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QTc normalises the QT interval for heart rate. Prolonged QTc (>450ms men, >470ms women) signals risk of torsades de pointes, a potentially fatal arrhythmia.
Formula
QTc (Bazett) = QT (ms) / √RR (seconds); QTc (Fridericia) = QT / ∛RR; Normal < 450 ms (men), < 460 ms (women)
- QT
- QT interval duration (Milliseconds)
- RR
- RR interval (heart rate) (Seconds)
- QTc
- Corrected QT interval (Milliseconds)
Guida passo passo
- 1Bazett: QTc = QT / √RR (RR in seconds)
- 2Fridericia: QTc = QT / RR^(1/3) — more accurate
- 3RR (sec) = 60 / HR (bpm)
- 4Critical: QTc > 500ms requires urgent review
Esempi risolti
Ingresso
QT = 380ms, HR = 60 bpm (RR = 1.0s)
Risultato
QTc (Bazett) = 380ms — Normal
Domande frequenti
Why correct QT for heart rate?
QT interval shortens with faster heart rate. Raw QT depends on HR. Correction isolates intrinsic QT duration. Allows comparison across patients/time.
What does prolonged QTc mean?
Risk factor for torsades de pointes (dangerous arrhythmia). Causes: medications (antipsychotics, antibiotics, antiemetics), electrolyte abnormalities (K, Ca, Mg), congenital (Long QT syndrome).
When should I check QTc?
Baseline ECG before starting QT-prolonging medications. Repeat if adding second drug, or symptoms (syncope, palpitations). Monitor electrolytes (K, Mg critical).
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