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Formula
Adjusts the QT interval for heart rate to identify risk of dangerous arrhythmias.
Worked Example
Why Correct the QT Interval?
- Bazett's: QTc = QT / √RR (most common, but overcorrects at high HR)
- Fridericia's: QTc = QT / ∛RR (often preferred at higher heart rates)
- Normal QTc is usually < 440ms in men and < 460ms in women
- Prolonged QTc (>500ms) is associated with an increased risk of ventricular arrhythmias like Torsades de Pointes
The QTc is only one part of an ECG assessment. Clinical context, electrolyte levels, and medications MUST be considered when evaluating a prolonged QT.
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Frequently Asked Questions
What is QTc?
QTc is the QT interval of your heart rhythm adjusted for your heart rate. It helps doctors see if the heart's electrical recharging system is functioning properly regardless of how fast the heart is beating.
Which formula should I use?
Bazett's is the most traditional. Fridericia's is often considered more accurate for patients with very fast or very slow heart rates.
What is a dangerous QTc level?
Generally, a QTc over 500ms is considered high risk for clinical problems, though individual targets vary.
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