Implantable Cardiac Devices and
       Electromagnetic Tracking Systems
                Are Patients at Risk?


          ...
Abstract

        By definition, an active implantable medical device (AIMD) is a device that is inserted,
partially or fu...
Table of Contents

Abstract..................................................................................................
Table of Illustrations



    Figure 1: 1950's Era Pacemaker                                  Figure 2: Modern Pacemaker.....
Introduction

       One research topic that has received much attention by the academic and commercial

world is that of ...
Literature Review

       By definition, an active implantable medical device (AIMD) is a device that is inserted,

partia...
Figure 1: 1950's Era Pacemaker           Figure 2: Modern Pacemaker


       The causes that attribute to an AIMD to misin...
(Scholten and Silny, 2001). Figure 3 pictorially demonstrates the different placement options of

pacemakers within a pati...
being re-programmed (Grant, 1998) (Kuriger, 1998). Based on prior in vitro results, in vivo

testing showed that there wer...
upgrade from the optical systems that have been widely used for many years. Using GSM

wireless signals, this technology p...
Analysis of Problem

       Electromagnetic fields can be either continuous or pulsed. The ETS uses pulsed signals

to car...
Figure 4: Electromagnetic Spectrum




    Figure 5: Pulsed EM Field




      Holmes 8 McKinney
Solution Methods Employed

    All testing will be conducted at the EMC Center on the University of Oklahoma’s campus.

Si...
One important factor of the test procedure is generating an artificial heart signal.

Generating and monitoring a heart rh...
Recommendations

       Recommendations can be made for future research of implantable cardiac device

interaction with el...
Limitations

       The major limitation involved with this particular study is time. It has proven difficult to

obtain t...
References

Ashley, Robert J., et al, 1998, Measurement of Potential Magnetic Field Interference with
     Implanted Cardi...
Appendix
Table 1: Test Procedure
 Torso Simulator
         • Fill tank with 1.8 g/l saline solution
         • Measure sal...
•   Ensure vertical menu settings on Channel 1
      “Coupling” set to “DC”                    “Offset” set to “0 V”
   ...
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  1. 1. Implantable Cardiac Devices and Electromagnetic Tracking Systems Are Patients at Risk? 2004 Authors: Chris Holmes – Southern Illinois University at Edwardsville Amy McKinney – University of Nebraska-Lincoln Faculty Sponsor: Dr. Hank Grant, EMC Center Director Glenn Kuriger, EMC Center Assistant Director
  2. 2. Abstract By definition, an active implantable medical device (AIMD) is a device that is inserted, partially or fully, into a human body or body cavity for permanent use by medical intervention. These devices include equipment such as pacemakers, implantable cardioverter defibrillators (ICDs), pain stimulators, respiration-stimulators, insulin or drug pumps, cochlea implants, and electrocardiogram monitors. Of particular concern are pacemakers and ICDs, which are cardiac implantable devices that treat different heart conditions. According to Faraday’s law, for any time varying magnetic field, a voltage may be induced at the input of an implanted cardiac device, thus creating a surge of excess electricity. These fields may emanate from any electronic device, such as electronic article surveillance system, weapon detectors, or high voltage overhead lines. Hospitals are now utilizing electromagnetic tracking systems during surgery as a more accurate way to view the area being operated. A wireless probe is inserted into the patient and communicates with a base station to relay information through pulsed electromagnetic waves. Hence, these waves could possibly interfere with patients who have implantable cardiac devices if the base station is located too close to the device. The Center for the Study of Wireless Electromagnetic Compatibility at the University of Oklahoma is conducting in vitro testing to find if there is any possible interaction between implantable cardiac devices and electromagnetic tracking systems. Four questions are under consideration: 1) What degree of interaction, if any, is present between a wireless tracking system base station and various implantable cardiac devises? 2) What is a safe distance between a patient wearing an implantable cardiac device and the base station during transmission? 3) Is there a relationship in the placement of the implantable cardiac device within the body and the corresponding interaction that could occur from exposure? 4) Do some implantable cardiac devices have greater interactions with an electromagnetic tracking system than others? By using a torso simulator, systematic testing of various degrees of interaction is possible. Due to limited research in the field of medical electromagnetic device interference, a study is warranted to investigate these issues. However, as of the writing of this report, cardiac equipment has yet to be shipped, therefore causing the delay of measurement. As a consequence, it is unwarranted to attempt any speculation on possible results. Hopefully, future research will continue with the aforementioned goals presented in consideration.
  3. 3. Table of Contents Abstract............................................................................................................................................2 Table of Contents..............................................................................................................................i Table of Illustrations........................................................................................................................ii Introduction......................................................................................................................................1 Literature Review.............................................................................................................................2 Problem Definition...........................................................................................................................5 Analysis of Problem.........................................................................................................................7 Solution Methods Employed............................................................................................................9 Results............................................................................................................................................10 Recommendations..........................................................................................................................11 Limitations.....................................................................................................................................12 Appendix..........................................................................................................................................a Holmes i McKinney
  4. 4. Table of Illustrations Figure 1: 1950's Era Pacemaker Figure 2: Modern Pacemaker............................3 Figure 1: 1950's Era Pacemaker Figure 2: Modern Pacemaker............................3 Figure 3: Left vs. Right Side Orientation........................................................................................4 Figure 4: Electromagnetic Spectrum..............................................................................................8 Figure 5: Pulsed EM Field..............................................................................................................8 Figure 6: Torso Simulator...............................................................................................................9 Holmes ii McKinney
  5. 5. Introduction One research topic that has received much attention by the academic and commercial world is that of electromagnetic interference with active implantable medical devices (AIMDs). Specifically, cardiac devices such as implantable pacemakers and cardioverter defibrillators have been shown to have potential hazards associated with electromagnetic interference from various sources such as wireless phones or security systems. The Center for the Study of Wireless Electromagnetic Compatibility (EMC Center) at the University of Oklahoma has conducted several studies examining such interactions. In their research, as well as other academic investigations, interference has proven minimal, if not nonexistent. However, even with these results, further examination must continue to determine compatibility between new wireless technology and AIMDs. Medical technology in particular is experiencing rapid technological advances, which may have benefits for some patients, but hazards for others. In the mid 1990’s, the need arose for an independent center to investigate the use of wireless devices and their potential interaction with AIMDs. In response, Dr. Hank Grant at the University of Oklahoma created the Center for the Study of Electromagnetic Compatibility (EMC Center), shortly after his arrival at the university in 1994. Since then, the EMC Center has investigated wireless interference with devices such as hearing aids, pacemakers, and implantable defibrillators. In recent years, cardiac devices have received much attention from the EMC Center, with investigations revealing that while several select models of pacemakers or ICDs have shown interaction with older style analog wireless phones, newer digital phone formats such as PCS or GSM are essentially interaction free. However, wireless technology is always changing, proliferating in both format and use. Holmes 1 McKinney
  6. 6. Literature Review By definition, an active implantable medical device (AIMD) is a device that is inserted, partially or fully, into a human body or body cavity for permanent use by medical intervention. These devices include equipment such as pacemakers, implantable cardioverter defibrillators (ICDs), pain stimulators, respiration-stimulators, insulin or drug pumps, cochlea implants, and electrocardiogram monitors (Irnich, 2002). Of particular concern are pacemakers and ICDs, which are cardiac implantable devices that treat different heart conditions. A pacemaker is utilized in patients experiencing heart failure, which is when heart muscle has become diseased to the point that it lacks the ability to beat on its own (Ashley, et al, 1998). The device supplies electric shocks to “pace” the heart either continuously or as needed. A heart “attack” is another condition altogether. During this time, the heart beats faster than blood can flow, causing the heart muscle to become starved for oxygen, thus damaging the muscle. An ICD monitors for this type of activity, then provides a shock of electricity to correct the heart’s rhythm (some cutting- edge models also function as pacemakers) (Irnich, 2002). ICDs are relatively new compared to pacemakers, first implanted in 1980 (Cannom and Prystowsky, 2004), as opposed to pacemakers in 1952 (Hayes and Furman, 2004). However, since the devices use electric signals for both programming and monitoring of a patient, it can be dangerous if a patient is exposed to any electric equipment emitting harmful levels of electromagnetic radiation. Figure 1 and Figure 2 demonstrate the extreme change that pacemakers have undergone in the last 50 years. Pacemakers have now become smaller and more versatile in their use. Holmes 2 McKinney
  7. 7. Figure 1: 1950's Era Pacemaker Figure 2: Modern Pacemaker The causes that attribute to an AIMD to misinterpret a signal can easily be explained. According to Faraday’s law, for any time varying magnetic field, a voltage may be induced at the input of an implanted cardiac device, thus creating a surge of excess electricity (Scholten and Silny, 2001). These fields may emanate from any electronic device, such as electronic article surveillance system, weapon detectors, or high voltage overhead lines (Witters, et al, 2001). Some studies have constructed specific “Faraday Cages” to examine this phenomenon (Hedjiedj, 2002). Assuming that the magnetic field is sinusoidal and located in the AIMD range, acting perpendicularly to the frontal plane of the thorax and is homogeneous, there exists the possibility that a voltage could be produced. Also, if pacemakers or ICDs are under consideration, the placement of the device can also greatly influence any induced voltage. Left side implantation creates an induction loop, versus a right side that typically has an “s-shape” wire lead orientation Holmes 3 McKinney
  8. 8. (Scholten and Silny, 2001). Figure 3 pictorially demonstrates the different placement options of pacemakers within a patient’s chest, and the resulting reference loops that are incurred. Different types of wireless technologies, primarily found in wireless phones, also attribute to AIMD interaction. Figure 3: Left vs. Right Side Orientation The FDA has found that many different electrically powered medical devices such as pacemakers and implantable defibrillators can be affected by electromagnetic interference (Witters, et al, 2001). Both in vitro and in vivo testing has been conducted dealing with this issue. Studies have focused on GSM (Global System for Mobile Communication) wireless technology and any interactions that may occur with a cardiac device’s functionality (Barbaro, et al, 2003b). In vitro results have concluded that when the worst-case scenario is tested (phone at maximum output and implantable cardiac device at its highest sensitivity) there is some interaction between certain types of implantable cardiac devices and certain types of wireless phones. The interaction found could be that the device perceived the electromagnetic waves as a heart beat, or that the device “fired” when it should not have. However, in all cases, when the wireless phone was removed and turned off the implantable cardiac device showed no signs of Holmes 4 McKinney
  9. 9. being re-programmed (Grant, 1998) (Kuriger, 1998). Based on prior in vitro results, in vivo testing showed that there were no threatening interactions between specific devices and phones when in close contact (Barbaro, et al, 2003a). However, it should be noted that in the Barbaro study, only two phone models and one pacemaker model was examined, so these results may not hold true for all combinations of pacemakers and wireless technologies. Hospitals are now utilizing electromagnetic tracking systems during surgery as a more accurate way to view the area being operated. This new technology is an upgrade from the optical systems that have been widely used for many years (Poulin, 2002). This technology provides the surgeon with a 3D “roadmap” of the patient as well as the exact location of the probe within the body. The system uses an emitter to produce an electromagnetic field that is received by a base station. Some stations are capable of converting this information into six degrees of freedom (Poulin, 2002), allowing the surgeon to view the patient in ways never before capable with optical systems. The possibility of interference with AIMD patients requires examination. Even though there is no major threat to the general public, there are a substantial number of AIMD patients who could be affected by an electromagnetic interference during surgery. Approximately 110,000 Americans (eighty percent of which are 65 years of age or older) are fitted with pacemakers each year (Business Word, 2003). In 2003, it was expected that nearly 130,000 implantable defibrillators were to be implanted worldwide (Cannom, 2004). These statistics justify the need for further research in the field of wireless electromagnetic interactions. Problem Definition Hospitals are now utilizing electromagnetic tracking systems (ETS) during surgery as a more accurate way to view the patient’s area being operated on. This new technology is an Holmes 5 McKinney
  10. 10. upgrade from the optical systems that have been widely used for many years. Using GSM wireless signals, this technology provides the surgeon with a 3D “roadmap” of the patient as well as the exact location of the probe within the body. Optical systems are unable to provide this level of precision. A wireless probe is inserted into the patient and communicates with a base station to relay information through electromagnetic waves. Hence, these waves could possibly interfere with patients who have implantable cardiac devices if the base station is located too close to the device. The EMC Center is conducting in vitro testing to find if there is any possible interaction. Four questions are under consideration: 1) What degree of interaction, if any, is present between a wireless tracking system base station and various implantable cardiac devises? 2) What is a safe distance between a patient wearing an implantable cardiac device and the base station during transmission? 3) Is there a relationship in the placement of the implantable cardiac device within the body and the corresponding interaction that could occur from exposure? 4) Do some implantable cardiac devices have greater interactions with an electromagnetic tracking system than others? Due to limited research in the field of medical electromagnetic device interference, a study is warranted to investigate these issues. Holmes 6 McKinney
  11. 11. Analysis of Problem Electromagnetic fields can be either continuous or pulsed. The ETS uses pulsed signals to carry digital information in the GSM wireless format at either 800 MHz or 1900 MHz (See Figure 4). Pulsed electromagnetic fields, such as in Figure 5, have the capability to create “false heart signals” which can cause AIMDs to misinterpret data. This creates inherent problems when in close proximity to AIMDs. However, depending on which cardiac device is under consideration, the pulsed field may have varying effects. The possibility exists that a pacemaker will be more sensitive to an exposure than an ICD due to their respective functions. Pacemakers continuously pace a heart based on measured readings that can be easily interfered with during exposure to pulsed electromagnetic fields. In contrast, an ICD shocks an erratic heart back into a normal rhythm, which requires the device to charge before treatment may be administered. Thus, in order for a pulsed electromagnetic field to become dangerous, the ICD must be subjected to the field for a longer period of time compared to a pacemaker. Therefore, with more hospitals utilizing ETS technology, the hazards to AIMDs patients cannot be ignored. Holmes 7 McKinney
  12. 12. Figure 4: Electromagnetic Spectrum Figure 5: Pulsed EM Field Holmes 8 McKinney
  13. 13. Solution Methods Employed All testing will be conducted at the EMC Center on the University of Oklahoma’s campus. Simulation of pacemakers and implantable defibrillators will be accomplished by way of a torso simulator and testing equipment which generate and monitor electrical signals. Specifically, an ECG signal injection system will be utilized to simulate heart activity and signal monitoring equipment for acquiring pacemaker and ICD signals. All equipment will be set up in and around the torso simulator. As can be seen in Figure 6, the torso simulator is a plastic box used to represent the human trunk cavity. The simulator measures 23” x 16.75” x 6” with a volume of 28 quarts. It is filled with 0.03 molar saline solution which simulates human body conductivity. Two horizontal grids placed one below the other support both the pacemaker or defibrillator under consideration and the tracking system base station. The lower grid, which supports the pacemaker or defibrillator, is completely submersed in the saline solution. The grids can be moved to different heights, allowing the testing of different separations distances to be measured. The tracking base station will be moved to every point on the grid to test various interactions. Figure 6: Torso Simulator Holmes 9 McKinney
  14. 14. One important factor of the test procedure is generating an artificial heart signal. Generating and monitoring a heart rhythm may be accomplished by placing stainless steel plates, measuring 50 mm x 50 mm x 2 mm, into the torso simulator. One pair of plates (on the long axis of the tank) monitor the pacemaker or ICD signal, and the second pair (on the short axis) inject a simulated heart signal into the tank. The signal received from the torso simulator is first applied to the input of a differential amplifier designed for ECG signal monitoring. After amplification, the signal is filtered for clarity before being inputted into a two-channel digital storage oscilloscope. Through observation of the ECG signal on the oscilloscope, any interaction of the pacemaker or ICD function with the electromagnetic tracking system base station will be recorded. A summary of this procedural setup can be found in the Appendix (Table 1). It is important to note that ICD and pacemaker parameters are typically programmed non- invasively by means of RF signals or pulsed magnetic fields. This ability of the device to respond to both internal and external magnetic and RF signals allows the device to be programmed for optimal clinical benefit as the patient’s needs change. Each pacemaker or ICD company will supply the appropriate instructions necessary for interrogating and programming its respective units. The programming features vary widely, but all units provide the control necessary to establish the common parameters needed. Each unit will be programmed for the worst-case condition (maximum sensitivity and minimum refractory period). Results Unfortunately, due to time constraints, testing was unable to commence as of the writing of this report. Due to limited research concerning this particular type of wireless interaction, it is unwarranted to attempt any speculation on possible results. Hopefully, future research will continue with the aforementioned goals presented in consideration. Holmes 10 McKinney
  15. 15. Recommendations Recommendations can be made for future research of implantable cardiac device interaction with electromagnetic tracking systems in relation to the general in vitro setup. Previous research at the EMC Center has not made a distinction between left and right side placement orientation of pacemakers or implantable defibrillators, and this can have a great effect on the level of interaction with not only electromagnetic tracking systems, but also technologies such as wireless phones or security systems. Also, previous research has not considered constant body temperature in the construction of torso simulators. A constant temperature of 98.6 degrees Fahrenheit would also have an effect on the conductivity of signals within the simulator, perhaps improving noise levels and accuracy. Holmes 11 McKinney
  16. 16. Limitations The major limitation involved with this particular study is time. It has proven difficult to obtain the proper implantable device equipment in the timeframe allowed, thus not allowing the study to commence. However, delays are sometimes unavoidable factors in any form of research, particularly ones that involve specialized equipment. Hopefully in time this study will be completed, providing an answer to the safety issue raised in the use of electromagnetic tracking systems and implantable cardiac devices. Holmes 12 McKinney
  17. 17. References Ashley, Robert J., et al, 1998, Measurement of Potential Magnetic Field Interference with Implanted Cardioverter Defibrillators of Pacemakers, Electro Int. Conf. Proc. of IEEE, 159-170. Barbaro, V., Bartolini, P., Calcagnini, G., Censi, F., Floris, M., et al, 2003a, In vitro and in vivo evaluation of electromagnetic interference between wireless home monitoring pacemakers and GSM mobile phones, Proc. Ann. Int. Conf. IEEE Engineering in Medicine and Biology Society, 4, 3602-3605. Barbaro, V., Bartolini, P., Calcagnini, G., Censi, F., Beard, B., et al, 2003b, On the mechanisms of interference between mobile phones and pacemakers: parasitic demodulation of GSM signal by the sensing amplifier, Physics in Medicine and Biology, 48, 1661-1671. Business Word, 2003, Pacemaker prices still declining, Hospital Materials Management, 28, i6, p1(4). Cannom, David S., and Prystowsky, Eric N., 2004, The Evolution of the Implantable Cardioverter Defibrillator, NASPE History Series, 27, 419-431. Grant, Hank and Schlegel, Robert E., 1998, In Vitro Study of the Interaction of Wireless Phones with Cardiac Pacemakers, EMC Report 1998-2. Hayes, D.L. and Furman, Seymour, 2004, Cardiac Pacing: How it Started, Where We Are, Where We Are Going, NASPE, 27, 693-704. Hedjiedj, A., Goeury, C., and Nadi, M., 2002, A Methodological approach for the characterization of cardiac pacemaker immunity to low frequency interferences: case of 50 Hz, 60 Hz, 10 kHz and 25 kHz led disruptions, Journal of Medical Engineering and Technology, 26, no.5, 223-227. Irnich, Werner, 2002, Electronic Security Systems and Active Implantable Medical Devices, Journal of Pacing and Clinical Electrophysiology, 25, no.8, 1235-1258. Kuriger, Glenn W., Grant, Hank, and Schlegel, Robert E., 1998, In Vitro Study of the Interaction of Wireless Phones with Implantable Cardioverter Defibrillators, EMC Report 1998-1. Poulin, Francois and Amiot, L.P., 2002, Interference during the use of an electromagnetic tracking system under OR conditions, Journal of Biomechanics, 35, 733-737. Scholten, A., and Silny, J., 2001, The interference threshold of unipolar cardiac pacemakers in extremely low frequency magnetic fields, Journal of Medical Engineering and Technology, 25, no.5, 185-194. Witters, Donald, et al, 2001, Medical device EMI: FDA Analysis of Incident Reports, and Recent Concerns for Security Systems and Wireless Medical Telemetry, IEEE International Symposium on Electromagnetic Compatibility, 2, 1289-1291. Holmes 13 McKinney
  18. 18. Appendix Table 1: Test Procedure Torso Simulator • Fill tank with 1.8 g/l saline solution • Measure saline properties with YSI Model 33 S-C-T Meter  Calibrate probe  Measure saline temperature  Measure salinity (0.18% to 0.21% acceptable)  Measure conductivity (nominal value of 3400 micro-mhos per cm) • Position Plastic Grids • Position pacemaker/implantable defibrillator on bottom grid over (0,0) grid point • Adjust height of top grid such that implantable device is 1 cm below test subject Waveform Generator • Set frequency to 66.66 Hz • Set unit to “Burst” mode • Set “Burst Rate” to 550 ms for pacemakers, 650 ms for implantable defibrillators • Connect cable from “Output” jack on generator to stainless steel plates on opposite ends of torso simulator Signal Amplifier • Enable signal path • Set “Gain/Time Constant” to “X10” and “3.2” for implantable pacemakers and “X100” and “3.2” for pacemakers • Set “Input” to “On” • Set amplifier filter to 10 KHz • Set amplifier gain to 500 mV/cm • Connect cable from “Input” jack on amplifier to remaining stainless steel plates on torso simulator • Connect cable from “Aux-Out” jack on amplifier to Channel 1 of oscilloscope Oscilloscope Holmes a McKinney
  19. 19. • Ensure vertical menu settings on Channel 1  “Coupling” set to “DC”  “Offset” set to “0 V”  “Invert” set to “Off”  “Fine Scale” as needed  “Bandwidth” set to “Full”  “Position” as needed • Ensure vertical menu settings for Channel 2  “Coupling” set to “AC”  “Offset” set to “0 V”  “Invert” set to “Off”  “Fine Scale” as needed  “Bandwidth” set to “Full”  “Position” as needed • Ensure horizontal menu settings  “Time Base” to “Main Only”  “Sec/Div” set to “250ms”  “Trigger Position” to “50%” • Set trigger settings  “Type” to “Edge”  “Slope” to increasing  “Source” to “Channel 1”  “Level” as needed  “Coupling” to “DC” Holmes b McKinney

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