Internodal pathways in the human atria: a model study

An electrophysical/anatomical computer model of human atrial excitation was used to investigate the controversy over specialized internodal pathways. The only atrial pathways that have been thoroughly described in the literature are those that connect the sinoatrial (SA) and atrioventricular (AV) nodes, and the right and left atria. By incorporating pathways of rapid propagation representing the internodal and interatrial tracts, anisotropy was introduced into an otherwise isotropic atrial model. Simulated epicardial isochrone maps, heart vector loops, and electrograms were calculated for both the isotropic and anisotropic atrial models, and the simulations were compared with observed normal data. Although the simulations using the anisotropic model compare more favorably with real data, the results suggest that there are more pathways of rapid propagation in the atria than those described and that a global anisotropy based on morphology and fiber direction is a more likely explanation than rapid propagation confined to a few specialized pathways.