J Artif Organs DOI 10.1007/s10047-014-0765-1
ORIGINAL ARTICLE
Pacemaker
Electromagnetic interference of implantable cardiac devices from a shoulder massage machine Saeko Yoshida • Kousaku Fujiwara Satoshi Kohira • Minoru Hirose
•
Received: 8 August 2013 / Accepted: 19 March 2014 Ó The Japanese Society for Artificial Organs 2014
Abstract Shoulder massage machines have two pads that are driven by solenoid coils to perform a percussive massage on the shoulders. There have been concerns that such machines might create electromagnetic interference (EMI) in implantable cardiac devices because of the time-varying magnetic fields produced by the alternating current in the solenoid coils. The objective of this study was to investigate the potential EMI from one such shoulder massage machine on implantable cardiac devices. We measured the distribution profile of the magnetic field intensity around the massage machine. Furthermore, we performed an inhibition test and an asynchronous test on an implantable cardiac pacemaker using the standardized Irnich human body model. We examined the events on an implantable cardioverter–defibrillator (ICD) using a pacemaker programmer while the massage machine was in operation. The magnetic field distribution profile exhibited a peak intensity of 212 (A/m) in one of the solenoid coils. The maximal interference distance between the massage machine and the
S. Yoshida (&) M. Hirose Department of Medical Safety Engineering, Graduate School of Medical Science, Kitasato University, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan e-mail: [email protected] M. Hirose e-mail: [email protected] K. Fujiwara M. Hirose Clinical Engineering Course, School of Allied Health Science, Kitasato University, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan S. Kohira Department of Medical Engineering, Kitasato University Hospital, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan
implantable cardiac pacemaker was 28 cm. Ventricular fibrillation was induced when the massage machine was brought near the electrode of the ICD and touched the Irnich human body model. It is necessary to provide a ‘‘don’t use’’ warning on the box or the exterior of the massage machines or in the user manuals and to caution patients with implanted pacemakers about the dangers and appropriate usage of massage machines. Keywords
Pacemaker EMI Massage machine
Introduction Significant research has been conducted on the electromagnetic interference (EMI) in implantable cardiac devices such as implantable cardiac pacemakers (pacemakers) and implantable cardioverter–defibrillators (ICDs). Numerous reports suggest that common electrical equipment utilized around the home affects the functioning of implantable cardiac devices, and many studies have been conducted to clarify the influence of such equipment [1–5]. Devices such as cellular phones and induction ovens are well-known to cause EMI in implantable cardiac devices because of the generated time-varying magnetic field. By Faraday’s law, an electromotive force is generated in a loop-shaped conductor when a magnet approaches it, causing current flow. Pacing leads serve as loop conductors in patients with implanted pacemakers, and current flows to the pacemaker through the electrodes. Therefore, it was surmised that other apparatuses that generated some amount of time-varying magnetic fields may also induce EMI in implantable cardiac devices. Massage machines designed to massage the shoulders are readily available from home electronics retailers or via mail order. These devices deliver a percussive massage to
123
J Artif Organs Fig. 1 Operation of the massage machine. This is a figure showing the operation of the massage machine. The massage machine has two solenoid coils positioned near the shoulders. The machine is often used for the improvement of stiff neck
Massage machine
Solenoid coil Front of the body
Backside
the shoulders via pads driven by two solenoid coils and are often used by subjects for the improvement of a stiff neck. There have been concerns that such massage machines might induce EMI in implantable cardiac devices because of the time-varying magnetic field associated with the activation of the solenoid coils. However, the nature of the influence has not yet been verified [6]. There are many types of massage machines that mechanically perform massages using rollers or solenoid coils and transcutaneous electrical nerve stimulation, which performs massages by electric stimulus. We conducted this study using a shoulder massage machine with solenoid coils, it was occurred magnetic field. The objective of this study was to investigate the potential EMI caused by a shoulder massage machine in implantable cardiac devices. We measured the distribution profile of the magnetic field intensity generated around the massage machine and performed the inhibition and asynchronous tests on a pacemaker in the standardized Irnich human body model. Furthermore, we measured the maximal distance up to which a massage machine can cause EMI in implantable cardiac devices.
implantation of this pacemaker into a human was in 2008, and it is widely used even today. As only one model of this pacemaker was used for this study, it is difficult to make definite conclusions about all pacemakers. However, the AdaptaTM pacemaker has an analog noise filter and the noise is removed. For this reason, we believe that other models have a similar influence or more. The pacemaker was programmed to unipolar and bipolar sensing and pacing under the following settings: pacing rate, 60 ppm; VVI-mode; the sensitivity was programmed to the maximal sensitivity of 1.0 mV. The ICD used was a Virtuoso DRTM (Medtronic, Inc., Minneapolis, MN). It was programmed such that ventricular fibrillation (VF) detection and ventricular tachycardia (VT) detection were on; however, VF therapy and VT therapy were off. The sensitivity was set at the maximal sensitivity of 0.15 mV, which is the highest ICD sensitivity that we used. We experimented under conditions where EMI is most likely to occur. We set the device such that when 18 or more beats among 24 beats occurring at cardiac rate intervals were shorter than 320 ms, VF was recognized. Additionally, when 16 beats were shorter than 400 ms, VT was recognized.
Methods
Measurement of the distribution profile of the magnetic field intensity
Pacemaker and massage machine We used the massage machine ‘‘Massager TON-101A’’ (Kuroshio International, Japan) that carried a current through solenoid coils positioned at the shoulders (Fig. 1). According to Ampere’s law, a magnetic field is generated by a current in a solenoid coil; this magnetic field moves the central iron core within each solenoid in the machine to massage the shoulders. The equipment is classified as class II according to the Global Harmonization Task Force. This device has passed the Japanese Industrial Standards. We used an AdaptaTM (Medtronic, Inc., Minneapolis, MN) pacemaker for this study. The first clinical
123
To measure the magnetic field intensity, a loop antenna with a diameter of 40 mm and 20 turns was created from an enameled wire. We used an oscilloscope ‘‘DS-5106A’’ (Iwatsu Test Instruments Corporation, Japan) with a frequency band of 60 MHz. We observed the output of the pacemaker using a recorder (Fig. 2). Each voltage level on the loop antenna was converted to magnetic intensity by multiplying it with a calibration factor [7]. The calibration factor was obtained using a standard electromagnetic field monitor ‘‘Electromagnetic wave monitor meter’’ (Holaday Industries, Inc.) at the same field intensity within the range of the monitor.
J Artif Organs Fig. 2 Method for measuring the maximum interference distance. We measured the voltage level in the magnetic field from the massage machine using a loop antenna
(a)
Pacemaker loop antenna
36 cm
36 cm
electrode
ch2 ch1 Square sine wave generator
34 cm
Square sine wave generator
(b)
Recorder
Recorder
Pacemaker
5 cm
0.5 cm
loop antenna
The distribution profile of the magnetic field intensity was measured in front of the massage machine. The measurement range in the vertical plane covered an area of 16 9 16 cm2, and the measurement was conducted at every point in this plane on a grid with 2 cm spacing. This vertical plane measurement was then repeated moving away from the massage machine. The measurement of the highest magnetic field in this plane was observed at distances of 1 and 8.5 cm in front of the massage machine. EMI in an implantable cardiac pacemaker We used the Irnich human body model because in vivo testing is difficult. There are ethical and safety issues involved with in vivo testing. We used the model [8] that was developed from the Irnich human body model [9]. It was made of acrylic plates filled with 0.18 wt% NaCl. The Irnich human body model was placed in front of the massage machine and parallel to the solenoid coils. We measured the maximal distance up to which the EMI occurred. The inhibition test was performed to determine whether the pacing pulses generated by the cardiac pacemaker were inhibited while the massage machine was in operation, and
if the massage machine pulses were judged as sinus pulses. When the pulses of the cardiac pacemaker were inhibited or the pacing intervals were extended, we considered the inhibition test to be positive. The asynchronization test was performed to determine whether unnecessary pacing pulses were generated during operation of the massage machine by the cardiac pacemaker set at a fixed pacing rate of 60 bpm. The simulated sinus pulses were generated by a square–sine wave generator (Ultra Mikiwame: Medtronic Japan Co. Ltd., Tokyo, Japan). It was according to ISO 14708(2005): Implants for surgery—Active implantable medical devices—Annex F [10]. When the cardiac pacemaker generated pacing pulses under simulated sinus pulses of 75 ppm, we considered the asynchronization test to be positive. The pacemaker started reversion when the cardiac pacemaker generated pacing pulses under simulated sinus pulses of 75 ppm; this is an EMI defense mechanism. Pulses of a fixed rate are generated by pacemakers to prevent malfunction when noise signals surpass their sensitivity threshold. If the amplitude of continuous interference is above the frequency-dependent interference threshold, pacemakers react by switching to their high frequency noise mode, which is asynchronous pacing at a determined rate.
123
J Artif Organs Fig. 3 The pattern of operation of the massage machine. The massage machine generated an electromotive force from the time-varying magnetic field once every 62–500 ms, with a fixed voltage. The magnetic field distributed on the solenoid coil is shown in this figure. The peak-to-peak voltage was 6.72 V, and the length of each cycle was 7.7 ms (130 Hz)
EMI in an ICD The simulated sinus pulses were generated by a square– sine wave generator (Ultra Mikiwame Medtronics Japan Co. Ltd., Tokyo, Japan). We examined the events of the ICD using a pacemaker programmer (CareLink: Medtronic, Inc., Minneapolis, MN) after the massage machine was in operation.
at a distance of 1 cm in front of the massage machine with a value of 212 A/m, and rapidly decreased toward the edge of the massage machine. The distribution profile of the magnetic field intensity at a distance of 8.5 cm in front of the massage machine was 21 A/m (Fig. 4). EMI in an implantable cardiac pacemaker and an ICD Unipolar sensing
Results Distribution profile of the magnetic field intensity
Inhibition test When the massage machine was switched on, the pacemaker pulses were inhibited by the massage machine (Fig. 5). The maximal interference distance was 28 cm.
The electromotive force generated by the time-varying magnetic field occurred once every 62–500 ms (Fig. 3). The magnetic field was distributed on the solenoid coil as shown in Fig. 4. The distribution profile of the magnetic field intensity was the highest on one of the solenoid coils
Asynchronization test The pacemaker started reversion when the massage machine was in operation; this is an EMI defense mechanism. The maximal distance up to which EMI occurred in the asynchronization test was 25 cm above the massage machine. There was a possibility that
123
J Artif Organs
touched the Irnich human body model, EMI occurred. However, no EMI occurred when the two did not touch.
Discussion
Fig. 4 Distribution profile of the magnetic field intensity. The magnetic field intensity from the massage machine was the largest, at 212 A/m, at the center of the solenoid coil. The magnetic field intensity was small at a distance of 8.5 cm above the center of the massage machine
RonT occurs when a pacemaker started reversion when the massage machine was in operation. EMI did not occur easily at the circumference of the pacemaker lead or an electrode but near the main part of the pacemaker. Bipolar sensing For bipolar sensing, the pacemaker pulses were inhibited or the pacemaker started reversion during operation of the massage machine, similar to the case for unipolar sensing. The maximal interference distance from the massage machine was 4 cm in the inhibition test and 3 cm above the massage machine in the asynchronization test. Both the inhibition and asynchronous tests were positive nearly at the electrode of the pacing lead in the Irnich human body model. ICD When the massage machine was brought near the electrode of the ICD, VF was observed. When the massage machine
A human body model was required for this study because it is difficult to test for EMI in vivo. An electromotive force is generated when a time-varying magnetic field occurs within a one-turn coil formed in the body, consisting of the cardiac pacemaker electrode and conductive body tissue. Therefore, the Irnich human body model is generally used to simulate the electromotive force generated by EMI within the human body [1–5, 11]. The area of the one-turn coil in the Irnich human body model is relatively larger than that of the coil in Japanese patients with implanted cardiac pacemakers [9]. Therefore, it is likely that the influence of the massage machine on the functioning of the cardiac pacemaker in our study was greater than that on the implanted cardiac pacemakers in patients. Therefore, if no EMI is observed in the Irnich human body model, it can be assumed that EMI would not occur in the implanted cardiac pacemakers in patients either. The demand mechanism of the sensing cardiac electric pulses needs to recognize the electrocardiogram. Only the R wave is alternatively passed and detected using filters because the P, R, and T waves of an electrocardiogram have different frequency components and amplitudes. With this set of frequencies, it is easiest to let an input of approximately 50 Hz pass. The pacemaker is recognized as an R wave and passes this filter owing to the EMI from the massage machine, generating a time-varying magnetic field of 130 Hz. The pacemaker that we used in this research is a model that has been in clinical use since 2008 and is widely used even today. As we used only this model, it is difficult to extrapolate our findings to all pacemakers. AdaptaTM includes an analog noise filter function, which eliminates noise [12]. For this reason, the influence of other models may be the same or more than that of AdaptaTM. Cardiac pacemakers in the bipolar sensing mode were less sensitive to EMI than those in the unipolar sensing mode. The electromotive force generated in cardiac pacemakers in the bipolar sensing mode has been reported to be 1/10th of that in cardiac pacemakers in the unipolar sensing mode [13]. The ICD sensed the electromotive force generated by the massage machine as VF; when the cardiac rate intervals were shorter than 320 ms, the ICD recognized the electromotive force as VF. The ICD tended to recognize the electromotive force as VF, because the massage machine generated the electromotive force by the time-varying magnetic field once every 62–500 ms (Fig. 2). The ICD
123
J Artif Organs Fig. 5 Inhibition test and asynchronization test. The inhibition test was positive. When the massage machine was switched on, pacing pulses were inhibited. When the massage machine was switched off, the pacing pulses became normal. The asynchronization test was positive. In the asynchronization test, the pacemaker generated pulses by the reversion mechanism
was less sensitive to EMI than the pacemaker, because the ICD only had bipolar sensing. When people with ICDs use a massage machine, the distance from the pacemaker to the massage machine is usually more than the maximal interference distance. Therefore, the possibility that EMI will not occur is high. Massage machines generate a time-varying magnetic field and induce EMI in the implantable cardiac devices. If a patient with an implanted pacemaker uses a massage machine, except in the case where the machine is switched off, the influence of the massage machine will be present for the entire time. If the massage machine is not switched off or it is closer than the maximal interference distance, pacing pulses will be inhibited or unnecessary pacing pulses will be generated and could pose a clinical problem. Therefore, it is necessary to provide ‘‘don’t use’’ warnings on the massage machine box, its exterior or in user manuals and to caution patients with implanted pacemakers about the dangers of using massage machines. Furthermore, we consider it necessary to be careful about electric-stimulus massage machines because there have been concerns that
123
such machines might cause EMI in implantable cardiac devices.
Conclusions Massage machines generate a time-varying magnetic field, and using an Irnich human body model, it was demonstrated that the massage machine created EMI in implantable cardiac devices. The maximal interference distance up to which this massage machine caused EMI in the pacemaker was determined to be 28 cm. Therefore, it is necessary to caution patients with implanted pacemakers about the EMI from massage machines using solenoid coils. Acknowledgments The authors would like to thank Hiroshi Fujimoto and Katsumi Yokomizo of Medtronic Japan Co. Ltd. for loaning us the implantable cardiac devices used in this study and for offering us their advice. Conflict of interest of interest.
The authors declare that they have no conflict
J Artif Organs
References 1. Hirose M, Hida M, Sato E, et al. Electromagnetic interference of implantable unipolar cardiac pacemakers by an induction oven. PACE. 2005;28:540–8. 2. Yamamoto T, Matsumoto K, Saitou J, et al. The effect of electromagnetic interference in pacemaker implanted patients by cellular phones. J Arrhythm. 1998;14:228–94. 3. Ministry of Internal Affairs and Communications (MIC) in Japan: Surveillance study report of Influence of the medical equipment on an electric wave. 2002. 4. Irnich W, Batz L, Muller R, et al. Electromagnetic interference of pacemaker by mobile phones. PACE. 1996;19:1431–46. 5. Gimble JR, Cox JW. Electronic article surveillance systems and interactions with implantable cardiac devices: risk of adverse interactions in public and commercial spaces. Mayo Clin Proc. 2007;82:318–22. 6. Toyoshima T. Electromagnetic interference for implantable device patients. Medical Review Co. Ltd. 2007. pp. 13–15 (Authors’ translation from Japanese).
7. Electromagnetic Compatibility Conference (EMCC). A glossary of EMC, Ohmsha. Ltd. 1999. pp. 122–123 (Authors’ translation from Japanese). 8. Toyoshima T. Electromagnetic interference for implantable device patients. Medical Review Co. Ltd. 2007. pp. 56 (Authors’ translation from Japanese). 9. Irnich W. Interference in pacemaker. PACE. 1984;7:1021–48. 10. ISO 14708(2005) Implants for surgery—Active implantable medical devices—Annex F. 11. Ministry of Internal Affairs and Communications (MIC) in Japan: Surveillance study report of Influence of the medical equipment on an electric wave. 2011. 12. Van Gelder BM, Van Den Broek W, et al. Paradoxical atrial undersensing: noise rate reversion or amplifier ringing? J Cardiovasc Electrophysiol. 2006;17:1371–4. 13. Toyoshima T, Tsumura M, Nojima T, et al. Electromagnetic interference of implantable cardiac pacemaker by portable telephones. Card Pacing. 1996;12:488–97.
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ORIGINAL ARTICLE
Pacemaker
Electromagnetic interference of implantable cardiac devices from a shoulder massage machine Saeko Yoshida • Kousaku Fujiwara Satoshi Kohira • Minoru Hirose
•
Received: 8 August 2013 / Accepted: 19 March 2014 Ó The Japanese Society for Artificial Organs 2014
Abstract Shoulder massage machines have two pads that are driven by solenoid coils to perform a percussive massage on the shoulders. There have been concerns that such machines might create electromagnetic interference (EMI) in implantable cardiac devices because of the time-varying magnetic fields produced by the alternating current in the solenoid coils. The objective of this study was to investigate the potential EMI from one such shoulder massage machine on implantable cardiac devices. We measured the distribution profile of the magnetic field intensity around the massage machine. Furthermore, we performed an inhibition test and an asynchronous test on an implantable cardiac pacemaker using the standardized Irnich human body model. We examined the events on an implantable cardioverter–defibrillator (ICD) using a pacemaker programmer while the massage machine was in operation. The magnetic field distribution profile exhibited a peak intensity of 212 (A/m) in one of the solenoid coils. The maximal interference distance between the massage machine and the
S. Yoshida (&) M. Hirose Department of Medical Safety Engineering, Graduate School of Medical Science, Kitasato University, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan e-mail: [email protected] M. Hirose e-mail: [email protected] K. Fujiwara M. Hirose Clinical Engineering Course, School of Allied Health Science, Kitasato University, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan S. Kohira Department of Medical Engineering, Kitasato University Hospital, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan
implantable cardiac pacemaker was 28 cm. Ventricular fibrillation was induced when the massage machine was brought near the electrode of the ICD and touched the Irnich human body model. It is necessary to provide a ‘‘don’t use’’ warning on the box or the exterior of the massage machines or in the user manuals and to caution patients with implanted pacemakers about the dangers and appropriate usage of massage machines. Keywords
Pacemaker EMI Massage machine
Introduction Significant research has been conducted on the electromagnetic interference (EMI) in implantable cardiac devices such as implantable cardiac pacemakers (pacemakers) and implantable cardioverter–defibrillators (ICDs). Numerous reports suggest that common electrical equipment utilized around the home affects the functioning of implantable cardiac devices, and many studies have been conducted to clarify the influence of such equipment [1–5]. Devices such as cellular phones and induction ovens are well-known to cause EMI in implantable cardiac devices because of the generated time-varying magnetic field. By Faraday’s law, an electromotive force is generated in a loop-shaped conductor when a magnet approaches it, causing current flow. Pacing leads serve as loop conductors in patients with implanted pacemakers, and current flows to the pacemaker through the electrodes. Therefore, it was surmised that other apparatuses that generated some amount of time-varying magnetic fields may also induce EMI in implantable cardiac devices. Massage machines designed to massage the shoulders are readily available from home electronics retailers or via mail order. These devices deliver a percussive massage to
123
J Artif Organs Fig. 1 Operation of the massage machine. This is a figure showing the operation of the massage machine. The massage machine has two solenoid coils positioned near the shoulders. The machine is often used for the improvement of stiff neck
Massage machine
Solenoid coil Front of the body
Backside
the shoulders via pads driven by two solenoid coils and are often used by subjects for the improvement of a stiff neck. There have been concerns that such massage machines might induce EMI in implantable cardiac devices because of the time-varying magnetic field associated with the activation of the solenoid coils. However, the nature of the influence has not yet been verified [6]. There are many types of massage machines that mechanically perform massages using rollers or solenoid coils and transcutaneous electrical nerve stimulation, which performs massages by electric stimulus. We conducted this study using a shoulder massage machine with solenoid coils, it was occurred magnetic field. The objective of this study was to investigate the potential EMI caused by a shoulder massage machine in implantable cardiac devices. We measured the distribution profile of the magnetic field intensity generated around the massage machine and performed the inhibition and asynchronous tests on a pacemaker in the standardized Irnich human body model. Furthermore, we measured the maximal distance up to which a massage machine can cause EMI in implantable cardiac devices.
implantation of this pacemaker into a human was in 2008, and it is widely used even today. As only one model of this pacemaker was used for this study, it is difficult to make definite conclusions about all pacemakers. However, the AdaptaTM pacemaker has an analog noise filter and the noise is removed. For this reason, we believe that other models have a similar influence or more. The pacemaker was programmed to unipolar and bipolar sensing and pacing under the following settings: pacing rate, 60 ppm; VVI-mode; the sensitivity was programmed to the maximal sensitivity of 1.0 mV. The ICD used was a Virtuoso DRTM (Medtronic, Inc., Minneapolis, MN). It was programmed such that ventricular fibrillation (VF) detection and ventricular tachycardia (VT) detection were on; however, VF therapy and VT therapy were off. The sensitivity was set at the maximal sensitivity of 0.15 mV, which is the highest ICD sensitivity that we used. We experimented under conditions where EMI is most likely to occur. We set the device such that when 18 or more beats among 24 beats occurring at cardiac rate intervals were shorter than 320 ms, VF was recognized. Additionally, when 16 beats were shorter than 400 ms, VT was recognized.
Methods
Measurement of the distribution profile of the magnetic field intensity
Pacemaker and massage machine We used the massage machine ‘‘Massager TON-101A’’ (Kuroshio International, Japan) that carried a current through solenoid coils positioned at the shoulders (Fig. 1). According to Ampere’s law, a magnetic field is generated by a current in a solenoid coil; this magnetic field moves the central iron core within each solenoid in the machine to massage the shoulders. The equipment is classified as class II according to the Global Harmonization Task Force. This device has passed the Japanese Industrial Standards. We used an AdaptaTM (Medtronic, Inc., Minneapolis, MN) pacemaker for this study. The first clinical
123
To measure the magnetic field intensity, a loop antenna with a diameter of 40 mm and 20 turns was created from an enameled wire. We used an oscilloscope ‘‘DS-5106A’’ (Iwatsu Test Instruments Corporation, Japan) with a frequency band of 60 MHz. We observed the output of the pacemaker using a recorder (Fig. 2). Each voltage level on the loop antenna was converted to magnetic intensity by multiplying it with a calibration factor [7]. The calibration factor was obtained using a standard electromagnetic field monitor ‘‘Electromagnetic wave monitor meter’’ (Holaday Industries, Inc.) at the same field intensity within the range of the monitor.
J Artif Organs Fig. 2 Method for measuring the maximum interference distance. We measured the voltage level in the magnetic field from the massage machine using a loop antenna
(a)
Pacemaker loop antenna
36 cm
36 cm
electrode
ch2 ch1 Square sine wave generator
34 cm
Square sine wave generator
(b)
Recorder
Recorder
Pacemaker
5 cm
0.5 cm
loop antenna
The distribution profile of the magnetic field intensity was measured in front of the massage machine. The measurement range in the vertical plane covered an area of 16 9 16 cm2, and the measurement was conducted at every point in this plane on a grid with 2 cm spacing. This vertical plane measurement was then repeated moving away from the massage machine. The measurement of the highest magnetic field in this plane was observed at distances of 1 and 8.5 cm in front of the massage machine. EMI in an implantable cardiac pacemaker We used the Irnich human body model because in vivo testing is difficult. There are ethical and safety issues involved with in vivo testing. We used the model [8] that was developed from the Irnich human body model [9]. It was made of acrylic plates filled with 0.18 wt% NaCl. The Irnich human body model was placed in front of the massage machine and parallel to the solenoid coils. We measured the maximal distance up to which the EMI occurred. The inhibition test was performed to determine whether the pacing pulses generated by the cardiac pacemaker were inhibited while the massage machine was in operation, and
if the massage machine pulses were judged as sinus pulses. When the pulses of the cardiac pacemaker were inhibited or the pacing intervals were extended, we considered the inhibition test to be positive. The asynchronization test was performed to determine whether unnecessary pacing pulses were generated during operation of the massage machine by the cardiac pacemaker set at a fixed pacing rate of 60 bpm. The simulated sinus pulses were generated by a square–sine wave generator (Ultra Mikiwame: Medtronic Japan Co. Ltd., Tokyo, Japan). It was according to ISO 14708(2005): Implants for surgery—Active implantable medical devices—Annex F [10]. When the cardiac pacemaker generated pacing pulses under simulated sinus pulses of 75 ppm, we considered the asynchronization test to be positive. The pacemaker started reversion when the cardiac pacemaker generated pacing pulses under simulated sinus pulses of 75 ppm; this is an EMI defense mechanism. Pulses of a fixed rate are generated by pacemakers to prevent malfunction when noise signals surpass their sensitivity threshold. If the amplitude of continuous interference is above the frequency-dependent interference threshold, pacemakers react by switching to their high frequency noise mode, which is asynchronous pacing at a determined rate.
123
J Artif Organs Fig. 3 The pattern of operation of the massage machine. The massage machine generated an electromotive force from the time-varying magnetic field once every 62–500 ms, with a fixed voltage. The magnetic field distributed on the solenoid coil is shown in this figure. The peak-to-peak voltage was 6.72 V, and the length of each cycle was 7.7 ms (130 Hz)
EMI in an ICD The simulated sinus pulses were generated by a square– sine wave generator (Ultra Mikiwame Medtronics Japan Co. Ltd., Tokyo, Japan). We examined the events of the ICD using a pacemaker programmer (CareLink: Medtronic, Inc., Minneapolis, MN) after the massage machine was in operation.
at a distance of 1 cm in front of the massage machine with a value of 212 A/m, and rapidly decreased toward the edge of the massage machine. The distribution profile of the magnetic field intensity at a distance of 8.5 cm in front of the massage machine was 21 A/m (Fig. 4). EMI in an implantable cardiac pacemaker and an ICD Unipolar sensing
Results Distribution profile of the magnetic field intensity
Inhibition test When the massage machine was switched on, the pacemaker pulses were inhibited by the massage machine (Fig. 5). The maximal interference distance was 28 cm.
The electromotive force generated by the time-varying magnetic field occurred once every 62–500 ms (Fig. 3). The magnetic field was distributed on the solenoid coil as shown in Fig. 4. The distribution profile of the magnetic field intensity was the highest on one of the solenoid coils
Asynchronization test The pacemaker started reversion when the massage machine was in operation; this is an EMI defense mechanism. The maximal distance up to which EMI occurred in the asynchronization test was 25 cm above the massage machine. There was a possibility that
123
J Artif Organs
touched the Irnich human body model, EMI occurred. However, no EMI occurred when the two did not touch.
Discussion
Fig. 4 Distribution profile of the magnetic field intensity. The magnetic field intensity from the massage machine was the largest, at 212 A/m, at the center of the solenoid coil. The magnetic field intensity was small at a distance of 8.5 cm above the center of the massage machine
RonT occurs when a pacemaker started reversion when the massage machine was in operation. EMI did not occur easily at the circumference of the pacemaker lead or an electrode but near the main part of the pacemaker. Bipolar sensing For bipolar sensing, the pacemaker pulses were inhibited or the pacemaker started reversion during operation of the massage machine, similar to the case for unipolar sensing. The maximal interference distance from the massage machine was 4 cm in the inhibition test and 3 cm above the massage machine in the asynchronization test. Both the inhibition and asynchronous tests were positive nearly at the electrode of the pacing lead in the Irnich human body model. ICD When the massage machine was brought near the electrode of the ICD, VF was observed. When the massage machine
A human body model was required for this study because it is difficult to test for EMI in vivo. An electromotive force is generated when a time-varying magnetic field occurs within a one-turn coil formed in the body, consisting of the cardiac pacemaker electrode and conductive body tissue. Therefore, the Irnich human body model is generally used to simulate the electromotive force generated by EMI within the human body [1–5, 11]. The area of the one-turn coil in the Irnich human body model is relatively larger than that of the coil in Japanese patients with implanted cardiac pacemakers [9]. Therefore, it is likely that the influence of the massage machine on the functioning of the cardiac pacemaker in our study was greater than that on the implanted cardiac pacemakers in patients. Therefore, if no EMI is observed in the Irnich human body model, it can be assumed that EMI would not occur in the implanted cardiac pacemakers in patients either. The demand mechanism of the sensing cardiac electric pulses needs to recognize the electrocardiogram. Only the R wave is alternatively passed and detected using filters because the P, R, and T waves of an electrocardiogram have different frequency components and amplitudes. With this set of frequencies, it is easiest to let an input of approximately 50 Hz pass. The pacemaker is recognized as an R wave and passes this filter owing to the EMI from the massage machine, generating a time-varying magnetic field of 130 Hz. The pacemaker that we used in this research is a model that has been in clinical use since 2008 and is widely used even today. As we used only this model, it is difficult to extrapolate our findings to all pacemakers. AdaptaTM includes an analog noise filter function, which eliminates noise [12]. For this reason, the influence of other models may be the same or more than that of AdaptaTM. Cardiac pacemakers in the bipolar sensing mode were less sensitive to EMI than those in the unipolar sensing mode. The electromotive force generated in cardiac pacemakers in the bipolar sensing mode has been reported to be 1/10th of that in cardiac pacemakers in the unipolar sensing mode [13]. The ICD sensed the electromotive force generated by the massage machine as VF; when the cardiac rate intervals were shorter than 320 ms, the ICD recognized the electromotive force as VF. The ICD tended to recognize the electromotive force as VF, because the massage machine generated the electromotive force by the time-varying magnetic field once every 62–500 ms (Fig. 2). The ICD
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J Artif Organs Fig. 5 Inhibition test and asynchronization test. The inhibition test was positive. When the massage machine was switched on, pacing pulses were inhibited. When the massage machine was switched off, the pacing pulses became normal. The asynchronization test was positive. In the asynchronization test, the pacemaker generated pulses by the reversion mechanism
was less sensitive to EMI than the pacemaker, because the ICD only had bipolar sensing. When people with ICDs use a massage machine, the distance from the pacemaker to the massage machine is usually more than the maximal interference distance. Therefore, the possibility that EMI will not occur is high. Massage machines generate a time-varying magnetic field and induce EMI in the implantable cardiac devices. If a patient with an implanted pacemaker uses a massage machine, except in the case where the machine is switched off, the influence of the massage machine will be present for the entire time. If the massage machine is not switched off or it is closer than the maximal interference distance, pacing pulses will be inhibited or unnecessary pacing pulses will be generated and could pose a clinical problem. Therefore, it is necessary to provide ‘‘don’t use’’ warnings on the massage machine box, its exterior or in user manuals and to caution patients with implanted pacemakers about the dangers of using massage machines. Furthermore, we consider it necessary to be careful about electric-stimulus massage machines because there have been concerns that
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such machines might cause EMI in implantable cardiac devices.
Conclusions Massage machines generate a time-varying magnetic field, and using an Irnich human body model, it was demonstrated that the massage machine created EMI in implantable cardiac devices. The maximal interference distance up to which this massage machine caused EMI in the pacemaker was determined to be 28 cm. Therefore, it is necessary to caution patients with implanted pacemakers about the EMI from massage machines using solenoid coils. Acknowledgments The authors would like to thank Hiroshi Fujimoto and Katsumi Yokomizo of Medtronic Japan Co. Ltd. for loaning us the implantable cardiac devices used in this study and for offering us their advice. Conflict of interest of interest.
The authors declare that they have no conflict
J Artif Organs
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