Kaip apskaičiuoti Corrected QT
Kas yra Corrected QT?
QTc normalises the QT interval for heart rate. Prolonged QTc (>450ms men, >470ms women) signals risk of torsades de pointes, a potentially fatal arrhythmia.
Formulė
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)
Žingsnis po žingsnio vadovas
- 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
Worked Examples
Įvestis
QT = 380ms, HR = 60 bpm (RR = 1.0s)
Rezultatas
QTc (Bazett) = 380ms — Normal
Frequently Asked Questions
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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