QTc Calculator
Corrects the QT interval for heart rate to assess risk for Torsades de Pointes.
Clinical Significance
Prolongation of the QTc interval indicates delayed ventricular repolarization, which increases the risk of early afterdepolarizations and Torsades de Pointes (TdP) — a potentially fatal ventricular arrhythmia.
Normal Ranges (99th percentile)
- Adult Males: < 440 ms (Prolonged if > 450 ms)
- Adult Females: < 460 ms (Prolonged if > 470 ms)
- Extreme Risk: QTc > 500 ms in either sex represents a high risk for TdP.
Choosing a Formula
Bazett's formula is the most widely used historically and is built into most ECG machines. However, it over-corrects at high heart rates (making QTc seem falsely prolonged) and under-corrects at low heart rates.
Fridericia's formula is preferred by the FDA and many cardiologists for heart rates outside the normal 60-90 bpm range.