Simulation of the electrogram from ion currents.

Abstract

The electrogram can be constructed as the difference between two action potentials starting with a slight time difference. In the present study, the action potentials were simulated from ion currents showing time- and voltage-dependent activation and inactivation. Simple mathematics like straight lines and single exponential functions were used. The aim was not to give a precise description of the action potential but to obtain a model with electronic interaction between action potentials. Four currents were incorporated. The upstroke of the action potential was due to the inflow of sodium ions. The plateau was maintained by a calcium current and repolarization followed from a slowly activated and outwardly directed potassium current. There was also a time-independent background current of potassium showing inward rectification. Basically the same equations were used for calculation of the four current voltage relations. Also, currents during a depolarizing voltage step could be reproduced by the model. Two action potentials were coupled 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 action potentials had the same characteristics because of the electrotonic interaction. When the first action potential was longer than the second in a pair positive T-waves were seen. A negative T-wave occurred when the second action potential of the pair was made longer. The model forms a base for further simulations of ECG.