Figure 3. Discordant alternans before wavebreaks.

Wavebreaks were detected by tracking split of wave fronts into multiples. Traces around neighboring 8 pixels showed spatially discordant alternans before wave breaks occurred. (A) snapshot of fluorescence image. (B) first derivative image to isolate wave fronts. (C) automated wavebreak detection (red circle). The degree of local synchronization was calculated using cross correlation among neighboring pixels. (D) Case of collision. V_m traces were synchronized before the wave split. Cross correlations from 200 ms traces (see figure) were calculated from all possible pairs of 8 neighboring pixels. The minimum correlation was 0.59 ± 0.05 (n=5). Traces in blue and red represent the pair of minimum correlation. (E) Case of wave break. V_m traces were highly asynchronous with out-of-phase alternantion. The minimum correlation was 0.47 ± 0.05, significantly lower than collision case (n=5, p=0.012).