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Uncertainty in the input parameters used in simulation studies needs to be taken into account when evaluating the results produced. This work considers the effect of using various sets of bidomain conductivity values in two simulations: firstly, activation times, which indicate the propagation of the depolarisation wavefront through the cardiac tissue, and, secondly, the determination of defibrillation thresholds in a 'heart in a bath' model, where a shock is delivered from two opposing patch electrodes. Both simulations use the same two types of sets of bidomain conductivity values: four-conductivity datasets (where normal and transverse conductivities are assumed equal) and sixconductivity datasets, including newly proposed sets that are based on experimental measurements.The activation time maps show significant differences depending on the conductivity set used, as do the defibrillation thresholds. The defibrillation thresholds vary by more than 20%, whereas the activation times for epicardial breakthrough and total depolarisation both vary by approximately 50%. It is found that the most extreme values in each case are produced by two of the four-conductivity datasets. Since these differences are large enough to lead to different conclusions in such studies, it is suggested that the four-conductivity datasets may not be an appropriate choice for use in simulation studies in the heart.

This numerical study uses a simple bidomain model of cardiac tissue to compare the effect of three different ischaemic region geometries (rectangular, cylindrical and semi-ellipsoidal) on the extracellular epicardial potentials during the ST segment. Results are obtained using anisotropic conductivities based on experimentally derived data. The model is then altered, to include heterogeneous conductivities in the ischaemic region and larger border zone widths, in order to better reproduce realistic scenarios. Initial results for the rectangular and cylindrical ischaemic shapes show a central depression over the ischaemic region, for low ischaemic thicknesses, which separates into three depressions as the ischaemic thickness increases. For ischaemic thicknesses above 70% an elevation appears over the ischaemic region and this increases in magnitude as the ischaemia becomes transmural. Results for the semi-ellipsoidal shape, however, differ, with the central depression separating into only two depressions as the thickness increases. Changing the conductivity inside the ischaemic region significantly affects results for each geometry, with depression staying over the ischaemic region for much higher levels of ischaemia (up to 90% thickness). Increasing the intramural border zone thickness did not significantly affect the epicardial potential distributions.

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Cardiac ischaemia is a restriction of blood supply to tissues in the heart. It is often diagnosed via an electrocardiograph by looking at the segment of the electrocardiograph between the qrs complex and the t wave, which is known as the st segment. Previous work on ischaemia during the st segment has shown that the shape of the ischaemic region can significantly affect the epicardial potential distribution at the surface of the heart. This numerical study compares the results from the steady state simulations with a more realistic transient model. The model consists of a slab of ventricular tissue with an ischaemic region at the centre resting on a blood bath. The transient bidomain equations were solved using a finite volume method for the spatial discretisation and a semi-implicit method for the time