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					Arrhythmia/EP
MRI scan safe in ICD patients, provided precautions are taken
July 28, 2009 | Michael O'Riordan

Bonn, Germany - Patients with a non-pacemaker-dependent implantable cardioverter defibrillator
(ICD) can safely undergo an MRI scan provided certain precautions are taken, according to the
results of a new study [1].
Utilizing the various ICD, MRI, and monitoring-related safety precautions, investigators did not
observe any damage to the ICD systems or any unexpected changes in heart rate or rhythm. Also,
there were no inappropriate shocks delivered and no evidence of radiofrequency-related myocardial
thermal damage during or after the scan.
"The number of implanted pacemakers and ICDs, as well as the number of devices for cardiac
resynchronization therapy, are going up every year," said lead investigator Dr Claas Philip Naehle
(University of Bonn, Germany). "People are getting older, and the older they get, the greater the
likelihood they're going to need an MRI exam. Obviously that's a big overlap, and it's why we're
seeing a lot of patients referred to us for an MRI exam."
The results of the study are published in the August 4, 2009 issue of the Journal of the American
College of Cardiology.


Assess if the patient needs the exam
Speaking with heartwire, Naehle said MRI scans in patients with an ICD are still an off-label
procedure, but there are circumstances, such as a brain scan, where the modality's unparalleled
ability to discriminate between soft tissue is considered medically necessary.
One of the primary concerns when a patient with an ICD undergoes an MRI scan is the inadvertent
heating of the implanted leads, which can cause tissue damage and changes in thresholds. Other
concerns include movement of the device and potential loss of capture. With other pacemaker
devices, there are concerns about programming changes, asynchronous pacing, activation of
tachyarrhythmia therapies, inhibition of pacing output, and induced lead currents that could lead to
cardiac stimulation.
"The first thing you need to assess is if the patient really, really needs the exam," said Naehle. "The
benefit of the MRI exam has to outweigh the risk. For instance, if you suspect a brain tumor, there
really isn't much choice. You need to do the MRI for a proper diagnosis. If you simply want to see
if there is a spinal problem, say a prolapse of the discus in the spine, that might be something that
could be done by [computed tomography] CT."
In this study, 18 non-pacemaker-dependent ICD patients with a clinical need for MRI, including
five who required scans of the heart, underwent an examination. Prior to the scan, the ICDs were
reprogrammed to avoid competitive pacing and potential arrhythmias. In each patient, the lower rate
limit was programmed as low as possible, and arrhythmia detection remained on, but therapy
delivery was programmed off. In addition to these precautions, the specific absorption rate, a
measure of the energy absorbed by the body when exposed to a radiofrequency electromagnetic
field, was limited to 2W/kg.
After the MRI scan, an interrogation of the ICD revealed no significant changes of pacing capture
threshold or lead impedance. Also, serum troponin I levels, a measure of clinically relevant thermal
injury, were unchanged from baseline. No patient reported any torque or heating sensations or other
unusual symptoms during the MRI.
Despite the successful scans, Naehle told heartwire that "only centers that know what they're doing
should be doing it." He said physicians should always determine whether the ICD patient has
undergone a prior MR scan because the device might be damaged, and how many, if any,
ventricular arrhythmias requiring defibrillation occurred in the past month or so. He added that to
be performed safely, there is a need for collaboration between the cardiologist/electrophysiologist
and the radiologist. With older patients having more and more devices implanted, experienced
centers are likely to be increasingly busy with referrals for these complex patients, he added.


No blanket statement on MR and ICDs and pacemakers
In 2007, the American Heart Association issued a statement on the use of MRI in patients with
cardiovascular diseases and included guidance on using the scans in patients with ICDs and
pacemakers. While there are currently no MRI-safe ICDs, the scientific report does not provide any
blanket statements on their use and instead recommends that an MRI be performed only in ICD and
pacemaker patients who need them and only at expert MRI and electrophysiology centers.
In an editorial accompanying the published study [2], Dr Ariel Roguin (Technion-Israel Institute of
Technology, Haifa, Israel) notes that ICDs have more complex technology than pacemakers and
have larger capacitors and batteries. As a result, the magnetic forces are greater, and they are
theoretically more prone to electromagnetic and mechanical interference when a patient with an
ICD undergoes MRI. However, as Naehle told heartwire, ICD patients tend to be higher-risk
patients, with higher mortality rates, so the threshold of benefit for an MR scan must also be higher.
Roguin points out that although data are limited, it is estimated that at least 50% of patients with an
implanted device will probably need to undergo MRI over the lifetime of their device. Early data on
the relative safety of MR scans in device-implanted patients showed that no deaths have occurred in
various physician-supervised MR studies where patients are carefully monitored, but there have
been a few cases of changes in pacing threshold, the need for device reprogramming, and possibly
battery depletion.
"We must exercise caution, however, given the wide range of available MRI systems, MRI
scanning conditions, patient positions, pacemaker and ICD systems, and leads when extending these
results to recommendations for routine use of MRI in these patients," writes Roguin. "The fact that
several hundreds of patients with [implanted devices] underwent uneventful MRI does not allow us
to conclude that MRI in this population is indeed safe. All published studies were performed at
centers with expertise in MRI and electrophysiology and were limited to patients with a true clinical
need for MRI."


Like Naehle, Roguin stresses that MRI may be considered in selected patients and done only when
clinically indicated.

Roguin is a consultant to Medtronic. Naehle reports no conflicts of interest.
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Sources
    1. Naehle CP, Strach K, Thomas D, et al. Magnetic resonance imaging at 1.5-T in patients with
       implantable cardioverter defibrillators. J Am Coll Cardiol 2009; 54:549-55.
    2. Roguin A. Magnetic resonance imaging in patients with implantable cardioverter
       defibrillators and pacemakers. J Am Coll Cardiol 54: 556-57.


Related links
    •   No complications, no overheating with MRI-compatible pacemaker and leads
        [Arrhythmia/EP > Arrhythmia/EP; May 14, 2009]
    •   Rock on: Keep iPod headphones away from pacemakers/ICDs to avoid interference
        [Arrhythmia/EP > Arrhythmia/EP; Nov 10, 2008]
    •   Interference with ICU-type medical devices seen from radio-frequency "security tags"
        [Clinical cardiology > Clinical cardiology; Jun 25, 2008]
    •   New statement on safety of MRI with CV devices
        [Arrhythmia/EP > Arrhythmia/EP; Nov 30, 2007]
http://www.theheart.org/article/989093.do

				
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