QTc Calculation (Bazett) Normal Range

Bazett's Formula:

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

Corrected QT Interval (QTc):

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1. What is QTc Calculation (Bazett)?

The Bazett formula is used to calculate the corrected QT interval (QTc), which adjusts the measured QT interval for heart rate. This is important because the QT interval varies with heart rate, and QTc provides a standardized measure for comparison across different heart rates.

2. How Does the Calculator Work?

The calculator uses Bazett's 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 (s)
\( HR \) — Heart rate (bpm)

Explanation: The formula corrects the QT interval for heart rate by dividing by the square root of the RR interval (in seconds).

3. Importance of QTc Calculation

Details: QTc calculation is crucial for assessing cardiac repolarization and detecting prolonged QT intervals, which can increase the risk of life-threatening arrhythmias such as torsades de pointes.

4. Using the Calculator

Tips: Enter QT interval in milliseconds and heart rate in beats per minute (bpm). Both values must be positive numbers. Normal range: 350-440 ms for adults; prolonged if >440 ms for men, >460 ms for women.

5. Frequently Asked Questions (FAQ)

Q1: What is the normal range for QTc?
A: Normal range is 350-440 ms for adults. QTc is considered prolonged if >440 ms in men or >460 ms in women.

Q2: Why is QTc important?
A: QTc helps identify patients at risk for ventricular arrhythmias and sudden cardiac death, particularly those with congenital or acquired long QT syndrome.

Q3: Are there limitations to Bazett's formula?
A: Yes, Bazett's formula may overcorrect at high heart rates and undercorrect at low heart rates. Other formulas (e.g., Fridericia, Hodges) may be used in specific situations.

Q4: When should QTc be measured?
A: QTc should be measured in patients taking medications that prolong QT interval, those with syncope or family history of sudden death, and in certain cardiac conditions.

Q5: How is QT interval measured on ECG?
A: QT interval is measured from the beginning of the QRS complex to the end of the T wave, typically in lead II or V5. The longest measurable QT interval across leads should be used.