Prashant Nair MD,
DM , Ariel Roguin MD, PhD
Department of Cardiology, Rambam
Medical Center, B. Rappaport - Faculty of Medicine, Technion - Israel
Institute of Technology, Haifa, Israel.
Address for
correspondence: Ariel Roguin MD PhD, Department of Cardiology,
Rambam Medical Center, B. Rappaport - Faculty of Medicine, Technion -
Israel Institute of Technology, Haifa 31096 Israel.E-mail:
aroguin@technion.ac.il
Abstract
Magnetic
resonance (MR) imaging has unparalleled soft-tissue imaging
capabilities. The presence of devices such as pacemakers and
implantable cardioverter/defibrillators (ICDs), however, is
historically considered a contraindication to MR imaging. These devices
are now smaller, with less magnetic material and improved
electromagnetic interference protection. This review summarizes the
potential hazards of the device-MR environment interaction, and
presents updated information regarding in-vivo and in-vitro
experiments. Recent reports on patients with implantable pacemakers and
ICDs who underwent MR scan shows that under certain conditions patients
with these implanted systems may benefit from this imaging modality.
The data presented suggests that certain modern pacemaker and ICD
systems may indeed be MR safe. This may have major clinical
implications on current imaging practice.
Keywords: Imaging, MRI, safety, pacemaker, ICD
Introduction
Magnetic
Resonance (MR) imaging is a diagnostic technique used to obtain high
quality images of the human body. The structure and abundance of water
in the different tissues of the human body is the key to clinical MR
imaging. The basic concept of MR is the absorption or emission of
electromagnetic energy by atomic nuclei in a static magnetic field
after excitation by a radiofrequency (RF) pulse.
1
A powerful magnet generates a magnetic field roughly 10,000 times
stronger than the natural background magnetism from the earth. Various
types of clinical MR systems currently use the superconductive magnet
which utilizes 0.5 Tesla to 3.0 Tesla.
Unlike
conventional radiography and computed tomographic imaging, which make
use of potentially harmful radiation (X-rays), MR imaging has many
advantages, including its nonionizing nature and the unparallel ability
to discriminate different soft tissues without contrast media. MR
imaging has now become the image modality of choice for imaging the
brain, spine, musculoskeletal system, head and neck, complex pediatric
heart malformations and other tissue structures.
2
More recently, MR imaging has been applied successfully to assess
myocardial structure, wall motion, perfusion and viability. The number
of MR scans performed annually has increased dramatically over the past
few years.
3-6
The Growing Problem
Parallel to
the growth and evolution of the MR field, is the burgeoning number of
patients benefiting from implantable cardiac systems including
pacemakers and implantable cardioverter-defibrillatos (ICDs) (
Figure1). With new indications for
heart failure, innovative device features and expanded medical
coverage; this trend is likely to continue its trajectory. The
combination of these two growing phenomena results in an estimated
50-75% probability of a patient being indicated for an MR study over
the lifetime of their device creating an estimated 200,000 device
patients who were denied the MR scan and more in the future
7,8.
Figure
1: Number of annual MR scans and of newly implanted ICDs in the
USA.
Given the
rapid expansion of technology in the fields of both MR imaging and
device arrhythmia management, there is increasing interest in the issue
of implantable device safety in the MR environment. Currently no
implantable cardiac device has Food and Drug Agency (FDA) approval for
use in the MR environment and “Do not use magnetic resonance imaging on
patients who have an implanted device” appears on product labels
8. The current state of affairs
significantly limits the performance of MR imaging on device patients.
With a better understanding of the hazards of performing MR scans on
device patients as well as the development of MR safe devices, we may
soon enter an era where the ability of this imaging modality may be
more widely used to assist in the appropriate diagnosis of patients
with devices. Not only for heart imaging but mainly for brain, spine,
and joints as knees and shoulder
1,7.
Hazards and Safety concerns
Permanent
cardiac pacemakers have represented a contraindication to MR imaging.
Strong static, gradient and radiofrequency fields used for MR image
creation are thought to be detrimental to pacemaker function and cause
harm to patients undergoing MR examinations. The multiple potential
adverse interactions between pacemakers and MR imaging
1,2,9-12
(
Table 1) include heating,
rapid atrial pacing, pacing at multiples of the RF pulse and associated
rapid ventricular pacing, reed switch malfunction, asynchronous pacing,
inhibition of pacing output, alteration of programming with potential
damage to the pacemaker circuitry or movement of the device and the
potential thermal injury at the lead tip.
Table
1: Potential effects of MR imaging on pacemaker and ICD
systems
1. Static Magnetic Field
Mechanical forces on ferromagnetic
components
Unpredictable magnetic sensor activation, Reed-switch closure
Changes in electrocardiograms
2. Modulated Radio Frequency (RF)
Field
Heating of cardiac tissue adjacent
to lead electrodes
Possible induction of life-threatening arrhythmias
Pacemaker reprogramming or reset
RF interactions with the device (over- and under-sensing)
3. Gradient Magnetic Field
Possible induction of
life-threatening arrhythmias
Induced voltages on leads cause over- and under-sensing
4. Combined Field Effects
Alteration of device function due
to EMI
Mechanical forces (vibration)
Electronic reset of device
Supporting the
current practice comes from several reported lethal consequences of MR
imaging in patients with implanted pacemakers
13-15. During the late 1980s incidentally
10 deaths have been attributed to MR procedures in patients with
pacemakers. However these fatalities were poorly characterized and no
electrocardiographic data were available. Most importantly no deaths
have been reported during physician supervised MR procedures in the
last decade.
Despite the
above-mentioned concerns, the effects of MR on cardiac pacemakers
remain controversial. Most of the previous studies that prohibit MR in
pacemaker patients were based on in vitro and animal model data in the
1980’s using older pacemaker and lead technology. During the last
decade, anecdotal reports describe a small series
16-21 of pacemaker
patients who have safely undergone magnetic resonance scanning (
Table 2). Advance in device
technology drove extensive and seminal in-vitro and animal studies of
the pacemaker and ICD systems interaction with the MR, and in recent
years, several groups scanned safely larger number of patients.
Table
2: Published reports describing the non-lethal consequences of
magnetic resonance imaging n pacemaker patients (n=number of patients
studied; n.a.=data not available; PM=pacemaker;T=Tesla)
In-Vitro and Animal Studies:
The potential
hazardous effects of MR imaging in patients with cardiac pacemakers
have been studied since 1983. Pavlicek and colleagues were the first to
report the effects of MR imaging on pacemaker function
11. They showed that RF fields present in
an MR unit could possibly inhibit demand pacemakers and time-varying
magnetic fields could generate pulse amplitudes to mimic cardiac
activity. The threshold for initiating the asynchronous mode of a
pacemaker was reported to be as low as 17 Gauss (1 Gauss = 10
−4
Tesla). The possibility of altering pacemaker parameters was presented
as a serious limitation of MR imaging. Fetter et al.
12 showed that pacemakers reverted from
the demand to the asynchronous mode within the magnetic field of the
scanner (0.15 Tesla), but microscopic testing showed no evidence of
reed switch sticking or magnetizing, or damage to other discrete
pacemaker components. Other investigators studied the feasibility of
dual-chamber pacing systems in the MR environment. Erlebacher et al.
tested different DDD pacemakers in a saline phantom, and showed that
during scanning at 0.5 Tesla, all units malfunctioned due to RF
interference which caused total inhibition of atrial and ventricular
output, or resulted in atrial pacing at very high rates.
9 The potential for rapid cardiac
stimulation during MR was also reported in animal studies
22. Lauck et al. investigated the
performance of different stimulation modes (VVI, VVIR, VOO, DDD, DDDR
and DOO) during MR scan at 0.5 Tesla
23.
Reversible activation of the reed switch with consecutive asynchronous
stimulation was observed in all pacemakers. Pacemakers in the
asynchronous mode were not affected with regard to stimulation rate and
capture during scanning. In contrast, pacemakers with automatic mode
switching to demand pacing or programmed inactivation of the reed
switch were triggered in the dual chamber mode and were inhibited in
the single chamber mode. Thus, the investigators recommended
programming into the asynchronous mode prior to scanning, and in those
without permanent pacemaker dependency, complete inactivation of the
system, if possible.
The effects of
more powerful MR scanners (i.e., 1.5 Tesla) on cardiac pacemakers were
initially reported by Hayes et al
24.
In-vivo evaluation of different single and dual chamber pacemakers
showed reversion into asynchronous mode and transient reed switch
inhibition. Seven of the eight pulse generators paced rapidly when
exposed to the RF signal associated with a marked decrease in blood
pressure. Stimulation cycle length was 200 ms (300 beats/min)
corresponding to the frequency of pulsing. It was proposed that rapid
pacing was the result of an "antenna" effect that couples the RF energy
back into the pacemaker output circuits.
More recently,
Achenbach et al.
25 showed
in a phantom study on 11 pacemakers and 25 leads that no pacemaker
malfunction was observed in asynchronous pacing mode (VOO/DOO), whereas
inhibition and rapid pacing were observed during spin-echo imaging if
the pacemakers were set to VVI or DDD mode. The authors suggested that
rapid pacing was caused by induction of currents above sensing
threshold in the atrial lead and consequent triggering of ventricular
stimulation. Direct interference with the pacemaker electronics seemed
to be an unlikely explanation, because the rapid pacing rate was always
equal to the programmed frequency limit.
Importantly,
most of the above were reports of earlier generation pacemakers. Recent
reports testing improved technology devices found no functional issues
in most pacemakers exposed to prolonged MR scan
26,27.
Measuring lead
heat in the MR environment is technically difficult and depends on the
methods used; explaining why several group report different results.
Heating effect of pacemaker leads was investigated by Achenbach et al.
25 Continuous registration of the
temperature at the lead tip using an optical temperature sensor showed
a maximal temperature increase of 63.1ºC during 90 seconds of
scanning. In seven electrodes, the temperature increase exceeded
15ºC. Luechinger et al
28
used pacemaker leads with additional thermocouple wires as temperature
sensors implanted in nine animals to measure heating. They recorded
temperature increases of up to 20ºC were during MR imaging of the
heart. However, they found only minor stimulation threshold changes and
no pathology and histology heat-induced damage.
Roguin et al
26 found in-vitro, maximal heating of
7ºC. In vivo, when the leads were inserted into the right
ventricle, there was almost no rise in temperature. This was probably
due to the blood flow and heat dissipation. More importantly, in a
chronic animal model; of 15 dogs who had ICD leads implanted and all
scanned during prolonged (3-4 hours) MR scans, including high energy
protocols - revealed no heat induced injury. No heat and injury was
recently also reported by a Swiss group
27.
With regard to
force and torque, several studies found that in pacemakers the force in
negligible around 10 grams while with ICD it depends on the year it was
manufactured and the amount of ferromagnetic material. Older devices
exert significant forces of 400-500 grams however most newer ICDs exert
around 100 grams
26,29.
Human Studies:
Reports using
older technology:
In the
earliest years of MR, using older generation pacemakers devices, as
mentioned above there were few anecdotal reports of unexpected deaths
in patients undergoing MR imaging.
13-15 In one case, the patient had no
escape ventricular rhythm and apparently died due to systole. Another
patient developed ventricular fibrillation during the imaging procedure
that was not recognized immediately because ECG monitoring was not used.
30 On the other hand, there are also
reports of pacemaker patients who underwent MR imaging safely (
Table 2).
Therefore,
differences exist among clinicians regarding the perceived safety of
scanning paced patients. In patients who underwent MR imaging of the
head, no pacemaker malfunction was observed with the pacemaker turned
off or programmed to an asynchronous pacing mode prior to MR exposure.
16-20 In another study
on five patients with pacemakers, Gimbel et al. reported normal
pacemaker performance in four patients during MR (0.35 and 1.5 Tesla)
18. One patient had a pause of
approximately two seconds in duration near the completion of MR scan,
the cause of which could not be determined. This occurred in a
pacemaker dependent patient with a unipolar dual chamber device
programmed to DOO mode. No rapid cardiac pacing occurred and no patient
reported a torque or heating sensation. Fontaine et al. reported a case
of rapid cardiac pacing during MR imaging (1.5 Tesla) in a patient with
a dual chamber pacemaker.
19
The patient developed an irregular ventricular rhythm during RF pulsing
which terminated with the cessation of RF pulsing. MR at 0.5 Tesla was
shown to have no influence on atrial and ventricular stimulation
thresholds, P and R wave amplitudes, electrode impedance, battery
voltage, current, and impedance measurements in patients with implanted
pacemakers.
Reports using
present technology:
Vahlhaus et al
31 reported their experience using 0.5
Tesla MR system on 34 MR examinations in 32 patients with
implanted pacemakers and concluded that MR imaging at 0.5 Tesla does
not cause irreversible changes in patients' pacemaker systems. Lead
impedance and sensing and stimulation thresholds did not change after
MR imaging. Battery voltage decreased immediately after MR imaging and
recovered 3 months later.
In a recent
study
32, the largest human
report so far, 54 non dependent permanent pacemaker patients underwent
64 MR examinations at 1.5 Tesla . Only 9.4 % of the leads underwent
significant threshold changes and were easily addressed with subtle
programming changes. Patient's symptoms and electrographic changes were
mild and transient and did not warrant cessation of MR scan. The
authors concluded that the "performance of unrestricted MR procedures
using a 1.5-Tesla MR system was found to have an acceptable safety
profile". They cautioned, however, that the wide variety of pacing
systems and electromagnetic fields used in MR procedures implied that
the “absolute safety of pacemaker and MR interactions cannot be
assured".
Schmiedel et al
27 from Bonn, Germany, tested the
translational forces and temperature increase (max<2.98ºC) that
were in a range which does not represent a safety concern from a
biophysical point of view. They reported their experience with, 63 MR
imaging examinations at 1.5 Tesla in 45 patients with implanted
pacemakers. Prior to MR the devices were re-programmed in an
asynchronous mode. The maximum Specific absorption rate (SAR) of
MR-sequences was limited to 1.2 W/kg. Continuous monitoring of ECG and
pulse oximetry was performed during MR imaging. No changes to the
programmed parameters of the PM or damage of PM components were
observed neither In-vitro (n = 0/24) nor In-vivo (n = 0/63). All
patient studies (n = 63/63) could be completed without any
complications. Atrial and ventricular stimulation thresholds did not
change significantly immediately post-MR imaging nor in the 3 months
follow-up. They concluded "MR of the brain at 1.5 Tesla can be safely
performed in carefully selected clinical circumstances when appropriate
strategies are used (re-programming the device to an asynchronous mode,
continuous monitoring of ECG and pulse oximetry, limiting the SAR value
of the MR sequences, cardiological stand-by). Based on these studies,
implanted pacemaker should not longer be regarded as an absolute
contraindication for MR scan at 1.5 Tesla".
A similar
prospective study evaluated the risks of 2.0 T-MR in patients with
pacemakers and concluded that MR imaging in patients implanted with the
specific device and leads evaluated was safe however cautioned that the
results may not be applicable to all MR or pacemaker systems and
suggested limited MR exposure to pacemaker patients until larger trials
have been conducted (Roguin, personal communication).
Imaging in
Pacemaker Dependent Patients
Little has
been presented regarding MR imaging of pacemaker dependent patients. As
part of a series of five patients, Gimbel et al
33
reported one pacemaker dependent patient who safely underwent cranial
MR imaging. Safe inadvertent scanning of pacemaker dependent patient
also has been performed but not published yet [Roguin, personal
communication]. The results suggest that pacemaker dependent patients
might also be offered MR if careful patient monitoring and pacemaker
reprogramming is performed in concert with use of a transmit receive
coil (in cranial scans) and implementation of specific MR sequences
designed to limit power deposition over the device. A larger series of
pacemaker dependent patients need to be evaluated before a benign
outcome can be made.
Safety Issues
in Patients with Retained Pacing Leads
Many patients
have endocardial pacemaker leads left in place after pulse generator
removal. The safety of MR in patients with retained endocardial
pacemaker wires has not been systematically investigated to date.
However, due to the potential threat that they may act as “antennas”
with significant heating - we feel it is not recommended to scan those
patients.
Temporary
pacing wires, usually made of stainless steel, are sutured to the
epicardial surface of the heart over the right ventricle and right
atrium after cardiac surgery, and connected to an external pacemaker if
the patient develops bradycardia or atrioventricular block. Theoretical
calculations using a circuit formed by epicardial pacing wires showed
induction of currents up to 80μA by the beating heart in a magnetic
field strength of 1.5 Tesla
34.
Hartnell et al
35
investigated the safety of 1 or 1.5 Tesla MR systems operating with
conventional pulse sequences in 51 patients with retained epicardial
pacing wires, cut short at the skin, after cardiac surgery. None of the
patients reported symptoms suggesting arrhythmia or other cardiac
dysfunction during MR imaging, and there were no changes from the
baseline ECG rhythms. Therefore, retained epicardial wires do not seem
to present a hazard to patients in the MR environment. However, this
conclusion applies mostly to non-cardiac MR examinations
36.
Imaging
in Patients with Implantable Cardioverter Defibrillators (ICD)
Although
different as in the presence of large capacitors and larger batteries
that may cause higher magnetic forces., pacemakers and ICDs share
similar components and thus, to some extent, their response to the
electromagnetic interference (EMI) present during MR scanning might be
expected to be similar
1,8,14. Despite dramatic reduction in size
and weight, new generation ICDs have 10 times higher magnetic torque.
When tested this was found to be around 100gram/cm as compared to 10
gram/cm for pacemakers. Of note, for older ICDs (late 1990 models) the
torque was >300 gram/cm
26,27.
The implanted device has a fibrotic envelope around it several weeks
after implantation. Forces less than 200 gram will not be felt by the
patients
26. ICD devices may
falsely detect the MR RF noise as ventricular tachyarrhythmia and
subsequently deliver antitachycardia pacing, cardioversion or
defibrillation therapies. In addition, magnetic fields may prevent
detection of ventricular tachycardia or fibrillation. The heating
problem of ICD leads can be expected to be the same as in case of
pacemaker leads.
Despite many
pacemaker patients having reportedly undergone MR imaging using a
variety of strategies to allow safe MR scanning, relatively very little
has been reported regarding ICD patients undergoing deliberate MR. An
abstract and two case reports
37-39 have described the ill effects of
inadvertent MR imaging of ICD patients. Interestingly the same devices
were tested by Roguin et al, and the same findings were found – unable
to interrogate these older generation ICDs
26.
One case report of an ICD patient inadvertently undergoing MR imaging
noted a substantial rise in pacing thresholds subsequent to the MR
exposure
40. Concerns over a
possible rise in defibrillation test (DFT) was recently answered by, a
recent preliminary report of ICD patients undergoing MR that showed
greater than the 10 J safety margin of safety during post MR imaging
DFT testing
32. No thermal
injury was found by Roguin et al, in 15 dogs that underwent prolonged
MR scans 4 weeks after ICD implantation
26.
Recently
deliberate scanning of ICD patients was reported. Wollmann et al
41 report on a patient with an ICD who
intentionally underwent MR imaging of a malignant brain tumor. The ICD
was inactivated by programming the VT-detection and VT/VF-therapy
status off. The patient came through the protocol safely and without
any difficulty or discomfort. There was no arrhythmic event. MR imaging
affected neither programmed data nor the function of the ICD system.
Roguin et al
42, based on
their in-vitro and in-vivo results, implanted an ICD that was found to
be safe, in a young patient with ventricular arrhythmia and suspected
ARVD. To confirm the diagnosis a follow up MR scan was advised. So the
patient underwent intentional MR imaging 6 weeks after implantation.
The scan was safe and most of the MR images were of high quality.
Gimbel et al
43 reported their experience on seven
patients who underwent eight MR imaging scans at 1.5 Tesla. Post-MR
scan, all devices demonstrated no change in pacing, sensing,
impedances, charge times, or battery status. None of the patients had
any discomfort. They concluded that scanning of ICD patients might be
performed if appropriate reprogramming and monitoring is implemented.
Several patients with the newer biventricular ICD systems, were safely
scanned [Roguin, personal communication].
The rapidly
accumulating number of safely scanned patients with pacemakers directs
one to surmise that we might also safely scan patients with ICDs if
similar strategies that had allowed safe MR in pacemaker patients were
applied to ICD patients. Some investigators
26,44 have suggested that “modern” devices
are less prone to the effects of MR and because of better built in EMI
protection circuitry. Disabling the tachy-arrhythmia detection and
therapy is one strategy which has been recommended. Programming to
therapy off avoids delivering therapy as a result of interpretation of
noise as tachyarrythmia
26.
In the study carried out by Gimbel et al,
43
simple strategies that had allowed patients with pacemakers to safely
undergo MR imaging were applied to several ICD patients.
Image quality:
Though lot of studies have been
done to determine whether the devices are fully MR imaging-compatible
(function appropriately and without significant image distortion) very
little is known about the fact whether these device are MR-safe
(function appropriately in the MR environment but distort the image) or
may not be usable in an MR scanner
44,45. Image artifacts and RF noise can be
caused by the presence implanted devices in the MR environment which
are in or near the imaging field of view (such as implants or surface
electrodes). These materials produce their own characteristic static
magnetic field that can perturb the relationship between position and
frequency essential to accurate image reconstruction. If the object has
a magnetic susceptibility that is significantly different from that of
tissue, distortion will result. Primary concerns with image artifact
and noise include the production of a void where anatomical information
is needed as well as the production of artifacts that may be
misdiagnosed as pathology. Schueler et al
45
have offered an assessment of image quality according to four criteria:
geometric distortion; susceptibility-induced artifact; warping
artifact; and bending, warping, or obliteration of image contours.
Most artifacts
from pacemakers and leads result in local image distortion, signal
voids, or increased noise. In an in vitro study
26
in a dog model using the clinical scanning protocols this issue was
addressed and image distortion was analyzed by measuring the area where
there was a void in the MR image. The distortion was analyzed at the
level of the heart and at the level of the device. Artifacts due to the
devices and leads were observed in some MR sequences and less in
others. Most of the distortion was dependent on scan protocol and image
plane: Fast Spin Echo and FIESTA sequences had significant
distortion. Fast Gradient Recalled Echo, Tagging and FSPGR
sequences, however, yielded good images. Larger artifacts were observed
in image planes roughly parallel to the planes defined by the device
itself. Most distortion was at a distance of 10-15 cm around the device
generator. The authors concluded that image distortion was dependent on
the imaging plane and protocol used. Most image distortion was in the
area adjacent to the device generator. Therefore, organs visualization
beyond this distance, such as knees, lower spine, liver or brain, will
not be affected by the presence of the pacemaker or ICD.
Summary:
Most
researchers in the field agree that although several hundreds of
patients with implanted devices underwent safe MR scan – this does not
conclude that MR imaging in patients with pacemakers or ICDs is indeed
safe. According to the FDA’s definition, today’s ICDs are not “MR
Safe” nor “MR compatible”. Because of the small size of the series and
limited to few manufacturers one cannot conclude that MR imaging can
deliberately be performed routinely in Pacemaker/ICD patients without
risk. Further study is required to better understand the interaction
between pacemakers and ICD systems and the effects of MR imaging.
Ultimately, a
truly “MR safe” ICD system will need to be developed. Nevertheless, one
should be encouraged, and like the experience with pacemakers, the
initial encouraging reports of MR imaging in ICD patients reported only
a small series.
Like pacemaker
patients, ICD patients should not be considered for MR scan unless
appropriate precautions are undertaken and then only when other avenues
to acquire clinically relevant imaging data have been explored.
Should MR imaging be considered in a patient with an implantable
device, appropriate consultation with a qualified cardiologist or
electrophysiologist is strongly advised so that patients can be
adequately screened and correctable physiologic abnormalities (e.g.
hypoxia, electrolyte abnormalities, etc.) can be addressed prior to MR
imaging. The patient must not be pacemaker/ICD dependent. The
clinician needs to document in the chart, that MR imaging is crucial to
the management of the patient. No other imaging can be expected to
provide an alternative or has been unsuccessfully tried. The patient or
family will sign a preprinted consent form explaining potential adverse
reactions, invalidation of warranty, heating leads, rapid pacing,
alteration of programming, damage of circuitry requiring replacement
and movement of the device.
In 2004, the
American College of Radiology (ACR) issued an update of its 2001 MR
Safe Practices Guidelines
8
in which they reiterate their recommendation that implantable devices
should be a contraindication for MR imaging. They added, however, that
decisions for exceptions should be made on a case-by-case basis and
that all MR scans should be performed under the guidance of both an
experienced radiologist and cardiologist/ electrophysiologist, but
noted that "the expertise necessary to safely do so is exceedingly rare
throughout the MR industry today." Thoughtful pre-MR reprogramming,
careful monitoring during MR scan and thorough follow-up must be
performed in any device patient considered for MR imaging. Finally a
physician knowledgeable in device therapy and programming should be
present throughout the entire scanning event (
Table 3). The authors of the 1.5-T
pacemaker study
32 agree
with the ACR guidelines that continuous monitoring is needed and that
properly trained personnel and physicians with expertise in adjusting
device programming interrogate the devices before and after the scan.
Adherence to these practice guidelines may ensure the implantable
cardiac device patient can safely undergo MR imaging (
Table 4). As suggested by
the aforementioned studies, it may be an appropriate time to reconsider
whether the presence of an implantable cardiac device should be an
absolute contraindication to MR imaging.
Table
3: Magnetic Resonance Imaging and Pacemakers: Safety Concerns
and Guidelines.
* Due to higher degree of
interaction between MRI and ICD, the threshold for imaging is higher
than for pacemakers.
Table 4: Technical aspects in MR
imaging of patients with pacemakers/ICDs
Arranging the procedure:
Procedure must be approved by
attending radiologist
A Cardiology consult must be obtained to determine pacemaker- or
ICD-dependency.
Procedure will be scheduled with Radiology and Cardiology in
coordinated fashion.
MR imaging of pacemaker or ICD patients will only be performed in a
main Hospital.
The exam will only be performed on weekdays during regular business
hours.
Technical (MRI):
Field strength is limited
to 1.5 T.
Send/Receive volume coils are preferred over surface coils.
Technical (Pacemaker/ICD):
Device must have been in place
preferably for 4-8 weeks prior to MR imaging.
Immediately prior to MR imaging, the pacemaker must be programmed to
OFF or must be programmed to sub threshold outputs (rate response and
ventricular rate regulation features will need to be programmed OFF).
ICD programmed to therapy off.
Qualified personnel will perform a full device interrogation prior and
immediately after MR scan (if patient is an inpatient, it must be done
before the patient returns to the floor).
An interrogation of the pacemaker or ICD will be performed 3 months
after the exam to measure thresholds (and other measurements).
Patient Care:
An ACLS certified Cardiology
physician, nurse practioner or physician assistant, or alternatively,
an ACLS certified senior resident, fellow or attending physician of the
primary care team will be present at the MR-console during the entire
exam to monitor the patient.
A pacemaker programmer will be present at the MR-scanner.
The patient will be monitored with ECG and pulse oximetry during the
entire exam
A crashcart with an external defibrillator-pacemaker (not AED) must be
present at the MR-scanner.
A designated cardiologist needs to be within 5 minutes in of the
MR-scanner.
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