"
Augmentation and Pseudo-bidomain
\n\nAuthor: Gernot Plank gernot.plank@medunigraz.at,\ \ Anton Prassl anton.prassl@medunigraz.at\n<h2 id=\"augmentation-tutorial\"\
Bath Loading\n
In vivo, but also under all common in vitro\ \ experimental conditions, cardiac tissue is surrounded by conducting fluid. In\ \ vivo its blood at the endocardial surfaces and pericardial fluid at the epicardial\ \ surface. In experimental preparations tissue is perfused or superfused with Tyrode's\ \ solution. These surrounding fluid layers act to increase conduction velocity close\ \ to the tissue-bath interface by reducing the resistance of the interstitial current\ \ pathways as local circuit currents are shunted through the bath domain where conductivity\ \ is higher. Thus depolarization wavefronts propagating in the vicinity of the tissue-bath\ \ interface move faster than those in deeper layer of tissue, thus inducing transmural\ \ wavefront curvature. This effect is referred to as bath-loading.\ \ To account for bath loading in a computer model, in general, a full bidomain formulation\ \ is needed which is computationally expensive.
\n<h2 id=\"augmentation\">Augmentation\n\Bidomain theory explicitly considers current flow in both intra- and extracellular\ \ domains, and thus allows modeling of current flow and potential fields in the\ \ bath surrounding tissue. In spite of the knowledge that bath loading modulates\ \ wavefront morphologies close to the tissue-bath interface, the vast majority of\ \ simulation studies use the monodomain approximation. Monodomain models in a standard\ \ implementation are not able to account for bath loading effects, but are roughly\ \ ~10x faster to compute than a bidomain model. Thus in most computational model\ \ studies the monodomain model has been preferred. However, using a technique referred\ \ to as augmentation bath loading effects can be taken into account\ \ even when using a monodomain model. Briefly, the idea is to account for the lower\ \ interstitial resistance close to the tissue bath interface, mediated by the lower\ \ resistance of the adjacent bath which shunts extracellular currents of local circuits\ \ away from the interstitial current path, by using higher bath conducitivies within\ \ a thin layer along the tissue bath interface. The width of this thin layer, referred\ \ to as augmentation layer, and the bath conductivy introduce a\ \ bath loading effects very much comparable to those observed in full bidomain models.\ \ Details on augmentation are found in the literature where it\ \ has been demonstrated that augmented monodomain models faithfully replicate bath\ \ loading effects with high fidelity, comparable to full bidomain simulation results.\ \ For details see the studies by Bishop et al. 1 .