1. What is the Mayo Clinic QTc Calculator?

The Mayo Clinic Corrected QT Interval (QTc) Calculator uses Bazett's formula with additional adjustments for rhythm, gender, age, and wide QRS to provide a more accurate assessment of cardiac repolarization time.

2. How Does the Calculator Work?

The calculator uses the Mayo Clinic adjusted Bazett's formula:

With Mayo Clinic adjustments:

• Subtract 20 ms for wide QRS (>120 ms)
• Add 6 ms for female gender
• Subtract 2 ms for age >50 years

Explanation: The equation corrects the measured QT interval for heart rate and incorporates demographic and clinical factors that affect QT interval duration.

3. Importance of QTc Calculation

Details: Accurate QTc calculation is crucial for assessing risk of arrhythmias, particularly torsades de pointes, and for monitoring patients on medications that prolong QT interval.

4. Using the Calculator

Tips: Enter QT interval in milliseconds, heart rate in beats per minute, select gender, enter age, and indicate if wide QRS is present. All values must be valid (QT > 0, HR > 0).

5. Frequently Asked Questions (FAQ)

Q1: Why use Mayo Clinic adjustments to Bazett's formula?
A: The Mayo Clinic adjustments improve accuracy by accounting for factors known to influence QT interval beyond just heart rate correction.

Q2: What are normal QTc values?
A: Normal QTc is typically <450 ms for men and <460 ms for women. Values >500 ms are associated with increased arrhythmia risk.

Q3: When should QTc be measured?
A: QTc should be measured in patients starting QT-prolonging medications, with electrolyte abnormalities, or with symptoms suggesting arrhythmia.

Q4: Are there limitations to this calculation?
A: Bazett's formula may overcorrect at high heart rates and undercorrect at low heart rates. Clinical correlation is always necessary.

Q5: How does wide QRS affect QT measurement?
A: Wide QRS prolongs the QT interval due to delayed ventricular depolarization, requiring adjustment for accurate repolarization assessment.