Electromagnetic Interference on Pacemakers
Okan Erdogan, MD
Department of Cardiology, School
of Medicine, Trakya University, Edirne, Turkey
Address for correspondence: Dr.
Okan Erdogan, MD, Trakya Universitesi, Tip Fakultesi,
Kardiyoloji, Edirne, Turkey, 22030
Email: okanerdogan@yahoo.com
Abstract:
External sources, either within or outside the hospital
environment, may interfere with the appropriate function of pacemakers
which are being implanted all around the world in current medical
practice. The patient and the physician who is responsible for
follow-up of the pacing systems may be confronted with some specific
problems regarding the various types of electromagnetic interference
(EMI). To avoid these unwanted EMI effects one must be aware of this
potential problem and need to take some precautions. The effects of EMI
on pacemaker function and precautions to overcome
some specific problems were discussed in this review article. There are
many sources of EMI interacting with pacemakers. Magnetic resonance
imaging
creates real problem and should be avoided in pacemaker patients.
Cellular
phones might be responsible for EMI when they were held on the same
side
with the pacemaker. Otherwise they don't cause any specific type of
interaction with pacemakers. Sale security systems are not a problem if
one walks
through it without lingering in or near it. Patients having unipolar
pacemaker
systems are prone to develop EMI because of pectoral muscle artifacts
during
vigorous active physical exercise.
Pacemakers (PM), either dual or single chamber,
are currently being implanted in an increasing number for various
indications all around the world. Although PM are very sophisticated
and technically challenging devices, they may be affected by many
internal and external factors. Patients with PM need to be regularly
and carefully evaluated
for any source of environmental factors that might interfere with
pacemaker function. Patients who are dependent on pacemaker are
especially at increased risk for developing adverse effects in case of
an electromagnetic interference (EMI). EMI is generally defined as
interference of pacemaker function
by the signals generated by external sources. Current PM are relatively
immune to EMI because the circuitry is shielded inside a hermetically
sealed titanium or stainless steel case that often has an additional
insulative
coating. In addition, increased use of bipolar leads also decreased the
susceptibility of pacing systems to EMI. Pacing systems are capable of
filtering out some noncardiac signals by using bandpass filters that
might
prevent sensing of external signals responsible for EMI. Within the
context
of EMI which may be prevented by some precautions there are many
external
environmental sources to be discussed in this article.
Common sources for EMI
a) Transthoracic DC cardioversion
Among the problems caused by DC shock on pacemaker function some are
to be mentioned: reversion to back-up mode, transient increases in
capture threshold and loss of capture as well as destruction of the PM
generator and circuitry1,,3.
A clinical study involving 36 patients with unipolar PM implanted on
the right pectoral side revealed that 50 % of patients developed loss
of capture due to increased stimulation thresholds. They received
higher cumulative shock energies.
Seven patients had sensing failure and three patients developed
generator
failure requiring replacement. The authors suggested that the utilized
shock
energy should be as low as possible and before shock attempt the PM
should be programmed to its maximal output 2.
These
problems can be prevented by placing the paddles or patches at least 15
cm away from the generator or using an anterior-posterior approach. The
pacemaker should always be interrogated before and after the attempt of
cardioversion.
b) Radiofrequency catheter ablation
Radiofrequency (RF) generators produce unmodulated signals with
frequencies between 400 and 500 kHz. Patients having Thera and Kappa
model PM underwent RF ablation and exhibited excellent protection
against interference produced by RF current. Pacing inhibition,
under-or over sensing were not observed4.
Pfeiffer et al.5 evaluated 25 patients with
13 different PM models, most of them with unipolar leads, during RF
current delivery. In contrast to the previous study result
they observed sensing failure in 8 and pacing failure in 4 patients.
In general, patients with PM undergoing RF ablation have their PM
checked
before and after ablation. The dependency status should be ascertained
and temporary pacing must be available. Rate response function should
be turned off. RF applications should be as brief as possible and
remote
from the pacing electrode tip. If the patient is not dependent, the
pacemaker
can be programmed to OOO or VVI at a lower rate than the intrinsic
heart
rate. If the patient is dependent, the PM should be programmed to VOO
mode and a temporary PM wire should be in place as back-up.
Reinterrogation
of the PM after the procedure is essential and integrity of the pacing
circuit should be evaluated.
c) Electrocautery
Electrocautery uses radiofrequency current to cut or coagulate tissues.
It may produce signals that might inhibit the pacing stimuli or trigger
ventricular pacing due to atrial oversensing. Additionally, current
generated by the electrocautery can cause myocardial damage due to
concentration
of current at the electrode-tissue interface and subsequent elevation
of
pacing threshold. Use of the electrocautery tip close to the PM may
cause
it to revert to a noise reversion fixed rate mode or inhibit it due to
oversensing of signals. Therefore, electrocautery should be bipolar, if
possible and not be used in the vicinity of the PM. The orientation of
current flow should be perpendicular to the lead of the PM system6. Electrocautery application should be limited to
a few seconds. The PM should be programmed to asynchronous VOO mode
and/
or a temporary PM should be inserted as back-up in case of dependency.
Instead
of electrocautery use of an ultrasonic scalpel reduces EMI7 . Minimal power settings should be used for
electrocautery.
The heart rhythm should be monitored and the PM checked after the
surgery.
d) Magnetic resonance imaging
Magnetic resonance imaging (MRI) is a very important diagnostic tool
and widely available today. MRI which is contraindicated in patients
with PM utilizes strong electromagnetic fields that further interferes
with PM function. Exposure to the magnetic field of MRI closes the reed
switch which enables the PM function in the magnet mode and rate.
Magnetic
field may also cause significant torquing effect on the generator
though
reports about newer PM with little amount of ferromagnetic material in
their
construction revealed no significant physical movement 8,9. A clinical
prospective
study conducted by Vahlhaus et al. 10
comprised
32 patients with PM. Patients were exposed to MRI at 0.5 Tesla. Lead
impedance,
sensing and stimulation thresholds did not change after MRI. Battery
voltage
decreased immediately after MRI and recovered 3 months later. Battery
current and impedance tended to increase. MRI affected neither PM
programmed
data, nor the ability to interrogate, program or telemetry. Temporary
deactivation of the reed switch occurred in 12 patients in the center
of
the magnetic field. MRI at 0.5 Tesla did not cause irreversible changes
in PM systems. Rapid pacing in unipolar systems exposed to the pulsing
radiofrequency field owing to the antenna effect of the electrode
system has been demonstrated 11. Another
potential adverse effect of MRI
is electrode heating. MRI at 1.5 Tesla caused major temperature rise at
the electrode-tissue interface 12. In
some
patients who definitely need MRI study for any reason it might be
cautiously
undertaken with the following recommendations. The PM should be fully
checked
before and after MRI and dependency status should be evaluated. In
non-PM
dependent patient the device should be programmed to OOO, if it is
available.
Low magnetic field (0.5 Tesla) is preferable. The patient should be
monitored
by pulse oximetry, blood pressure, heart rate and electrocardiogram. My
personal experience with non-pacemaker dependent patients undergoing
head
MRI confirmed no obvious signs of device failure and patient discomfort
after the above mentioned precautions have been undertaken.
e) Radiotherapy
High energy radiation may be responsible for many types of adverse
effects such as direct damage of the PM circuitry or transient
electromagnetic field effect. Modern PM use complementary metal oxide
semiconductor circuitry which is very reliable, energy and space
efficient. Radiation can cause damage to the thin oxide layers and
transistors because of accumulation
of positive charge inside the circuitry leading to failure of various
battery components or accelerated battery depletion 13.
Type of radiation, cumulative dose and location of the device predicts
the amount of damage. Changes in sensing capability, failure of
telemetry
function, runaway function and complete shut down may all occur 14,15,16(14-16).
Souliman et al.17 tested 18 PM during
radiotherapy. They observed temporary change to safety mode pacing
lasting for the
duration of irradiation; change to interference mode pacing from which
recovery may occur after reprogramming the PM; severe damage in which
case the PM stops generating pulses. Recovery from this takes a long
time.
They recommended that patients undergoing radiotherapy be monitored
closely
during the course of the treatment and a few weeks thereafter. Some
precautions
need to be undertaken before exposing the patient with PM to
radiotherapy,
if it is absolutely necessary. The PM should be checked thoroughly and
patients dependency status should be verified. One must position the
field
of radiation at an angle oblique to the PM in order to minimize the
amount
of radiation delivered at the PM site. A total accumulated dosage limit
of 2 rad should be estimated using either luminescent dosimeters or a
diode dose measurement system and additional shielding of the PM with
a 1cm margin may be required. Direct irradiation of the PM must be
avoided and if this is not possible, the PM should be explanted and
moved to another suitable site13. Careful
monitoring of the
patient and temporary PM availability should be assured.
f) Extracorporeal shock wave lithotripsy
Because most PM are implanted in the pectoral area, there is little
chance of damage to the generator. If the shock wave is directly aimed
at a
PM, it can be damaged. The delivery of the shock wave should be timed
to the ventricular stimulus output in patients who are being paced to
avoid PM inhibition owing to oversensing of the shock wave13. The lithotriptor focal point should be placed
at least 25 cm away from the PM which should be checked before and
after the procedure.
g) Cellular phones
Mobile or cellular phones may interact with PM function by inhibiting
the pacing output, asynchronous pacing and ventricular triggering 18,19. When the antenna is
located near the pulse generator header, interaction may occur very
easily. Hayes DL et al. 20 published a
landmark article
which was a clinical, multicenter study comparing the effects and
interaction of different cellular phones with PM. A total of 980
patients were included into the study. The incidence of all types of
interference was 20%. Ventricular tracking of signals sensed on the
atrial channel, noise reversion and
inhibition of ventricular output were the most commonly observed types
of interference. The incidence of overall clinical significant
interference
was 6.6 %. There was no clinically significant interference when the
phone
was placed in the normal position over the ear. Interference that was
definitely
clinically significant occurred in only 1.7 % of tests and only when
the
phone was held over the pacemaker. Interference was more common in dual
chamber systems (25.3 %) than in single chamber systems (6.8 %) and in
digital telephones (24%) compared to analog telephones (3 %). Patients
who are PM dependent should use an analog type cellular phone system.
Carrying the phone on the same side of the body as the implanted PM may
cause interference. When using the phone, it should be held at least 15
cm away from the PM and on the opposite ear.
Uncommon sources of EMI
Transcutaneous nerve stimulation is a method for pain relief used in
medical facilities. In rare cases it may be sensed by the PM,
especially
in unipolar systems. However, a recent study showed that it can be
safely
used in PM patients21. Hospital pager
systems
may disturb telemetry in the form of inaccurate battery voltage,
current
and impedance measurements, disturbances in intracardiac electrogram
tracings
or total interruption of telemetric communications. The reason for EMI
in this setting was an overlap of carrier frequencies of some PM
programmers
(32-37 kHz) with those of 36.11 kHz pager system22.
Electromagnetic energy generated from a variety of dental instruments,
including ultrasound scalers and cleaners, and electrosurgical
instruments
can also cause transient inhibition of pacemaker output23. Certain cardiac monitoring systems used for
recording
continuous electrograms in hospitalized patients can cause
inappropriate
rate changes in patients with rate adaptive pacing systems that use a
minute
ventilation sensor24. Antitheft devices
are
currently being used almost everywhere. They may cause EMI with
pacemakers.
A study revealed that acoustomagnetic systems are more responsible for
EMI than the other systems25. Reversion to
asynchronous pacing and rapid ventricular pacing owing to tracking of
high
frequency signals sensed in the atrial channel are the two most common
observed
interactions. They are transient and return to normal function once the
patient was out of the field. Patients with any type of implanted
electronic
medical system should be forewarned: Dont lean, dont linger near any
potential
source of EMI 26. Electric arc welding
causes
interference by the electrical fields generated by the welding
electrode and magnetic fields generated by the large current flowing
through the welding electrode or cable. In a recent study, patients
working with arc welding demonstrated no interference of a specific PM
model in certain conditions 27.
In conclusion, during our daily life patients with PM are potentially
vulnerable to the adverse effects of many EMI sources. Physicians
taking
care about PM patients should be aware of these problems and
precautions
need to be undertaken for prevention of possible EMI.
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