The QT interval is the total time taken for ventricular depolarization and repolarization. Prolongation of the QT interval:
a. decreases the risk of lethal dysrhythmias.
b. usually occurs when heart rate increases.
c. increases the risk of lethal dysrhythmias.
d. can only be measured with irregular rhythms.
C
The QT interval is measured from the beginning of the QRS complex to the end of the T wave. This interval measures the total time taken for ventricular depolarization and repolarization. Abnormal prolongation of the QT interval increases vulnerability to lethal dysrhythmias, such as ventricular tachycardia and fibrillation. Normally, the QT interval becomes longer with slower heart rates and shortens with faster heart rates, thus requiring a correction of the value (QTc). Generally, the QT interval is less than half the RR interval. QTc accuracy is based on a regular rhythm. In irregular rhythms such as atrial fibrillation, an average QTc may be necessary because the QT varies from beat to beat.
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