Electrocardiogram (ECG) monitoring inside the MRI environment is unique and requires
additional precautions to permit safe patient procedures. It is always important to remember
that the risk of radio frequency (RF) heating is ever present when any electrical conductors (for
example, ECG lead cables) are placed in the MR system bore. By following the operating
precautions, warnings and the guidelines below, these risks can be minimized. The ECG
parameter is intended for ECG monitoring mode and not diagnostic ECG monitoring.
Pacer pulses are not specifically rejected by the MR400 and may be treated as part of MRI
gradient noise. Gradient filtering attempts to remove high frequency pulse-shaped waveforms
from the ECG signal which may resemble pacer waveforms, and it is possible that the pacer
waveform may be removed with the gradient noise.
ECG Monitoring Considerations for the MR Environment
Monitoring ECG in the MR environment is particularly challenging because of the inherent
distortion of the ECG waveform caused by the combined electromagnetic fields generated by the
MRI scanner. In particular, certain ECG interference appears when the patient is placed inside the
bore before scanning begins. These blood flow induced distortions of the ECG are due to the
large amount of blood moving through the vessels of the heart (aorta). Blood (a very good
electrical conductor) moving through the large magnetic field of the MR produces an electrical
potential that adds to the ECG signal. This induced electrical potential is seen primarily as an
augmentation of the ECG T‐wave amplitude, although other non‐specific waveform changes are
also apparent on the ECG. Since an elevated T‐wave or ST segment will be associated with true
physiologic disorders, the static magnetic field‐induced ECG‐distortions may prohibit effective
ECG monitoring in the MRI. For this reason, a baseline recording of the ECG prior to sliding the
patient inside the bore or outside the MR magnet room will be necessary.
Expression MR400 Instructions for Use Monitoring ECG 5‐1
The MR400 is not intended for use with patients using pacemakers or electrical
Arrhythmias, erratic heartbeats, operation of electrical stimulators, pacemakers and
patient motion can result in inaccurate readings. Rate meters may continue to count
pacemaker rates during occurrences of cardiac arrest or some arrhythmias. Do not
rely entirely upon rate meter alarms. If questionable readings are obtained, check the
patient's vital signs by alternate means before administering medication.