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Figure 3 Main automatic QT measurement techniques. From top to bottom: threshold method applied to the original T wave (TH), or to its differential (DTH), tangent method with a tangent to the steepest point of the descending limb of the T wave (SI), tangent method with a line through the T wave peak and the maximum slope point (PSI). (Reproduced with permission from McLaughlin NB, et al. Comparison of automatic QT measurement techniques in the normal 12 lead electrocardiogram. Br Heart J 1995;74:84–89).