Dyssynchrony between Endo- and Epicardial Activation in a Bilayer Model of the Left Atrium with Heterogeneous Endoepicardial Dissociation

Endoepicardial delays in activation observed in patients with atrial fibrillation have been hypothesized to be associated with structural remodeling and layer dissociation.We aim to explore in a computer model how synchrony in endo-and epicardial activation during fibrillation is affected by local layer dissociation.A bilayer interconnected cable model of the left atrium was used to simulate atrial fibrillation on different arrhythmogenic substrates with epicardium-only diffuse fibrosis and heterogeneous endoepicardial dissociation.Activation time series were extracted in both layers to compute endoepicardial delays and a measure of synchrony based on a coincidence window.The simulations showed that reentrant activity was driven by the endocardium, thus generating an endoepicardial delay.Heterogeneous layer dissociation prolonged that delay locally.In regions with decoupled layers, the synchrony index was lower, illustrating how synchrony in activation may be related to the tissue structure.