HEALTH CANADA’S RESEARCH ON INTERFERENCE EFFECTS OF ELECTROMAGNETIC FIELDS ON IMPLANTABLE CARDIAC DEVICES

Kok-Swang Tan, Irwin Hinberg
Medical Devices Bureau
Therapeutic Products Directorate, Health Products and Food Branch, Health Canada
Ottawa, Ontario, Canada K1A 1C1

Abstract: Laboratory and clinical studies have shown that electromagnetic interference (EMI) from radio-frequency sources can cause a variety of electromedical devices to malfunction, leading to adverse effects on patients. This paper presents an overview of Health Canada’s studies to assess the susceptibility of implanted cardiac devices to EMI from wireless radiofrequency communication sources and security systems and to determine potential risks to patients.

INTRODUCTION

Laboratory tests and clinical incident reports have confirmed that some medical device malfunctions are caused by electromagnetic interference (EMI) from radio-frequency sources [1-8]. To identify emerging EMI issues and risk management strategies, Health Canada investigated the electromagnetic compatibility (EMC) of some critical-care and implantable medical devices in the presence of the following radiofrequency sources: wireless telecomm-unication devices, such as analog and digital cellular phones; analog two-way radios; digital personal communication service (PCS) systems; companion technology systems; analog family radio services (FRS) systems; wireless local area network (LAN) systems; medical telemetry systems; and electronic security systems, such as electronic article surveillance (EAS) systems, walk-through metal detectors (WTMDs) and hand-held metal detectors (HHMDs).

In addition, Health Canada is collaborating with three Canadian university medical centres and the R. Samuel McLanghlin Centre for Population Health Risk Assessment of the University of Ottawa on a multicentre clinical study on the effects of wireless cell phones on implantable cardioverter defibrillators (ICDs). The objective of the study is to determine the prevalence and clinical significance of interference from the exposure of ICDs to five cell phone technologies.

METHODOLOGY

In vitro tests of implantable cardiac devices

The setup for testing the susceptibility of implantable cardiac pacemakers and implantable cardioverter defibrillators to EMI has been described previously [3, 5]. The following telecommunication devices were tested: five cell phone technologies and two family radio two-way systems; three models of EAS systems from 2 manufacturers; six WTMDs from 3 manufacturers; and 13 HHMDs from 9 manufacturers.

RESULTS AND DISCUSSION

Wireless telecommunication systems

Nine of the twenty pacemakers tested were susceptible to EMI from 4 models of nearby digital cellular phones (TDMA-50 mode). Interference effects were generally not observed when the cell phone was more than 15 cm from the pacemaker. Dual-chamber (DC) pacemakers were more susceptible to interference than single-chamber (SC) models. The 3.4% rate of interference observed with the TDMA-50 technology is consistent with the results reported in other studies [9, 10]. The EMI generated by the wireless devices did not reprogram or damage the pacemakers. The interference effects ceased when the phones were turned off and the pacemakers reverted to their normal operations. Other cell phone technologies (analog cell phones, digital PCS systems, DECT, CT2 Plus) and FRS two-way radio systems did not cause any interference with pacemakers. These findings suggest that pacemaker-dependent patients should use analog or digital PCS phone systems. No interference was observed with two models of implantable cardioverter defibrillators. These findings support the recommendation of Health Canada and the pacemaker industry that patients should hold the phone to the  ear farthest from the pacemaker and avoid carrying it in a breast pocket directly over the implanted device [11].

Radio and television broadcasting signals

Broadcasting signals from three digital television (DTV) channels, four analog channels and one FM channel were tested. Neither simulated nor actual broadcast DTV signals and FM radio signals affected the performance of any models of pacemakers and defibrillators tested.

Electronic security systems

The susceptibility of 22 pacemakers and two implantable defibrillators to EMI from three types of EAS systems, six WTMDs, and 13 HHMDs were studied. During static tests, 15 pacemakers were affected by EASs and WTMDs at distances up to 33 cm from the transmission panel (Table 1). The same EMI effects were observed inside and outside the transmission panels of the EAS gate. There was no interference when the simulator was rolled through  any  EAS system during the dynamic tests. The two defibrillators were unaffected by any EAS and WTMD systems. None of the 13 HHMDs interfered with the 22 pacemakers and the 2 implantable defibrillators tested. None of the security systems caused any permanent damage or reprogramming to the pacemakers and defibrillators. These findings suggest that pacemaker patients should not stop within 33 cm of either side of the transmission panel of an EAS or WTMD.

Table 1  Effects of Security Systems on Implantable Cardiac Pacemakers  
(* Measured at 15 cm from the transmission panel of EAS and WTMD systems, and 2.5 cm from HHMDs; 0 % indicates no interference effects)

CONCLUSIONS

These findings suggest that digital cell phones and security systems can potentially interfere with implantable cardiac devices. The risk of EMI occurring is relatively small. Although many implantable cardiac device manufacturers have addressed EMC, there still appears to be insufficient awareness of EMI problems. There continues to be a need to educate users, manufacturers and regulators about EMI and to develop EMC standards. Preventing all EMI malfunctions is difficult because it is a challenge to make medical devices immune to all sources of EMI. The exposure to EM environment, frequency, location, orientation, and design of an implanted device can influence whether and how the device will be affected by EMI. In  practice, it is impossible to stop EM energy completely at its source. Many EMI malfunctions could be prevented through education. Health Canada places a high priority on providing  information to the public, such as published Alert Letters [11, 12]. The need for establishing specific EMC standards for medical electrical equipment and systems is well recognized. Specific EMC standards for implantable cardiac pacemakers and defibrillators are currently being drafted by the International Organization for Standardization (ISO) Technical Committee TC150 Subcommittee SC6 Working Group [13, 14].

REFERENCES

[1]   Medical Devices Incident Report Database, Medical Devices System, Medical Devices Bureau, Therapeutic Products Directorate, Health Canada.

[2]   K.S. Tan, and I. Hinberg, “Investigation of electromagnetic interference with medical devices in Canadian hospitals,” Proc. Workshop on Electromagnetic, Health Care & Health, Montreal, Canada, September 19-20, 1995.

[3]   K.S. Tan, and I. Hinberg, “Can wireless communication systems affect implantable cardiac pacemakers? An  in-vitro laboratory study,” Biomed. Instru. Technol. 32: 18-24, 1998.

[4]   K.S. Tan, and I. Hinberg, "Can electronic article surveillance systems affect implantable cardiac pacemakers and defibrillators?” Pacing  Clin. Electrophysiology 21: 960, 1998.

[5]   K.S. Tan, and I. Hinberg, “A laboratory study of electromagnetic interference effects from security systems on implantable cardiac pacemakers,” Proc. XXVI Intl. Union Radio Science on Electromagnetic Interference with Medical Devices, Toronto, 868, 1999.

[6]   K.S. Tan, I. Hinberg, J. Wadhwani, “Electromagnetic interference in medical devices: Health Canada’s past and current perspectives and activities”, Proc. IEEE Intl. Sym. Electromagnetic Compatibility, 1283-88, 2001.

[7]   D. Witters, et al. “Medical devices EMI: FDA analysis of incident reports, and recent concerns for security systems and wireless medical telemetry”, Proc. IEEE Intl. Sym. Electromagnetic Compatibility, 1289-91, 2001.

[8]   B. Segal, et al. “Risk of patient injury due to electromagnetic interference malfunctions: Estimation and minimization”. Proc. IEEE Intl. Sym. Electromagnetic Compatibility, 1308-12, 2001.

[9]   D.L. Hayes et al. “Interference with cardiac pacemakers by cellular phones”, N. Engl. J. Med. 336: 1473-79, 1997.

[10] F.H. Grant and R.E. Schlegel, “Wireless phones and cardiac pacemakers: An in vitro study”. Proc. IEEE. Eng. Med. Biol., October 1997.

[11] Alert Letter No.108: “Digital cellular phone interference with cardiac pacemakers”, Health Canada, Ottawa, Canada, November 6, 1995.

[12] Alert Letter No.111: “Interference between digital TV transmissions and medical telemetry devices”,  Health Canada, Ottawa, Canada, September 29, 1999.

[13] Implants for Surgery - Active implantable medical devices. Part 1: General requirements for safety, marking and for information to be provided by the manufacturer ISO 14708-1 (1^st edition), International Organization for Standardization, Geneva, 2000.

[14] Implants for Surgery - Part 1: Implantable pacemakers, Committee Draft CD 5841-1 (draft 2^nd edition), 2001.