Corrected QT (Bazett)

The QT interval on an ECG changes with heart rate, so Bazett’s correction rescales the measured QT by the square root of the RR interval to estimate what the QT would be at a standardized rate. This helps distinguish a truly prolonged repolarization time from a QT that only looks long because the heart is beating slowly, or short because it is beating quickly. The correction comes from an empirical relationship observed in many patients, so it is useful clinically, though it is not perfect at very high or very low heart rates.

Use this when interpreting an ECG to compare QT length across different heart rates, especially when screening for QT prolongation or monitoring medications that affect ventricular repolarization. It is commonly used in cardiology, emergency medicine, and pharmacology studies involving arrhythmia risk.

• Using QT and RR in mixed units, such as milliseconds for one and seconds for the other
• Confusing RR interval with heart rate in beats per minute
• Assuming Bazett correction is equally accurate at all heart rates, especially extremes