MDCalc QT Correction

Bazett Formula:

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

Corrected QT (QTc):

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1. What is QT Correction?

QT correction (QTc) is a calculation that adjusts the measured QT interval for heart rate, allowing for comparison of QT values across different heart rates. The Bazett formula is the most commonly used method for this correction.

2. How Does the Calculator Work?

The calculator uses the Bazett formula:

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

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)

Explanation: The formula normalizes the QT interval to a standard heart rate of 60 bpm, allowing for consistent interpretation across different heart rates.

3. Importance of QTc Calculation

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

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: Why use Bazett formula for QT correction?
A: Bazett formula is the most widely used and recognized method for QT correction in clinical practice, though it may overcorrect at high heart rates.

Q2: What are normal QTc values?
A: Normal QTc values are typically <440 ms for men and <460 ms for women. Values >500 ms are associated with increased risk of torsades de pointes.

Q3: When should QT measurement be performed?
A: QT interval should be measured during electrocardiogram (ECG) assessment, preferably from lead II or V5 where the T wave is most clearly defined.

Q4: Are there limitations to the Bazett formula?
A: The Bazett formula tends to overcorrect at high heart rates and undercorrect at low heart rates. Alternative formulas (Fridericia, Framingham) may be used in specific situations.

Q5: Should QTc be used for medication monitoring?
A: Yes, QTc monitoring is essential for patients taking medications known to prolong QT interval, such as certain antibiotics, antipsychotics, and antiarrhythmics.