A Prospective Pediatric Clinical Trial of Digital Music Players: Do They Interfere with Pacemakers?

Christine C. Chiu, M.Sc.; June Huh, M.D., Ph.D.; Laura De Souza, B.Sc.; Armando Alfaro-Ramirez, M.D.; Robin Clegg, M.D.; Laura Fenwick, B.Sc.; Robert M. Hamilton, M.D., M.H.Sc.; Joel A. Kirsh, M.D.; Gil J. Gross, M.D.; Dongsheng Gao, Ph.D.; Elizabeth A. Stephenson, M.D., M.Sc.

Disclosures

J Cardiovasc Electrophysiol. 2009;20(1):44-49. 

In This Article

Discussion

From this large series of patients with systematic testing of different types of pacemakers, sensing configurations, and DMP, we were unable to show interference with any pacemaker or ICD function by use of these players. This finding is important to reassure patients against the powerful lay media publication of a detrimental interaction between iPod™ and pacemaker function.[5] Furthermore, manufacturers of implanted devices conducted in vitro bench testing with iPod™ to confirm if pacemaker or ICD function interference can be detected. No interference with device function was observed.[6,7] Telemetry interference was observed in some instances. The FDA conducted its own independent measurements of magnetic field emissions from hard disk iPod™ and found emission levels of less than 0.2 µTesla 1 cm from the case, which is equivalent to about 0.002 Gauss.[8] The reed switch of pacemakers typically requires 5 to 10 Gauss to activate. Thus, the emissions from iPod™ are extremely low and unlikely to interfere with pacemaker function. Similarly, the induced voltages in the pacemakers were less than 140 µV RMS (root mean square), well below the detectable noise levels of their instruments.[8] Consequently, one device manufacturer posted safety information on the website to reassure patients that the iPod™ does not interfere with pacemaker function.[9]

RF energy has been used to achieve bidirectional telemetry since 1970s.[10] These RF pulses (carrier frequency) are centered between 16 kHz and 175 kHz depending on the implanted device manufacturer. The transfer of digital information from a pacemaker to the programmer is known as "interrogation" or uplink while the reverse is known as "programming" or downlink telemetry.[11] Communication is established through proper alignment of the magnetically coupled antenna coils inside the pacemaker and the programmer wand. Telemetry can be initiated by mechanical reed switches activated by a magnetic field. In newer devices, solid-state Hall magnetic sensors are used and telemetry is established by "hand shake" of secure verification signal pulses sent between the programmer and the pacemaker. In other systems, a downlink from the programmer initiates telemetry. Data information is transferred via encrypted binary data bits embedded in the carrier frequency that are either amplitude or frequency modulated.[12] The accuracy of the data transfer or programing commands is then vigorously verified by manufacturer specific parity checking schemes and "hand shake" algorithms. Any detected errors or mismatches in the process will result in aborting the programing command or transfer of data.

Factors that may impede entirely or reduce the quality of the telemetry include inadequate alignment of the receiving and transmitting antennas (e.g., in very obese patients there may be a large distance between antennas), the presence of electromagnetic interference, noise of sufficient strength, or objects that form a physical barrier in the telemetry field. These can result in inaccurate or corrupted uplink (e.g., dropouts of marker data), noise artifacts on the EGM channel, partial, or complete interruption of the uplink or downlink telemetry.[6,7,13] Telemetry interference was observed in our study in 16% (11 of 67) of the patients tested: ranging from 13% (Medtronic programmer) to 28% (St. Jude Medical programmer) while in a similar study, Webster et al. reported interference in 41% (21 of 51) of the patients tested.[14] The lower incidence of telemetry interference in our study may be related to the constant 1 cm distance we placed between DMP and the programmer wand as well as our precautions to ensure stable telemetry and wand position during testing. In addition, we tested for potential pacemaker interference in the absence of the programmer wand in the patient's usual programmed settings and did not observe any ECG changes to suggest pacemaker misbehavior.

The initial abstract of Thaker reported a 20% rate of oversensing, a 29% rate of telemetry interference, and a 1.2% rate of pacemaker inhibition.[1] They concluded that iPod™ and other MP3 players may "possibly interact with pacemakers." Subsequently, their full report indicated spurious "oversensing" in 19% of tests that manifested as high rates in the histogram counter as well as telemetry interference but saw no evidence of pacemaker inhibition in all 100 patients who were tested.[15] They drew a slightly different conclusion that iPod™ may cause interference during wanded telemetry that may be an important issue in remote follow-up. The accompanying editorial carefully highlighted areas in which the researchers misinterpreted telemetry interference as signals that are detected by the pacemaker sensing circuitry.[16]

Numerous early studies have evaluated the effects of extraneous sources of EMI that patients may encounter in daily life. These included cellular or mobile phones, electronic article surveillance systems, induction ovens, and airport metal detectors.[17,18,19,20,21,22,23,24] Current implantable device technology has greatly improved protection against EMI, including the titanium metal case, feed-through filters, interference rejection circuits, and use of bipolar leads for sensing. In general, the risk of pacemaker interference with any type of EMI is associated with several factors, the first being the distance between the source of EMI and the implanted device. Second, the field strength of the EMI and its oscillation frequency are of paramount importance in determining if the implanted device's sense amplifiers will detect the interference. Last, the device's programmed sensitivity and sensing polarity may further reduce the likelihood of interference.[21] Guidelines have been established to reduce incidence of device interference.[25,26,27] In general, keeping electronics approximately 6 inches away from the pacemaker area will reduce the likelihood of interference with pacemaker function, although some sources of EMI may require a larger separation distance as specified by the device manufacturers.

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