Abstract:

Under atrial fibrillation (AF), cardiac tissue undergoes electrophysiological and structural remodeling. Structural remodeling is characterized by the formation of fibrotic tissue. Atrial fibrosis plays a role in sustaining the arrhythmia. Thus, one could say that "AF begets AF". Dealing with such a high level of complexity makes the understanding of the mechanisms underlying AF quite the challenging task. This work focuses on the effect of fibrosis density and transmurality on electrogram morphology and atrial fibrillation dynamics. For that purpose meshes of atrial substrate were simulated. Each mesh was constituted of an extracellular bath, intracellular tissue, fibrotic patch and a grid of sixteen electrodes. Density and transmurality of the fibrotic tissue were varied, so that in the end a total of 9 meshes was generated. The atrial substrates were electrically stimulated with two pulses of monophasic square pulse. The resulting bipolar electrograms were calculated for 3 bipolar orientations: perpendicular, diagonal and parallel. The intracardiac atrial electrograms were then analysed and compared according to 4 parameters: peak-to-peak amplitude, non linear energy operator (NLEO) active segment duration, sample entropy and spectral entropy. The goal was to investigate if one could distinguish different fibrosis densities and transmuralities from analysing electrogram morphology. Additionally, this thesis aimed to analyse the effect of varying those fibrotic tissue features on AF dynamics. For this work, results showed that increasing fibrosis density and transmurality slowed down wave propagation across the tissue but did not initiate reentry. It was also possible to distinguish certain transmuralities namely 0.5mm and 2mm relying on peak-to-peak amplitude, sample entropy or spectral entropy. Additionally, the results highlighted that transmural meshes with 40% density had longer active segments compared to the rest of the meshes. Detailed results and limitations of the study will be explained in further sections.