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Figure 2 QT dispersion as a result of both different real duration and different measurable duration of QT intervals. Two hypothetical T waves of the same amplitude have different offset (dashed lines) when the heart vector becomes perpendicular to the axis of one of the leads. This results in "real" dispersion of the QT intervals (vertical dashed lines). In addition, different proportion of the final part of the two T waves is below the threshold level (e.g., with an automatic threshold method). This leads to the measured dispersion of the QT intervals (vertical solid line), which is different from the real dispersion.