Download MRI study - Vanderbilt

Effects of magnetic resonance imaging on cardiac
pacemakers and electrodes
Stephan Achenbach, MD, Werner Moshage, MD, Bj6rn Diem, MD, Tobias Bieberle, a Volker Schibgilla, MD, and
Kurt Bac]hmann, MD Erlangen, Germany
In phantom studies we investigated the effects of magnetic resonance imaging (MRI) on pacemakers and electrodes.
Twenty-five electrodes were exposed to MRI in a 1.5T scanner with continuous registration of the temperature at the
electrode tip. Eleven pacemakers (five single chamber and six dual chamber) were exposed to MRI. Pacemaker output was
monitored to detect malfunction in V O O / D O 0 and VVI/DDD modes. A temperature increase at the electrode tip of up to
63.1 ° C was observed during 90 seconds of scanning. In seven electrodes the temperature increase exceeded 15 ° C.
Although no pacemaker malfunctions were observed in asynchronous pacing mode (VOO/DO0), inhibition and rapid
pacing were observed during spin-echo imaging if the pacemakers were set to VVI or DDD mode. Pacemaker function was
not impaired during scanning with gradient-echo sequences. Next to pacemaker dysfunction, electrode heating has to be
considered a possible adverse effect when exposing patients with pacemakers to MRI. (Am Heart J 1997;134:467-73.)
Implanted cardiac pacemakers are commonly regarded
to constitute a contraindication to magnetic resonance
imaging (MRI). 1-5 All the same, there has b e e n a number of recent publications reporting successful MRI in
patients w h o carried pacemakers. 6-~2 In spite of reports
of a patient w h o died during MRI and rapid cardiac
pacing observed in another patient, 8 some authors
conclude that MRI can be peffomed safely in patients
with implanted permanent cardiac pacemakers. 8,11-13
The effects of MRI on cardiac pacemakers are
complex and difficult to investigate systematically.
Several theoretic and p h a n t o m studies have looked at
t h e behavior of pacemakers w h e n e x p o s e d to the
strong magnetic and rapidly changing electromagnetic
fields of MRI scanners. 13-18 Again, some of the authors
concluded that MRI raay be performed safely in patients
with pacemakers. However, the results were
heterogeneous, partly because of the high number of
possible combinations of pacemaker models, MRI
scanners with various field strengths, and different
imaging sequences that can be applied. The effects of
MRI on implantable pacemaker electrodes has never
b e e n studied systematically. Therefore w e attempted to
investigate several commonly used pacemaker models
From Medizinische Klinik II mit Poliklinik and the °lnstitut f~JrBiomedizinische Technik,
University of Erlangen-NiJrnberg.
Received for publication Oct. 4, 1996; acceptedApril 24, 199Z
Reprint requests: Stephan Achenbach, MD, Medizinische Klinik II mit Poliklinik,
Universit~t Erlangen-NOrnberg, C)stliche Stadtmauerstr. 29, D-91054 Erlangen,
Germany.
Copyright © 1997 by Mosby Year-Book, Inc.
0002-8703/97/$5.00 + 0 4/1/82873
in various pacing modes, as well as different electrode
types, as to their behavior w h e n e x p o s e d to imaging
sequences used for routine investigations in a 1.5T
MRI unit.
During MRI scanning, rapidly changing magnetic and
electromagnetic fields, next to a strong static magnetic
field, are generated. Their interaction with metallic
implants such as cardiac pacemakers could lead to
several adverse effects: The static magnetic field could
cause dislocation of the pacemaker and electrodes,
should they contain ferromagnetic material. Because of
the electromagnetic fields, pacemaker electronics could
be destroyed or the programmed settings could be
altered and, through induction of currents in the
electrodes, sensing and triggering with consequent
inhibition or rapid pacing, as well as heating of metallic
components, could occur. By exposing 11 pacemakers
and 25 electrodes in different settings to commonly
used MRI sequences, w e studied these possible
adverse effects.
Methods
Magnetic resonance imaging
The phantom studies were performed in a con~mercial
Magnetom 1.5T (Siemens) magnetic resonance system
installed at our hospital. To test pacemaker electrodes,
untriggered Tl-weighted spin-echo sequences with an echo
time (TE) of 20 msec and repetition time (TR) of 0.3 seconds,
slice thickness of 8 mm, gap of 2 mm, a field of view of 400
mm, and a matrix 128 x 256 were chosen. Continuous
scanning was performed for 90 seconds.
To test pacemaker performance during MRI scanning, three
468
Achenbach et al.
M a x i m u m temperature increase
(dT, o C after 90 sec)
Electrode
CPI 4185
CP14161
Biotronic TIR 60-UP
Biotronic TIJ 53-UP
Medtronic Capsure SP 4023
Medtronic Target Tip 4581
Medtronic Target Tip 4081
Biotronic SD 60-UP (V126)
Biotronic EL 004128
Baxter 97-130-5F
Biotronic Multicath 3
Biotronic TIJ 53-BP
Biotronic TIR 60-BP
Biotronic SD 60-BP
Biotranic 385139
CPI 4268
CP14270
Medtranic Capsure SP 4524
Medtronic Capsure SO 4024
Medtronic Target Tip 4582
Medtronic AJ 049896V
Siemens-Pacesetter 1450T
Pacesetter 1188T
Teletronics 033-301
Teletronics 033-856
Bipolar/
unipolar
unl
unl
unl
unl
unl
unl
unl
unl
unl
bi (trap)
bi (tmp)
bi
bi
bi
bi
bi
bi
bi
bi
bi
bi
bi
bi
bi
bi
Length (cm)
Air, no PM
Air, connected
to PM
NaCI solution
connected to PM
59
59
59
51.5
58
53
65
59.5
60
16.9
20.4
16.6
0.9
9.3
-0.3
26.9
32.5
0
2.8
2.9
3.0
2.2
5.7
3.1
3.1
3.7
0
0.9
0.8
0.9
1.0
3.0
0.6
0.6
3.7
1.1
*
NA
NA
38.2
0.5
4.8
0.4
0.6
0.1
1.3
0.3
0.8
2.1
1.3
1.7
0,2
3.1
0,3
NA
0.1
0.0
-0.4
1.1
-0.1
2.3
0.8
2.0
0.4
3.3
1.2
-0.1
1.7
0.2
NA
0.5
0.7
0.3
4.9
0.4
4.4
8.9
1.2
3.8
2.4
1.1
0.1
0.9
1.4
116
114
51.5
58.5
59
59.5
52.5
52.5
53
58
53
58
58
52.5
58
48
Thetemperatureincreaseduring90 secondsof continuousscanningis givenfor threedifferentsellings:electrodeinsertedto the porcineheart,electrodeconnectedto a pacemaker
and insertedto the heart,and dectrodeand pacemakersubmersedin NaCI solution.
PM, Pacemaker;uni, unipdar;bi, bipolar;trap, temporarypacemakerelectrode;NA, not applicablebecausetemporarypacemakercould not be exposedto MRI.
*Scanninginterrupledbecausetemperatureexceeded88.8° C (maximumrangeof thermometer).
different scanning sequences were chosen as used in routine
applications and modified only to limit the overall scan time
to 90 seconds: (1) untriggered Tl-weighted spin-echo
sequence (TR 0.3 seconds, TE 20 msec, 8 m m slice thickness,
2 m m gap, FOV 400 mm, and matrix 128 x 256); (2)
electrocardiographic-triggered Tlweighted spin-echo
sequence (TR 0.7 seconds, TE 20 msec, 8 m m slice thickness,
gap 2 mm, FOV 400 mm, and matrix 128 x 256); and (3)
electrocardiographic-triggered gradient-echo sequence (TR
0.7 seconds, TE 10 msec, flip angle 40 degrees, 8 m m slice
thickness, 2 m m gap, FOV 400 ram, and matrix 128 x 256).
Electrode testing
To test the heating of pacemaker electrodes during MRI, 25
different electrodes were exposed to MRI with continuous
registration of the temperature at the electrode tip. Two
temporary electrodes and 23 implantable electrodes (nine
unipolar and 14 bipolar) were investigated (Table I). To
achieve conditions similar to those of the in vivo situation,
the electrodes were connected to an isolated porcine heart
by inserting them into a deep cut in the left ventricular
myocardium of the heart. The impedances of the electrodes
were measured and were around 1000 m in all cases. An
optical temperature sensor was connected to the electrode
tip. Through an optical conductor (length 10 m), it was
connected to the registration electronics outside the magnetic
resonance scanning room (Luxtron 1000B Biomedical
Fluoroptic Thermometer; Polytec).
In a series of tests it was determined that maximum
electrode heating occurred if the electrodes were arranged in
a circular manner and laid fiat on the scanning table
(electromagnetic field gradient perpendicular to electrode
loop). Consequently, all electrodes were tested by exposing
them to MRI scanning in the configuration of a circle with a
diameter of 16 cm, which was oriented parallel to the plane
of the MRI bed. Every electrode was tested without being
connected to a pacemaker and while connected to a
pacemaker (Paragon, SSI mode; Siemens-Elema), both in air
and submersed in 0.9% NaC1 solution. Scanning sequences as
described above were performed for 90 seconds with
American HeartJournal
September 1997
Achenbach et ak
100
Pacemaker
Single/dual
chamber
°C
Modes tested
80
Telectronics Meta 1206
Telectronics Simplex
Biotronik Pikos
CPI Vigor 460
CPI Vigor 1130
TelectronicsMeta 1254
Biotronik Ergos 03
Biotronik Physios01
CPI Delta T
Pacesetter Paragon II
Pacesetter Synchrony I!1
Single
Single
Single
Single
Single
Dual
Dual
Dual
Dual
Dual
Dual
VOO*
VOO*
VOO, VVI
VOO, VVI
VOO, VVI
DOO*
VOOI VVI, DOO, DDD
VOO, WI, DOO, DDD
VO©, VII, DOO, DDD
VOO, VII, DOO, DDD
VOO, VII, DOO, DDD
* Magneteffectcouldnotbe suppressedby programming.
continuous monitoring of the temperature at the electrode
tip. They 'were interrupted if the temperature exceeded 88.8 °
C, the maximum range of the temperature measurement
device used. After scanning, the porcine heart was examined
for visible lesions.
Pacemaker testing
Five single-chamber and six dual-chamber pacemakers
were included in the investigation (Table II). If possible, the
pacemakers were programmed to suppress the magnet
function (mode switch to VOO pacing at a fixed rate when
exposed to a static magnetic field). All pacemakers were
programmed in VOO and VVI modes (single-chamber
pacemakers) or VOO, VVI, DOO, and DDD modes (dualchamber pacemakers), respectively. Pacing rates were
programmed to be betweeen 60 and 75 beats/min.
The pacemakers were connected to an isolated porcine
heart through commonly used atrial or ventricular electrodes
(Medtromc Target Tip 4582 [Medtronic Inc., Minneapolis,
Minn.] or Biotronik SD 60-BP), as described previously. The
impedances were measured to be between 1000 and 1200 m.
Bipolar sensing and pacing configurations were programmed
for the atrial and ventricular electrodes. The atrial sensing
threshold was programmed to 1.5 mV and the ventricular
sensing threshold to 3.0 inV. The atrial and ventricular pacing
amplitudes were set at 4 to 5 V. The upper frequency rate in
DDD pacing was set to 150 beats/min.
With the MRI system's electrocardiographic monitoring
equipment, electric recordings from the surface of the
isolated heart were registered continuously to monitor
pacemaker output. Because the pacemakers had a stimulus
duration of only 0.5 to 1.5 msec, their stimuli would have
been undetectable in. these electrocardiographic registrations
during MRI scanning, because low-pass filters are used to
suppress high-frequency artifacts from the electrocardiographic tracings. Therefore a combination of a diode and a
AmericankieartJournaJ
Volume 134,Number3
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2O
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20
30
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40
50
60
70
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go
Recordings of temperature at electrode tip during 90 seconds
of MRI for seven electrodes in which temperature increase of
more than 15 ° C was observed. (All measurements were in air
without pacemaker connected. )
capacitor (capacity 1 I-tF) was connected to the pacemakers,
parallel to the electrode. Thus a wider pacemaker signal of
3 to 4 msec was obtained. This guaranteed reliable
registration of pacemaker signals and electrocardiographic
triggering of the MR1 scanner to the pacemaker output.
The electrocardiographic traces recorded during MRI
scanning in the different pacing modes were evaluated to
detect sensing and pacing defects and changes in pacing
rate. After scanning, the pacemakers' settings were compared
with those programmed before the MRI scan and all
pacemaker functions were checked thoroughly to detect
possible changes in pacemaker settings or damage to the
electronics.
Results
As r e p o r t e d in prior publications, 17,18 forces acting o n
the p a c e m a k e r s and electrodes c o u l d be felt o n
e x p o s i n g t h e m to the MRI system's static magnetic field.
In t w o p a c e m a k e r s (Me m 1206 and Meta 1254,
Telectronics Pacing Systems), the ferromagnetic forces
w e r e strong e n o u g h to cause the p a c e m a k e r to m o v e
w h e n placed o n the MRI bed. In all other p a c e m a k e r s
and in all electrodes, h o w e v e r , the forces w e r e too
w e a k to result in dislocation of the e q u i p m e n t .
Electrodes
The primary aim of the investigation was to detect
heating of the electrodes during MRI b y m e a n s of an
optical temperature p r o b e c o n n e c t e d to the electrode
tip. Reproducibly, an increase in the temperature
m e a s u r e d at the electrode tip that e x c e e d e d 15 ° C was
r e c o r d e d in s e v e n of the 25 electrodes tested (Fig. 1).
469
470
Achenbach et al,
Electrode type
Temporary
Unipolar
Bipolar
Setup
No PM, air
No PM, air
PM, air
PM, NaCI
No PM, air
PM, air
PM, NaCI
Mean dT (o C)
Maximum dT (o C)
50.7-+ 1Z6
13.7+ 12.0
2.9_+2.0
1.5 _+ 1.1
1.3 _+ 1.3
0.9 _+ 1.2
2.2_+2.5
63.1
32.5
5.7
3.7
4.8
3.3
8.9
PM, Pacemaker.
The maximum temperature that could be documented
was 88.8 ° C, the upper limit of the themlometer's
measurement range. This corresponded to a
temperature increase of 63.1 ° C, from a starting
temperature of 25.7 ° C. The two electrodes with the
highest increase in temperature were temporary pacing
electrodes (Table I). Severe burns occurred at the
insertion site of the electrodes; in one case confirmation
was obtained in a histologic specimen. Only in four
electrodes was the temperature increased less than 1.0 °
C for all of the three configurations tested, whereas the
remainig 14 electrodes showed a temperature increase
between 1.0 ° and 15 ° C (Table I).
The average temperature increase of the electrodes at
the electrode tip tended to be less pronounced when
the electrodes were connected to a pacemaker and
further attenuated when both the pacemaker and
electrode were submersed in a tank filled with saline
solution (Tables I and III). In general, heating of
unipolar electrodes was stronger than that of bipolar
electrodes.
Pacemakers
In all 11 pacemakers studied, MRI, with the scanning
sequences described, showed no effect on the
programmed pacemaker settings. Neither the setting nor
pacemaker programmability was changed when
checked after MRI.
In all pacemakers the reed switch was operated by
the static magnetic field. This resulted in asynchronous
pacing at the preprogrammed rate when the pacemaker
was attached to the MRI unit. None of the pacemakers
displayed a pacing dysfunction when programmed to
VOO or DOO mode (asynchronous mode) and
exposed to MRI, regardless of the scanning sequence
used.
In three pacemakers the magnet effect could not be
switched off by programming before MR[ (Meta 1206,
Meta 1254, and Simplex, Telectronics). For this reason,
these three pacemakers could not be studied in modes
other than VOO or DOO. In the remaining three singlechamber pacemakers and five dual-chamber
pacemakers, severe effects on the pacing function were
observed after programming the pacemakers to DDD or
VVI mode. The effects were observed in all of the
pacemaker models, but they varied according to the
pacemaker settings and applied MRI sequences.
Untriggered spin-echo sequences. In all singlechamber and dual-chamber pacemakers programmed to
VVI mode, inhibition was observed on exposing the
pacemakers to MRI with the magnet function
inactivated. In one case the pacemaker was inhibited
during the complete duration of the MRI acquisition. In
the other models the duration of inhibition ranged from
1.4 to 9 seconds.
Complex effects were observed when dual-chamber
pacemakers set to DDD pacing were exposed to MRI
scanning: Complete inhibition of the atrial and ventricular lead and isolated sensing/inhibition of one lead
was observed (Fig. 2). Atrial triggering with consequent
rapid ventricular pacing at the upper frequency limit
(150 beats/rain) was also documented (Fig. 3).
Electrocardiographically triggered spin-echo
sequences. The same effects as in untriggered imaging
sequences were observed during electrocardiographically triggered spin-echo sequences. However,
because these scanning sequences are interrupted after
700 msec (the preset TR value) to wait for the next
electrocardiographic trigger, total inhibition was not
observed. The effect resulted in a decreased pacing
frequency of as low as 27 beats/min (Fig. 4). Again,
atrial triggering was observed in DDD pacemakers,
resulting in ventricular pacing at the upper programmed
frequency limit.
American Heart Journal
September 1997
Achenbach et al.
Dual-chamber pacemaker, DDD pacing mode. After onset of
spin-echo sequence (arrow), complete inhibition occurs.After
2.4 seconds,single ventricular spike follows, caused by atrial
sensing/triggering.
Rapid ventricular pacing at upper frequency limit of 150/min
after onset of MRI (arrow, untriggered spin-echosequence),
with pacemaker in DDD mode. After scanning is interrupted
(arrowhead), normal atrial and ventricular pacing continuesat
75/min.
Eleetrocardiographically triggered gradient-echo
sequences. Pacemaker functions remained completely
uninfluenced by MRI when electrocardiographically
triggered gradient-echo sequences were used.
Discussion
During diagnostic MRI, several forms of scanning
sequences (spin-echo sequences or gradient-echo
sequences) are applied. All are based on the
electromagnetic deflection of hydrogen atoms that were
aligned in a strong static magnetic field and subsequent
measurement of the energy emitted. They differ only in
the magrfitude, spatial orientation, and temporal
coordination of the applied fields. The static magnetic
field, the rapidly changing magnetic field (gradient field,
100 to 200 Hz), and the electromagnetic radiofrequency
field (63 MHz) interact with implanted pacemakers and
electrodes. For this reason, patients with pacemakers
have by general policy been excluded from MR[.1-4 All
the same, several authors have reported MRI
investigations of patients with implanted pacemakers. In
a thorough search of the literature, we found reports of
a total of 36 patients. Side effects, including one death,
were reported in four of these patients (Table IV).
Because the interactions between MRI scanning and
pacemakers are complex and not yet fully understood,
and the effects of MRI on electrodes have not been
investigated, we investigated the effects of the static
magnetic field and the electromagnetic fields on both
pacemakers and electrodes in phantom studies.
Static magnetic field
The static magnetic field can exert forces of up to 5N
(about tenfold the pacemaker's weigh0 on pacemakers
containing ferromagnetic materials. 18 Only two of the
pacemakers in our study were moved when positioned
freely on the MRI examination bed. The danger of
American Heartjournal
Volume 134, Number 3
Slow ventricular pacing (37/min) during MRI with
electrocardiographically triggered spin-echosequences.
Normal rate (60/min) resumesafter termination of scanning
(arrow).
dislocation can be ruled out for the other models when
implanted in a patient. Also, the static magnetic field
usually operates the pacemaker's reed switch, causing
asynchronous pacing, which, according to our results,
seems to be the safest pacing mode during MRI.
However, it is theoretically possible that the reed switch
is not activated if the MRI static magnetic field is
oriented perpendicular to the reed-switch axis. 18 In this
case, the effects of inhibition or triggering that we could
observe during pacing in VVI and DDD pacing modes
may constitute a danger to the patient. Also, the
operation of the reed switch itself and consequent
asynchronous pacing have been reported to be the
cause of ventricular fibrillation in a patient. 19 For this
reason, no patient with a pacemaker should approach
an MRI Unit without availability of a defibrillator.
Gradient magnetic field and radiofrequency field
The effect of these rapidly changing electromagnetic
fields on electrodes has been investigated systematically
for the first time in our study. In our phantom
experiments, exposing isolated pacemaker leads to MRI
caused significant heating of the electrodes. The heating
is caused by the induction of currents in the electrodes,
471
472
Achenbach et al.
Author
Gimbel et al. 8
Johnson 11
Achenbach et al. 6
Alagena et al. 7
Iberer et al. 9
Inbar et al. 1°
Lauck et al. 12
No. of patients studied
MR scanner field strength (T)
20
4
1
1
1
1
8
which act as antennas for the electromagnetic fields. We
recorded maximum temperatures of almost 90° C, and
myocardial necrosis could be demonstrated in histologic
studies, but there were large differences between the
different electrodes: only seven electrodes showed an
increase in temperature of more than 15° C during 90
seconds of imaging. The effects were attenuated when
a pacemaker was connected to the electrodes and the
electrodes were submersed in saline solution. The in
vivo effect might be even less pronounced because the
electrodes are not arranged in a full loop, and the
moving blood can be expected to reduce heating of the
electrodes further by means of convection.
Nevertheless, we believe that electrode heating
constitutes an eminent danger for patients subjected to
MRI: Because imaging usually extends for a longer time
than our 90-second sequences (usually 4 to 10 minutes
of uninterrupted scanning) and the electrode
temperatures were rising continuously to the
interruption of scanning (Fig. 1), the in vivo heating
effects might be more pronounced than in our study. In
addition, electrode heating is not detectable by
monitoring and the effects such as an increase in pacing
threshold, right ventricular or atrial perforation, or even
reentry arrhythmias caused by tissue scars can occur
long after imaging. Because heating varies considerably
between different electrodes, it is mandatory that every
electrode be tested in phantom studies before exposing
any patient with an implanted electrode of that type to
MRI. It must also be kept in mind that many patients
carry isolated pacemaker leads left in place after
pacemaker removal. In animal studies conducted to test
the behavior of transesophageal pacing leads during
MR[, heating with consequential necrosis has also been
observed. 20
The postulated effects of the gradient field and
radiofrequency fields on the pacemakers themselves
0.5-1.5
Not given
0.5
1.5
1.5
1.5
0.5
Adverse effects
Discomfort at PM pocket (1 patient), rapid
heart rate (1 patient), death in
unmonitored patient (1 patient)
Transient inhibition (1 patient)
include interference with pacemaker electronics ,
inhibition, and rapid pacing. 2-4 In all 11 pacemakers
tested in our series, pacemaker electronics seemed to
be unharmed by MRI: all pacemakers had unchanged
programmability when checked after MR[, and the
settings were not altered during the scanning
procedure.
Inhibition, caused by the induction of currents above
sensing threshold in the pacemaker leads, was observed
in all pacemakers set to VVI or DDD mode if spin-echo
sequences were used. The same has been reported in
previous studies of other pacemaker models. 14,15,17
Gradient-echo sequences, which require less highfrequency energy, showed no effect in our
investigation. To avoid inhibition, setting the pacemaker
to VOO, DOO, or, preferably, OOO mode seems
necessary when attempting MR[.
Rapid pacing can be the result of two mechanisms: In
our study we observed rapid pacing at the upper
frequency limit for short periods in all DDD pacemakers investigated. In our opinion, this effect is caused
by induction of currents above sensing threshold in the
atrial lead and consequent triggering of ventricular
stimulation. Direct interference with the pacemaker
electronics seems unlikely because the rapid pacing rate
was always equal to the programmed frequency limit.
However, in animal studies that Were conducted with
different implantable pacemakers, pacing of up to 300
beats/min has been observed synchronized to the
radiofrequency pulses and was attributed to
interference with pacemaker electronics. 1416
,
In summary, both our results and those published by
other authors indicate that only under very special
circumstances can MR[ be performed safely in patients
with implanted cardiac pacemakers. Inhibition, rapid
pacing, and induction of arrhythmias have been
reported previously as possible adverse effects. They
American Heart Journal
September 1997
Achenbach et al.
can be detected by adequate patient monitoring during
MRI and can most probably be prevented by suitable
scanning strategies. Heating of the electrodes, however,
is a potentially harmful effect that has never before
been investigated systematically and is especially
dangerous because it cannot be detected by patient
monitoring.
In our studies only one magnetic resonance scanner
was used, the field strength of which is typical for those
used in diagnostic imaging (1.5T). It can be expected
that adverse effects are less pronounced in scanners
with a lower magnetic field strength, 16 but differences
would be only quantitative, not qualitative.
We agree with several previous publications that MRI
should never be conducted in a patient with a
pacemaker without the highest urgency, the pacemaker
and electrodes identical to those implanted in the
patient have to be tested in phantom studies, and
results and observations with one pacemaker must
never be extrapolated to other, even very similar,
products.. It is our concern that reports of successful
MRI in a limited group of patients with pacemakers may
dilute the general policy of never exposing a patient
with a pacemaker to MRI. Carelessness or reduced
awareness of the potential dangers could cost a
patient's life.
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