Evaluating the effects of border zone approximations with subject specific ischemia models

Current computational models of acute ischemia are deficient because of their inability to be validated against experimental data and their lack of geometric realism. Past models of ischemia have been based on geometric primitives or hearts for which no electrical measurements exist. One consequence is that it is necessary to make modeling assumptions that are not supported by measurements or direct validation with experiments. Based on our subject specific simulations and measurements, we hypothesize that assumptions about the nature and scale of the border zone play a significant role in determining the cardiac potential distributions from ischemic sources of injury current. Geometrically accurate models were created from Magnetic Resonance Imaging (MRI) and Diffuser Tensor Imaging (DTI) after an in situ canine ischemia experiment. The ischemic zone was defined based on transmural electrode readings and was used in a static bidomain simulation representing a time point during the ST segment. Varying the width of the border zone in the simulations changed the magnitude and distribution of epicardial depressions and elevations. We also found that a border zone with linear variation of potential from healthy to ischemic regions was not adequate to simulate measured potentials. A more sophisticated border zone that included an explicit region of partial ischemia was necessary to simulate the field gradients seen in experimental data.