Figure 6.
Anisotropic medium: example of successful termination of the pinned spiral after the second stimulus has been delivered. The overdrive pacing protocol was applied, with (Tp=0.9Tsp) and t1=300 ms. In (a) the applied far field pulse is strong enough to exceed the excitation threshold and to induce a new wave nucleating from the heterogeneity. Since part of the boundary is still refractory due to the tail of the original spiral, only a small portion of the new wave is able to propagate. Within this part, one end disconnects from the obstacle because its propagation is inhibited by the refractory tail of the spiral, as shown in (b). The other end forms a pinned wave and collides with the tip of the original spiral (c,d). Panel (e) shows how this collision leads to the annihilation of the two waves and hence to the termination of the pinned spiral, as shown in figure 6f. The snapshots are taken at 3 ms (a), 14 ms (b), 34 ms (c), 64 ms (d), 134 ms (e) and 180 ms (f) after the delivery of the pulse. (Online version in colour.)