QT interval represents which of the following?

• A. Represents the total time for ventricular depolarization and repolarization
• B. Represents left ventricular contraction only
• C. Represents atrial depolarization
• D. Represents AV node conduction

Answer: (A)

The QT interval measures the entire electrical cycle of the ventricles, from the start of ventricular depolarization to the end of ventricular repolarization. It begins with the start of the Q wave and ends at the end of the T wave, encompassing the QRS complex, the ST segment, and the T wave. This is why it reflects the total time the ventricles are electrically active. Left ventricular contraction is a mechanical event that follows electrical activation, not the timing the QT interval reflects. Atrial depolarization is shown by the P wave, and AV node conduction is represented by the PR interval, which tracks conduction from atria through the AV node. So the QT interval best represents the total time for ventricular depolarization and repolarization.