Magnetic Resonance Imaging in patients with ICDs and Pacemakers



Prashant Nair, Ariel Roguin,                                                      203

“Magnetic Resonance Imaging in patients with ICDs and Pacemakers”

Imaging in Patients with Implantable Cardioverter Defibrittators (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
27-22 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
22. 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 al41 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 al42 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,42 simple
strategies that had allowed patients with pacemakers to safely undergo MR imaging were applied
to several ICD patients.

Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(3): 197-209 (2005)



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