5 ECG, Arrhythmia, ST and QT Monitoring
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Changing the Trending Interval
To determine how frequently the monitor displays a trended sample,
1 In Trend view, select Select Interval.
2 Select the required interval from the menu. The interval ranges between 12 seconds to 30 minutes.
Printing an ST Map Report
To print the most recently viewed (current or trend) window,
1 Select Main Setup then select Reports.
2 Select ST Map.
3 Press Print.
About QT/QTc Interval Monitoring
The QT interval is defined as the time between the beginning of the Q-wave and the end of the T-
wave. It measures the total duration of the depolarization (QRS duration) and repolarization (ST-T)
phases of the ventricular action potential. QT interval monitoring can assist in the detection of
prolonged QT interval syndrome.
The QT interval (1) has an inverse relationship to heart rate. Faster heart rates shorten the QT interval
and slower heart rates prolong the QT interval. Therefore there are several formulas used to correct
the QT interval for heart rate. The heart rate corrected QT interval is abbreviated as QTc. The monitor
uses as a default the Bazett correction formula and the alternative Fridericia formula can be selected in
Configuration Mode.
For QT interval monitoring to be effective, basic or enhanced arrhythmia monitoring should be turned
on.
QT Measurement Algorithm
The QT values are updated every five minutes except in the initial phase (first five minutes) where they
are updated once per minute. Normal or atrial paced beats and beats with a similar morphology are
averaged to form a representative waveform for further processing. Normal beats followed by a
premature QRS will be excluded from the measurements to prevent the premature beat from
obscuring the end of the T-wave. If the algorithm cannot form a representative waveform, for example
because the morphology of the beats is too varied, a
CANNOT ANALYZE QT INOP will be generated
after 10 minutes. This is also the case if normal beats have been falsely labeled so that the algorithm
does not have enough valid beats to make QT measurements. No QT value is calculated if the QT-HR
is >150 bpm (Adult) or >180 bpm (Pedi/Neo).
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