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Figure 1 Effect of the shape of the T loop on the QT interval measurement in a hypothetical lead. Projections of T loops with different shapes and at different angles to the axis of the lead result in T waves with different amplitude and morphology. Only an insignificant proportion of the final part of a T wave with high amplitude may be unmeasurable because of falling into the noise band (A); T waves with smaller amplitude as a result of wider T loop (C) or elongated loop at different angle (B), have a greater proportion of their final parts falling into the noise band. Thus, the measurable QT interval can almost coincide with the real end of repolarization (A), or be significantly smaller (B,C). Points 1, 2 and 3 indicate three time instants of the T loop and of the T wave. (Reproduced with permission from Kors et al. QT dispersion as an attribute of T-Loop morphology. Circulation 1999;99:458–63.)
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