Mindray BeneView T1, Operator'S Manual

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8.7 QT/QTc Interval Monitoring (For Mindray ECG Algorithm)
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 the ventricles. QT interval
monitoring can assist in the detection of long QT syndrome.
The QT interval has an inverse relationship to heart rate. As heart rate increases, the QT interval shortens, while at lower
heart rates QT interval gets longer. Several formulas are available to correct QT interval for heart rate. The heart rate
corrected QT interval is abbreviated as QTc.
QT/QTc Interval Monitoring is intended for adult, pediatric, and neonate patients.
8.7.1 QT/QTc Monitoring Limitations
Some conditions may make it difficult to achieve reliable QT monitoring, for example:
R-wave amplitudes are too low

The presence of frequent ventricular ectopic beats

Unstable RR intervals

P-waves tending to encroach on the end of the previous T-wave at high heart rates

T-waves are very flat or not well defined
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The end of the T-wave is difficult to delineate because of the presence of U-waves

QTc measurements are not stable

In the presence of noise, asystole, ventricular fibrillation, and ECG lead off
For these cases you should select a lead with good T-wave amplitude and no visible flutter activity, and without a
predominant U-wave or P-wave.
Some conditions such as left or right bundle branch block or hypertrophy can lead to a widened QRS complex. If a long
QTc is observed you should verify it to ensure that it is not caused by QRS widening.
Because normal beats followed by ventricular beats are not included in the analysis, no QT measurement will be
generated in the presence of a bigeminy rhythm.
If the heart rate is extremely high (over 150bpm for adults and over 180bpm for pediatrics and neonates), QT will not be
measured. When the heart rate changes, it can take several minutes for the QT interval to stabilize. For reliable QTc
calculation it is important to avoid the region where the heart rate is changing.