Bidomain ECG Simulations Using an Augmented Monodomain Model for the Cardiac Source

The electrocardiogram (ECG) is an essential clinical tool for the noninvasive assessment of cardiac function. Computational simulations of ECGs using bidomain models are considered the biophysically most detailed approach, but computational costs are significant. Alternatively, pseudo-bidomain formulations can be used, combining a monodomain model with an infrequent bidomain solve to obtain full extracellular potential (Φ_e) distributions, and traces. However, previous attempts at such approaches did not see the expected significant decrease in compute time and did not include important effects of bath-loading on activation wavefront morphology (present in full bidomain models), representing a less accurate source term for Φ_e solution. ECG traces can also be derived from computationally cheaper Φ_e recovery techniques, whereby the time-course of Φ_e is approximated at a particular point using the monodomain transmembrane potential as source term. However, Φ_e recovery methods also assume tissue to be immersed in an unbounded conductive medium; not the case in most practical scenarios. We recently demonstrated how bath-loading effects in bidomain simulations could be replicated using an augmented monodomain model, faithfully reproducing bidomain wavefront shapes and activation patterns. Here, a computationally-efficient pseudobidomain formulation is suggested which combines the advantages of an augmented monodomain method with an infrequent bidomain solve, providing activation sequences, ECG traces and Φ_e distributions in a bounded medium surrounding the heart which closely match those of the full bidomain, but at ≈10% the computational cost. We demonstrate the important impact of both bath-loading and a finite surrounding bath on spatiotemporal Φ_e distributions, thus demonstrating the utility of our novel pseudobidomain model in E- G computation with respect to previous pseudobidomain and Φ_e recovery approaches.