Figure 4.

(a–d) Discordant APD alternans in 2D simulations during deterministic (a and b) and stochastic (c and d) pacings. (a) APD as a function of the beat number during the deterministic pacing phase with the target BCL = 245 ms. Traces at two locations, (x,y) = (0,0) and (10,10) mm, are shown in gray and black, respectively. A transition from concordant to discordant alternans can be seen at beat 33. (b) Short segments of membrane voltage during deterministic pacing after beat 33 clearly illustrate the appearance of discordant alternans. (c and d) A typical case in which stochastic pacing (with σ = 3.5 ms) diminished the transition from concordant to discordant alternans in 2D simulations. Panels are organized as in a and b.