Propagation in the AV node: a model based on a simplified two-dimensional structure and a bidomain tissue representation

A model is proposed to explain mechanisms of propagation in the atrioventricular (AV) node of the heart. The model is based on a simplified two-dimensional anatomic description of the central node region and on a bidomain tissue model for the propagation. The central region is described as a three-tissue compartment model; the proximal tissue composed of ANL cells, the central tissue composed of N cells and the distal tissue composed of NH cells. The central N region is outlined as an unexcitable gap by forcing these cells to behave as depressed cells for which the fast ionic currents are inactivated. This model has allowed the authors to test the electrotonic gap hypothesis, which explains the time-delay properties of the AV node. Typical conduction curves have been obtained, as well as common patterns of Wenckebach blocks. Premature stimulus and resulting mapping of cell responses in the N region of the model show typical membrane potential dissociation in two components. The model has also been submitted to several programmed stimulation protocols in documented anterograde and retrograde conduction. The results show that the model is valid and covers several well known dynamic properties of the AV node.