© 2004 by European Society of Cardiology
Interference by cellular phones with permanent implanted pacemakers: an update
aDepartment of Cardiothoracic Surgery, University of Cologne 50924 Cologne, Germany; bDepartment of Cardiovascular Engineering Jülich, University of Aachen Germany; cDepartment of Cardiology, University of Cologne Germany
Manuscript submitted 23 December 2003. Accepted after revision 6 March 2004.
*Corresponding author. Tel.: +49-221-4785359; fax: +49-221-4787927. E-mail address: E-mail address: khosro.hekmat{at}medizin.uni-koeln.de
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Abstract |
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AIMS: The aim of this study was to test pacemakers with feedthru filters for interference with a digital cellular telephone.
METHODS: The study comprised 100 patients having their first pacemaker implantation between January 2001 and May 2003. A GSM-standard cellular phone was tested in the standby, dialing and operating mode against 23 single-chamber and 77 dual-chamber pacemakers. Continuous surface electrocardiograms, intracardiac electrograms, and marker channels were recorded when calls were made by a land phone to the cellular phone.
RESULTS: In 2 patients we observed pacing inhibition with the cellular phone positioned directly above the pacemaker pocket. The unipolar and bipolar ventricular sensitivity setting was 0.25 mV in one dual-chamber pacemaker, and when we changed the sensitivity to 0.50 mV and higher no interference could be detected. The second inhibition occurred in a single-chamber pacemaker with unipolar and bipolar ventricular sensitivity setting of 0.5 mV, where a sensitivity change to 1.0 mV eliminated the interference.
CONCLUSION: Anticipating a correct setting of ventricular sensitivity, currently available pacemakers equipped with feedthru filters do not show any interference with cellular phones. Since interference was only observed with sensitivity settings below 0.50 mV, we recommend that permanent programming of ventricular sensitivity should be set at 2.0 mV and higher.
Key Words: cellular telephones, interference, feedthru filter, pacemaker
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Introduction |
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It has been estimated that there will be more than 1 billion subscribers to cellular telephone services worldwide by the year 2003 [1]
. Electromagnetic fields may interfere with normal pacemaker function at a rate up to 41% [2–10]. Although development of new feedthru filters may have lessened this problem [1,11,12], it remains unclear whether these features are incorporated in currently available pacemakers, and if they protect pacemakers from digital cellular telephone interference.
Studies of the interactions between electromagnetic interference caused by cellular phones and permanent implanted pacemakers require testing under a "worst-case scenario" [1]. This includes a programming of the pacemaker to unipolar sensing and pacing modes and inducing of a maximum sensitivity setting during continuous pacing of the patient.
The aim of this study was to test pacemakers with modern feedthru filters under worst-case conditions for evidence of interference by a digital cellular telephone.
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Methods |
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The study population included 100 patients (58 males and 42 females), 23 with single-chamber and 77 with dual-chamber pacemakers. All patients had pacemaker implantation between January 2001 and May 2003. The mean age was 60.6±23.0 years with a range of 4–88 years. All patients or their parents gave informed consent prior to the study.
The GSM (Global Systems for Mobile Communications) cellular phone used was a single-band Siemens S4 working in the German D-net with a transmission frequency of 900 MHz. This phone uses digital transmission and has a maximum power output of 2 W.
Prior to the study, a routine pacemaker check was performed with determination of pacing and sensing thresholds. Then atrial and ventricular sensitivity settings were programmed to their most sensitive values, and all pacemakers were programmed to unipolar atrial and ventricular sensing. Only in patients who showed evidence of interference did we also test the bipolar lead configuration.
In patients with spontaneous rhythm the pacemaker rate was programmed higher than the spontaneous rate in order to detect inhibition of the pacemaker. In addition, the pacemaker rate was programmed to 40 beats per minute in all patients in order to exclude pacemaker triggering by the cellular phone during spontaneous rhythm.
The antenna of the cellular phone was positioned directly above the pacemaker pocket. Separate tests were performed to measure the distance at which any interference occurred. Continuous surface electrocardiograms, intracardiac electrograms, and marker channels were recorded when calls were made by a land phone to the cellular phone. The following operations were performed:
- Switching the phone on and connecting to the net.
- Receiving a call and letting the phone ring for 10 s.
- Receiving a call without talking.
- Ending the connection.
During the whole test procedure, the ECG was continuously observed by a physician to detect interference and to terminate the test if necessary. After completion of the test the pacemaker was checked for changes in the programmed parameters.
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Results |
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Thirty-one different devices were tested from the following manufacturers: Medtronic (Minneapolis, MN, USA), CPI Guidant (St. Paul, MN, USA), Biotronik (Berlin, Germany), Pacesetter (Sylmar, CA, USA) and Vitatron (Dieren, The Netherlands). Table 1 shows the 23 single-chamber pacemakers, where 4 pacemakers were atrial-inhibited and 19 pacemakers ventricular-inhibited. Table 2 shows the 77 dual-chamber models. Only one model was a single lead (VDD) pacemaker. An inquiry to all five companies showed that all tested devices were equipped with modern feedthru filters.
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In 2 patients we observed pacing inhibition with the cellular phone positioned directly above the pacemaker pocket. The atrial sensitivity was 0.18 mV and the ventricular sensitivity setting was 0.25 mV in one dual-chamber pacemaker (CPI Guidant Pulsar Max II DR), and when we changed the ventricular sensitivity to 0.5 mV and higher no interference could be detected. The second inhibition occurred with ringing of the cellular phone in a single-chamber pacemaker (Biotronik Actros VVIR) with a ventricular sensitivity setting of 0.5 mV, which is shown in Fig. 1. A sensitivity change to 1.0 mV eliminated the interference (see Fig. 2). In both cases the antenna of the cellular phone was in direct contact with the skin of the patients over the implanted pacemaker. Separate tests were performed to measure the distance at which the interference was produced. The cellular phone was moved away from the pacemaker at a steady rate of about 1 cm/s. In both cases no interference could be detected at a distance >2 cm.
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When we changed the lead configuration from unipolar to bipolar in the affected pacemakers the interference could not be eliminated in both cases. Both affected pacemakers returned to normal operation after the interference ended.
In order to exclude pacemaker triggering by the cellular phone during spontaneous rhythm all pacemakers were programmed to 40 beats/min. With this setting, 26 patients showed no spontaneous rhythm at all. The other 74 patients did not show any pacemaker triggering. A change in pacemaker programming or a switch to asynchronous pacing was not observed in any patient.
All evaluated models showed significant noise in the telemetric transmission when the cellular phone was located near the programming head. Sometimes the interference was great enough to cause loss of telemetric monitoring of the intracardiac ECG and marker channel. Fig. 3 shows the interference on the marker channel and the intracardiac ECG (CPI Guidant) with the cellular phone. With the ringing of the cellular phone the loss of telemetric monitoring is obvious. The same was true for all other companies.
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Discussion |
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The potential for electromagnetic interference with implanted pacemakers by cellular phones has been recognized since 1994 [7,
13,14]. Several investigators have demonstrated in vitro [3,8,15–17] and in vivo [2,4,5,7,9,10,13,18] the possibility of interference between cellular phones and pacemakers. Table 3 gives an overview of the in vivo studies. The reported incidence of interference was between 0 and 41%. We believe that this broad span has two main reasons:
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- 1. different types of cellular phones used in these studies;
- 2. inclusion of pacemakers with and without feedthru filters.
Assessment of the effects of cellular phones on pacemakers has been complicated by the wide variety of technologies in use [1,6]. Table 4 shows the different wireless communication devices used worldwide [1,6,7,14,19]. There are 3 different generations of mobile phones characterized by the type of multiple access. First generation phones are analog with frequency division multiple access. Second generation phones are digital with time division multiple access, whereas third generation phones are also digital with code division multiple access. In the past, some investigators favoured the use of analog phones by pacemaker patients, because interference was found to be less with these devices [1,6]. With digital transmission modes becoming dominant worldwide, such a recommendation is no longer practical.
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In this study, we examined the effects of a GSM phone with a peak power of 2 W, which is the one most commonly used in Europe. The GSM system is a time division multiple access technology working with a maximum number of transmissions from the mobile phone of 217 times per second (217 Hz). The GSM system also contains other frequency components of 2 Hz and 8 Hz. The 2 Hz component is known as the Discontinuous Transmission mode (DTX) and predominates during ringing of the cellular phone and listening. The 8 Hz mode is associated with system control functions.
As shown in Table 4 several subgroups exist under the category GSM. Irnich et al. [8] was not able to find any interference with a GSM mobile phone operating in the German E-Net at 1800 MHz. Therefore, we used a single-band mobile phone with 900 MHz operating in the German D-Net. This is important, because dual-band cellular phones are able to switch between 900 MHz and 1800 MHz.
Not all studies were performed under worst-case conditions. Therefore, we changed the programme of all tested pacemakers in order to make them most sensitive to electromagnetic interference. Atrial and ventricular sensitivity settings were programmed to their most sensitive values, and all pacemakers were programmed to unipolar atrial and ventricular sensing. In patients with spontaneous rhythm the pacemaker rate was programmed higher in order to detect inhibition of the pacemaker.
In 2 patients we observed pacing inhibition with the antenna of the cellular phone positioned directly above the pacemaker pocket. When we changed the lead configuration from unipolar to bipolar in the two affected pacemakers the interference could not be eliminated in either case. Irnich et al. [8] concluded in an in vitro study with 231 different pacemakers from 20 manufacturers that bipolar pacemakers do not possess a higher protection against electromagnetic interference.
Hayes et al. [7] reported a switch to asynchronous pacing in 7.3% of the patients. Although we programmed all pacemakers to 40 beats/min we were not able to find any pacemaker triggering by the GSM telephone. With this setting 26 patients were still pacemaker-dependant. Pacemaker triggering may be masked in these patients.
The ventricular sensitivity setting is most critical, which has been confirmed in several studies [1,7,11,14]. Manufacturers allow different most sensitive values for permanent programming of the pacemaker. In CPI Guidant pacemakers a permanent sensitivity setting of 0.25 mV is possible, Medtronic pacemakers do not allow permanent sensitivity setting below 2.0 mV. With a ventricular sensitivity setting of 2.0 mV and higher, we would not have detected any interference in this study.
Third generation mobile phones will be introduced in the next few years. In Europe, this is called Universal Mobile Telecommunication System (UMTS). The frequency band for this system is between 1800 and 2200 MHz and the power output between 0.01 W and 0.25 W. The safety of these devices is as yet unknown.
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Limitations |
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We tested only one GSM mobile phone with a maximum power of 2 W. The GSM cellular phone modifies the power output between 0.02 W and 2.0 W. Therefore, we are not able to give any information about the peak power values. Based upon previously published work by Sparks et al. [20]
there may be techniques available to avoid this limitation. Use of marker channel(s) implies telemetric communication with the implanted generator plus monitoring by means of a surface electrocardiogram may have imposed greater susceptibility to interference. A way, at least partially, to overcome this might have been to use finger plethysmography. This would have registered each arterial pulse without involving electromagnetic fields.
It is possible that a weak rather than a strong signal path might cause automatic adjustments in the phone, which may produce more interference with the pacemaker. This was not tested.
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Conclusion |
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Anticipating a correct setting of ventricular sensitivity, currently available pacemakers equipped with feedthru filters do not show any interference by cellular phones. However, we still recommend that patients should not carry the phone close to the pacemaker, which is the only place where high risk interference has been observed. At these high sensitivities programming from unipolar to bipolar sensing failed to prevent interference. Since interference was only observed with sensitivity settings of 0.25 mV and 0.5 mV. We recommend that permanent programming of ventricular sensitivity should be set at 2.0 mV or less sensitive.
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Footnotes |
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Presented at Europace 2003, Paris December 14–17, 2003. 
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References |
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