Figure 5.
Mechanisms of acceleration in multiwave spirals. (A) Mutual entrainment and advancement of individual spiral phases in multiwave spirals. (A1) Isochrone lines during rotation of a single spiral. Red arrows denote rotational phase of the spiral at times t1–t4. (A2) Wavefront collision between two spirals yields faster phase advancement. Isochrones t1–t4 show the same time interval as in A1. Note negative curvature at t3 and the greater advancement of spiral phase between t2 and t3 and between t3 and t4 compared to A1. (B) Schematic of a spiral CL (CLs) reduction (rate acceleration) due to the application of external stimulus. Two tissues with different excitation threshold versus premature interval curves at the spiral tip are shown in blue and orange. The negative curvature due to wave collision creates excess depolarizing current, which is equivalent to a suprathreshold stimulus. If Istim, the current supplied to the spiral tip from the site of collision, is sufficient to excite downstream tissue near the tip, it will advance the spiral phase and decrease the CL. Note that the difference between CLs and minimum CL at which tissue can be excited represents the available room for rate acceleration. The slope of the curve and the amount of supplied excitatory current, Istim, determine ΔCL and the resulting degree of rate acceleration (ΔCL/(CLs − ΔCL)).