The QT interval is the time from the start of the Q wave to the end of the T wave.It represents the time taken for ventricular depolarisation and repolarisation.
QT shortens at faster heart rates
prolonged QT is associated with an increased risk of ventricular arrhythmias
MEASUREMENTS:
measured in either lead II or V5-6
Large U waves (> 1mm) that are fused to the T wave should be included
Large U waves (> 1mm) that are fused to the T wave should be included
Smaller U waves and those that are separate from the T wave should be excluded
The maximum slope intercept method is used to define the end of the T wave
Corrected QT
estimates the QT interval at a heart rate of 60 bpm.
improves detection of patients at increased risk of arrhythmias.
improves detection of patients at increased risk of arrhythmias.
Bazett’s formula: QTC = QT / √ RR
QTcis prolonged if > 440ms in men or > 460ms in women
prolonged QTc
Hypokalemia, hypocalcemia, hypomagnesemia, hypothermia, myocardial infarction, congenital long QT, drugs, raised ict
SHORT QT INTERVAL
Hypercalcemia, congenital short QT , digoxin effect
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