CLINICAL RESEARCH: ELECTROPHYSIOLOGICAL DISORDERS
Do airport metal detectors interfere with implantable pacemakers or cardioverter-defibrillators?
Christof Kolb, MD*,*,
Sebastian Schmieder, MD*,
G.ünter Lehmann, MD*,
Bernhard Zrenner, MD*,
Martin R. Karch, MD*,
Andreas Plewan, MD* and
Claus Schmitt, MD*
* Deutsches Herzzentrum München and 1. Med. Klinik, Klinikum rechts der Isar der Technischen Universität München, Munich, Germany
Manuscript received November 30, 2002;
revised manuscript received February 7, 2003,
accepted February 20, 2003.
* Reprint requests and correspondence: Dr. med. Christof Kolb, Deutsches Herzzentrum München, Elektrophysiologie, Lazarettstrasse 36, 80636 Munich, Germany.
Kolb{at}dhm.mhn.de
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Abstract
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OBJECTIVES: The aim of this study was to determine whether airport metal detector gates (AMDGs) interfere with pacemakers (PMs) or implantable cardioverter-defibrillators (ICDs).
BACKGROUND: It is currently unknown whether AMDGs interfere with implanted PMs or ICDs.
METHODS: A total of 348 consecutive patients (200 PM and 148 ICD recipients) have been tested for the occurrence of electromagnetic interference (EMI) within the electromagnetic field of a worldwide-used airport metal detector.
RESULTS: No interference, such as pacing or sensing abnormalities, was observed in any of the 200 PM and 148 ICD patients; also no reprogramming occurred.
CONCLUSIONS: In vivo testing of PM and ICD systems showed no EMI with a standard AMDG. Clinically relevant interactions with implanted PMs or ICDs seem unlikely.
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Abbreviations and Acronyms
| | AMDG | | airport metal detector gate | | ECG | | electrocardiogram | | EMI | | electromagnetic interference | | ICD | | implantable cardioverter-defibrillator | | PM | | pacemaker |
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Electromagnetic interference (EMI) with implanted pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs) has been reported under various circumstances in patients’ daily life (1–9). Thus, EMI should be considered as a serious hazard for PM and ICD recipients.
The risk of EMI depends on several factors such as: 1) the distance of the PM/ICD from the potential source of EMI; 2) the oscillation frequency and field strength of the disturbing electromagnetic field as parameters for induced voltage; and 3) device-dependent technical details such as PM sensitivity or unipolar or bipolar lead configuration.
Atrial oversensing due to detection of electric disturbances may result in a sudden increase of the ventricular pacing rate or inappropriate mode switching to VDI or DDI mode. Oversensing in the ventricular channel will cause an inhibition of ventricular pacing and may result in bradycardia-associated symptoms such as dizziness or even syncope. In patients with an ICD, EMI may lead to false arrhythmia detection and may cause inappropriate anti-tachycardia pacing or internal shock delivery.
For the purpose of metal detection, one or several coils are incorporated in airport metal detector gates (AMDGs). Using alternating current, a primary magnetic flux is produced within the coil. Movement of a metal object within these coils will induce a secondary magnetic flux, which produces voltage changes in the coils that can be used for metal detection.
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Study objectives
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It is unknown whether the primary magnetic flux generated by the AMDG interferes with current PM or ICD systems. At a time of increasing security requirements, we evaluated the influence of the AMDG on ICDs and permanent PMs in vivo in a large series of patients.
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Methods
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The study comprised 348 consecutive patients presenting for routine follow-up of their PM or ICD devices at the outpatient clinic of our institution. During routine check-up, the correct PM/ICD function was tested by performing a standardized follow-up protocol, including interrogation of the device, arrhythmia diagnosis, atrial and ventricular sensing, and pacing threshold tests, and exclusion of sensing failures or oversensing by isometric contraction of the pectoral and/or abdominal muscles. Any atrial or ventricular sensing abnormality that could not be avoided by reprogramming of device parameters led to exclusion from the study. Informed consent was obtained from all patients before testing for interference with the AMDG.
A standard AMDG security gate (model 02PN10, C.E.I.A., Viciomaggio, Italy) was used. The AMDGs constructed in the same way are presently used in the majority of airports in the U.S., Canada, and Europe. Electromagnetic flux density, oscillation frequency, and detection sensitivity were programmed according to the current standard for international airports. The electromagnetic field of the AMDG used is characterized by three peak levels with pulse rates of 3.73, 4.98, and 5.98 kHz and reaches a maximal electromagnetic flux density of 42 µT.
Test protocol for implanted PMs.
The basic rate and/or atrioventricular delay were adjusted for the testing, with the aim of permanent ventricular pacing. This was achieved by either atrioventricular-sequential pacing or atrial-triggered ventricular pacing in dual-chamber PMs. The basic pacing rate of single-chamber devices was programmed to be above the intrinsic heart rate. Preprogrammed sensitivity remained unchanged for EMI testing. All PMs were interrogated before the start of the test protocol, and all parameters were recorded. The patients were advised to cross the AMDG at a normal walking speed back and forth. To simulate a "worst-case scenario," the patients were then asked to remain at least 20 s within the AMDG and to perform a 360° torsion around the body axis. Thereafter, patients were advised to place the chest side with the implanted PM device as close as possible toward the transmitting side of the AMDG. An external six-lead electrocardiogram (ECG) was continuously recorded and evaluated with respect to sensing abnormalities, such as atrial or ventricular oversensing, or pacing abnormalities, such as a loss of capture or pacing in the asynchronous mode. Interrogation of the PM was repeated and analyzed for the occurrence of spontaneous reprogramming.
Test protocol for ICD.
The test protocol for the patients evaluated for EMI in the ICD group was carried out in a similar fashion as that in the PM group. In contrast to the PM patients, the ICD was programmed to maximal sensitivity before being exposed to the AMDG field. The minimal heart rate for the detection of arrhythmias was set at 100 beats/min. The detection interval was programmed to the shortest value available.
In all patients, ICD detection remained active while delivery of therapies was programmed "off" (not applicable to the Biotronik [Berlin, Germany] Belos VR/DR and St. Jude/Ventritex [Sylmar, California] ICDs). Patients were exposed to the AMDG, as described earlier. After AMDG exposure and repeated interrogation of the ICD, Holter monitoring data acquired by the ICD and all parameters were printed out and analyzed for possible occurrence of EMI.
Temporary suspension of therapies due to EMI (reed-switch mechanism) was assessed by an acoustic signal incorporated in Guidant/CPI (St. Paul, Minnesota) and Medtronic (Minneapolis, Minnesota) devices or by interrogation for magnet reversion in St. Jude/Ventritex devices.
Statistical data.
Data are presented as the mean ± SD or range.
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Results
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PMs.
A total of 203 PM systems were studied in 200 patients (3 patients with testing before and after exchange of the pulse generator due to battery depletion). The mean age of patients was 65 ± 20 years (range 9 to 101 years), and 68 patients were female. Among the devices, there were 53 single-chamber PMs, 140 dual-chamber PMs, 9 VDD systems with single-pass electrodes, and one biventricular system for cardiac resynchronization therapy. The pacing modes at the time of testing of interference were AAI(R) (n = 3), DDD(R) (n = 111), two of which were in mode switching due to atrial fibrillation at the time of testing, DDDRV (n = 1), DDI(R) (n = 11), VDD (n = 9), and VVI(R) (n = 68).
Atrial sensitivity was programmed at 0.6 ± 0.3 mV (range 0.1 to 2.0 mV) for bipolar leads (n = 117) and 1.3 ± 0.8 mV (range 0.5 to 3.0 mV) for unipolar leads (n = 16). Ventricular sensitivity was programmed at 2.6 ± 0.8 mV (range 0.6 to 5.6 mV) for bipolar leads (n = 95) and 3.8 ± 1.2 mV (range 1.3 to 8.0 mV) for unipolar leads (n = 105). The different PM and lead models are shown in Tables 1 and 2.
None of the following was observed in any of the 203 systems tested: atrial oversensing/inappropriate mode switching, ventricular oversensing, atrial/ventricular loss of capture, pacing in the magnet mode, or spontaneous reprogramming of the PM.
ICDs.
A total of 151 ICD systems were studied in 148 patients (3 patients with testing for EMI before and after exchange of the pulse generator due to battery depletion). The mean age in the ICD group was 61 ± 15 years (range 10 to 86 years), and 26 were female. Among the devices, there were 101 single-chamber devices, 46 dual-chamber devices, and 4 systems for cardiac resynchronization therapy. Right ventricular sensing leads had a true bipolar sensing configuration in 52 cases and integrated bipolar sensing in 92 cases; the type of lead was unknown in 4 patients. Detailed information on the type of leads and ICD are given in Tables 3 and 4. Maximal ICD sensitivity could be programmed before the AMDG test in 142 (94.0%) of 151 ICD systems without T-wave oversensing or detection of myopotentials.
In none of the 151 systems studied was ventricular oversensing resulting in inappropriate detection of (non)sustained ventricular arrhythmias, spontaneous reprogramming of the ICD, or temporary suspension of therapies observed (test protocol not applicable to all systems in the last case).
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Discussion
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Electromagnetic interference with PMs or ICDs is a relatively rare but potentially serious adverse event in clinical practice. Interactions with electronic article surveillance systems and cellular telephone systems have been extensively evaluated, showing a risk for both PM and ICD patients in the case of acoustomagnetic article surveillance systems (1–4) and for PM recipients (5–7,10–12) in the case of cellular telephones. In contrast to potential interactions of cellular telephones or electronic article surveillance systems with implanted pacing devices that operate at much higher pulse rates than the AMDG, data on interference caused by AMDG are limited.
Regarding implanted PM systems, a study performed more than a decade ago showed no interactions with the AMDG (13). However, currently implanted PM systems significantly differ from those previously studied: multi-programmable PMs have become standard, the percentage of dual-chamber PMs has largely increased, and the atrial sensing threshold is programmed to lower values (higher sensitivity) in order to recognize atrial arrhythmias. To date, ICD recipients have not been tested within the electromagnetic field of an AMDG.
Theoretical and in vitro studies have shown that low-frequency magnetic fields can interfere with PMs at a magnetic flux density >16 to 42 µT (14,15)—a value that is also reached by the AMDG (16). However, the oscillation frequency of the AMDG’s electromagnetic field is different from that used in the calculations, and PM filter characteristics have not been considered. Therefore, the reports mentioned previously may not be transferable to the AMDG.
In none of the PM patients was atrial or ventricular oversensing, loss of capture, pacing in the magnet mode, or spontaneous reprogramming observed. This is in accordance with the findings of Copperman et al. (13). In none of our ICD patients did inappropriate tachyarrhythmia detection occur, despite programming of the highest sensitivity, shortest detection interval, and detection rates lower than those usually applied. Spontaneous reprogramming was not observed.
Pacemaker sensitivity for the EMI test was unchanged when compared with the individually optimized programming obtained during the preceding follow-ups, thus avoiding oversensing. Programming of increased PM sensitivity for the AMDG test would have introduced difficulties in determination of the source of interference in the case of PM inhibition (i.e., EMI vs. intermittent myopotential oversensing). To obtain an additional safety margin for the evaluation of possible interference, the ICDs were programmed to maximal sensitivity.
In ICD patients, evaluation of possible interference was mainly based on ICD Holter monitoring data acquired after passing the AMDG. This enables sensitive detection of even short-lasting episodes of interference and interpretation of stored electrograms.
Study limitations.
Interpretation of the six-lead ECG in PM patients may be difficult in some instances, with respect to evaluation of absolute correct sensing and pacing behavior. Some special functions of the PM (e.g., automatically adjusted refractory periods, sensing thresholds, pacing outputs) cannot be judged solely by the surface ECG. Short-term atrial oversensing exclusively presenting within refractory periods cannot be precluded from the surface ECG. In these circumstances, continuous marker recordings would help to analyze PM behavior. Recording of the marker ECG in our study was abandoned after a pilot phase, for practical reasons such as frequent loss of telemetry in older PM systems when following the patient through the AMDG, as well as the electromagnetic field disturbing telemetry (12). Thus, minor sensing abnormalities that are undetectable by surface ECG recordings cannot be ruled out completely.
Conclusions.
In vivo testing of 203 PM and 151 ICD systems revealed no EMI with a standard AMDG. Considering a period of just a few seconds within the electromagnetic field for routine airport security controls, clinically relevant interactions with PMs or ICDs seem to be unlikely.
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Acknowledgments
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We thank Gudrun Schuler, Dorit Jedlitschka, Katrin Becker, and Marianne Lösel, all from Deutsches Herzzentrum München, for their excellent technical assistance.
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Abstract
Study objectives