Electrophysiology And Arrhythmia Scores

QTc Fridericia Calculator

Clinical calculation support · Verify results before clinical use

Calculate the heart-rate corrected QT interval using the Fridericia formula (QTcF).

QT Interval (ms) Enter the measured QT interval from the ECG in milliseconds.

Heart Rate (bpm) Enter the heart rate corresponding to the measured QT interval.

Sex for QTc Interpretation Sex-specific adult reference thresholds are used for interpretation.

About QTc Fridericia

The Fridericia method corrects the measured QT interval for heart rate using the cube root of the RR interval.

QTcF = QT / RR^1/3

QT is expressed in milliseconds (ms), while RR must be expressed in seconds. In this calculator, RR is derived from heart rate using RR = 60 / HR.

Fridericia is one of the established heart-rate correction methods and is commonly used in clinical pharmacology and QT/QTc assessment. However, no single correction formula is universally optimal across all heart rates and clinical situations.

Adult QTc Reference Thresholds

The AHA/ACCF/HRS recommendations describe practical adult thresholds for considering QT prolongation as:

Adult men >450 ms

Adult women ≥460 ms

These are practical adult reference thresholds and should not be interpreted as a standalone diagnosis of congenital long-QT syndrome or as a complete assessment of arrhythmic risk.

Important Clinical Considerations

QT measurement should be visually reviewed on the ECG, particularly when automated measurements are used.

Rate correction may be unreliable when RR interval variability is substantial, such as in atrial fibrillation. A single heart rate may not adequately represent the underlying RR variability in such situations.

QTc interpretation should also consider the clinical context, ECG quality, measurement method, medications, electrolyte abnormalities, conduction abnormalities, and other relevant patient factors.

References

1. Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469-486.

2. Rautaharju PM, Surawicz B, Gettes LS, et al. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part IV: The ST Segment, T and U Waves, and the QT Interval. Circulation. 2009;119:e241-e250.

3. International Council for Harmonisation (ICH). E14: Clinical Evaluation of QT/QTc Interval Prolongation and Proarrhythmic Potential for Non-Antiarrhythmic Drugs.

This calculator is intended for educational and clinical reference purposes. It does not replace direct ECG review or professional clinical judgment.