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QTc Formula:
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The QTc (corrected QT interval) is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle, adjusted for heart rate. Bazett's formula is the most commonly used method for this correction.
The calculator uses Bazett's formula:
Where:
Explanation: The formula adjusts the QT interval for heart rate by dividing by the square root of the RR interval, providing a rate-corrected value that can be compared across different heart rates.
Details: Accurate QTc calculation is crucial for assessing cardiac repolarization, identifying prolonged QT intervals that may indicate increased risk of ventricular arrhythmias, and monitoring patients on medications that affect cardiac conduction.
Tips: Enter QT interval in milliseconds, RR interval in seconds. Both values must be positive numbers. The RR interval should be measured from consecutive R waves on the ECG.
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 may indicate prolonged QT syndrome.
Q2: Why use Bazett's formula?
A: Bazett's formula is the most widely used and clinically validated method for QT correction, though it may overcorrect at very high heart rates.
Q3: When should QTc be measured?
A: QTc should be measured in patients with suspected arrhythmias, those taking medications known to prolong QT interval, and in routine cardiac assessments.
Q4: Are there limitations to Bazett's formula?
A: The formula may be less accurate at extreme heart rates (very fast or very slow) and alternative formulas (Fridericia, Framingham) may be used in these cases.
Q5: What clinical conditions affect QTc?
A: Various conditions including congenital long QT syndrome, electrolyte imbalances, and certain medications can prolong QTc and increase arrhythmia risk.