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Mayo Clinic (Hodges) Formula:
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The Mayo Clinic (Hodges) formula is used to calculate the corrected QT interval (QTc) which accounts for heart rate variations. This correction is essential for accurate assessment of cardiac repolarization and detection of potential arrhythmia risks.
The calculator uses the Mayo Clinic (Hodges) formula:
Where:
Explanation: The formula linearly adjusts the measured QT interval to what it would be at a standard heart rate of 60 bpm, allowing for consistent interpretation across different heart rates.
Details: Accurate QTc calculation is crucial for assessing cardiac repolarization abnormalities, identifying long QT syndrome, evaluating drug safety, and monitoring patients with potential arrhythmia risks.
Tips: Enter the measured QT interval in milliseconds and heart rate in beats per minute. Both values must be valid positive numbers.
Q1: Why use the Mayo Clinic (Hodges) formula instead of Bazett's?
A: The Hodges formula provides more accurate correction at extreme heart rates and is less likely to overcorrect at high heart rates compared to Bazett's formula.
Q2: What are normal QTc values?
A: Normal QTc values are typically between 350-440 ms for men and 350-460 ms for women. Values above these ranges may indicate prolonged QT syndrome.
Q3: When should QTc be measured?
A: QTc should be measured in standard 12-lead ECGs, especially when evaluating patients for arrhythmia risk, before starting certain medications, or in patients with syncope or family history of sudden cardiac death.
Q4: Are there limitations to this formula?
A: While more accurate than Bazett's at extreme heart rates, all QT correction formulas have limitations and should be interpreted in clinical context with consideration of other factors.
Q5: How many measurements should be averaged?
A: For increased accuracy, measure multiple QT intervals (preferably 3-5 beats) and average them, using the same lead for consistency.