Abstract
There is a growing body of evidence from in
vitro and in vivo studies that mobile
phones may cause electromagnetic
interference with implanted cardiac
pacemakers. Pacemaker-dependent patients
without an appreciable underlying rhythm
are at greatest risk from these effects.
There is, however, an overwhelming lack of
knowledge about this subject among
physicians, partly because of the rarity
of publications on this subject in medical
journals. In this article we present a
summary of available literature on such
interactions and try to reach general
recommendations.
Key words: Cellular telephones, cardiac
pacemakers & electrical interferences.
Introduction
Cellular telephones (mobile phones) constitute a
popular and a rapidly spreading form of
technology. There is increasing
concern in the medical societies and in
the public, however, that the
electromagnetic waves generated by
cellular telephones may cause electrical
interference with medical equipment,
especially cardiac pacemakers. This
article presents a review of available
pertinent data on this subject from
published literature and studies.
Cardiac Pacemakers
The earliest cardiac pacemakers did not sense
spontaneous beats, and their asynchronous
stimuli competed with patients' intrinsic
heart rhythms (if any were present).
Later, "demand" or
"inhibitory" pacemakers could
sense spontaneous depolarizations and
synchronize with them. This prevented
competition with the patient's intrinsic
rhythm but created the potential for
inappropriate inhibition of stimuli during
single-chamber pacing when extraneous
electromagnetic interference was mistaken
for spontaneous cardiac
depolarization. With the advent of
dual-chamber pacing, extraneous
electromagnetic interference sensed in the
atrium could trigger inappropriate stimuli
in the ventricle, producing palpitations
or even inducing ventricular tachycardia.
Many forms of electromagnetic energy could
potentially interfere with the function of
implanted cardiac pacemakers. In
hospitals, magnetic resonance imaging
scanners, lithotripsy and electrocautery
devices, and other medical equipment can
result in interference. In other settings,
there are relatively few electromagnetic
sources that would interfere with the
function of pacemakers - examples include
high-amperage welding equipment and
degaussing equipment. The potential
for cellular telephones to interfere with
pacemakers has only been recognized
since1994.
Mobile Phone Technology
Mobile phones generally use one of two forms of
technology, analogue or digital. In
the analogue system, the conversation is
transmitted by continuously varied radio
frequency signals. In the digital
systems, the conversation itself is
encoded as a string of pulses[1].
Most cellular telephones in the United States
today use analogue technology. The
digital system GSM (Global System for
Mobile Communication) is the standard used
all over Europe. The TACS (Total
Access of Communication System) standard
is the analogue transmission in use in the
U.K., Italy and Spain. It is
postulated
that the GSM pulse shaped signal is potentially more
dangerous and can cause more interference
than the TACS (continuous signal).
Studies of
Mobile phones-Pacemaker Interactions
The interactions of mobile cellular telephones
with pacemakers have been the subject of
considerable recent interest[2].
This interest started in 1994[3-5] when
several investigators reported various
forms of interference resulting from
cellular telephones. These reports
initiated several in vitro and in vivo
studies examining this issue;
In vitro studies:-
In 1995, Pacesetter AB published the results of
a study conducted in vitro describing
interference from GSM cellular phones (7.6
W power) on unipolar pacemakers immersed
in a saline solution[6]. The authors
observed no interference from the
telephones and therefore stated that
pacemaker patients could use cellular
telephones without danger. In contrast, a
similar study by Barbaro et al, noticed
some temporary interference with the GSM
phone (power 2 W) in more than 50% of the
tested pacemakers immersed in a saline
solution[7].
In 1996, Naegeli et al. published a study performed to
evaluate the possible interactions between
mobile phones and implanted pacemakers[8].
They used transportable telephones with a
digital transmission system, a maximal
power output of 2 W and a maximal power of
8 W. The authors found reproducible
interference in 18 % of 39 patients. The
interference was: atrial triggering (2.8%)
and ventricular inhibitions (2.8%) in 22
dual-chamber pacemakers, and pacemaker
inhibitions (5.6%) in 17 VVIR devices. The
interferences were related to the high
level of telephone power output and to the
maximal sensitivity of the pacemaker.
Ventricular inhibition was induced only in
the unipolar pacing, when unipolar and
bipolar configurations were compared in
the same patient The authors do not
specify the duration of these
interferences.
In the
same year Inrich et al, [9] published an
in vitro study in which three different
kinds of mobile telephones ( a 450 MHz,
analogue, a 900 MHz, digital pulsed, and a
1800 MHz, digital pulsed signal) were
tested on 231 different pacemaker models
from 20 manufactures. Interference
was observed with 450 MHz (30.7%) and 900
MHz (34.2%) telephones, but not with the
1800 MHz ones. The influence of the
electromagnetic interference was observed
when the telephone antenna was placed
close to the pacemaker pocket. No
telephone interference was observed when
the antenna was more than 20 cm from the
pacemaker.
In vivo studies
The largest study conducted on mobile phone
interferences in patients with implanted
pacemakers so far was by Hayes et al.[10]
published in 1997. A multicenter,
prospective crossover study in which they
tested 980 patients with cardiac
pacemakers with five types of telephones
(one analogue and four digital) to assess
the potential for interference.
Telephones were tested in a test mode and
were programmed to transmit at the maximal
power, simulating the worst-case scenario;
in addition, one telephone was tested
during actual transmission to simulate
actual use. Patients were
electrocardiographically monitored while
the telephones were tested at the
ipsilateral ear and in a series of
maneuvers directly over the
pacemaker. Interference was
classified according to the type and
clinical significance of the effect.
They reported that the incidence of any
type of interference was 20 % in the 5533
tests, and the incidence of symptoms was
7.2 %. The incidence of clinically
significant interference was 6.6 %.
There was no clinically significant
interference when the telephone 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
telephone was held over the pacemaker.
Interference was more frequent with
dual-chamber pacemakers (25.3 %) than with
single-chamber pacemakers (6.8 %, P <
0.001) and more frequent with pacemakers
without feed-through filters (28.9 to 55.8
%) than with those with such filters (0.4
to 0.8 %, P = 0.01). They concluded
that cellular telephones could interfere
with the function of implanted cardiac
pacemakers. However, when telephones
were placed over the ear, the normal
position, this interference did not pose a
health risk.
Another
study published in 1997 by Altamura et
al,[11] comprised of continuous ECG
monitoring of 200 pacemaker
patients. During monitoring the GSM
system telephones interfered with pacing
97 times in 43 patients (21.5%) while TACS
telephones interfered 60 times in 35
patients (17.5%). There were 131
interference episodes during ringing
versus 26 during the on/off phase;
(P<0.0001); 106 at maximum sensitivity
versus 51 at the ÔbaseÕ value;
(P<0.0001). Prolonged pacing
inhibition (>4 seconds) was seen at the
pacemaker 'base' sensing value in 6
patients using the Global system but in
only one patient using Total access. With
both GSM and TACS telephones the most
frequent and longest interference occurred
when the telephone antenna was placed on
or close to the pacemaker. When the
telephone was placed at the belt position
or near the ear not less than 20 cm away
from the pacemaker, only one short episode
of synchronization to the upper rate
(lasting <1 second) was noticed in a
total of 400 tests done with the pacemaker
programmed at the base sensing value.
Conclusions and recommendations
The likelihood of clinically important mobile phone interference with
pacemaker function depends on four major
factors:
a)
The
characteristics of the telephone (mainly
the power of the transmitted signals),
b)
The
pacing system (including pacing mode,
electrode configuration, site and
orientation of the pulse generator, and
filtering),
c)
The
orientation of the telephone relative to
the pacemaker electrodes or the pulse
generator, and
d)
The
patient's underlying heart rhythm.
Therefore to avoid interference the following guidelines are recommended:-
1.
Patients with pacemakers should not carry
the mobile phone close to the pacemaker.
This is especially important to discourage
the male patient who may carry a telephone
in the pocket of a jacket or shirt in
close proximity to the pacemaker box.
2.
The
phone should be more than 20 cm from the
pacemaker, so the ear contralateral to the
pacemaker should be used.
3.
Avoid
programming pacemaker sensing at or near
the maximum sensitivity value.
4.
The high upper rate limit should not be
selected for VDD-DDD patients wishing to
use mobile phones.
5.
Pacemaker-dependent
patients without an appreciable underlying
rhythm are at greatest risk from the
effects of interference and therefore
should be discouraged from using mobile
telephones altogether.
References
