QT interval: how to measure it and what is "normal".

Abnormally long and short QT intervals have been shown to be associated with an increased risk for life-threatening ventricular arrhythmias and sudden cardiac death. In recent years, various methods for QT-interval measurement have been developed, including individual-based corrections for repolarization duration, quantitative assessment of repolarization morphology, correction for repolarization dynamicity, and analysis of repolarization variability. However, these methods require computer-processed digital-signal analysis of electronically stored ECG data and have been used most frequently in the assessment of repolarization changes in drug trials. In the present review, we will focus on methods for clinically relevant visual and manual assessment of QT-interval duration from a 12-lead ECG, which can be utilized in day-today practice for the diagnosis of long QT syndrome (LQTS) and other repolarization disorders.