1. What is QTc Calculation in Atrial Fibrillation?

The Fridericia formula is used to calculate corrected QT interval (QTc) in atrial fibrillation, using the average RR interval over 10 beats. This correction accounts for heart rate variations to provide a standardized QT measurement.

2. How Does the Calculator Work?

The calculator uses the Fridericia formula:

Where:

• \( QT \) — QT interval measured from start of Q wave to end of T wave (ms)
• \( RR \) — Average RR interval = 60 / HR (seconds)
• \( HR \) — Heart rate (beats per minute)

Explanation: The cube root correction (³√RR) provides a more accurate QT correction for heart rate, especially useful in atrial fibrillation where RR intervals vary.

3. Importance of QTc Calculation

Details: Accurate QTc measurement is crucial for assessing cardiac repolarization, identifying risk of arrhythmias, and monitoring drug effects that may prolong QT interval.

4. Using the Calculator

Tips: Enter QT interval in milliseconds and heart rate in beats per minute. Use average values from ECG measurements for accurate results.

5. Frequently Asked Questions (FAQ)

Q1: Why use Fridericia formula in atrial fibrillation?
A: Fridericia formula with average RR over 10 beats provides more reliable QTc calculation in AFib where RR intervals are irregular.

Q2: What are normal QTc values?
A: Normal QTc is typically <440 ms for men and <460 ms for women. Values >500 ms indicate high risk for torsades de pointes.

Q3: How to measure QT interval accurately?
A: Measure from start of Q wave to end of T wave in lead II or V5, using the tangent method for T wave end determination.

Q4: When is QTc most important to calculate?
A: Essential when prescribing QT-prolonging medications, in patients with syncope, or when assessing arrhythmia risk.

Q5: Are there limitations to Fridericia formula?
A: While better than Bazett's formula at extreme heart rates, all QT correction formulas have limitations and clinical correlation is always needed.