Should the JT rather than the QT interval be used to detect prolongation of ventricular repolarization? An assessment in normal conduction and in ventricular conduction defects.

It has been suggested that the JT rather than QT interval properly reflects repolarization duration in ventricular conduction defects (VCD). The authors examined the influence of QRS duration on the JT and QT intervals in 20,687 normal adult subjects and 2,865 subjects with various categories of VCD. Estimates for coefficients for multiple regression of QRS duration on QT and JT intervals combined with a correction term for heart rate (HR) were determined for each VCD category. QRS duration accounted for about 16% of total QT variation, but had a practically negligible effect on JT interval in complete bundle branch blocks. A single-parameter formula was derived for the JT prolongation index of the form JTI = JT(HR + 100)/518, with a JTI > or = 112 identifying repolarization prolongation in all VCD categories. It is concluded that it is preferable to predict JT rather than QT as a more appropriate index of duration of repolarization in VCD.