1. What is QTc Calculation?

The QTc (Corrected QT Interval) calculation adjusts the measured QT interval for heart rate using Bazett's formula. This provides 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 (seconds)
• \( HR \) — Heart rate (beats per minute)

Normal Ranges:

• Men: <440 ms
• Women: <460 ms

3. Importance of QTc Calculation

Details: QTc prolongation is associated with increased risk of ventricular arrhythmias, particularly torsades de pointes. Accurate QTc measurement is essential for cardiac risk assessment and medication safety monitoring.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: Why correct QT interval for heart rate?
A: The QT interval naturally shortens with increasing heart rate. Correction allows comparison of QT values across different heart rates.

Q2: What is considered a dangerously prolonged QTc?
A: QTc > 500 ms is associated with significantly increased risk of torsades de pointes and requires immediate attention.

Q3: Are there alternative correction formulas?
A: Yes, other formulas include Fridericia's (QTc = QT/RR^1/3) and Framingham (QTc = QT + 0.154*(1-RR)), but Bazett's is most commonly used.

Q4: When should QTc be measured?
A: QTc should be measured when starting medications that may prolong QT interval, in patients with syncope, or with family history of sudden cardiac death.

Q5: What factors can affect QTc measurement?
A: Electrolyte imbalances, medications, myocardial ischemia, and autonomic nervous system activity can all affect QTc duration.