1. What is QTc?

QTc (Corrected QT interval) is a heart rate-corrected measurement of the QT interval from an electrocardiogram. It accounts for variations in heart rate to provide a standardized measure of ventricular repolarization.

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 Bazett formula is the most commonly used method for QT correction, though other formulas exist for specific populations.

3. Importance of QTc Calculation

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

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 <440 ms for men and <460 ms for women. Values above these thresholds may indicate prolonged QT syndrome.

Q2: Why use Bazett formula?
A: Bazett is the most widely used and recognized formula for QT correction, though it may overcorrect at high heart rates.

Q3: Are there alternative correction formulas?
A: Yes, other formulas include Fridericia, Framingham, and Hodges. Different formulas may be preferred in specific clinical situations.

Q4: 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.

Q5: What factors can affect QT interval?
A: Electrolyte imbalances, medications, heart disease, and genetic factors can all affect QT interval duration.