SIMULATION OF THE ELECTROGRAM FROM ION CURRENTS

The electrogram can be constructed as the difference between two actio n potentials starting with a slight time difference. In the present st udy, the action potentials were simulated from ion currents showing ti me- and voltage-dependent activation and inactivation. Simple mathemat ics like straight lines and single exponential functions were used. Th e aim was not to give a precise description of the action potential bu t to obtain a model with electronic interaction between action potenti als. Four currents were incorporated. The upstroke of the action poten tial was due to the inflow of sodium ions. The plateau was maintained by a calcium current and repolarization followed from a slowly activat ed and outwardly directed potassium current. There was also a time-ind ependent background current of potassium showing inward rectification. Basically the same equations were used for calculation of the four cu rrent voltage relations. Also, currents during a depolarizing voltage step could be reproduced by the model. Two action potentials were coup led to each other by means of a resistor to simulate the behaviour of gap junctions. A flat T-wave in the electrogram occurred when the acti on potentials had the same characteristics because of the electrotonic interaction. When the first action potential was longer than the seco nd in a pair positive T-waves were seen. A negative T-wave occurred wh en the second action potential of the pair was made longer. The model forms a base for further simulations of ECG.