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Figure 9: Anisotropic propagation of graded responses (GR). Plot (mean ± SD of ten tissue samples) shows effects of distance from cathodal pole of S2 source (abscissa) on GR (ordinate). Open circles, GR amplitude along fiber; solid circles, across it. S2 current strength was 50 mA and coupling interval 140 ms. Recordings below double-headed arrow (fiber orientation) are sequential action potential recordings along fiber from cells at increasing distances (1-6mm) from S2 stimulus site (asterisk). Vertical recordings are from cells across fiber orientation toward top of tissue

Figure 9: Anisotropic propagation of graded responses (GR). Plot (mean ± SD of ten tissue samples) shows effects of distance from cathodal pole of S2 source (abscissa) on GR (ordinate). Open circles, GR amplitude along fiber; solid circles, across it. S2 current strength was 50 mA and coupling interval 140 ms. Recordings below double-headed arrow (fiber orientation) are sequential action potential recordings along fiber from cells at increasing distances (1-6mm) from S2 stimulus site (asterisk). Vertical recordings are from cells across fiber orientation toward top of tissue real electrode depolarization and virtual electrode hyperpolarization replicated the figure-8 reentry that was observed with bipolar stimulation in isolated canine epicardial tissue slices.56 Furthermore, these findings demonstrate that the graded response hypothesis of reentry, first formulated using bipolar stimulation, is also operative for unipolar stimulation.56

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