Question

Normal QT interval. What does it correspond to? When it exceeds _____ sec, there is an increased risk of torsades.

a) Represents ventricular depolarization and repolarization; 0.4 seconds
b) Represents atrial repolarization; 0.6 seconds
c) Represents ventricular depolarization; 0.3 seconds
d) Represents atrial depolarization and repolarization; 0.8 seconds

Answer 1

The normal QT interval corresponds to ventricular depolarization and repolarization. A QT interval exceeding 0.4 seconds indicates an increased risk of torsades de pointes.

Step-by-step explanation:

The normal QT interval on an electrocardiogram (ECG) represents the period from the start of ventricular depolarization to the end of ventricular repolarization. This interval includes the QRS complex, which indicates ventricular depolarization, and the T wave, which signifies ventricular repolarization. Atrial repolarization also occurs but is not visible on the ECG as it is masked by the QRS complex. The normal QT interval is usually less than 0.44 seconds. When the QT interval exceeds 0.5 seconds, there is an increased risk of torsades de pointes, a specific type of abnormal heart rhythm that can be life-threatening.

Therefore, the correct answer to the question would be a) Represents ventricular depolarization and repolarization; 0.4 seconds.