Corrected QT Interval (QTc)
Calculate the rate-corrected QT interval using Bazett's formula (Heart, 1920). Used in cardiology to screen for long QT syndrome. Normal QTc: < 450 ms (male), < 460 ms (female).
Results
What is it?
Calculates the rate-corrected QT interval using Bazett's formula: QTc = QT / √(RR interval). Published in Heart (1920), this correction normalizes the QT interval for heart rate, enabling screening for long QT syndrome — a condition predisposing to potentially fatal arrhythmias (Torsades de Pointes).
How to use
Enter the measured QT interval (in milliseconds from the ECG) and the resting heart rate (in bpm). The calculator converts heart rate to the RR interval in seconds (60/HR) and applies Bazett's correction.
Example scenario
QT = 400 ms at a heart rate of 75 bpm: RR = 60/75 = 0.800 sec, QTc = 400 / √0.800 = 447 ms. For a male patient, this is borderline (normal < 450 ms). At a heart rate of 60 bpm, the same QT gives QTc = 400 ms (normal).
Pro tip
Bazett's formula overcorrects at high heart rates (> 100 bpm) and undercorrects at low rates (< 60 bpm). For tachycardic patients, consider Fridericia's correction (QT / ∛RR). Always review QTc in context of QT-prolonging medications (antiarrhythmics, certain antibiotics, antipsychotics).