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

Other ECG Recording Techniques

Holter and exercise testing have also been used to evaluate the QT interval. Holter monitoring is not sufficiently well standardized to serve in the primary assessment for ventricular repolarization analysis. However, we sometimes employ this method for the detection of extreme QT-interval events that occur infrequently during the day. Since QT intervals measured using the Holter methodology do not correspond quantitatively to those for standard ECGs, data obtained from the two methodologies are not suitable for direct comparison. Exercise testing with a standard activity protocol can be used for evaluation of QT prolongation during exercise and recovery periods. Intermittent 12-lead ECGs or continuous multichannnel ECG recordings can be used. However, the adaptation of QT-interval duration to heart rate is not instantaneous, and substantial errors may be introduced if nonstationary episodes are analyzed.

Recent analysis from the International LQTS Registry demonstrates that there is individual subject variability in QTc duration on repeat ECGs during long-term follow-up extending over several years. Therefore, we suggest that several ECGs recorded over time should be more useful in identifying subjects with abnormally long or short QT intervals than simply one baseline ECG recording.