1. What is QTc Interval Calculation?

The QTc (Corrected QT) interval calculation using Bazett's formula adjusts the measured QT interval for heart rate, providing 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 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, providing a rate-independent measure of ventricular repolarization.

3. Importance of QTc Calculation

Details: Accurate QTc calculation is crucial for assessing risk of arrhythmias, monitoring drug effects (especially those that prolong QT interval), and evaluating cardiac repolarization abnormalities.

4. Using the Calculator

Tips: Enter QT interval in milliseconds and heart rate in beats per minute. Both values must be positive numbers.

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 may indicate prolonged QT interval.

Q2: Why is QTc prolongation dangerous?
A: QTc prolongation increases the risk of life-threatening ventricular arrhythmias, particularly torsades de pointes.

Q3: Are there limitations to Bazett's formula?
A: Yes, Bazett's formula tends to 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 when starting medications known to prolong QT interval, in patients with syncope or arrhythmias, and in those with family history of sudden cardiac death.

Q5: How should multiple QT measurements be handled?
A: When multiple measurements are available, use the average of several beats (usually 3-5) from the same lead for more accurate results.