User's Manual Part 2

6-1
6. Using Vital Sign Parameters
6.1. Cardiac Monitoring
6.1.1. ECG Overview
The electrocardiography, ECG, reflects the electrical activity generated by the heart muscle and
displays it on the patient monitor as a waveform and numeric heart rate value. ECG monitoring
in the MRI is used for a heart rate measurement and is not intended to diagnose arrhythmic
cardiac conditions. The 3880 MRI Patient Monitor uses a sophisticated heart rate averaging
algorithm which uses a multi-point median filter displaying the average of the middle three
points. The conditions found inside the MRI area are unique and require additional precautions
to be followed in order to permit the safe ECG monitoring of the patient during MRI procedures.
Monitoring ECG in the MRI environment is challenging because of the inherent distortion of the
ECG waveform caused by the MRI magnetic field that adds to the ECG T-wave amplitude.
Additional artifacts caused by the static, gradient, and RF electromagnetic fields can also
severely distort the ECG waveform. Since distortions may be associated with true physiologic
disorders a baseline recording of the ECG prior to placing the patient inside the MRI system
room will be necessary. The proper placement of the ECG electrodes in the MRI is critical to
reducing the distortion of the ECG waveform. Monitoring a different ECG lead (I, II, III, AVL,
AVR, AVF, V) can minimize some of these artifacts.
High radio frequency (RF) power used in MRI scanning poses a risk of excessive heat at the
monitoring sites and the risk of patient burn greatly increases with increased power levels are
used. As a result, monitoring of ECG at power levels of greater than a MRI system reported,
whole body averaged SAR of 4 W/kg is not recommended for the general patient population.
Such monitoring must only be attempted on conscious patients with normal thermoregulatory
capabilities so they may warn the operator of possible excessive heat at the monitoring sites.
The ECG patient lead wires are short and constructed of special lossy material to reduce the
amount of radio frequency (RF) energy that can flow through these wires to mitigate risk RF
heating hazard. The lead wires nor the POD should not touch the MR system bore. Contact with
the MR system bore may cause heating of the POD or lead wires or patient electrode site. Use
of lead wires other than the
IRadimed lead wires may cause excessive RF current to flow
through the wires, thus causing the potential for patient heating or burn. Use only the leads
described in section 9.3.
! WARNING
• Use only MRI lead wires and electrodes described in section 9.3
• Do not used damaged ECG lead wires, electrodes or ePODs
• Do not use electrodes with expired dates
• Do not immerse the ePOD or Lead wires completely in water solvents, or cleaning
solutions.
• Arrhythmias, erratic heart beats, operation of electrical stimulators, pacemakers and
patient motion can result in inaccurate readings. Rate meters may continue to count
pacemaker rates during occurrence of cardiac arrest or some arrhythmias. Do not rely
entirely upon rate meter alarms. If questionable readings are obtained, confirm patient’s
vital signs by alternate means before administering medication.
• The lead wires nor the POD should not touch the MR system bore. Contact with the MR
system bore may cause heating of the POD or lead wires or patient electrode site.
• When connecting electrodes and/or patient wires, make sure that the connectors never
come into contact with other conductive parts. In particular, make sure that all of the
ECG electrodes are attached to the patient, to prevent them from contacting conductive
parts or earth.