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APPLICA
TION
APPLICATION
Electromagnetic fields and implantable
medical cardiac apparatus
by Dr. Martine Souques, EDF Gaz de France
The sources of electromagnetic interference that can affect the operation of implantable pacemakers and cardioverter
defibrillators (ICD) are more and more numerous, and cover the whole range of frequencies from 0 to 300 GHz,
including very low (ELF) and radio frequencies (RF). For a patient with this apparatus, the possible consequences
range from a lowering of the person
’s well being, with no clinical repercussions, to a dangerous situation
person’s
situation..
Now, the recommended limit values [1] for
human exposure, are much higher than the
threshold of immunity required by the
standard of electromagnetic compatibility
of this apparatus [2]. Moreover, the
European Recommendation excludes
cardiac pacemakers and ICD patients from
its scope [3].
From the 1980s onwards, experimental
studies with cardiac pacemakers on a
laboratory table revealed dysfunction risks.
This has led manufacturers to offer innovative
technological solutions, using filters
positioned on the input of the electronic
circuits, and software solutions, with the
introduction of so-called “reversion mode”
emergency programmes, should an
interference be detected.
This article intends to report the chief
conclusions of the studies on the possible
interference between electromagnetic
fields and implantable medical cardiac
apparatus, following upon the scientific
conference, “Electromagnetic fields,
cardiac pacemakers and defibrillators”,
organised by the Non Ionising Radiation
Section of the Societe Franqaise de
Radioprotection and the Cardiac
Stimulation Group of the Societe Francaise
de Cardiologie held on 25 October 2002 in
Paris.
What is a cardiac pacemaker?
A pacemaker is made up of a case
including a batter y and a computer
controlled electronic circuit. This circuit
allows the detection of the electric pulses
emitted by the auricles and/or the ventricles
and the consequential action. The case is
implanted in the upper thorax, most
frequently to the left. It is connected to the
heart by one or more probes. It is designed
to detect cardiac activity and automatically
stimulate the heart. It enables bradycardia
(very slow heart beat) to be treated. It
analyses the signals received within a range
of 10 to 100 Hz.
The sensitivity of the pacemaker to
electromagnetic interference depends on
several factors, the most important of which
are the setting of the probe: single- pole
detection (between an electrode and the
case), or two-pole detection (between two
electrodes located on the probe at the
heart), and the adjusting of the detection
sensitivity: the higher the sensitivity, the more
receptive the apparatus is to interference.
Other factors also have an influence such
as the frequency of the field or its
orientation.
An interference arises when the circuit thinks
it detects cardiac activity when there is
none. This can be an outside source, or
due to muscular activity i.e. from the greater
pectoral muscle, above all with single-pole
detection.
Approximately 50 000 cardiac pacemakers
are implanted in France each year.
Today, pacemakers and ICD are capable
of stimulating or giving a shock, storing
diagnostic information in its memory, and
providing graphs with electrograms that
enable the fine adjustment of settings, the
adjustment of treatment and the spotting
of interference. The consequences of
interference range from an acceleration
of the heart rate to cardiac arrest, an
inappropriate shock, or even a
deprogramming. Generally speaking, the
consequences are reversed when the
patient is no longer exposed. With ICD,
interference cannot go unfelt, since it
generates an inappropriate shock, while
the stopping of a pacemaker for a few
seconds only causes a slight turn or may
not even be felt.
In the literature we can find three types of
study:
!
In vitro tests: with the apparatus on a
laborator y table. These tests fail to
reproduce all the constraints that apply
to implanted apparatus. At present, they
are often carried out with phantoms, as
in the example of Pr. Nadi’s work at the
Laboratoire
d’Instrumentation
Electronique de Nancy (LIEN).
Therefore, these studies are more
credible.
!
In vivo tests: on voluntary patients during
or after implantation, with a standard
programme or with a specific
programme reproducing the most
unfavourable case (single-pole
detection, maximum sensitivity).
!
Clinical cases: reported in literature.
What is an implantable
cardioverter defibrillator (ICD)?
An ICD is made up of the same
components as a pacemaker, but with a
larger battery, to give electric shocks in
answer to the disturbance detected in the
cardiac rate.
They are designed to detect and
automatically treat episodes of troubled
heart rate, i.e. tachycardia, and ventricular
fibrillation, but they can also have a
stimulation function. Detection is
necessarily two-pole, which greatly
reduces the risk of perceiving interference.
However, ICD are naturally more sensitive
than pacemakers, since they have to
detect lower signals.
Approximately 2000 ICD are implanted
annually in France, a figure that is
constantly rising. The first operation dates
back to the beginning of the 1980s. There
are far fewer studies for this kind of
apparatus that is of a more recent
technology.
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Power frequency electric and
magnetic fields (ELF)
The case of pacemakers
In the 1980s, studies of interference with
50 Hz chiefly concerned the effects of
induced current in the human body. In
1983, Butrous [4] showed that the
interference threshold varied with the
model, and the size and position of the
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patient. The induced current modifying the
operation of the pacemaker varies
between 20 and 337 µA, which
corresponds to fields of 2 kV to 24 kV/m.
The interference described takes the
form of permanent or intermittent reversals
in an asynchronous mode (the
emergency programme written by the
manufacturer), slowing down or irregularity
of the heart rate. The asynchronous mode
can be unpleasant for patients.
In 1988, Kaye [5] directly applied a 50 Hz
current to patients which simulates the
exposure to a high voltage electric field.
He found a great variation in the threshold
current which triggered an interference,
27 to 246 µA, and the role of the position
of the patient. He showed that by gradually
increasing the intensity of the current, it
moves from normal operation to failure
of detection and then intermittent
inhibition.
Astridge [6] widened this study to dual
chamber pacemakers, and, in 1993,
showed the importance of the polarity,
the single pole mode being more sensitive
(10 to 40 µA) than the two pole mode (80
to 170 µA) for the highest sensitivity settings.
This corresponds to electric fields
respectively of 1,5 kV/m and 13 kV/m for
the most sensitive apparatus.
Toivonen [7] is the only person who,
besides electric fields, took an interest in
magnetic fields in an in vivo study. The
latter was carried out in an electric
substation, by var ying the polarity and the
sensitivity of pacemakers and measuring
the electric and magnetic fields in
different places, with continuous
monitoring via telemetry. He again found
a relative lack of sensitivity in the two pole
mode compared with the single pole
mode, and the harmful effect of
programming with a maximum sensitivity,
in the single pole mode, that causes
disturbances starting at 1,7 kV/m, whilst
the two pole mode is exceptionally
disturbed by intense fields of 7 to 8 kV/m.
He found no anomaly for magnetic fields
of between 48 and 90 µT, with normal
sensitivity, whilst the same fields disturb the
operation of a pacemaker when the
settings are sirigle pole with a high
sensitivity.
In 1990, in an in vitro study in old single
chamber models, Salmi [8] showed that
the lowest magnetic field that changed
the functioning of the pacemaker was
40 µT, for frequencies of 40 Hz to 70 Hz.
However, it is difficult to draw conclusions
for present day apparatus, whose
technology is based on microprocessors.
In this study, it was purely a question of the
switching to an interferential mode,
without interrupt¬ing stimulation, or any
other anomaly.
More recently, Silny [9] studied 100
pacemakers in vitro. He showed that a
50 Hz vertical electric field of over 6 kV/m
could lead to an interference in the most
unfavourable case. In the case of a
magnetic field, the interference threshold
is between 552 µT at 10 Hz and 20 µT at
250 Hz (a frequency found in some
electronic article surveillance gates: EAS
gates).
The French study by Frank [10] concerns
60 volunteers representing the 9
manufacturers of pacemakers implanted
in France. They were exposed to a
magnetic field of 50 µT at 50 Hz and 60 Hz
with two apparatus settings. With the basic
setting, no disturbance was revealed. With
the most unfavourable setting (maximum
sensitivity, single pole detection), 6 cases
of transient reversions and 3 cases of
transient acceleration were detected.
However, no deprogramming, or
inhibition was observed. There was no
interference below 40 µT.
The case of ICD
We have found no
study published for this
frequency
range
regarding ICD. An in
vitro study is underway
at the Laboratoire
d’Instrumentation
Electronique
de
Nancy (Pr. Nadi).
Induction heating
(kHz range)
The
only
study
published is that of
Frank quoted above
[10] which concerns
cardiac pacemakers.
The volunteers were
invited to use a normal
induction hob (3rd
generation),
with
different methods. This
hob operates with
fields of between 20
and 50 kHz. No
disturbance
was
detected, neither with
the basic setting, nor
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with the most unfavourable setting, whether
the hob was used on a low or high power
setting, or with a sequential mode.
Metal detectors
For 20 years, all cardiac pacemaker
patients have been warned of the
dangers of gates used in airports, banks
of prisons to detect weapons. Starting in
1988, the Copperman [11] study regarding
single-pole pacemakers proved that
these detectors had no influence even
with apparatus programmed for the
maximum sensitivity. In 2003, Kolb [12]
tested 200 volunteers with an implanted
pacemaker and 148 with an ICD. No
interference or deprogramming was
observed with this recent apparatus. The
main risk remains the triggering of the
detector alarm by the pacemaker or ICD
case which is made of metal!
Mobile telephones (RF)
The case of cardiac pacemakers
These potential EMC problems have been
the subject of numerous publications. The
first were alarming: Barbaro [13], Hayes
[14] or Nuegell [15] described inhibitions
or accelerations in the heart rate, mainly
with 8 W analogue telephones placed at
less than 10 cm from the case, set at the
maximum sensitivity, and with a single-pole
detection (the most unfavourable setting).
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In 1997, Hayes [16], in a multecentric in
vivo study, found 20% interference with
digital telephones, 7% of which being
symptomatic, and only 2,5% interference
with analogue telephones.
Recently, Trigano [17, 18] carried out in
vivo studies on 255 patients, representing
82 pacemaker models, of the 9
manufacturers represented in France,
with the most unfavourable setting
conditions (maximum sensitivity of the
pacemaker, contact with an analogue
telephone with a maximum power of 2
W). The results show that the pacemaker
model is a deciding factor. They also
highlight the importance of the distance
between the telephone and the window
of the connector of the “sealed
feedthrough” (the part of the pacemaker
linking the connector to the metal case).
The interference found is above all
inhibitions or salvos of fast ventricular
stimulation. In 4% of the cases, the
inhibitions was sustained and potentially
symptomatic. At the same time,
Jacquemart [19] showed that the design
of the “sealed feedthrough” seems to play
a major role in sensitivity with regard to
mobile telephones. For a few years now,
these works have led manufacturers to
modify this sealed feed through by adding
filters (RF are easy to filter because they
are not within the range of the cardiac
frequency).
The case of ICD
Irnich [20] and then Occhetta [21] studied
the interference between telephones and
ICD and drew the same conclusions. In
Occhetta’s in vivo study, analogue and
digital telephones were brought into
contact with 5 ICD for 5 min when a
defibrillator was being implanted. No
inappropriate shock, nor a fault in the
detection of an induced ventricular
ICD cases
Ele ctronic article surveillance
gates (EAS)
Only clinical cases have been published,
describing inappropriate shocks received
by patients remaining within EAS [29, 30].
The case of cardiac pacemakers
With EAS gates, the problem is more
complex because it is a question of
apparatus
whose
frequencies
are
multiple and cover the whole range. Each
one has its own signature.
Beaugeard [22] in an in vitro study, as early
as 1992, insisted on the danger of EAS
gates in shops. The following year, Dodinot
[23] confirmed the high potential sensitivity
of cardiac pacemakers with regard to
EAS gates, in his in vitro study. However, in
his in vivo study, asking patients to walk
through a 300 kHz EAS gate, he observed
a ventricular pause with one single type
of pacemaker (already out-of-date in
1993) that had no safety ventricular
stimulation (reversion mode). The pause
was
transient
and
spontaneously
reversible. There was no deprogramming.
As for Lucas [24], he observed reassuring
in vitro results, only bringing to light minor
fibrillation were observed. Hence, there is
no reason to forbid the use of mobile
telephones for ICD patients.
dysfunctions with the maximum sensitivity
Conclusion on mobile telephones
was asynchronous stimulations (switching
It is recommended to hold a safety
distance between the case of the
pacemaker or the ICD and the telephone,
ranging from 15 to 20 cm for a telephone
with a maximum power of 2 W, to 40 cm
deprogramming.
for a maximum power of 8 W. A piece of
advice that is common sense is not to put
a telephone in a chest pocket on the side
where the case of the pacemaker or ICD
is implanted.
[28],
and single-pole detection. For Fetter [25]
and Mc Ivor [26], the main interference
to emergency mode). They observed no
Wilke [27] published an in vivo study of 53
patients with different pacemaker models
which confirmed Lucas’ results. For Trigano
the
dangerous
systems
are
magneto-acoustic gates emitting a
pulsed field (58 kHz). The other risk factors
are above all the movement in the field
and the exposure duration.
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Conclusion for electronic article
surveillance gates
It is recommended not to remain
unnecessarily inside the gate, in particular
for ICD patients. This of course means that
the EAS must be visible! “Don’t lean, don’t
stop, just go”.
Interference in the work place
These different ranges of frequency can also
be found in the industrial sector.
For static fields, it is recommended not to
exceed 0,5 mT, but the compatibility standard
is 10 mT, a level that is practically never
exceeded in the professional environment.
For the other frequency ranges (ELF,
induction, RF) the interference risks are
negligible but there is no guarantee of an
absence of risk [31]. There is no exhaustive
study that has researched into disturbances
according to a particular type of exposure
for all existing apparatus. Usually a
pacemaker or ICD patient would be said to
be inapt or require a job change, in the
case of exposure to electric or magnetic
fields. In fact, conflict is rare and the
psychosocial problems raised by this attitude
are much higher than the interference risk.
The procedure is rather to wear a holter at
the work station or to interrogate the
apparatus if it has sufficient memory, after
setting it to the maximum sensitivity with a
single-pole detection, whilst working with a
cardiologist. If no anomaly is detected, it is
preferable not to change the work
conditions, with the pretext of a potential,
but not real risk.
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Clin Electrophysiol 1988 ; 11 (7) : 999
1008.
In the case of ICD there is however, a strict
contra-indication, i.e. arc welding.
Conclusion
Interference with cardiac stimulation is quite
well apprehended and the consequences
are generally low. The same fails to apply
to defibrillation, where interference can be
the source of an inappropriate operation
of the apparatus, the first consequence
being for the patient to receive an
unjustifiable shock.
In the case of cardiac stimulation, the
interference problem often remains
anecdotal, without major practical
consequences. Regarding ICD, data from
publications incite us to be more careful,
in particular regarding EAS gates. However,
for ICD, there is one formal contraindication, i.e. arc welding.
[6]
[7]
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Acknowledgement
[12] Kolb C, Schmieder S, Lehmann G, Zrenner
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Referen
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[20] Irnich W, Batz L, Muller R, et al.
Electromagnetic interference of
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[8]
Cardiac pacemakers and automatic
implantable cardioverter defibrillators (ICD)
are frequently well protected from outside
interference. A little common sense,
advice and elementary precautions are
often sufficient to reduce risks, e.g. do not
put a drill against a pacemaker or ICD
case; put a mobile telephone on the
opposite side to the case; do not lean
inside an EAS gate; etc.
This article was published in the October
2003 issue of Electra, the members
magazine of Cigré, www.cigre.org, and is
republished with permission.
[19] Jacquemart JF, Razzani M. Stimulateurs
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effect of metal detector gates on
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European GSM mobile phones pose a
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[14] Hayes DL, Von Fekt LK, Neubauer SA,
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pacemakers. Pacing Clin Electrophysiol
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[15] Nuegell B, Osswald S, Deola M, Burkat F
Intermittent pacemaker dysfunction
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Griffith JL, Steffens RA, et al. Interference
with cardiac pacemakers by cellular
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de perturbations induites par la
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[24] Lucas EH, Johnson CM, Mc Elroy P The
effects of electronic article surveillance
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[25] Fetter JG, Benditt DG, Stanton MS.
Electromagnetic interference from
welding and motors on implantable
cardioverter defibrillators as tested in the
electrically hostile work site. J Am Coll
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[26] Mclvor ME, Sridhar S. Interactions between
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[27] Wilke A, Kruse T, Hesse H, Funck R, Maisch
B. Interactions between pacemakers and
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[28]
Trigano A J. Interferences et stimulateurs
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radiofrequences. Arch Mal Coeur Vaiss
2003 ; 96 (Special III) : 42 45.
[29] Mclvor
ME.
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[30] Mathew P, Lewis C, Neglia J, Krol RB,
Saksena S. Interaction between electronic
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Contact Ken King,
SA National Committee of Cigré,
Tel (011) 886-6573, [email protected]
"