Spatially discordant alternans (SDAs) in intracellular calcium in paced quasi-1D cardiac tissue

We characterize the development of calcium alternans in a long thin strip of cardiac tissue (cell monolayer). Our findings are compared to predictions of theoretical models about parameter profiles over space and nodal locations. We find that fine discordant regions emerge before macroscale propagation is visibly disturbed. SDA regions as small as 1-2 pixels are found and transitions between regions seem instantaneous in some cases, i.e. within the spatial resolution of the system (44 mm). These fine SDA regions (fSDA) differ from our findings when synchronized large-scale SDA regions emerge (ISDA), where transition/nodal lines tend to be in the mm-range and the regions are at least a couple of millimeters in size. On the other hand, these results are in accord with theoretical predictions about the ability of intracellular calcium to alternate at a very fine scale. Our data show that fSDAs and ISDA differ in magnitude, spatial scale and level of spatial coherence; same samples can exhibit f SDA and ISDA at a higher pacing frequency. We discuss differences in the spatial distribution of major parameters of SDA between experiments and theory.