1. What is QTc Calculation?

The QTc (Corrected QT Interval) calculation adjusts the measured QT interval for heart rate, providing a standardized measure of ventricular repolarization. It is essential for assessing the risk of arrhythmias, particularly Torsades de Pointes.

2. How Does the Calculator Work?

The calculator uses the Bazett's formula:

Where:

• \( QT \) — Measured QT interval from start of Q wave to end of T wave (ms)
• \( RR \) — RR interval = 60 / HR (s)
• \( HR \) — Heart rate (bpm)

Explanation: The formula corrects the QT interval for heart rate by dividing by the square root of the RR interval (in seconds).

3. Importance of QTc Calculation

Details: Accurate QTc calculation is crucial for diagnosing long QT syndrome, monitoring drug effects on cardiac repolarization, and assessing arrhythmia risk in various clinical settings.

4. Using the Calculator

Tips: Enter QT interval in milliseconds and heart rate in beats per minute. All values must be valid (QT > 0, HR > 0).

5. Frequently Asked Questions (FAQ)

Q1: Why correct QT interval for heart rate?
A: The QT interval naturally shortens with increasing heart rate. Correction allows comparison of QT values across different heart rates.

Q2: What are normal QTc values?
A: Normal QTc is typically <440 ms for men and <460 ms for women. Values >500 ms indicate high risk for arrhythmias.

Q3: When should QTc be measured?
A: QTc should be measured in patients taking medications that prolong QT interval, those with syncope, or with family history of sudden cardiac death.

Q4: Are there limitations to Bazett's formula?
A: Bazett's formula may overcorrect at high heart rates and undercorrect at low heart rates. Other formulas (Fridericia, Framingham) may be used in specific situations.

Q5: How is QT interval measured on ECG?
A: QT is measured from the beginning of the QRS complex to the end of the T wave, typically in lead II or V5. The longest QT across measurable leads should be used.