does high-power computed tomography scanning equipment

Circulation Journal Vol.70, February 2006

alfunctioning of a pacemaker because of electro-magnetic interference (EMI) was reported afterdevelopment of the demand pacemaker.1 Clinical-

ly, a variety of medical appliances that produce electromag-netic or radiofrequency waves are now used for diagnosticor therapeutic purposes, and precautions or restrictions ontheir use have been enforced to protect patients with animplanted pacemaker from possible hazards.2–6

Computed tomography (CT) is widely used in clinicalpractice, but a detailed report has not been published of theeffects of CT scanning on the operation of pacemakers. Al-though it is commonly believed that CT scanning does notaffect the functioning of pacemakers, we have previouslyreported a transient malfunction of the pacemaker probablycaused by over-sensing.7

The present study was undertaken to examine the influ-ence of multislice spiral CT on pacemakers in patients andexperimental models of the human body.

MethodsECG Monitoring During Chest CT Scanning in Pacemaker-Implanted Patients

In 11 patients with implanted demand-type pacemaker,chest CT scanning using a multislice spiral CT system (4-detector row, SOMATOM Volume Zoom, Siemens,Germany) was performed for further evaluation of abnor-mal shadows that had been observed on chest X-ray.

During the CT scanning, the ECGs of the extremity leadswere recorded at a paper feed rate of 25mm/s. All patientsgave informed consent.

Measurement of Alternating Electric and Magnetic Fields in the CT Room and on CT Scan Lines

This experiment was conducted to examine whether theCT procedure produces electromagnetic fields in the CTroom and induces EMI with pacemakers. Alternations ofthe electric and magnetic fields on the CT scanning line,and at points 1m distant from the CT scanning line withinthe CT room, were measured during CT scanning using an electric-field measuring device (FD-1, Combinova,Sweden) and a magnetic-field measuring device (Model5080, F.W. Bell, Orlando, FL, USA). The measurementswere repeated 3 times, and the maximum values wereadopted.

Effects of CT Scanning on Pacemaker Function in Human Body Models

The pacemakers, Thera SR8960i and Kappa SR701(Medtronic, Minneapolis, MN, USA), combined with a5024M lead (Medtronic) were mounted in Irnich’s humanbody model (Fig1)8–10 and subjected to CT scanning. Thebench model (Fig 2) was constructed for this study toclarify the conditions induced by CT scanning that mightinfluence pacemaker function.

Measuring Systems The Irnich’s body model was filledwith 0.18w-% saline, and the electroconductivity of themodel was set at a value equivalent to that of the humanbody. Pick-up electrodes to receive pacing pulses from thepacemaker were attached to the pacemaker lead. Specificelectrodes to input the sensing signals (known as cenelicpatterns) produced by the pseudo-beat generator were alsoarranged on the model. The model was connected to thepseudo-beat generator and recorder via a 20-m cable that

Circ J 2006; 70: 190–197

(Received August 24, 2005; revised manuscript received November24, 2005; accepted December 7, 2005)Division of Cardiovascular Medicine, Department of Medicine,Nihon University School of Medicine, Tokyo, JapanMailing address: Shinobu Imai, MD, Division of CardiovascularMedicine, Department of Medicine, Nihon University School ofMedicine, 1-8-13 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8309,Japan. E-mail: [email protected]

Does High-Power Computed Tomography Scanning Equipment Affect the Operation of Pacemakers?

Satoshi Yamaji, MD; Shinobu Imai, MD; Fumio Saito, MD; Hiroshi Yagi, MD; Toshio Kushiro, MD; Takahisa Uchiyama, MD

Background Computed tomography (CT) is widely used in clinical practice, but there has not been a detailedreport of its effect on the functioning of pacemakers.Methods and Results During CT, ECGs were recorded in 11 patients with pacemakers and the electromagneticfield in the CT room was also measured. The effect of CT on a pacemaker was also investigated in a human bodymodel with and without shielding by rubber or lead. Transient malfunctions of pacemakers during CT occurredin 6 of 11 patients. The model showed that malfunctioning of the pacemaker was induced by CT scanning andthis was prevented by lead but not by rubber. The alternating electrical field was 150V/m on the CT scanningline, which was lower than the level influencing pacemaker functions. The alternating magnetic field was 15 Ton the CT scanning line, which was also lower than the level influencing pacemaker functions.Conclusions Malfunctions of the pacemaker during CT may be caused by diagnostic radiant rays and althoughthey are transient, the possibility of lethal arrhythmia cannot be ignored. (Circ J 2006; 70: 190–197)

Key Words: Asynchronous pacing; Computed tomography; Electromagnetic interference; Over-sensing;Pacemaker

M

191Effect of CT on Pacemakers


Fig1. Schematic of Irnich’s human body model. Pick-up electrodes to receive pacing pulses from the pacemaker andspecific electrodes as input of simulated signals are arranged on the lead. Simulated signals are produced from the pseudo-beat generator, which is battery-driven. The signals from the pacemaker are connected via a differential amplifier to therecorder driven by an alternating current from a commercial power source.

Fig2. Schematic of the bench model. A 510- load resistance is placed between the tip and the ring of the pacemakerlead. At both ends, a differential simulated signals output unit is attached via a 240k attenuation resistance. Simulatedsignals are produced from the pseudo-beat generator. The signals collected from the pacemaker are fed from both ends ofthe 510- resistance into the differential amplifier. The pseudo-beat generator is battery-driven. The signals from thepacemaker are perceived by the differential amplifier and fed through the isolation amplifier into the recorder driven byalternating current from a commercial power source.

192 YAMAJI S et al.


was shielded against noise. They were driven by theinput/output differential method. The pseudo-beat genera-tor was battery-driven to avoid generation of alternatingcurrent noise.

In the bench model, 510- load resistance was placedbetween the tip and the ring of the pacemaker lead. A cablefor differential output of the simulated signals was attachedvia a 240k attenuation resistance to both ends of the loadresistance. The simulated signals from the pseudo-beatgenerator assumed the form of a cenelic pattern output, aswith the Irnich’s model. The signals collected from thepacemaker were fed from both ends of the 510- resis-tance into the differential amplifier, which was connectedvia an isolation amplifier to a recorder driven by alternatingcurrent from a commercial power source. This was toshield out noise produced by the commercial power source.The cable was a 20-m shielded cable, similar to the oneused in the Irnich’s model. The pseudo-beat generator wasbattery-driven to avoid generating alternating current noise.

Setting of the Pacemaker and CT Output In the studiesusing Irnich’s human body model, the pacemaker was set toAAI mode, the sensitivity setting was 0.5mV, the rate set-ting was 60pulses/min, and the sensing polarity was unipo-lar. The CT output was 140kV and 150mAs (collimation2.5mm, feed/rotation 10mm, gantry rotation time 500ms).

During CT scanning of the human body model, if non-standard movement of the pacemaker was observed, furtherexperiments using the bench model were conducted bychanging the sensing polarity (bipolar, unipolar) andsensing sensitivity (0.5, 1.0, 2.8, 4.0mV). The CT outputwas 140kV and 300mAs, or 140kV and 100mAs (collima-tion 2.5 mm, feed/rotation 10 mm, gantry rotation time500ms).

Determination of Malfunction Caused by CT ScanningThe pacemaker mounted on the model was tested under 2conditions in order to simulate the presence or absence ofthe patient’s own pulse.

Inhibition Test The pacemaker, without signal inputfrom the pseudo-beat generator and with the stimuluspulse output at a setting rate of 60beats/min, was CTscanned.

If pulse inhibition, or prolongation of the pulse inter-val, even for a single pulse, occurred during scanning,and if the same phenomenon occurred during repeatscanning, the malfunction was taken to be caused by CT.

Asynchronous Test CT scanning was performedwhen the pacemaker sensed the pulse at 60 beats/minfrom the pseudo-beat generator and inhibited the stimu-

lus pulse output. If asynchronous pacing occurred evenonce, or transferred to the asynchronous mode, and if thesame phenomenon occurred during repeat scanning, themalfunction was taken to be caused by CT.During CT scanning, in order to identify the site from

which the effect arose, scanning was performed in 2 direc-tions, the long and short axis of the pacemaker generator,and the affected site was confirmed from the imagesscanned.

Identification of the CT Scanning Parameter Influencingthe Pacemaker If the pacemaker was affected by CTscanning then, to refine the factor, the pacemaker wasmounted on the Irnich’s human body model under thefollowing conditions, and the inhibition test and asynchro-nous test were again conducted.

(1) To exclude effects of conduction current or alternat-ing current, the pacemaker and lead were CT scanned whileinsulated with rubber.

(2) To exclude direct effects of irradiation on pace-maker function, the pacemaker was shielded by lead duringCT scanning.

It could not be ruled out that the noises that were en-tered into the connecting cable, oscilloscope, or recorder inthe experimental circuit would be mistaken for interfer-ence. The pacemaker and the lead, not mounted on themodel, were therefore CT scanned at a setting rate of60 pulses/min and programmed to detect a high rateepisode (≥80pulses/min).

ResultsEffects of CT Scanning on Pacemaker Function in Patients

Table1 shows the patients’ backgrounds and ECG pat-terns observed during CT imaging. Transient nonstandardmovement of the pacemaker occurred in 6 of the 11 pa-tients. In the telemetric data analyzed after CT scanning,neither modification nor resetting of the program occurred.Two patients in whom there was nonstandard movementduring CT scanning are described.

Case 1 A 65-year-old man had undergone permanentpacemaker (Kappa KDR701, Medtronic) insertion for sicksinus syndrome. He was scheduled for a CT scan of thechest for more detailed evaluation of a mass lesion found inthe right upper zone on chest X-ray. The CT was conductedat 150kV and 150mAs (collimation 2.5mm, feed/rotation17.5mm, gantry rotation time 500ms).

Before the CT, the ECG showed full-beat atrial pacingand ventricular sensing pattern, with an atrial pacing inter-

Table 1 Characteristics of the Patients With an Implanted Pacemaker

Patient no. Age (years) Pacemaker mode ECG pattern before CT Malfunction during CT

1 80 VVI VP Over-sensing 2 77 VVI VP None 3 78 VVI VP None 4 56 VVI Own beats + VP None 5 87 VDD ASVP Over-sensing 6 72 VDD ASVP Over-sensing 7 66 VDD ASVP Over-sensing 8 77 DDD Own beats None 9 65 DDD APVS Over-sensing10 74 DDD APVP None11 77 DDD APVP Over-sensing

CT, computed tomography; VP, ventricular pacing; ASVP, atrial sensing-ventricular pacing; APVS, atrial pacing-ventricular sensing.



val of 857ms. During CT scanning through the pacemakergenerator, the atrial pacing interval increased to 1,200ms,returning to 857ms after the scanning line had passed thegenerator (Fig 3). Changes in pacemaker activity wereobserved only during scanning through the pacemakergenerator, and no effect was seen during scanning throughthe lead.

Case 2 An 87-year-old man had undergone permanentpacemaker (Kappa KVDD701, Medtronic) insertion forcomplete atrioventricular block. During hospitalization heunderwent CT for detailed evaluation of a mass observed in the right pulmonary hilum on chest X-ray. The CT wasconducted at 150 kV and 150 mAs (collimation 2.5 mm,

feed/rotation 17.5mm, gantry rotation time 500ms).Before CT scanning, the pacemaker was running to an

atrial sensing-ventricular pacing pattern regulated by thepatient’s own PP interval of 1,200ms. During CT scanningthrough the pacemaker generator, ventricular pacing ap-peared approximately 40 ms earlier than in the previousatrial sensing-ventricular pacing pattern. Also, 500 mslater, ventricular pacing occurred (Fig4) during scanningthrough the upper part of the generator, and not duringscanning through the lead (as in Case 1). Telemetric dataanalyzed after CT scanning did not show modification orresetting of the program that required re-programming.

Fig3. Case 1. Before computed tomography (CT) scanning, the ECG shows full-beat atrial pacing (AP) and ventricularsensing (VS) pattern, with an atrial pacing interval of 857ms. During CT scanning through the pacemaker generator, theatrial pacing interval increases to 1,200ms, returning to 857ms after the scanning line had passed the generator.

Fig4. Case 2. Before computed tomography (CT) scanning, the pacemaker has to an atrial sensing-ventricular pacing(AS-VP) pattern regulated by the patient’s own PP interval of 1,200ms. During CT scanning through the pacemakergenerator, ventricular pacing appears approximately 40ms earlier than in the previous AS-VP pattern. Ventricular pacingoccurs 500 ms later.

194 YAMAJI S et al.


Alternating Electric and Magnetic Fields in the Vicinity of the CT Scanning Line and in the CT Room

During scanning the alternating electric field parameterswere 150V/m on the CT scanning line and 80V/m in theCT room, and the values for the magnetic fields were 15 Ton the CT scanning line and 300nT in the CT room.

Effects of CT Scanning on Pacemaker FunctionInterference by CT Scanning In the inhibition test,

pacing was inhibited for approximately 4 s during scanningabove the pacemaker (Fig5). In the asynchronous test, 2asynchronous pacing spikes appeared from the pacemakergenerator during CT scanning above the pacemaker (Fig6).

Both phenomena were reproducible only when the upperpart of the pacemaker was scanned, and there was nodifference between types of pacemaker. These phenomenasubsided rapidly after the CT scan lines passed through thepacemaker, without causing any modification or re-settingof the program.

Conditions and Site of the CT Scanning Table2 showsthe conditions in which effects caused by CT scanning ap-peared on the bench model. Identical results were obtainedfor the 2 types of pacemaker.

The transient inhibition of pacing observed during CTscanning in the inhibition test depended on the sensingsensitivity of the pacemaker, not on the sensing polarity.

Fig5. Inhibition test in the Irnich’s model. Pacingstimulation was inhibited for approximately 4 s duringcomputed tomography (CT) scanning through thepacemaker.

Fig6. Asynchronous test in the Irnich’s model. Pacemaker senses the pulse at 60beats/min from the pseudo-beat genera-tor, and inhibits the stimulus pulse output. Two asynchronous pacing spikes appear from the pacemaker generator duringcomputed tomography (CT) scanning through the pacemaker.

Table 2 Relationship Between Pacemaker Malfunction and Settings of CT and Pacemaker

Inhibition test Asynchronous testCT output CT output

140 kV/300 mAs 140 kV/100 mAs 140 kV/300 mAs 140 kV/100 mAs

Sensing polarity Bipolar Unipolar Bipolar Unipolar Bipolar Unipolar Bipolar UnipolarSensitivity (mV) 0.5 I I I I A A × × 1.0 I I × × × × × × 2.8 I I × × × × × × 4.0 × × × × × × × ×

CT, computed tomography; I, pacing inhibition; A, asynchronous pacing; ×, no malfunction.



The transient asynchronous pacing observed during CTscanning in asynchronous testing also depended on thesensing sensitivity, and showed no relation to the sensingpolarity.

Examination using CT output revealed that higheroutput tended to affect the pacemaker.

Fig 7 is a transparent image of the site at which allmalfunctions occurred reproducibly in the tests, and noeffect was observed during scanning through the lead.

Identification of Factors Affecting Pacemaker FunctionIn both the inhibition test and the asynchronous test, pace-maker malfunctioning was not prevented by insulation withrubber but was prevented completely by lead shielding.Insulation with rubber did not alter any of the malfunctionsthat appeared in either test.

Telemetric data from the pacemaker not mounted on themodel were analyzed after the CT scanning and high rateepisodes were observed during the scanning process(Fig8).

DiscussionWith the development of electromagnetic devices, such

as mobile phones, electromagnetic cookers and antitheftdevices, EMI of the operation of implanted pacemakers anddefibrillators has become a serious problem, and a numberof reports addressing this issue have been published.2,3,11

The effect of medical appliances, such as magnetic reso-nance imaging or an electrosurgical knife, on an implantedpacemaker presents a similar problem.4–6 High-dose irradia-tion equipment can interfere with pacemaker function,which necessitates re-programming, and may even perma-nently damage the pacemaker.12–16 According to the exist-ing American Association of Physicists in Medicine TaskGroup 34 Guidelines,17,18 the total irradiation exposurelevel of a pacemaker in patients receiving radiotherapyshould not exceed 2.0Gy. It has also been recommendedthat there be no direct irradiation of the pacemaker. How-ever, the effect of CT equipment on the functioning ofpacemakers has not yet been clarified, and guidelines arenot available for patients undergoing diagnostic testingwith equipment that emits radiation (CT devices etc). Weconducted experiments to clarify the effects of electric andmagnetic fields and radiation used in CT scanning.

Our main results are that transient malfunctions of pace-makers during CT scanning occurred in 6 of 11 patients.Experimental studies using a model showed that malfunc-tioning of pacemakers induced by CT scanning was

prevented by lead shielding but not by rubber.Conducting currents, and alternating magnetic and elec-

tric fields are generally known to cause EMI of pacemak-ers.1,8 We found that the maximum alternation of electricfields on the CT scanning line was 150V/m. Butrous et alreported that a current of about 10 A was induced per1 kV/m at a frequency of 50 Hz, and that pacemakersimplanted in patients were affected by alternating electricfields of over 5 kV/m,19 which is 33-fold more than themaximum in the present study. Furthermore, in the presentstudy rubber insulation, which completely intercepts theinfluence of alternating electric fields and conducting cur-rents, could not prevent pacemaker malfunctioning inducedby CT scanning, so we therefore believe that the observedpacemaker malfunctions were not caused by alternation ofthe electric fields or the conduction currents.

The maximum alternation of the magnetic field on theCT scan lines in the present study was 15 T. Irnichreported that a unipolar pacemaker and a lead may form asemicircle with an area of up to 570cm2, and if an environ-mental magnetic field is approximately 20 T at 50Hz, theinduced voltage according to Faraday’s law is 1mV peak topeak.8,9 However, Irnich looked at the unipolar electrodepacemaker, and a bipolar electrode pacemaker should notbe affected by alternating magnetic fields that are approxi-mately 6–10 times larger.1 For a bipolar electrode, the

Fig7. Site at which pacemaker malfunctions occurred reproduciblyduring computed tomography scanning tests. There was no effectduring scanning through the lead shield.

Fig8. Telemetric data from the pacemakerafter computed tomography scanning showshigh-rate episodes (≈200–250 pulses/min)recorded during scanning.

196 YAMAJI S et al.


region between the ring and the tip of the lead may beaffected. However, in our experiment there was no differ-ence between bipolar and unipolar electrodes. Furthermore,the effect was observed reproducibly during scanning ofthe same site in the upper part of the generator. We there-fore believe that the alternating magnetic fields do notsignificantly affect the pacemaker.

The X-rays used for CT scanning are also electromag-netic waves (wave length: 0.01–10nm) with high penetra-bility, but which can be cut off by lead shielding. Toexamine the effect of irradiation on pacemaker function,the pacemakers were shielded by lead and mounted onIrnich’s human body model during CT scanning. In thissetting, direct exposure to the X-ray was prevented by thelead, but conducting current can affect the pacemakerthrough saline. With this shielding the pacemaker malfunc-tions ceased, indicating that the irradiation used in CTscanning, which was previously thought to have little influ-ence, affects the function of pacemakers. Analysis of thetelemetric data recorded during the scanning revealed thatthese pacemaker malfunctions were recorded as high-rateepisodes, which rules out interference with the measuringsystem, and demonstrates that the malfunctions were aneffect of irradiation of the pacemaker itself.

Pacemaker malfunctions associated with irradiation havebeen reported in patients receiving radiotherapy,12–15 and theexplanation has been that high-dose irradiation producesunnecessary electric currents within the semi-conductorcircuit (C-MOS type) used in the present generation ofpacemakers, sealing electrons within the insulator andcausing malfunctions. Adamec et al reported that once thestimulus pulse width or the preset rate was altered duringradiotherapy, the resulting failure lasted for periods varyingfrom less than 1h to more than 24h.15 It is known that C-MOS type semiconductor elements are damaged whenexposed to 6–10Gy radiation.15,16

Recently, the radiation dose rate during CT scanning hasbecome higher to shorten the scanning time and improve thequality of the image. Furthermore, multislice CT requireshigher radiation doses rate than single spiral CT and thusaffects more of the C-MOS semi-conductor circuit. In addi-tion, the size of the pacemaker transistor is getting smallerby high integration degree and a power-saving function isrequired to maintain many pacemaker functions, with theconsequence that the electrical circuit has become moresensitive to minute electrical currents caused by the photo-electric effect.

The sensing circuit, called a hybrid integrated circuit,was located in the upper part (Fig7) of the generator usedin this study, which is the amplifying part. We thereforebelieve that the phenomenon occurred because radiationdirectly entering the sensing circuit was amplified by thepacemaker.

The effect of cell phones and other wireless communica-tion devices has also been studied in detail.11 Changes inpacemaker function occurring as a result of EMI include in-hibition of stimulus pulses, over-sensing, and asynchronouspacing because of an anti-EMI mechanism.

The inhibition of pacing that occurred for several secondsin our inhibition test may have been caused by over-sensing, in view of the noise from the radiation entering thesensing circuit of the generator during CT scanning. Thephenomenon observed in the asynchronous test may haveoccurred as follows. If the noises enter during simulatedsignal sensing, the pacemaker corrects the stimulus cycle

and enters a refractory period, during which noises exceed-ing the sensing sensitivity enter for a certain time, activat-ing the EMI preventive mode and causing a change toasynchronous pacing. A smaller effect was observed in theasynchronous test than in the inhibition test because, in theformer, if even a single shot of noise entered it was falselyrecognized as the heart’s own beat and pacing inhibitionmay occur. In contrast, in the asynchronous test, even ifnoise is entered, the pacemaker enters the refractory period,and time is needed for the EMI preventive mode to be acti-vated, during which, if the scanning line passes through it,the effect may not occur.

In Case 1, inhibition of pacing probably occurred as aresult of over-sensing, as described above, on the atrial orventricular side or both.

In Case 2, ventricular pacing of the fourth beat (Fig2)appeared about 40 ms earlier than in the other atrialsensing-ventricular pacing. It was therefore considered thatnoise induced by radiation, and not the p-wave, was over-sensed in the atrial side; ventricular pacing followed thissensing. Furthermore, subsequent ventricular pacing at theupper rate may have been caused by over-sensing of theatrial side, in view of the continuing irradiation.

These phenomena were transient because the CT scan-ning was completed within a few seconds. However, thelowest sensitivity of the pacemaker affected during the CTscanning in the present study was 2.8 mV, which is thesensitivity level usually used for ventricular sensing, and isnot an exceptional value.

The output of CT can clearly affects pacemakers underthe conditions used for chest imaging. Recently, because ofits typical high output and resolution CT has been used toimage the coronary arteries. In dynamic CT, scanning isrepeated at the same site, so the pacemaker could be irradi-ated for much longer. In fact, Medtronic Company releaseda warning about pacemaker implanted patients undergoingdynamic CT. Moreover, the pacemaker indication nowencompasses biventricular pacing, and compact thin-typepacemakers, or pacemakers with high performance, highfunction, and complicated circuits, have been developed,and the sensing circuit has also become complex. Thus theincreasing indications for CT and the increasing complex-ity of pacemakers worsen the problem.

The present study shows that pacemaker malfunctiongenuinely occurs in clinical cases, and was reproducible inour experimental studies using human body models.

The pacemaker malfunctions observed were transientbecause CT scanning passed rapidly through the crucial partof the pacemaker and none of the patients showed clinicalsymptoms. However, under certain conditions asynchronouspacing may generate a spike on the T wave of the patient’sown pulses and induce ventricular tachycardia or ventricu-lar fibrillation.

Study LimitationsThere were 5 cases that did not show pacemaker mal-

functions during CT scanning, and the pacemakers used inour experimental studies were both made by the MedtronicCompany. Further studies using pacemakers from othermanufacturers, with different design parameters, are neces-sary.

ConclusionEMI may occur in the pacemaker during CT scanning.



The malfunctions are transient, but we cannot rule out thepossibility of lethal arrhythmia. During CT scanning of theimplantation site, medical staff, including medical doctor,nurse, and radiological technologist, need to be aware ofthis phenomenon and ECG monitoring is recommended.Further studies to examine the effect of CT scanning on thefunction of all types of pacemaker are needed.

AcknowledgmentsWe thank Mr Hiroshi Fujimoto and Mr Katsumi Yokomizo (Education

Department, Medtronic, Inc) for their cooperation during this study.

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does high-power computed tomography scanning equipment

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