1. What is QTc Interval?

The QTc (Corrected QT) interval is a heart rate-corrected measurement of the QT interval from an electrocardiogram (ECG). It represents the time from the start of the Q wave to the end of the T wave, adjusted for heart rate using Bazett's formula.

2. How Does the Calculator Work?

The calculator uses 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, providing a standardized measurement that can be compared across different heart rates.

3. Importance of QTc Calculation

Details: QTc interval measurement is crucial for assessing cardiac repolarization and identifying potential risk for arrhythmias, particularly torsades de pointes. Prolonged QTc intervals may indicate increased risk of sudden cardiac death.

4. Using the Calculator

Tips: Enter the measured QT interval in milliseconds and heart rate in beats per minute. Both values must be valid positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

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

Q2: Why is QTc correction important?
A: The QT interval naturally varies with heart rate. Correction allows for comparison of QT intervals at different heart rates and helps identify abnormal repolarization.

Q3: 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.

Q4: When should QTc be measured?
A: QTc should be measured in patients taking medications that may prolong QT interval, those with syncope, or when arrhythmia risk assessment is needed.

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