QT Interval: How to Measure It and What Is "Normal"

Ilan Goldenberg, M.D.; Arthur J. Moss, M.D.; Wojciech Zareba, M.D., Ph.D.


J Cardiovasc Electrophysiol. 2006;17(3):333-336. 

In This Article

Normal Values of the QT Interval (12-Lead ECG)

Bazett's formula has been more frequently used in medical publications than Fridericia's formula. Therefore, most reported criteria for normal and abnormal values for QTc are derived from Bazett's formula. Our research group has utilized digitized data file for QT- and RR-interval measurements on 581 healthy individuals: 158 children aged 1-5 years (80 boys and 78 girls) and 423 adults aged 16-81 years (223 men and 200 women). Using this data set, we evaluated the range of Bazett QTc values by age and gender. The QTc values were stable for children, with no gender difference, while there was a significant difference between adult men and women in this healthy population.[2] A suggested three-level classification based on this analysis is presented in Table 2 .

A simple graphical display of lower and upper limits of QT interval for different RR cycle lengths based on population studies has been developed in our laboratory (Fig. 2). The data can be used by clinicians for reference purposes.

Figure 2.

Lower and upper limits of QT interval for different RR cycle lengths based on QT-interval measurements in normal healthy subjects.