Ionic current model based differences in propagation characteristics in the vicinity of bifurcation sites in a model of cardiac tissue

A number of ionic current models have been used to describe the cardiac propagating ventricular action potential. It is expected that in decremental conduction situation such as can happen at the exit of a narrow isthmus or at a bifurcation site where there is an increase in electrical load the wave sees that decreased dV/dt_max is linked with decreased peak I_na. However, we show that depending on the ionic current model used the results may considerably vary. In particular three ionic current models were used to simulate increased electrical impedance in a case of bifurcation strand. Beeler-Reuter (BR) model, Beeler-Reuter/Ebihara-Johnson (BR-EJ) model and Luo-Rudy (LR) model. It is shown that only the BR model where the I_na activation kinetics are slower follows what is expected from theory and experiment (i.e. reduced dV/dt_max is accompanied by reduced I_na, at the bifurcation site exit). The other two models showed an opposite direction as it concerns the changes in these two parameters (i.e. reduced dV/dt_max is followed by increased I_na). This result shows the problems associated with I_na representations, and raises questions regarding the behavior of ionic current models with fast kinetics in multi-dimensional models simulating complex propagation phenomena such as zig-zag pathways in infarcted tissue.