What does QTc represent on ECG interpretation?

• A. Heart-rate–corrected QT interval
• B. Uncorrected QT interval
• C. QRS duration
• D. PR interval

Answer: (A)

QTc is the heart-rate–corrected QT interval. On an ECG, the QT interval spans from the start of the Q wave to the end of the T wave and reflects the total time for ventricular depolarization and repolarization. Because this interval shortens at high heart rates and lengthens at low heart rates, we adjust it to a standard heart rate to compare across different conditions—this corrected value is QTc. Clinically, QTc helps identify prolonged ventricular repolarization that can increase risk for dangerous rhythms like torsades de pointes, and it’s especially useful when evaluating drug effects or electrolyte disturbances. The other terms refer to different measurements: the raw QT interval, which varies with heart rate; the QRS duration, which measures ventricular depolarization width; and the PR interval, which covers atrioventricular conduction from the start of atrial to the start of ventricular depolarization.