FIG. 3.

Electromechanically concordant and discordant spatially discordant alternans (SDA). (a) An example of an electromechanically concordant SDA in which action potential duration (APD) and Ca alternate in-phase. Top: APD vs cell no. for two consecutive beats. Middle: Peak Ca vs cell no. for the same two consecutive beats. Bottom: Alternans amplitude of APD ($\mathrm{\Delta }a$) and $\text{Ca}\left(\mathrm{\Delta }c\right)$ calculated from the two beats. (b) Same as (a) but for an electromechanically discordant SDA in which APD and Ca alternate in antiphase. (a) and (b) are simulation results of the coupled map lattice (CML) model (see the Appendix) with the following parameters: $T=250\text{ms},\gamma =0.002,{\sigma }_R=0.8,{\tau }_a=40$, and $\beta =4$ for (a) and $T=250\text{ms},\gamma =-0.002,{\sigma }_R=0.8,{\tau }_a=38$, and $\beta =4.6$ for (b).