QTc calculator (Bazett, Fridericia and Framingham)
Enter your values. The answer and the full worked solution update as you type.
Result
Bazett over-corrects at fast heart rates and under-corrects at slow ones; Fridericia and Framingham are more accurate away from 60 beats/min. For exam practice only. This is a study aid, never a clinical decision: always follow the prescription, local protocols and the product information.
Correct the QT interval for heart rate. Enter the measured QT in milliseconds and the heart rate or the RR interval; the calculator gives the QTc with the Bazett, Fridericia and Framingham formulas side by side and compares the result with the usual limits for men and women. Each formula is worked out with your numbers.
Step-by-step solution
RR interval in seconds
Bazett
Other formulas
Interpretation
Key formulas
- Heart rate, regular rhythm
- 300 ÷ large boxes = 1500 ÷ small boxes = 60 ÷ RR (s)
- QTc (Bazett)
- QT/√RR
- QTc (Fridericia)
- QT/∛RR
- QTc (Framingham)
- QT + 154·(1 − RR)
How to calculate the QTc
- Measure the QT interval from the start of the QRS complex to the end of the T wave, in ms.
- Find the RR interval in seconds: RR = 60 ÷ heart rate, or measure it between two R waves (1 small square = 0.04 s at 25 mm/s).
- Bazett: QTc = QT/√RR. Fridericia: QTc = QT/∛RR. Framingham: QTc = QT + 154 × (1 − RR), with QT in ms and RR in s.
- Compare: a QTc of 450 ms or more in men or 460 ms or more in women is prolonged, 500 ms or more is markedly prolonged, and 390 ms or less is short.
Questions and answers
Which QTc formula is best?
Bazett (1920) is the most widely taught, but it over-corrects at fast heart rates and under-corrects at slow ones. Fridericia (1920) and the Framingham formula (Sagie and colleagues, 1992) are more accurate away from 60 beats/min.
Where do the limits come from?
From the AHA/ACCF/HRS recommendations for the standardisation and interpretation of the electrocardiogram (Rautaharju and colleagues, 2009): a QTc of 450 ms or more in men and 460 ms or more in women is prolonged, and 390 ms or less is short.
Why does a long QTc matter?
A prolonged QT increases the risk of torsades de pointes, a dangerous ventricular arrhythmia. Many medicines can lengthen it, which is why it comes up in pharmacology and ECG exams.
What is the QTc at 60 beats/min?
The RR interval is then exactly 1 s, so all three formulas give QTc = QT.
Practise it yourself
Practise ECG rhythm strip interpretation
A calculator gives the answer. In the exam you need the method: practise it with new problems, hints and worked solutions.