Subject-Specific Modeling in Computational Cardiac Electrophysiology

Computational simulation has become an indispensable tool in the study of both basic mechanisms and pathophysiology of all forms of cardiac electrical activity. Because the heart is comprised of approximately 4 billion electrically active cells, it is not possible to geometrically model or computationally simulate each individual cell. As a result computational models of the heart are, of necessity, abstractions that approximate electrical behavior at the cell, tissue, and whole body level. In this work we have used a set of modeling approaches in the field of cardiac electrophysiology and developed means to evaluate their errors and the impacts of those errors.

The first project used subject specific models and experiments with acute myocardial ischemia to show that one common simplification used to model myocardial ischemia was not supported by the experimental results. We propose a alternative approximation that better simulates the experimental results.

The second study examined the impact of simplifications in geometric models on simulations. Such models consist of a connected mesh of polygonal elements and must often capture complex external and internal boundaries. A conforming mesh contains elements that follow closely the shapes of boundaries; non-conforming meshes fit the boundaries only approximately and are easier to construct but their impact on simulation accuracy was unknown. We evaluated the impact of this simplification on a set of three different forms of bioelectric field simulations.

The third project evaluated the impact of an additional geometric modeling error; positional uncertainty of the heart in simulations of the ECG. We applied a relatively novel and highly efficient statistical approach, the generalized Polynomial Chaos-Stochastic Collocation method (gPC-SC), to a boundary element formulation of the electrocardiographic forward problem to carry out the necessary comprehensive sensitivity analysis. We found variations large enough to mask or to mimic signs of ischemia in the ECG.