1. What is the Mayo Clinic QTc Calculator?

The Mayo Clinic QTc Calculator uses Bazett's formula to correct the QT interval for heart rate, with additional adjustments for rhythm, gender, age, and QRS duration. It provides a more accurate assessment of cardiac repolarization.

2. How Does the Calculator Work?

The calculator uses Bazett's formula with clinical adjustments:

Where:

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

Clinical Adjustments: The calculator applies additional adjustments for wide QRS (×0.95), female gender (×1.03), age >60 years (×0.98), and irregular rhythm (×1.02) based on Mayo Clinic protocols.

3. Importance of QTc Calculation

Details: Accurate QTc calculation is crucial for assessing risk of arrhythmias, monitoring drug effects, and evaluating patients with congenital or acquired long QT syndrome.

4. Using the Calculator

Tips: Enter QT interval in milliseconds, heart rate in bpm, select gender, age, rhythm regularity, and QRS duration. All values must be valid (QT > 0, HR > 0).

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 >480 ms indicate high risk for arrhythmias.

Q2: Why are adjustments needed for wide QRS?
A: Wide QRS prolongs the QT interval but doesn't necessarily reflect prolonged repolarization, so adjustment improves accuracy.

Q3: How does age affect QTc?
A: QTc tends to increase slightly with age, but significant prolongation may indicate pathology.

Q4: When should QTc be measured?
A: QTc should be measured in lead II or V5 where T waves are most prominent, and averaged over 3-5 beats.

Q5: Are there limitations to Bazett's formula?
A: Bazett's formula may overcorrect at high heart rates and undercorrect at low heart rates. Alternative formulas (Fridericia, Hodges) may be used in specific situations.