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QTc With Bundle Branch Block Formula:
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The QTc calculation with bundle branch block adjusts the measured QT interval for prolonged QRS duration caused by bundle branch block, providing a more accurate corrected QT interval that reflects true ventricular repolarization time.
The calculator uses the following formulas:
Where:
Explanation: The formula first adjusts the QT interval for bundle branch block by subtracting half of the QRS prolongation beyond 120ms, then applies standard Bazett's formula for heart rate correction.
Details: Accurate QTc calculation is crucial for assessing ventricular repolarization abnormalities, identifying long QT syndrome, and evaluating arrhythmia risk, especially in patients with bundle branch block where standard QTc calculation may be inaccurate.
Tips: Enter QT interval in milliseconds, QRS duration in milliseconds, and heart rate in beats per minute. All values must be positive numbers.
Q1: Why adjust QT for bundle branch block?
A: Bundle branch block prolongs the QRS duration, which artificially lengthens the QT interval. This adjustment removes the conduction delay component to assess true repolarization time.
Q2: What are normal QTc values?
A: Normal QTc is typically <450ms for men and <460ms for women. Values >500ms are associated with increased risk of torsades de pointes.
Q3: When should this correction be used?
A: This correction should be applied when calculating QTc in patients with bundle branch block (QRS >120ms) to obtain accurate repolarization assessment.
Q4: Are there limitations to this method?
A: This method may not be accurate in cases of extreme tachycardia or bradycardia, or in patients with complex conduction abnormalities.
Q5: How does this differ from standard QTc calculation?
A: Standard QTc calculation uses the measured QT interval directly, while this method first adjusts for the prolonged depolarization time caused by bundle branch block.