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(c)

Figure 8.3. Simulation of the spread of excitation in canine ventricles. Ventricular cell models are based on a simplified version of
the Oxsoft v.4.6 ionic models. Membrane potentials are grey-level coded (dark – resting potential, light – action potential) and ECG
equivalents are computed (curves below the images). (a) Normal spread of excitation. Frames illustrate the normal sequence of
excitation and repolarisation during one cardiac cycle (from left to right). (b) Spread of excitation in a congestive heart failure model.
The initial activation sequence (frames 1 and 2) is followed by irregular re-entrant excitation (frames 3 and 4). Note the typical, for
this pathology, saw-tooth shaped ECG. (c) Simulation of the effect of ATP-modulated potassium channel openers on the spread of
excitation in the same congestive heart failure model. The first three frames are closely reminiscent of those leading to re-entrant
excitation in (b), with the saw-tooth like ECG shape still apparent. Due to the drug effect, however, the heart does reach a resting
state before a new cycle of cardiac excitation is triggered (‘dark’ cardiac chamber and ‘flat’ segment in the ECG, frame 4). This
allows time for diastolic filling and permits pumping action of the heart. From Kohl et al. 2000.