train-of-four mode at 2 Hz. It should benoted that frequencies , 4 Hz (240 beats/min) areunlikely to invoke the noise reversion mode inmost pacemakers. Further studies are needed toassess the risks presented by this source of EMI.Diagnostic nerve conduction studies with needleelectrodes introduced at or distal to elbows orknees appear safe in pacemaker patients.28

Transcutaneous Electric Nerve Stimulation(TENS)

TENS is a popular method for the relief ofacute and chronic musculoskeletal pain. A TENSunit consists of electrodes placed on the skin andconnected to a generator that applies 20 ms rectan-gular pulses of up to 60 mA at a frequency of20–110 Hz. Output and frequency are adjusted toprovide maximum pain relief. Erikson et al.29 re-ported inhibition by TENS in four patients withnonprogrammable unipolar pacemakers. In twopatients with unipolar pacemakers, inhibition bya TENS machine could be eliminated by increas-

ing the sensing threshold (in one case to 5 mV).30

In a study of the effects of TENS (four sites, 51 pa-tients with 20 different pacemaker models), therewere no instances of interference, inhibition, orreprogramming.31 It appears that TENS can beused safely in patients with modern implantedbipolar pacemakers and in patients with unipolarpacemakers if sensitivity is reduced. It has beenrecommended that TENS electrodes not be placedparallel to the lead vector.

There is much less experience with the use ofTENS in patients with ICDs. Several well-docu-mented cases of spurious shocks triggered by TENSapplication in patients with a variety of lead con-figurations and sensing algorithms have been pub-lished.32–34 ICDs constitute a relative contraindica-tion to TENS therapy. If TENS is deemedindispensable, provocative testing should be per-formed with the ICD in the “monitor-only” mode.32

Ambulatory TENS therapy should be allowed onlyin the absence of interactions during testing.

Percutaneous Coronary InterventionRizk et al.35 described a patient who received

a spurious ICD discharge secondary to oversens-ing while a Teflon-coated coronary guidewire wasin place in a diagonal branch close to the defibril-lator lead. No right heart catheters were present,and other causes of oversensing were carefullyruled out. It was suggested that the guidewirepicked up EMI present in the catheterization labo-ratory and delivered it to the proximity of thedefibrillator lead. Until more information is gath-ered, it appears prudent to disable tachyarrhyth-mia detection while the heart is being instru-mented for interventional procedures.

ElectrosurgerySeveral electrosurgical techniques can gener-

ate EMI. At times, the nomenclature of these tech-niques is confusing to the nonsurgeon. In Europe,the term surgical diathermy is often used to de-scribe electrosurgical techniques, while in theUnited States, (short-wave) diathermy refers to thetherapeutic application of current directly to theskin and is used for musculoskeletal ailments.Short-wave diathermy should be avoided in pa-tients with implanted devices.36

Some techniques are used in general surgery,while others find their most frequent use in der-matologic surgery.37 Although the term electro-cautery is often used when referring to electro-surgery, in its strict sense electrocautery describesa technique that promotes hemostasis by heating ametal instrument. As no current is passed in thebody, there is little or no risk of EMI. Battery op-erated, “pencil” electrocauteries are often usedduring pacemaker implantation. Electrofulgura-

PINSKI, ET AL.


tion and electrodessication are monoterminaltechniques that destroy only superficial tissues.They are used mostly in dermatological surgery.Because there is no dispersive ground electrode,little current is generated in the body away fromthe lesion being treated. The most common elec-trosurgery modalities, electrocoagulation andelectrosection (electrocutting), involve passingcurrent through tissue. Coagulation and cuttinguse high voltage, low amperage current with highfrequency radio wave oscillations 100,000 Hz. Co-agulation is achieved with short bursts of currentand uses lower energy levels than the cuttingmode. The short intermittent bursts produce heatwithin the tissue to control bleeding by thermallysealing the end of a blood vessel. Cutting currentis continuous and creates high temperatures, caus-ing cell explosion and evaporation. Coagulationand cutting current is usually delivered in amonopolar configuration. Current begins at the ac-tive electrode located on the surgical instrumentand after traveling through the body it returns tothe electrosurgical generator through a dispersingground pad. Cutting current is more likely tocause interference than coagulation current.38 Intrue bipolar electrocoagulation, the current flow islocalized across the two poles of an instrument(e.g., coagulation forceps). Because there is littleflow of current outside of the surgical site and lesspower is used, EMI is unlikely to occur. However,it is useful only for delicate surgical proceduresand small vessels. Monopolar and bipolar config-urations are used during therapeutic endoscopicprocedures (e.g., polypectomy, bleeding vesselcauterization).39 Alternative surgical tools that

will not produce EMI include the Shaw scalpel40

(Oximetrix, Inc., Mountain View, CA, USA), laserscalpels,41,42 and ultrasound scalpels (HarmonicScalpel, Ultracision, Inc, Smithfield, RI, USA).43

A microwave thermotherapeutic device have beenintroduced in clinical practice for transurethralablation of benign prostatic hyperplasia. Exten-sive in vitro testing suggests that this device doesnot interact with pacemakers or ICDs.44

During electrosurgery in monopolar modes,the electric current spreads out and penetrates theentire body of the patient. This stray current maybe interpreted by an implanted device as an in-tracardiac signal. Pacing inhibition, pacing trig-gering, automatic mode switching, noise rever-sion, or spurious tachyarrhythmia detection45 canoccur, depending on the type of device, the pro-grammed settings, the duration of EMI, and thechannel in which the current is oversensed. Al-though some investigators have suggested thatelectrosurgery is safe in patients with activatedICDs,46 the risk of spurious tachyarrhythmia de-tection is clearly present (Fig. 1). Electrosurgerycan also induce sensor mediated pacing at the up-per rate limit in minute ventilation pacemak-ers.47,48

Other types of interaction are more commonduring electrosurgery than with other sources ofEMI.49 With older technology, up to 21% of pace-makers reverted to the power on reset mode. In arecent prospective study of 45 patients undergo-ing electrosurgery, electric reset occurred only in7%.50 Reset is more common when the surgicalwound is closer to the pacemaker pocket.51 Abipolar configuration is not protective.

Figure 1. Spurious ventricular fibrillation detection due to electrosurgical equipment. Storedatrial (A), ventricular (V), and shocking lead (S) electrogram in a patient with a Ventak AV III(Cardiac Pacemakers, Inc., St. Paul, MN, USA) who underwent placement of a Hickman cathetercontralateral to the implantable cardioverter defibrillator pocket. Nonphysiological signals areseen in both sensing channels. Tachyarrhythmia therapy had been disabled prior to surgery. Theatrial sensitivity was nominal; the ventricular sensitivity was programmed to “less.” The devicelogged in seven detections during the surgical procedure.



Myocardial electrical burns may occur whenthere is conductivity between the pacing electrodeand the indifferent (return) electrode of the elec-trosurgical unit. This may be facilitated by a pac-ing electrode with a small surface area and ahigher current density. Furthermore, protectivecircuitry (i.e., zener diodes, thyristors) that shuntcurrent away from the device may also contributeto the development of myocardial burns. Eleva-tion in pacing thresholds can occur, although exitblock has not been documented. More severe dam-age (and even ventricular fibrillation) can occur ifthe dispersive electrode is disconnected from thecircuit, as the pacing electrode becomes the activeelectrode in the cautery circuit and can directlydeliver current to the heart.52 Irreversible genera-tor failure due to damage to the internal circuitrycan occur, especially when applying current closeto the device pocket. Permanent loss of output orrunaway syndrome53 can be life threatening. Volt-age control oscillator lockout has been identifiedas a mechanism of sudden output failure afterelectrosurgery current.54,55 Irreversible loss of out-put has been reported after an initial applicationof electrocoagulation current far away from thepacemaker system (e.g., during hip replace-ment).56 Although late recovery of function canoccur,55 the device should not be trusted after ini-tial failure.

Several reviews describe the optimal manage-ment of patients with implanted devices undergo-ing electrosurgery (Table II).57,58 Short notice andscarcity of specialized personnel make compli-ance with such guidelines difficult, even in thelarge hospital with a well-staffed pacemakerclinic. Ideally, the patient should be seen beforesurgery to determine pacemaker dependency andto document pacing and sensing thresholds. In pa-tients with dual chamber generators that revert tosingle chamber pacing under electric reset, it maybe valuable to observe the hemodynamic toler-ance to the reset mode. In general, rate responseand tachyarrhythmia detection should be disabledjust before surgery. In patients who are not pace-maker dependent, it is best not to change the pro-grammed mode. Pacemaker dependent patientsshould be reprogrammed to an asynchronousmode (DOO, VOO, AOO, according to the device)above the intrinsic rate. The VVT mode with along refractory period can be useful in selected in-stances. It should be noted that asynchronous pac-ing modes are not available in many ICDs. It ispreferable to program the pulse generator preoper-atively to an asynchronous mode rather than do-ing it by application of the magnet. With someolder pacemakers, application of the magnet al-lowed inappropriate random reprogramming bythe radiofrequency current.59 Taping the magnet

to the pacemaker pocket is still useful in emer-gency situations in which there is no time for re-programming. It should be remembered, however,that magnet application suspends detection butdoes not trigger asynchronous pacing in ICDs. TheSmartmagnet (Medtronic Inc.) 9322 has been de-signed to safely suspend tachyarrhythmia detec-tion by Medtronic ICDs during surgical proce-dures without the need for reprogramming.60 Thebattery-operated device contains a magnet, a ra-diofrequency transmitter, and light-emittingdiodes. A green diode remains lit as long as themagnet is properly placed, indicating that tach-yarrhythmia detection and therapy are sus-pended. Its use could facilitate the management ofnonpacemaker dependent ICD patients undergo-ing procedures that can produce EMI.

Communication with the operating room per-sonnel, including nurses, anesthesiologists, andsurgeons is important. Electrocautery distorts theECG and it may be impossible to determine ifpacemaker inhibition occurs. Arterial pressuremonitoring may be invaluable in this situation.The grounding (dispersive) plate or pad should beplaced as close as possible to the operating siteand as far away as possible from the pulse genera-tor and lead(s), so that the electrical pathway be-tween the electrosurgical probe and the ground isdirected away from the pacing system. For exam-ple, during transurethral resection of the prostate,the grounding pad should be on the buttocks orlower leg. Good contact of the pad is mandatory,because with poor contact the pulse generator be-comes the anode for the applied current. The pa-tient’s body should not come in contact with anygrounded electrical device that might provide analternate pathway for current flow. Proper ground-ing of all electronic equipment used near the pa-tient is essential.

The monopolar probe should not be usedwithin 15 cm of the pulse generator or lead. Cut-ting and coagulation time should be as short aspossible with the lowest feasible energy level. Ifelectrosurgery causes inhibition of an implantedpacemaker, it should be used in short bursts so asto produce only 1–2 dropped beats at a time. Ifthere is no underlying rhythm, only brief applica-tions (, 1 s) should be used, followed by 5- to 10-second periods free from current to allow resump-tion of rhythm and normal hemodynamics.Ideally, a trained physician and the correspondingprogrammer should be available within the hospi-tal whenever a patient with an implanted deviceundergoes electrosurgery. Since damage of thepacing system may occur, the capability of insti-tuting emergency pacing must be present. An ex-ternal transcutaneous pulse generator (and defib-rillator) should be available. In case of inadvertent

PINSKI, ET AL.


reprogramming that is not hemodynamically tol-erated, the pulse generator must be reprogrammedas soon as possible. Magnet application can be at-tempted as an interim measure (the magnet rateusually varies from 60 to 100 beats/min) but is un-likely to help in these cases.

A damaged pulse generator should be re-moved and replaced expeditiously, especially ifrunaway syndrome occurs. All devices must becarefully tested after the operation because repro-gramming may be inapparent, especially if thespontaneous rhythm is faster than the lower rateof the pulse generator. Ideally, testing should beperformed immediately after the operation and re-peated 24 to 48 hours later. Endocardial burns

should be suspected if the capture and sensingthresholds have increased. Follow-up is then re-quired until stability can be demonstrated. Occa-sionally, a rise in threshold may require place-ment of a new pacing lead or, rarely, a high outputpulse generator.

As more surgical procedures are performedoutside the hospital (in physicians’ offices or free-standing ambulatory surgery centers) these recom-mendations become difficult to implement. Al-though industry-employed allied professionalsoften participate in the perioperative managementof device patients in those settings, current guide-lines suggest that they should perform technicalsupport tasks only with an appropriately trained

Table II.

Management of Patients with Implanted Devices Undergoing Electrosurgery

Preoperative

� Consider alternative tools (knife and ligatures, ultrasonic scalpel, laser scalpel)� Identify device and determine “reset” mode� Check device (programming, telemetry, thresholds, battery status)� Develop a contingency plan in case arrhythmias or device malfunction occurs during the procedure

In the Operating Room

� Disable tachyarrhythmia therapies� Deactivate rate responsive features� If the patient is pacemaker dependent, reprogram device to asynchronous or triggered (with long

refractory period) mode. Remember that asynchronous pacing is not available in many ICDs. Inthese cases:

� Decrease the maximum sensitivity� If available, program the noise reversion mode to asynchronous� Preapply external transthoracic pacing system� Consider insertion of separate transvenous pacing wire� Monitor peripheral pulse or oximeter (ECG is obscured by artifact)� Position the ground pad to keep the active-to-dispersive current pathways as far as possible and

perpendicular from the pulse generator-to-electrode pathway. The current should flow away fromthe pulse generator

� Use true electrocautery or bipolar electrocoagulation whenever possible� Limit cutting current to short bursts interrupted by pauses of at least 10 seconds� Use the lowest effective cutting or coagulation power output� Do not use cautery near device� Reprogram if reset mode hemodynamically unfavorable� Use magnet with caution (may permit inadvertent reprogramming in some older devices)

Postoperative

� Reactivate ICD tachyarrhythmia therapy as soon as possible� Check device (programming, telemetry, thresholds, battery status)� Reprogram if necessary� Replace generator if circuit damage documented� Replace lead(s) if pacing threshold too high

ECG 5 electrocardiogram; ICD 5 implantable cardioverter defibrillator.



and experienced physician in close proximity(i.e., accessible to attend to the patient within afew minutes).61 It is not clear what precautionarypractices are standard in the community. A recentsurvey of 166 cutaneous surgeons62 (mostly in-volved in electrosurgery of epitheliomas in the of-fice setting), revealed that, although many had en-countered instances of EMI with pacemakers orICDs, few routinely checked or reprogrammed de-vices before or after surgery. The types of interfer-ence reported were skipped beats (8 patients), re-programming of a pacemaker (6 patients), ICDfiring (4 patients), asystole (3 patients), bradycar-dia (2 patients), and premature pacemaker batterydepletion (1 patient). The estimated overall inci-dence of complications was low (0.8 cases/100years of surgical practice). Precautions exercisedby most dermatologists included use of shortbursts of less than 5 seconds, use of minimalpower, and avoiding use around the pacemaker orICD. Bipolar forceps were used by 19% of respon-dents and were not associated with any inci-dences of interference.

It is necessary to gather more clinical evi-dence regarding the incidence and severity of EMIwith current implantable devices and differentelectrosurgical techniques and operations. It islikely that current “blanket” recommendationswill need to be revised to accommodate differentdegrees of risk and allow efficient, cost-effective,high quality perioperative management of pa-tients with implanted devices.

Direct Current Cardioversion and DefibrillationDirect current (DC) external cardioversion/

defibrillation with paddles (or disposable elec-trodes) can apply several thousand volts and tensof amperes of current to implantable device sys-tems.63 Of all sources of EMI, this represents thehighest amount of energy delivered in the vicinityof these devices, and have the potential to damagethe pulse generator and the myocardial tissue incontact with the lead(s). Current devices incorpo-rate elements (zener diodes, thyristors) to protectthe pacing output circuitry and sensing amplifiersby shunting excess energy away from the device.The zener diode behaves as a short circuit as soonas the voltage exceeds a certain value, like 10–15V, substantially above the output voltage of thepulse generator. Other, less common circuit de-signs can also limit the current flowing down thelead, but at the expense of inhibiting pacing out-put during the reception of large voltage.64 The be-havior of the Telectronics Meta 1254 (Engelwood,CO, USA) pacemaker during radiofrequency abla-tion (see next section) highlights some limitationsof this approach. At times, the backup (reset)mode is activated by the countershock. However,

if the protection mechanism is overwhelmed byhigh energy input, permanent pulse generator cir-cuitry damage may ensue. In addition, capacitivecoupling or shunting in the pacemaker circuit mayinduce currents in pacemaker or defibrillatorleads sufficient to cause thermal damage (burn) tothe electrode to tissue interface and result inchronic threshold elevation.65,66 In dual chamberpacemakers, cardioversion energy may be prefer-entially shunted to the ventricular lead.67

The risk of damage to the implanted devicedepends on the amount of energy applied, thecharacteristics of the device and lead, and the dis-tance between the paddles or pads and the pulsegenerator and lead(s). In elective situations, theminimum energy likely to be successful should bedelivered. External cardioversion68 or defibrilla-tion69 with a biphasic waveform is more efficient(i.e., requires less energy) than the conventionaldamped sine wave monophasic shocks andshould be preferred in patients with implanted de-vices. It should be noted that unipolar pacing sys-tems are more susceptible to damage than bipolarsystems. Whenever possible, an anterior-posteriorconfiguration of the shocking electrodes should beused, as it maximizes the distance between thesource and the implanted generator. If an antero-apical position must be used, the electrodesshould be at least 10 cm from the pulse generator.However, this may be impossible with devices im-planted in a right pectoral pocket, as the anteriorpaddle will lie directly on top of it. Transient ele-vations in capture thresholds are common follow-ing direct current shocks and should be antici-pated. The threshold rise is usually temporary,lasting up to a few minutes, but occasionally itmay remain elevated permanently and necessitatelead replacement. Pre- and postprocedural inter-rogation and testing for proper function shouldfollow external DC shocks in all implantable de-vices (Table III).

Internal cardioversion is at times attempted inpatients who fail external cardioversion of atrialfibrillation. There is limited published experiencewith this procedure in pacemaker patients. Therewere no instances of pacemaker malfunction inseven patients who underwent internal cardiover-sion of atrial fibrillation with electrodes in theright atrium and the coronary sinus or left pul-monary artery with biphasic shocks up to 20 J.70

However, when high energy endocavitary shockswere used for ablation purposes, pacemaker fail-ure was common.71

The availability of dual chamber rate respon-sive ICDs has greatly reduced the need for separatepacemakers and ICD systems. Among the manypossible interactions when using separate de-vices, electric reset of the pacemaker by a defibril-

PINSKI, ET AL.


lator shock was common.72 To avoid the potentialinterference with ventricular fibrillation detectionby unipolar pacing pulses, only pacemakers thatreset to the bipolar mode should be used in con-junction with ICDs. Limited experience suggeststhat automatic internal defibrillator shocks do notinterfere with the function of the dedicated car-diomyostimulator used in patients with dynamiccardiomyoplasty.73

Radiofrequency Catheter AblationRadiofrequency catheter ablation is first line

therapy for a variety of supraventricular and ven-tricular arrhythmias. The interaction between ra-diofrequency current and implantable devices hasbeen studied most thoroughly during palliativeablation of the atrioventricular junction for drugrefractory atrial fibrillation. There is also consid-erable clinical experience with the ablation ofmonomorphic ventricular tachycardia in patientswith ICDs.74

Radiofrequency current (delivered as an un-modulated sine wave at 500–1,000 kHz) is an in-tense source of pulsed interference that interactsunpredictably with implanted devices. Energy de-livery may result in asynchronous pacing, rapidtracking, spurious tachyarrhythmia detection, andelectrical reset. Different interactions may be seen(in the same patient) during consecutive energy

applications. Most of the interactions are transientand terminate with cessation of energy delivery.75

Animal and clinical studies have examinedthe incidence, mechanisms, and risk factors forthese interactions. Chin et al.76 studied 19 pulsegenerators implanted in 12 dogs. They found thatinteractions depended on the proximity of currentapplication to the pacing leads. Interactions werefrequent at 1 cm and absent at . 4 cm. The mostdangerous interaction was “runaway” pacing withpossible induction of ventricular fibrillation. In atissue bath model, Dick et al.77 investigated the ef-fects of radiofrequency current (55 W; tip temper-ature 65°C–70°C) applied to four different pacingor defibrillation leads. Photographic and micro-scopic examination after energy delivery revealedno damage to the target lead. There was no mal-function of the attached pulse generators. Themagnitude of induced current measured at the tar-get tip lead was inversely proportional to the dis-tance. Significant current was detected only whenthe ablation catheter was less than 1 cm from thetarget lead tip.

The clinical incidence of acute interaction be-tween radiofrequency current application andpermanent pacemakers has ranged widely. The in-cidence and severity of interference depends inpart on the protective circuits of the implanted de-vice. For example, the Telectronics Meta DDDR1254 pacemaker presented a unique response toradiofrequency energy delivery.78 When currentwas applied at the same time as the pacing pulse,the pacemaker output switched open to protectthe circuitry. No pacing output was emitted untilradiofrequency energy delivery ceased, althoughthe event markers indicated normal pulse deliv-ery. The combined incidence of acute pacemakermalfunction during radiofrequency current appli-cation in three relatively large series including atotal of 125 patients with assorted pacemakers was44%.78–81 The most common interaction wasasynchronous pacing due to noise reversion, fol-lowed by oversensing resulting in refractory pe-riod extension and “functional undersensing,”pacemaker inhibition, or antitachycardia pacingin special pacemakers. Electrical reset, radiofre-quency induced pacemaker tachycardia, erraticbehavior, and transient loss of capture were lessfrequent. In contrast, Proclemer et al.82 did not ob-serve transient or permanent pacemaker dysfunc-tion in 70 consecutive patients with MedtronicThera I and Kappa single and dual chamber pace-makers with unipolar leads who underwent atri-oventricular (AV) junction ablation. The pace-makers were implanted prior to radiofrequencyablation in a single session procedure and weretransiently programmed to VVI mode at a rate of30 beats/min.

Table III.

Management of Patients with Implanted DevicesUndergoing External Cardioversion or Defibrillation

Before Procedure

� In patients with implantable cardioverter defibrillators,consider internal cardioversion via the device withcommanded shock

� Have pacemaker programmer available in the room� Determine (if possible) degree of pacemaker depen-

dency� Have transcutaneous external pacemaker available� Use self-adhesive patches or paddles in an antero

posterior configuration� Keep patches or paddles as far from generator and

lead(s) as possible� Use lowest possible energy for cardioversion or defibril-

lation� If available, use a biphasic waveform

After Procedure

� Repeat determination of pacing and sensing thresholdsimmediately, and 24 hours later

� Consider monitoring for 24 hours



The long-term effects of radiofrequency appli-cation on permanent pacing systems have beenless well studied. Exit block (possibly due to scarat the lead to tissue interface), lead damage, andchronic generator malfunction (requiring replace-ment) have been reported.75,81,83 In the multicen-ter report of Ellenbogen et al.78 and the series byProclemer et al.,82 changes in lead impedancesand pacing and sensing thresholds did not appearclinically significant. In a study of 72 patientswith a preexistent pacemaker (n 5 59) or defibril-lator (n 5 13) leads undergoing AV junction abla-tion, Burke et al.84 observed a significant increasein pacing thresholds that was present immediatelyafter ablation and became more marked 24 hourslater. A twofold increase in pacing threshold wasmuch more likely to occur in patients with defib-rillator leads. Two of the ICD patients (15%) andtwo of the pacemaker patients (3%) presented aprogressive rise in pacing threshold requiring leadrevision. The mechanism of the increased vulner-ability of the ICD leads was not clear.

Following a few simple precautions can min-imize adverse outcomes. Complete pacemakerinhibition is dangerous in patients without an es-cape rhythm during ablation of the atrioven-tricular junction. It is prudent to always insert atemporary transvenous pacemaker (programmedto a high output and, if necessary, to an asyn-chronous mode) to avoid asystole. The preexistentunit should not be trusted to provide backup pac-ing because loss of output or capture can occur de-spite programming an asynchronous mode. Therisk of pacemaker runaway may be reduced byprogramming the device OOO or to subthresholdoutputs.76 Rate responsiveness should be dis-abled. Pacing at the upper rate limit may occurwhen minute ventilation pacemakers that mea-sure transthoracic impedance misinterpret ra-diofrequency current.85 Tachyarrhythmia detec-tion should be disabled in patients with ICDs toprevent spurious therapies. Attempts should bemade to perform ablation as far as possible fromthe pacing leads. In some instances, a left-sidedapproach to ablation of the AV junction should beconsidered. Patients with previously implantedpacemaker or ICD systems should be followedclosely after radiofrequency catheter ablation.

LithotripsyAcoustic radiation, from extracorporeal shock

wave lithotripsy (ESWL) machines, provides anoninvasive means to disintegrate renal, ureteral,gallbladder, and biliary calculi. With the originaldevice (Dornier HM3, Kennesaw, GA, USA), thepatient lies in a water bath, and multiple (~ 1,500)hydraulic shocks are generated from an underwa-ter 20-kV spark gap and focused on the calculi by

an ellipsoid metal reflector. The shock wave canproduce ventricular extrasystoles, so it is synchro-nized to the R wave. Implanted devices could besubject to electric interference from the spark gapand mechanical damage from the hydraulic shockwave. Newer units (e.g., Dornier Compact Delta)use an enclosed water cushion for shock wavecoupling. Other units use electromagnetic (e.g.,Lithostar Plus Siemens AG, Erlanger, Germany) orpiezoelectric (e.g., Piezolith 2500, Richard WolfGmbH, Knittlingen, Germany) shock wave genera-tors.86 Most information regarding interactionswith implanted cardiac devices has been collectedwith the Dornier HM3 unit.

Several investigators have studied the effectof ESWL on pacemakers in vitro.87–89 Pacemakeroutput was not inhibited by properly synchronousshocks, but asynchronous shocks caused inhibi-tion in unipolar and bipolar devices. During AVsequential pacing, a shock inappropriately syn-chronized to the atrial pacing pulse is often sensedby the ventricular channel, with the potential tocause inhibition of the ventricular output. Inter-mittent reversion to magnet mode can occur be-cause of transient closure of the reed switch fromthe high energy vibration. Other responses notedduring in vitro testing include an increase in pac-ing rate secondary to tracking of EMI in the atrialchannel, noise reversion, spurious tachyarrhyth-mia detection,90 and malfunction of the reedswitch. Activity-sensing pacemakers increasedtheir pacing rate to the upper pacing rate within 1minute of the shock. ESWL caused no physicaldamage to the hermetic seal or the internal com-ponents of the pacemakers tested, except thatwhen an activity-sensing pacemaker was placed atthe focal point of the ESWL, the piezoelectric crys-tals shattered.89 In vitro testing of two ICDs with anew generation lithotripter did not disclose ad-verse interactions (even when the generator wasplaced within the focus of the lithotripter), pro-vided the shockwaves were applied synchronizedto the R wave.91

There is limited clinical experience with theuse of ESWL in patients with pacemakers or ICDs.Drach et al.92 reported only four mild complica-tions in a worldwide series of 131 pacemaker pa-tients. One device exhibited power-on-reset, onepatient developed irregular heart rhythm if morethan 22 kV was used, one device exhibited inter-mittent asynchronous operation, and one a 10-beat/min increase in pacing rate with several ex-trasystoles. Albers et al.93 did not observedetrimental interactions in 20 pacemaker patientsundergoing ESWL for urinary tract calculi. SafeESWL has been reported in a patient with an ab-dominal contralateral early model ICD shieldedwith polyestyrene foam94 and in a patient with an

PINSKI, ET AL.


unshielded tiered-therapy ICD ipsilateral to the re-nal stone.95 In a third patient with an Intermedics(Angelton, TX, USA) abdominal ICD near electivereplacement time, contralateral ESWL triggeredthe elective replacement indicator.95 It appearsthat ESWL is safe to use with implantable antiar-rhythmic devices as long as the device and targetare at least 6 cm apart. Activity-sensing rate adap-tive devices implanted in the thorax can undergolithotripsy safely, but the procedure should beavoided if the device is located in the abdomen.Synchronization of the shocks to the R wave iscrucial. Activity sensors and tachyarrhythmia de-tection should be temporarily disabled in allcases. Reprogramming dual chamber pacemakersto VVI or VOO (if the patient is pacemaker depen-dent)96 is safe, and will avoid ventricular inhibi-tion due to shocks synchronized to the atrial out-put, irregular pacing rate, tracking of inducedsupraventricular tachycardia, or triggering of theventricular output by EMI. In patients with AV se-quential pacing (DDD or DDI) who cannot tolerateloss of AV synchrony during the procedure, en-abling of safety pacing (or extending the postatrialpacing ventricular blanking when safety pacing isnot available) should prevent ventricular inhibi-tion. Safety pacing will result in a short AV inter-val that should not be detrimental. Careful follow-up should be performed over the next severalmonths to ensure appropriate function of the reedswitch. In patients with abdominal ICDs, full elec-trophysiological testing to confirm satisfactory de-tection and therapy of induced tachyarrhythmiasmay be warranted.

RadiotherapyRadiotherapy can induce different responses

in implanted devices. EMI produced by the radio-therapy machine can result in pacing inhibition,tracking, noise reversion, or inappropriate ICDdischarges. Usually, the effects are mild and ob-served only while the machine is switched on oroff.97 Interference may be more severe with beta-trons98 or with linear accelerators that misfire(spark).

More important is the risk of permanent gen-erator damage due to ionizing radiation.99 Al-though early pacemakers were not susceptible,newer devices incorporating complementarymetal oxide semiconductor-integrated (CMOS)technology, may incur cumulative damage duringradiation therapy.100 Ionizing therapeutic radia-tion acts on the silicone and silicone oxide insula-tors within the semiconductors. Radiation may besufficiently intense to cause complete failure orrandom damage to circuit components. Intense ra-diation may alter transistor parameters or createelectrical shorts that result in premature battery

depletion. Failure may also involve changes insensitivity, amplitude or pulse width, loss oftelemetry, output failure, or runaway rates. Be-cause the damage to the circuit is random and theradiation dose cumulative from one therapeuticexposure to the next, no specific prediction rela-tive to dose can be made. Last101 has presented acomprehensive review of in vitro studies assess-ing the effects of ionizing radiation on pacemakersand ICDs. It should be remembered that total ther-apeutic radiation doses may be as high as 70 Gy(7,000 rad) given over several weeks. In studiesthat have used conventional (i.e., fractionated)dosage regimens, minor pacemaker malfunctionhas been reported with doses as low as 2 Gy, butno significant failure has been observed withdoses less than 10 Gy. Changes in sensing andtelemetry functions and pulse width often occurfirst. Total loss of output has resulted from dosesof 16–300 Gy. The degree of susceptibility may beinversely proportional to the oxide thickness. Ro-driguez et al.102 found that more current deviceswith the thinner 3-mm CMOS technology wereless sensitive than the older ones with 5 or 8 mmCMOS circuits. Although one study reported noICD failures at doses lower than 50 Gy, chargetimes increased dramatically. The available evi-dence does not suggest differences in risk of pace-

Table IV.

Management of Patients with Implanted DevicesUndergoing Radiotherapy

� Avoid betatron� Evaluate device and pacemaker dependency prior to

therapy� Plan radiotherapy to minimize total dose (including scat-

ter) received by generator:� Avoid direct irradiation� Maximize shielding and distance of pulse generator

from radiation beam� Consider moving the pulse generator away from the

field if the estimated dose is . 10 Gy� Institute appropriate level of monitoring:

� If estimated dose , 2 Gy and patient not pacemakerdependent clinical monitoring suffices

� If estimated dose . 2 Gy or patient pacemakerdependent high level monitoring is necessary� Continuous electrocardiogram monitoring during

treatments� Have staff competent in advanced cardiac life sup-

port nearby� Check device function after each therapy session

and regularly for several weeks thereafter� Consider generator replacement at the earliest evidence

of circuitry damage



maker damage for the different available types oftherapeutic radiation. Diagnostic radiology proce-dures pose no immediate or cumulative effects onpulse generators.

Radiation oncology centers should have pro-tocols for patients with implantable antiarrhyth-mic devices (Table IV).103 Shielding and obliquefields may reduce the dose received by the device.This is particularly important in patients under-going radiation for thoracic or chest wall malig-nant disease. If the pacemaker is within the fieldof radiation (e.g., in patients with carcinoma of thebreast), there may be no alternative but to remove

the device and reimplant it away from the area tobe radiated. In many cases, the device can be relo-cated in an ipsilateral abdominal pocket and thepreexistent leads reused with the aid of extenders.If the pulse generator is not in the field radiation,it should nevertheless be shielded to prevent dam-age. It is essential that patients with implanted de-vices undergoing radiation therapy be monitoredclosely during the course of the treatment and fora few weeks thereafter. Although some pacingchanges may resolve in hours to days, the long-term reliability of the pulse generator is uncer-tain99 and should always be replaced.

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Interference in Implanted Cardiac Devices, Part II