Cardiac conductivity values — A challenge for experimentalists?

Recent experimental studies have challenged the usual assumption that cardiac conductivities in the direction normal to the fibres but in the plane of the fibre sheet are equal to those in the direction normal to the sheet. Here, a simulation study, using a simple model of cardiac tissue, is undertaken to consider the effect that this experimental observation has on the resulting epicardial potential distribution. Results indicate that there is a significant difference when using six conductivity parameters as opposed to the usual four values, where the approximation of equality of the above mentioned conductivities is made. The results are compared with experimentally observed epicardial potential distributions and an explanation of the results is offered in terms of voltage dividers. It is concluded that further experimental studies are required to obtain reliable conductivity values which can be used in simulation models.