Corrected QT Interval (QTc) Calculator

How to calculate Corrected QT Interval (QTc)?

The QT interval varies with heart rate; QTc normalizes this value to a heart rate of 60 bpm for standard clinical assessment.

Formula (Bazett): QTc = QT / √RR where RR is the interval between heartbeats in seconds.

Using the QTc calculator: an example

Consider a patient with a QT Interval of 400ms and a Heart Rate of 75 bpm.

Step-by-step calculation:

• Convert HR to RR interval: 60 / 75 = 0.8 seconds.
• Calculate the square root of RR: √0.8 ≈ 0.894.
• Divide QT by the result: 400 / 0.894 ≈ 447ms.

Frequently Asked Questions

Why is QTc clinically important?

A prolonged QTc interval is a biomarker for ventricular tachyarrhythmias like Torsades de Pointes and is used to monitor drug safety.

Which formula is most accurate?

Bazett is most common but tends to over-correct at high heart rates; Fridericia or Framingham are often preferred for tachycardia.

What are normal QTc ranges?

Generally, QTc > 470ms in men and > 480ms in women is considered definitely prolonged.