Simulation of ECG from two pairs of action potentials

A simple model for simulation of ECG is presented with the purpose to mimic some common ECG configurations and to generate a hypothesis regarding their electrophysiological background. Action potentials (AP) were simulated on a personal computer from ion currents as described previously (Wohlfart & Arlock, 1993). The difference between two APs of a pair was used to create an electrogram (EG). The subendocardial AP of the pair was triggered by means of a simulated current injection and the subepicardial Ap was triggered from the first AP due to electric coupling within the pair. The subendocardial APs were of longer duration than the epicardial AP because of differences in background currents. A second pair of APs representing another ventricular site was simulated in an analogous way and this pair was activated somewhat later in time. ECG was calculated as the difference between the two EGs. Right-bundle branch block could be imitated by reducing the coupling between the APs representing the right ventricle. Left-bundle branch block was generated in an analogous way. ECG in acute myocardial infarction was created after making one of the epicardial APs ischaemic in appearance (reduced amplitude, short duration). Status-post infarction ECG (Q-wave and negative T) was produced by reducing the influence from the EG of the infarcted area. Negative T and increased R-wave as in hypertrophy could also be reproduced. Down sloping ST-segment and negative T as in subendocardial ischaemia was also possible to imitate. The simulations showed that biphasic T-waves or T and U-waves follows when the two EGs are separated properly in time.