Figure 7. Tracings showing oscillation of activation times (A) and action potential duration parameters (B). We monitored the intracellular potential of cells in the array. Shown here is the time to activation for a cell located at (20,30) in a 40x40 array. Note that after an initial transient associated with the short S1S2 coupling, the activation time of the cell oscillates. The source of the oscillation is determined by the movement of the spiral wave front from one cycle to the next. When the tip trajectory falls within a small region, there is little movement of the spiral from one cycle to the next, the ECG appears monomorphic, and activation times are regular. However, when the tip trajectory falls within a larger area, the spiral will move significantly from one cycle to the next (see Fig 3), thereby changing the time to reactivation of each cell. The oscillation in activation time determines the recovery period of the cell, and because reactivation occurs before the membrane is completely recovered, the action potential duration will also oscillate, as shown in B. gK indicates potassium conductance; a.t.u., arbitrary time units.
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