Prashant Nair, Ariel Roguin, 202
“Magnetic Resonance Imaging in patients with ICDs and Pacemakers”
Schmiedel et al27 from Bonn, Germany, tested the translational forces and temperature
increase (max<2.98°C) 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 al33 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 Tesla34. Hartnell et
al— 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 examinations36.
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(3): 197-209 (2005)