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Corrected QT interval accounts for heart rate, predicting arrhythmia risk. QTc >460 ms females, >450 ms males increases torsades risk.
Fórmula
Apply Bazett formula: QTc = QT / √RR (RR in seconds)
- QT
- QT value — Variable used in the calculation
- RR
- RR value — Variable used in the calculation
Guia passo a passo
- 1Measure QT interval from ECG
- 2Apply Bazett formula: QTc = QT / √RR (RR in seconds)
- 3Or use other formulas for extreme heart rates
Exemplos resolvidos
Entrada
QT 420 ms, HR 80 (RR 0.75 s)
Resultado
QTc ≈ 420/√0.75 ≈ 485 ms (prolonged)
Elevated arrhythmia risk
Erros comuns a evitar
- ✕Using Bazett formula at extreme heart rates (use Fridericia for HR >100)
- ✕Forgetting electrolyte abnormalities (low K, Mg, Ca) prolong QT
Perguntas frequentes
Which drugs prolong QT?
Antiarrhythmics, antipsychotics, antiemetics, fluoroquinolones, and many others. Check before prescribing.
What QTc values are safe?
<450 ms males, <460 ms females normal; 450-480 borderline; >500 ms high torsades risk.
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