Prashant Nair, Ariel Roguin,
201
“Magnetic Resonance Imaging in patients with ICDs and Pacemakers
threshold changes and no pathology and histology heat-induced damage.
Roguin et al26 found in-vitro, maximal heating of 7°C. 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 group27.
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 grams26,29.
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.20 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 al21 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 study32, 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".
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(3): 197-209 (2005)