1. What Is QTc Calculation?

The QTc (Corrected QT Interval) calculation adjusts the measured QT interval for heart rate using Bazett's formula. This provides a standardized measure of ventricular repolarization that can be compared across different heart rates.

2. How Does The Calculator Work?

The calculator uses Bazett's formula:

Where:

• \( QT \) — Measured QT interval in milliseconds (ms)
• \( RR \) — RR interval in seconds (s)

Explanation: The calculator counts the number of small boxes on ECG paper (1 box = 40 ms at standard 25 mm/s speed), converts to milliseconds, then applies Bazett's formula to correct for heart rate.

3. Importance Of QTc Calculation

Details: Accurate QTc calculation is essential for detecting prolonged QT intervals, which can indicate increased risk of life-threatening arrhythmias such as torsades de pointes. It's used in clinical practice, drug safety monitoring, and cardiac risk assessment.

4. Using The Calculator

Tips: Count the number of small boxes between the start of the Q wave and end of the T wave for QT interval. Count boxes between consecutive R waves for RR interval. Enter both values (must be > 0).

5. Frequently Asked Questions (FAQ)

Q1: What is a normal QTc value?
A: Normal QTc is typically <440 ms for men and <460 ms for women. Values above these may indicate prolonged QT syndrome.

Q2: Why use boxes instead of direct time measurements?
A: Counting boxes on standard ECG paper (25 mm/s) provides a quick, visual method that doesn't require precise time measurements.

Q3: What are the limitations of Bazett's formula?
A: Bazett's formula tends to overcorrect at high heart rates and undercorrect at low heart rates. Other formulas (Fridericia, Hodges) may be more accurate in certain situations.

Q4: When should QTc be measured?
A: QTc should be measured when evaluating syncope, arrhythmias, before starting medications that prolong QT interval, and in family screening for congenital long QT syndrome.

Q5: How many leads should be measured?
A: The longest measurable QT interval among leads II, V5, and V6 is typically used. Measurements should be averaged over 3-5 beats in sinus rhythm.