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Figure 2 Mathematical simulation of effects of epicardial versus endocardial pacing on QT interval, T peak–T end (Tp-Te), and TDR. (Top) Homogeneous myocardium. QT interval, T peak–T end, and TDR are unchanged when pacing site is shifted from endocardium (Endo) (left) to epicardium (Epi) (right) (basic cycle length = 2,000 ms). (Bottom) Heterogeneous myocardium. QT interval, T peak–T end, and TDR all increase after reversal of direction of activation of the transmural cable. Modified and reprinted, with permission, from Fish et al. (5).