Many persons with hearing aids also have implanted cardiac pacemakers, as the need for both devices increases with advancing age.
Pacemakers rely on obtaining a clear signal from the atrial and ventricular leads in contact with the cardiac muscle. Reception of this signal will instruct the pacemaker that pacing is not necessary, and pacemaker activity will be inhibited. Also, reception of atrial signals in a dual-chamber pacemaker will elicit ventricular pacing after an appropriate interval.
Signals from cellular phones and electronic surveillance equipment have already been shown to interfere with pacemaker function in this way.1,2 Applying proper caution, some instructional booklets for hearing aid remote control devices (RCDs) have also included a warning that pacemaker patients should not operate an RCD very close to their pacemaker, such as in a breast pocket. Such warnings are only precautionary because the potential of RCDs to interfere with pacemaker function has never been demonstrated. On the contrary, there is a general presumption of safety regarding RCDs, which is based on their necessary conformance with standards applicable to all Class I medical devices.
However, there have been no published studies putting the question of possible RCD-pacemaker interaction to a rigorous test. Empirical evidence is called for because there are potential risks involved, especially for the patient who is pacemaker-dependent. In fact, hearing aid RCDs are generally used close to the person's chest, so they may be emitting signals quite close to the pacemaker. There may be potential for interference with pacemaker function if the signals are of sufficient amplitude and the appropriate frequency. In addition, pacemakers require periodic evaluation and reprogramming, which involves computer telemetry between the pacemaker and its programmer, as well as electrocardiography. Potential interference here—if an RCD was activated during a routine pacemaker check-up—could also put a pacemaker patient at risk.
The impetus for the present studies was the observation that a patient (not pacemaker-dependent) became pale while operating a remote control device (RCD) to adjust his programmable hearing aids.3 In an exploratory follow-up study, the patient's cardiac pacemaker was monitored by transmitting its output via telephone lines to his physician at a hospital-based pacemaker center while the patient operated the RCD at another facility. Unfortunately, artifacts related to telephone-line transmission prevented a clear interpretation of the electrocardiogram.
In the present investigation two studies are described. The first was an in vivo study, in which the same patient was evaluated for possible RCD-pacemaker interaction, but this time at the pacemaker center with his physician present. This study made possible a direct recording and reading of the patient's pacemaker activity and electrocardiogram by his physician without artifact related to telephone transmission. The second study was an in vitro exploration of possible interfering effects of a variety of RCD types on several different cardiac pacemakers and their telemetric evaluation. This study was carried out within an artificial chest cavity designed by the investigators for this purpose.
In this study, an experienced hearing aid user who had an implanted cardiac pacemaker wished to compare several programmable hearing aids operated by remote-control devices. Since he appeared to show cardiac-related symptoms when operating the RCD during a hearing aid fitting and since the source of the symptoms could not be defined (see Reiter 19973), the subsequent fitting procedures were moved into the office of his physician at the pacemaker center. During the investigation, the patient's electrocardiogram was monitored to see if there was any communication between the RCDs that the patient was considering and the patient's pacemaker output.
The subject was a socially active 88-year-old male who had worn hearing aids binaurally for 20 years. He had bilateral sensorineural hearing loss secondary to presbycusis. Positive prior experience with a remote control had led him to consider only hearing aids that could be controlled remotely for volume and program selection. The patient had sinus node dysfunction with bradycardia and symptoms. A dual-chamber pacemaker, Pacesetter, model 2022T, was implanted in October 1991.
The patient is not pacemaker-dependent, and it was determined that potential transient inhibition of the pacemaker would pose no harm to him. The patient was thoroughly debriefed prior to setting up this study. Other than the presbycusis and an irregular heart beat he was in good health.
The patient owned a programmable hearing aid system that was operated by an FM RCD. He was considering two new hearing aid systems which were programmable and could be operated by a remote control. The RCD was designed in each case to turn the hearing aids on and off, as well as to select the volume level and the program appropriate for a given listening situation. Hearing aid system #1, his own, used an RCD which emitted an FM signal of 137 kHz and 147 kHz when operated. System #2's RCD emitted an electromagnetic signal of 50 kHz, at 7 mA/m, in 150-ms bursts, and system #3's RCD emitted a tonal signal of 26 kHz.
For the study, the patient was lying in a supine position in an office of the Pacemaker Division of the Mount Sinai Medical Center. A baseline surface electrocardiogram and rhythm strip were obtained prior to the study, followed by continuous cardiographic recording of pacemaker function throughout the phases of the study. The pacemaker's programmer was used to obtain a telemetered endocardial electrocardiogram and to improve our chances of detecting any possible interference. The pacemaker was interrogated and the programming head was left over the pacemaker to obtain the telemetered signal. Representative strips were saved and printed.
The investigation consisted of activating each RCD in the following four positions: 18 inches away from the pacemaker, 4 inches away, near the tip of the ventricular lead, and directly over and touching the site of the pacemaker. Each position was preceded and followed by a 15-second baseline electrocardiographic recording.
There was no detectable interference in the function of the pacemaker with any of the devices tested in any of the positions tested. However, there was transient loss of telemetry between the pacemaker and its programmer with the FM and the electromagnetic RCDs when the RCD was operated at positions within 18 inches of the pacemaker and the programming head. A simultaneous surface EKG showed that there was no interaction with pacemaker function (see Figure 1). A rhythm strip recorded from the anterior chest also showed considerable distortion of the EKG signal during RCD activation; however, the regularity of the EKG revealed that there was no interaction with pacemaker function (see Figure 2).
This study showed that normal operation of the three hearing aid RDCs described did not interfere with pacemaker function at any of the positions tested. In addition to the normal cardiographic results the patient reported no ill effects during operation of any of the RCDs, nor were any symptoms noted, e.g., dizziness or light-headedness.
However, pacemaker function must be evaluated periodically, and this is done electronically via telemetry and electrocardiography. Here it was shown that operating the FM and electromagnetic RCDs during these procedures can degrade, distort, or obliterate the recordings.
This type of interference may be significant because oral communication between patient and physician during a pacemaker check-up is used to provide information necessary for the evaluation and adjustment of the pacemaker. When a patient is hearing-impaired, the need to adjust the level or change the listening program of his/her hearing aids to optimize communication during the procedures becomes a real possibility.
It is important that users of hearing aid systems with RCDs and their cardiologists be informed that certain hearing aid RCDs can distort or obliterate the reading of pacemaker function by their telemetric programmers and electrocardiography. Appropriate precautions can then be taken, e.g., adjusting the hearing aids in the manual (non-remote) mode if possible, or waiting for the effect of the interference to subside before analyzing the pacemaker function.
The results of this study apply to a particular cardiac pacemaker (Pacesetter, model 2022T) and cannot necessarily be generalized to other pacemakers with different operating systems. Therefore, we conducted a second study using an artificial chest cavity designed to test several different pacemakers representing the range of available pacemaker types.
Several studies investigating the potential effects of certain devices on pacemaker function have relied on artificial chest cavities rather than the human chest because of the greater experimental control, efficiency, and safety they afford.2
In this study, a chest cavity simulator was developed that would hold the leads and the pacemaker in a position similar to that which occurs in vivo. This simulator allowed for the switching of pacemaker models. In addition, the anatomically correct placement of recording leads made it possible to make a realistic assessment of the various RCDs at the operating sites and positions of concern.
In this study, six different pacemaker models were examined via telemetry and electrocardiography, while each of four RCD types was operated at each of four positions. It should be noted that to increase the sensitivity of the tests to detect possible interactions, we programmed each pacemaker to a unipolar sensing configuration and selected the most sensitive settings that would allow proper pacemaker function.
The chest cavity simulator consisted of a shallow rectangular plastic container (13.5 x 8.25 x 4.25 inches) placed horizontally and filled with saline solution (see Figure 3). The pacemaker and the leads were immersed in the saline solution.
The pacemaker was placed on a small Styrofoam cup (2 inches in height) to make its position more anterior, as it is in vivo. The ventricular and atrial leads were held in a position similar to that which would occur in vivo by means of small amounts of silicone glue applied to the inside of the plastic container.
Metal nails pierced the plastic wall of the container at positions similar to those used for electrocardiographic recordings for a person's torso, i.e., right and left shoulders, right and left thighs, and an anterior precordial lead. These five locations were connected to the electrocardiographic recording sites of the pacemaker-specific programmer. The programming head of the appropriate device was placed over the pacemaker to obtain the telemetered signals (see Figure 4).
The chest cavity simulator was designed to allow detection of two different types of potential interference from the RCD. One type of interference is with the telemetry signal between the pacemaker and its programmer. This signal is used both to program the pacemaker and to record and transmit the electrograms from the leads. The second type of interference is with the pacing function of the pacemaker itself. A continuous “surface” electrocardiogram recorded from the saline bath will show if the signals from the RCD interfere with pacemaker function independently of the telemetry.
Six pacemakers were selected for study because they represent some of the most frequently implanted models. The pacemakers and their telemetry frequencies are listed in Table 1.
Four different hearing aid RCDs were chosen that emitted four different types of operating signals: FM, electromagnetic induction, tones, or infrared. These and their signal characteristics are shown in Table 2.
The RCDs were to be operated at the following four positions: (1) directly over the pacemaker at a distance of 1 inch, (2) directly over the pacemaker at a distance of 18 inches, (3) within 1 inch of the atrial lead, and (4) within 1 inch of the ventricular lead.
An electrocardiogram was run for 15 seconds prior to manipulation of each of the RCDs, during RCD operation, and for 15 seconds following each RCD trial.
None of the four RCDs tested interfered with the pacing or sensing functions of any of the six pacemakers. However, transient loss of telemetry occurred with the electromagnetic and FM units in all six pacemaker models at distances of 1 inch from the pacemaker.
At a distance of 18 inches, loss of telemetry occurred with the FM unit for pacemaker model 7652 and with the electromagnetic device in pacemaker model 292–05. With the RCD held 1 inch from the atrial or ventricular leads, loss telemetry resulted only in pacemaker models 7962, 5330, and 292-05 with the FM and electromagnetic RCDs. Finally, activating the FM or electromagnetic RCD close to the pacemaker resulted in a delay in either the programming or the confirmation of programming of all pacemaker models. Programming and confirmation resumed as soon as the RCD operation ended. The results are depicted in Figures 5, 6, and 7.
As in Study I, the non-telemetered EKG recorded via rhythm stripper showed degradation of the EKG signal resulting from RCD activation. There were no interactions of any sort with the infrared or tonal types of RCDs.
We found no instances of inappropriate pacing or of inhibition of pacing with any of the remote control devices that we tested, even when the device was placed close to the pacemaker or the leads in a “worst case scenario.”
However, use of the electromagnetic or FM RCD in close proximity to the pacemakers and their programmers did interfere with the telemetry between the pacer programmer and the pacemaker, and in some models even delayed programming or confirmation of programming of the pacemaker. Programming or confirmation, however, always took place as soon as the hearing aid remote was de-activated. When a rhythm stripper was used to record non-telemetered EKG activity from the anterior chest itself, significant distortion resulted in the EKG signal when the FM or the electromagnetic RCD was operated near the pacemaker.
The specific instance in which loss of telemetry resulted when the RCD was activated near the atrial or ventricular leads was found to be artifactual. That is, when the RCD was held close to these leads it was also close enough to the pacemaker to have caused the telemetry-only type of interference. If the RCD signals had been sensed by either the atrial or ventricular leads, then the pacemaker's pacing function would have been interfered with. The simultaneously obtained electrocardiographic recording confirmed that no such interference occurred.
In general, the results of these studies do not indicate that use of remote control devices for programmable hearing aids poses any threat to the normal functioning of an implanted cardiac pacemaker. However, both studies show that there may be problems with evaluating or programming a pacemaker while a remote control device is being activated to adjust a hearing aid. Since this eventuality is a real one, information about this type of interference should be made available to both patient and physician to preclude confusion or possible erroneous suspicion of pacemaker malfunction during a routine pacemaker check-up.
Unsoon Shagong, RN, provided invaluable assistance in obtaining the materials for the study and its presentation. Rochel Leah Washkewicz prepared the figures with meticulous care and skill. Our patient was kind, patient, and understanding of our enthusiasm to learn more about the possible interaction between his pacemaker and the remote control hearing aid devices he was considering.
1. Hayes DL, Wang DM, Reynolds DW, et al.: Interference with cardiac pacemakers by cellular telephones. N Engl J Med
2. Ruggera PS, Witters DM, Bassen HI: In vitro testing of pacemakers for digital cellular phone electromagnetic interference. Biomed Instrum Technol
3. Reiter LA: Pacemakers and programmables. Presentation at the American Academy of Audiology Convention, April 1997, Fort Lauderdale, FL.
Other relevant articles/presentations
Irnich W: Interference in pacemakers. Pacing Clin Electrophysiol
1984;7(6, part 1):1021–1048.
Reiter LA, Camunas J: Pacemakers and programmables: An in vivo study. Presentation at the American Academy of Audiology Convention, March 2000, Chicago.
Reiter LA, Camunas J: Pacemakers and programmables: An in vitro study. Presentation at the American Academy of Audiology Convention, March 2000, Chicago.