User's Manual

QT Interval Monitoring
6-42 ECG and Arrhythmia Monitoring
QT Interval Monitoring
Of special concern for QT monitoring is the administration of QT
prolonging drugs to patients identified with risk factors for Torsade de
Pointe. Females, older patients and patients with bradycardia, impaired left
ventricular function (ischemia, left ventricular hypertrophy), hypokalemia
and hypomagnesemia are in this increased risk category.
QT interval monitoring can assist in the detection of prolonged QT interval
syndrome. The QT interval in an ECG lead is the time interval from the
onset of the earliest deflection in the QRS complex to the end of the T wave.
For patients being monitored by the MX40, the Information Center
measures the QT interval once every minute during startup, during the
learning phase and on lead mode change. After that the Information Center
updates the QT values every five minutes.
The QT interval has an inverse relationship to heart rate. Faster heart rates
shorten the QT interval and slower heart rates prolong the QT interval. To
correct the QT interval for heart rate the Information Center uses the Bazett
correction formula by default. Your system, however, may be set up to use
the Fridericia correction formula as an alternative. The heart rate corrected
QT interval is abbreviated as QTc.
Note — When operating with the IntelliVue Information Center Release N
or earlier, QT Data is not displayed at the MX40