MDCalc Corrected QT

Bazett Formula:

\[ QTc = \frac{QT}{\sqrt{RR}} \]

Corrected QT (QTc):

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1. What Is The MDCalc Corrected QT?

The MDCalc Corrected QT calculator uses the Bazett formula to adjust the QT interval for heart rate, providing a standardized measure of ventricular repolarization that accounts for variations in heart rate.

2. How Does The Calculator Work?

The calculator uses the Bazett formula:

\[ QTc = \frac{QT}{\sqrt{RR}} \]

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 formula corrects the measured QT interval for heart rate by dividing by the square root of the RR interval, providing a rate-independent measure of ventricular repolarization.

3. Importance Of QTc Calculation

Details: Accurate QTc calculation is essential for assessing risk of arrhythmias, monitoring drug effects on cardiac repolarization, and evaluating patients with suspected long QT syndrome.

4. Using The Calculator

Tips: Enter QT interval in milliseconds and heart rate in beats per minute. Both values must be positive numbers for accurate calculation.

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 may indicate prolonged QT syndrome.

Q2: Why use Bazett formula instead of other corrections?
A: Bazett is the most widely used and clinically validated formula, though it may overcorrect at very high heart rates and undercorrect at very low heart rates.

Q3: When should QTc be measured?
A: QTc should be measured in patients taking medications that affect QT interval, those with syncope or palpitations, and in screening for congenital long QT syndrome.

Q4: Are there limitations to the Bazett formula?
A: The formula may be less accurate at extreme heart rates (<40 bpm or >120 bpm) and in certain patient populations where alternative formulas might be preferred.

Q5: How should multiple QT measurements be handled?
A: When multiple measurements are available, use the average of several beats from the same lead for improved accuracy, typically lead II or V5.