Which statement about QT interval measurement is true?

Which statement about QT interval measurement is true?

• A. QT measures ventricular depolarization and repolarization
• B. QT measures atrial depolarization
• C. QT measures AV nodal conduction
• D. QT measures ventricular hypertrophy

Answer: (A)

QT interval represents the total time for ventricular electrical activity, from the start of ventricular depolarization to the end of ventricular repolarization. It spans the QRS complex (depolarization) plus the ST segment and T wave (repolarization), so it reflects how long the ventricles take to activate and then recover. It’s not a measure of atrial depolarization (that’s the P wave), nor of AV nodal conduction (the PR interval), and it doesn’t indicate ventricular hypertrophy (a structural/voltage issue). Clinically we also adjust it for heart rate as QTc to compare across rates.

QT interval represents the total time for ventricular electrical activity, from the start of ventricular depolarization to the end of ventricular repolarization. It spans the QRS complex (depolarization) plus the ST segment and T wave (repolarization), so it reflects how long the ventricles take to activate and then recover. It’s not a measure of atrial depolarization (that’s the P wave), nor of AV nodal conduction (the PR interval), and it doesn’t indicate ventricular hypertrophy (a structural/voltage issue). Clinically we also adjust it for heart rate as QTc to compare across rates.