Correspondence
Cardiac Pacemakers and Cellular Telephones
N Engl J Med 1997; 337:1006-1008October 2, 1997
- Article
To the Editor:
Regarding the editorial by Roelke and Bernstein (May 22 issue)1 on electromagnetic interference with pacemakers caused by cellular telephones 2: We are concerned about the editorial's recommendation that physicians test patients with pacemakers and their cellular telephones in the office to assess the potential for interference. Such testing is likely to produce false negative and perhaps false positive results and thus has limited usefulness. To the extent that a false negative result induces an unwarranted sense of security in the physician and the patient, the testing could have serious adverse effects, particularly in pacemaker-dependent patients. If the office test is positive, the patient would presumably be instructed either to take precautions about the positioning of the telephone in relation to the pacemaker or to switch from a digital to an analogue phone (analogue phones pose a minimal risk of interference with pacemakers1). But there can be false positive results if the performance of the electrocardiograph used to monitor patients during ad hoc testing is interfered with by the cellular telephone being tested. The more serious situation, a false negative result, can occur because office testing cannot ensure that the cellular telephone is transmitting at peak power or that the antenna is positioned to maximize the likelihood of an interaction.
In short, testing in the office should not be relied on as the definitive test for interaction between a patient's pacemaker and a cellular telephone. A more reliable practice is to contact the manufacturer of the pacemaker to determine whether the specific model has been tested and, if so, what the test results were. If testing has not been performed or if it indicates the possibility of interference, the patient should be instructed to keep the telephone's antenna at least 6 in. (15 cm) from the pacemaker, a practice that will greatly reduce the possibility of interference.3 For most patients, this simply means using the telephone in the normal position near the ear, rather than storing it in a shirt or vest pocket. For the rare patient who cannot be relied on to remember this simple precaution or whose body configuration would place the antenna less than 6 in. from the pacemaker when the telephone is being used, the physician should consider recommending that the patient switch from a digital to an analogue cellular telephone.
3 ReferencesBram D. Zuckerman, M.D.
Mitchell J. Shein, M.S.
Food and Drug Administration, Rockville, MD 208531
Roelke M ,Bernstein AD . Cardiac pacemakers and cellular telephones. N Engl J Med 1997;336:1518-1519
Full Text | Web of Science | Medline2
Hayes DL ,Wang PJ ,Reynolds DW , et al. Interference with cardiac pacemakers by cellular telephones. N Engl J Med 1997;336:1473-1479
Full Text | Web of Science | Medline3
Ruggera P, Witters D. In vitro testing of pacemakers for digital cellular phone electromagnetic interference. In: Proceedings of the 31st Annual Meeting and Exposition of the Association for the Advancement of Medical Instrumentation, Philadelphia, June 1–5, 1996. Arlington, Va.: Association for the Advancement of Medical Instrumentation, 1996:92. abstract.
To the Editor:
The article by Hayes et al. and the accompanying editorial contain limited information about the documented interference by cellular telephones with electronic biomedical devices other than pacemakers.
Electromagnetic interference by cellular telephones with a variety of such devices, including electronic monitoring and ventilatory equipment, is well documented by reports filed with the Food and Drug Administration (FDA).1 Concern has been voiced since 1993 in the biomedical engineering literature about the safety of using cellular telephones and electronic paging equipment in hospitals, because of the potential they create for inappropriate therapy or diagnosis and life-threatening consequences.2
A study conducted in 1994 by the department of safety at our institution confirmed that false fire alarms have been set off by portable and cellular telephones and that there have been episodes of interference with telemetry monitors resulting in a flat line. The safety committee recommended to our medical executive committee that the use of portable and cellular telephones be totally prohibited at our institution, for safety reasons. The recommendation was adopted and implemented.
It is important that administrators and providers of health care know of the electromagnetic interference by cellular and portable telephones with various types of electronic medical equipment — not only cardiac pacemakers — and the resultant implications for safety.
2 ReferencesJ. Thomas Danzi, M.D.
Tampa General Health Care, Tampa, FL 33601Author/Editor Response
The authors reply:
To the Editor: Danzi correctly calls attention to the potential for interference by cellular telephones with biomedical devices in hospitals. Our research on cellular telephones and pacemakers has yielded findings that apply to other types of interference: the interference depends on the type of cellular telephone, the distance between the transmitter and the medical device, and the type, age, and condition of the device. Medical devices also interfere with one another.1 These interactions are complex. Our view is that hospitals should test their own environments for interactions and take precautions based on their situations. The uniqueness and complexity of particular hospital settings preclude general recommendations at this time.
Zuckerman and Shein recommend that physicians not test pacemakers and cellular telephones in their offices. We agree, and strongly advise against such ad hoc testing. Indeed, the power output of a cellular telephone during office testing may not be maximal, since it is influenced by a number of factors, including the distance from the telephone to the nearest base station. If a telephone is far from the base station, it will emit signals at a higher power. On the other hand, if the telephone is close to the base station, it will emit signals at a lower power. Thus, the power can be controlled only by placing the telephone in the test mode. Doing so requires specific, proprietary programming that can be obtained only by contacting the telephone manufacturer directly.
Office testing is also subject to confounding by outside interference in the environment that can affect either the pacemaker or the monitoring device. Studies have found that electrocardiographic leads, transmitters, and the monitor itself can pick up interference from a cellular telephone that may be misinterpreted as interference with the pacemaker. In our study, the possible sources of external interference were controlled. First, all potential outside sources of electromagnetic interference were removed from the testing center. Second, the presence of any other external source of electromagnetic fields was documented. Third, all the technicians were trained to recognize interference coming from outside sources and to take steps to eliminate it.
We believe that the rigor of our study allows our recommendations to be extrapolated generally and that the risks associated with ad hoc testing outweigh the benefits.
1 ReferencesGeorge L. Carlo, Ph.D., M.S., J.D.
Health and Environmental Sciences Group, Washington, DC 20036David L. Hayes, M.D.
Mayo Clinic, Rochester, MN 55905Claudine M. Johnson, M.A.
Rebecca A. Steffens, M.P.H.
Health and Environmental Sciences Group, Washington, DC 20036To the Editor:
We share the concern for patients with pacemakers expressed by Danzi and by Zuckerman and Shein, but some of their comments deserve clarification.
Standard electrocardiographs and electrocardiographic monitors use rigorous low-pass filtering that may be expected to attenuate interference by cellular telephones to the point of invisibility, but temporarily attaching the electrocardiograph or monitor actually used in the pacemaker clinic to someone who does not have a pacemaker and conducting a test with the patient's cellular telephone would allow that issue to be resolved. Even if interference by the monitoring instrument did occur while a patient with a pacemaker was being examined (provided the display does not become completely blank), a competent pacemaker clinician should have no difficulty distinguishing recording artifacts from abnormal pacemaker behavior produced by cellular-telephone interference. Intracardiac-electrogram or timing-diagram telemetry provided by the pacemaker and its associated programming device is another potentially useful diagnostic resource, provided the telemetry process itself is not disrupted by the interference. Manufacturers' assurances, especially if capacitive shunting at the feed-through assembly in the connection block is absent in the patient's pulse generator, are of limited value unless the manufacturer has conducted worst-case tests with pulse generators and cellular telephones of the particular models used by the patient. Such tests, of course, would need to be conducted separately with unipolar and bipolar electrode configurations if the pulse generator offers both, to distinguish the results obtained with the unipolar configuration from those obtained with bipolar leads, which have higher interelectrode capacitance.
We assume that precautions need to be taken when patients with pacemakers use any cellular telephones, and we routinely advise our patients accordingly. Even analogue cellular telephones produce broad-spectrum interference during dialing and ringing. In particular, we note that young and elderly right-handed patients with left-sided implants and good natural or corrected near-field vision tend to hold the telephone close to the pulse generator while dialing (when interference is most likely, because of the digital pulses produced) unless they are warned not to do so, whereas middle-aged patients with mild, uncorrected presbyopia are automatically better protected, because they must hold the device farther away while dialing in order to read the key pad and the display.
Unless manufacturers are willing to undertake worst-case tests of every possible combination of pulse generator and cellular telephone (perhaps even as an FDA requirement), this matter remains the responsibility of the managing physician, who must take whatever steps he or she can to ensure the patient's safety.
Alan D. Bernstein, Eng.Sc.D.
Marc Roelke, M.D.
Newark Beth Israel Medical Center, Newark, NJ 07112
