ST SETUP
VF6 Infinity Vista 10-5
Isoelectric and ST Measuring Points
ST segment deviations are specified in terms of a displacement above or below the
isoelectric level. To calculate this displacement, the monitor compares the amplitudes
of the signal at two user-selectable measurement points in the patient’s QRS
waveform. One point is typically set at the isoelectric level on the waveform. The
other point is typically set within the ST segment of the waveform. The difference (in
millimeters or millivolts) between the amplitude of the isoelectric point and the
amplitude of the ST measurement point represents the ST deviation. The available
settings for each point are:
z Isoelectric Point: from the start of the averaged ST complex to the Fiducial
point, in increments of 4 ms
z ST Measurement Point: from the Fiducial point to the end of the averaged ST
complex, in increments of 4 ms
The default position for the isoelectric point is -28 milliseconds before the start of the
QRS complex, as measured along the horizontal (time) axis. The default position for
the ST measurement point is +80 milliseconds after the end of the QRS complex. The
starting and ending points for the QRS complex are determined by the QRS detection
algorithm.
In practice, however, the determination of the isoelectric and ST measurement points
must be made on the basis of a careful clinical evaluation. The ST display provides the
means for changing the isoelectric and ST measurement points in order to ensure an
accurate ST deviation measurement.
STEPS: Setting the Isoelectric and ST Measuring Points
1. Click on the ST parameter box.
2. Click on
ISO. Two vertical lines, indicating the location of the ISO and the ST
measurement points, appear in the ST waveform channels.
.
3. With the rotary knob, move the position of the ISO point to the desired
location and click the knob. The corresponding value (in milliseconds) is
shown next to the ISO label.
4. Click on
ST.
NOTE: You should always check the position of the isoelectric and ST measurement
points before starting ST monitoring.
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