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Bazett's Formula:
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Bazett's formula is the most commonly used method for correcting the QT interval for heart rate. It calculates the heart rate-corrected QT interval (QTc) to standardize QT measurements across different heart rates.
The calculator uses Bazett's formula:
Where:
Explanation: The formula accounts for the inverse relationship between heart rate and QT interval duration, providing a standardized measure of ventricular repolarization.
Details: QTc calculation is essential for assessing cardiac repolarization abnormalities. Prolonged QTc intervals are associated with increased risk of life-threatening arrhythmias, particularly torsades de pointes.
Tips: Enter QT interval in milliseconds (ms) and RR interval in seconds (s). Both values must be positive numbers. The RR interval can be calculated as 60 / HR (where HR is heart rate in bpm).
Q1: What is a normal QTc value?
A: Normal QTc values are typically less than 440 ms for men and less than 460 ms for women. Values above these thresholds may indicate prolonged QT syndrome.
Q2: Why use RR interval instead of heart rate?
A: The RR interval (time between successive R waves) is the direct measurement used in the formula, though heart rate can be converted to RR interval using RR = 60 / HR.
Q3: What are the limitations of Bazett's formula?
A: Bazett's formula may overcorrect at high heart rates and undercorrect at low heart rates. Other formulas (Fridericia, Framingham) may be more appropriate in certain populations.
Q4: When should QTc be measured?
A: QTc should be measured in patients taking medications that prolong QT interval, those with syncope or palpitations, and individuals with family history of sudden cardiac death.
Q5: How is RR interval measured?
A: RR interval is measured on ECG as the time between two consecutive R waves. It can be calculated from heart rate using the formula: RR (s) = 60 / HR (bpm).