Influence of left atrial geometry on rotor core trajectories in a model of atrial fibrillation

Abstract

IntroductionAtrial fibrillation (AF) is the most common type of cardiac arrhythmia. One theory about AF maintenance is the presence of localized sources termed rotors [1]. A rotor is defined as a high frequency curved wavefront, which meets the wavetail at a single point and is characterised by the absence of refractory tissue at the centre [2]. Until recently, the presence of rotors was only observed in animal experimental studies [3], but localized and stable rotors in human AF have now been identified [4,5]. This progress may increase the efficacy of targeted left atrial ablation therapy.Clinical studies [6] and human myocardium-based computational studies [7] suggest that rotors may be constrained temporarily or persistently in limited areas of the LA, because of discontinuities in the fibre architecture. In addition, human atria exhibit fibrosis and scar outside the pulmonary veins (PV) to a considerable degree, which may contribute to the initiation mechanisms for AF in many patients [8]. A variety of computational models propose that fibre orientation, fibrosis and the geometry of LA together can play an important role for the generation of anisotropic conductivity [9,10].Clinical studies show that LA size and diameter and the PV structural characteristics in isolation [11][12] are related with the outcome of catheter ablation and are useful as independent predictors of AF recurrence. In this paper, we investigate, using a computational model, and anatomically accurate LA geometries derived from persistent AF patients, the effect of geometry in isolation on the maintenance of localised fibrillatory propagation, the spatiotemporal evolution of rotors over time and their association with anatomical characteristics. Methods Mesh generationThe closed three-dimensional LA endocardial surface geometry was segmented from late-gadolinium enhanced magnetic resonance imaging (LG-MRI) data, using ITK-SNAP [13]. The mitral valve and the PV sleeves were opened in order to produce a topologically accurate finite element mesh of the atrial chamber and PV sleeves. Gmsh [14], a high-order three-dimensional finite element mesh generator, was used to remesh the surface using a coarser uniform triangulation, which consisted of elements of approximately the same characteristic length of a size appropriate for use with a high-order spectral element discretisation [10]. A second mesh, which was used for generating a two-dimensional unwrapping of the surface, was created by adding cuts on either side of the atrium from the mitral valve up to the ends of the veins. Simulation ProtocolSimulations, using the uncut finite element mesh were performed using the Nektar++ high-order spectral/hp element framework [16], in which the solution on each mesh element is approximated using a basis of high-order polynomials. Spectral/hp element methods support convergence of the solution through both mesh refinement and enrichment of the polynomial space, permitting accurate representation of propagating action

Novel Radiofrequency Ablation Strategies for Terminating Atrial Fibrillation in the Left Atrium: A Simulation Study

“…PS and rotor density were calculated by counting the number of occurrences of a PS or rotor at each mesh element over the duration of the simulation. This score was smoothed using an inverse distance squared weighting to give an average density measure across the mesh, which was then normalized (Tzortzis et al, 2015 ). Metrics were also considered on a regional basis by dividing the LA into eight subdivisions, as done similarly in non-invasive PS mapping studies (Haïssaguerre et al, 2014 ).…”