1. What is QTc Prolongation?

QTc prolongation refers to a heart-rate corrected QT interval that is longer than normal. It assesses risk for dangerous arrhythmias, particularly when QTc >500 ms.

2. How Does the Calculator Work?

The calculator uses the Bazett formula:

Where:

• \( QT \) — QT interval measured 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 to allow comparison across different heart rates.

3. Importance of QTc Calculation

Details: QTc prolongation >500 ms is associated with increased risk of torsades de pointes and sudden cardiac death. Monitoring is crucial for patients on medications that may prolong QT interval.

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 is typically <450 ms for men and <460 ms for women. Values >500 ms indicate high risk.

Q2: Why correct QT for heart rate?
A: QT interval naturally shortens with faster heart rates. Correction allows comparison across different heart rates.

Q3: When should QTc be measured?
A: QTc should be measured in patients taking medications known to prolong QT interval, and in those with symptoms suggesting arrhythmia.

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

Q5: What clinical actions are needed for prolonged QTc?
A: For QTc >500 ms, consider medication review, electrolyte correction, and cardiology consultation. Discontinue QT-prolonging drugs if possible.