What is the normal Q-T interval range?

• A. 0.35-0.43 sec
• B. 0.25-0.30 sec
• C. 0.30-0.35 sec
• D. 0.45-0.50 sec

Answer: (A)

The QT interval measures the time from the start of the Q wave to the end of the T wave, reflecting how long the ventricles take to depolarize and then repolarize. In adults, a normal QT interval is typically about 0.36 to 0.44 seconds, with many teaching references citing roughly 0.35 to 0.43 seconds as a practical normal window. The range given fits well within that normal span, so it best represents a normal QT interval.

Ranges shorter than this (roughly 0.25–0.30 or 0.30–0.35 seconds) are longer than normal only in certain circumstances or may reflect faster heart rates or measurement nuances. A range like 0.45–0.50 seconds is longer than normal and can indicate prolonged repolarization, which carries a risk for certain ventricular arrhythmias and warrants clinical attention.