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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 provides the corrected QT interval (QTc) which allows comparison of QT values across different heart rates.
The calculator uses Bazett's formula:
Where:
Explanation: The formula corrects the QT interval for heart rate by dividing by the square root of the RR interval, which represents the time between successive heartbeats.
Details: QTc calculation is essential for assessing cardiac repolarization and identifying potential arrhythmia risks. Prolonged QTc intervals may indicate increased risk of life-threatening ventricular arrhythmias.
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 divided by heart rate (HR 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: How do I measure the RR interval?
A: The RR interval can be measured from ECG as the time between two consecutive R waves, or calculated as RR = 60 / HR, where HR is heart rate in beats per minute.
Q3: Are there limitations to Bazett's formula?
A: Yes, Bazett's formula tends to overcorrect at high heart rates and undercorrect at low heart rates. Other formulas like Fridericia's may be used in certain cases.
Q4: When should QTc be measured?
A: QTc should be measured in patients taking medications that may prolong QT interval, in those with syncope or family history of sudden cardiac death, and in routine cardiac assessments.
Q5: What factors can affect QT interval?
A: Medications, electrolyte imbalances (especially potassium, calcium, magnesium), heart rate, age, gender, and underlying cardiac conditions can all affect QT interval duration.