Figure 12.

Block at a structural heterogeneity depends on the difference in Gj between the proximal and the distal sides of the heterogeneity. Changes in I_Na current peak for double premature impulses, with different coupling intervals (S2S3), as the impulses propagate away from the stimulation site (x = 0 mm), in a preparation with a structural heterogeneity with average cell-to-cell coupling Gj = 0.41 μS in the proximal side and Gj = 2.47 μS in the distal side (λ_distal/λ_proximal = 1.40, A) and Gj = 0.41 μS in the proximal side and Gj = 1.23 μS in the distal side (λ_distal/λ_proximal = 1.3, B). Also shown, for reference, are the changes in I_Na current peak for the single premature impulse (S1S2 = 200 ms) initiated before the double premature impulses. The dashed vertical line indicates the location of the heterogeneity. Note that when λ_distal/λ_proximal = 1.4 the window of vulnerability is 2–3 ms (S2S3 = 170–171 ms, A) and that when λ_distal/λ_proximal = 1.3 there is no block at the heterogeneity for any S2S3 coupling interval (B).