Figure 5. Computed ECGs (EKG in the figure) and tip trajectories. A, Computed ECGs for different values of potassium conductance (gK). B, Associated tip trajectories computed from a 40x40 array of excitable cells. Note that as the potassium conductance (gK) is reduced, the morphology of each complex in the computed ECG gradually shifts from an almost monomorphic ECG (gK, 1.13) to a polymorphic ECG similar to that seen in torsade de pointes (gK, 0.70). In addition, as the size of the flower increases, the degree of amplitude modulation displayed in the ECG is increased. The tip trajectories, shown for a single torsade cycle on the left and for multiple cycles computed over a 50time unit interval on the right, change from a four-petaled flower (gK, 1.13) to a eight-petaled flower (gK, 0.70). Note that the number of reentry complexes within each torsade cycle in the computed ECG is approximately one less than the number of flower petals. The number of petals is determined by the ratio of the spiral rotation frequency to the tip precession frequency. If the ratio is not an integer, then each flower will be rotated from one torsade cycle to the next (as shown on the left), thus introducing another degree of variability in the morphology of the polymorphic ECG.
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