Aim: There are evidences that the human right atrium and sinoatrial node (SAN) are functionally separated except at discrete SAN-atrial electrical junctions, called SAN-exit-pathways. We hypothesize that this type anatomy is a source of re-entry around the SAN.
Methods: A computationally efficient model was developed to reconstruct human right atrium electrophysiology. Activity of a myocyte was simulated by a timed automaton with continuous and discrete transitions reproducing stages of cellular membrane. A stochastic 2D-network of timed automata was designed to model the right atrium architecture: SAN, atria-ventricular node (AVN), SAN-exit-pathways and heterogeneous atrial tissue. Simulations were performed to measure effects of quantity of SAN-exit-pathways: all-, half-, few-cells connections, on development and propagation of normal versus arrhythmic excitations: SAN re-entry or fibrillation. Additionally, two parameters were controlled to measure an influence of (1) atrial tissue fibrosis: p_trans - probability for transversal intercellular network connections, and (2) impairment of individual cells: p_refuse - probability of a cell to refuse to excite. 100 simulations for wide range of studied parameters were performed.
Results: In case of normal density of intercellular connections (p_trans = 0.60), in large interval of p_refuse (0 <= p_refuse < 0.45), probability to observe normal rhythm/SAN re-entry/fibrillation changed from 0.33/0.66/0.00 for all-cells connections, to 0.96/0.04/0.00 for few-cells connections between SAN and atrium. Then at p_refuse > 0.45, all simulations led to stabilization with fibrillation. In case of high fibrosis (p_trans = 0.30), again systems with few-cells connections provided the highest ratio of normal states when p_refuse <= 0.20, which then switched rapidly to fibrillation.
Conclusion: The simulations provided a critical relationship between atrial anatomy and rhythm of heart excitations. A discrete model of cells and intercellular connections was found as efficient method for quantifying this relationship.