Fig 7. Conduction during reduced excitability.

(a) Reduction of excitability via sodium channel blockade with TTX in experimental monolayer results in a significant reduction in conduction velocity (n = 3–6 monolayers; mean ± se; main effect of TTX: F(1,46) = 24.02. p < 0.001; main effect of ratio: F(6,46) = 3.58. p = 0.007; interaction effect: F(6,46) = 0.38. p > 0.1). Conduction could not be reliably sustained at an obstacle-to-strand ratio of 7 and was meandering and irregular with numerous wavebreaks at an obstacle-to-strand ratio of 5. Simulated conduction with reduced excitability replicates experimental behavior at obstacle-to-strand ratios of up to 1.5, but exhibits conduction block at a ratio of 3.0 (n = 10 simulated monolayers per case; mean ± se) (b) Reduced excitability resulted in a reversal of the isochrones flattening observed at large obstacle-to-strand ratios. (n = 3–10 monolayers; mean ± sd; main effect of TTX: F(1,82) = 2.77. p = 0.101; main effect of ratio: F(4,82) = 5.21. p = 0.001; interaction effect: F(4,82) = 4.75. p < 0.002; * indicates significant difference between experimental control and experimental TTX, p < 0.05). Qualitatively similar changes in wavefront curvature are observed in simulations. (c-e). These changes can be attributed to globally reduced strand conduction velocity (c), in conjunction with increased activation delay at branch points along the principal axes (d) and minimal change in collision-induced acceleration along the diagonal (e).