Jinsi ya kukokotoa Corrected QT
Corrected QT ni nini?
QTc normalises the QT interval for heart rate. Prolonged QTc (>450ms men, >470ms women) signals risk of torsades de pointes, a potentially fatal arrhythmia.
Fomula
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)
Mwongozo wa Hatua kwa Hatua
- 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
Mifano Iliyotatuliwa
Ingizo
QT = 380ms, HR = 60 bpm (RR = 1.0s)
Matokeo
QTc (Bazett) = 380ms — Normal
Maswali yanayoulizwa mara kwa mara
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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