Fig. 1.

Alternans after single-step or decremental pacing. A: Ca²⁺ transient signals were recorded at a site ∼2 mm from the pacing site at different pacing cycle lengths (PCLs) after either single-step or decremental pacing. B: intracellular Ca²⁺ [Ca_i²⁺ (Ca_i)] alternans amplitude as a function of PCL. Ca_i²⁺ alternans amplitude at the recording site was averaged over six beats at each PCL. PCL_C and PCL_D, spatially concordant and spatially discordant alternans onset PCL, respectively; MCL, minimum cycle length for loss of 1:1 or 2:2 capture.