A computer model of human atrial arrhythmia

The purpose of this thesis is to present an original computer model of electrical propagation in a realistic model of human atria for the study of atrial arrhythmias. In the last years, the ever– increasing computer power has permitted the development of numerical models of cardiac electrical propagation in structures of increasing sizes. Recently, it has become possible to simulate propagations in whole parts of the human heart. However, modeling arrhythmias is still a numerical challenge since the simulation of several seconds of cardiac activity is required. In that case, the finite power of computers imposes trade–offs to limit the complexity of the models. This work demonstrates how models specifically targeted for long–term arrhythmias simulations can be efficiently constructed. The atrial anatomy is of primary importance in these developments, since the limited atrial wall thickness allows structural simplifications that would not be valid in the case of the ventricles. First, a very simplified geometrical model has been developed, based on a topological equivalent of the human atrial anatomy. The whole design process has been constrained by the use of known, efficient numerical methods. The atrial tissue has been hypothesized to be homogeneous at the exception of major anatomical obstacles. A tailored ventricular ionic model has been used for membrane activation. This model has been able to reproduce atrial flutters and multiple–wavelet atrial fibrillations. Fibrillation episodes lasting up to 40 seconds and involving up to 8 independently traveling wavelets have been simulated. These arrhythmic events have reproduced electrophysiological observations made in humans. This simplified model has been used to test the efficiency of ablation lines. The results have con- firmed the superiority of aggressive surgical procedures to terminate fibrillation. They have also highlighted some interesting characteristics of the model: the simulated fibrillations are a complex mixture between anatomical and functional re–entries, whose balance needs to be carefully controlled.