1. What is QTc Calculation?

The QTc (Corrected QT Interval) calculation adjusts the measured QT interval for heart rate using Bazett's formula. This is essential when assessing for prolonged QT, particularly before starting QT-prolonging drugs.

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 measure that can be compared across different heart rates.

3. Importance of QTc Calculation

Details: Accurate QTc calculation is crucial for identifying prolonged QT intervals, which can increase the risk of life-threatening arrhythmias like torsades de pointes, especially when initiating medications known to prolong QT.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: When should QTc be calculated?
A: QTc should be calculated when assessing for prolonged QT, particularly before starting medications known to prolong the QT interval.

Q2: What are normal QTc values?
A: Normal QTc is generally <450 ms for men and <470 ms for women. Values above these thresholds may indicate prolonged QT syndrome.

Q3: Are there limitations to Bazett's formula?
A: Yes, Bazett's formula may overcorrect at high heart rates and undercorrect at low heart rates. Alternative formulas like Fridericia's may be used in certain situations.

Q4: What factors can affect QT interval?
A: Electrolyte imbalances, certain medications, genetic factors, and various medical conditions can affect the QT interval.

Q5: When is QTc prolongation clinically significant?
A: QTc prolongation is clinically significant when it exceeds 500 ms or increases by more than 60 ms from baseline, as this significantly increases the risk of torsades de pointes.