Tissue-based optimization of a sino-atrial node disc model

A cardiac sino-atrial tissue model based on a simplified 2D disc geometry and a generic ionic model is described and optimized to fit intact-tissue microelectrode experimental recordings. Concentric regions were defined representing the central and peripheral sino-atrial node and the atrium, each with a unique set of ionic model parameters. Intracellular action potentials were recorded from the respective myocytes in an intact rabbit in vitro sino-atrial tissue preparation. The 2D disc geometry was described numerically using a modified version of the cable equation of electrical propagation. The cell-specific model parameters at three nodes representing each region of the disc geometry were optimized, using a curvilinear gradient optimization algorithm, to generate action potentials waveforms that fitted the experimentally recorded waveforms. The optimized model was able to reproduce spontaneous sino-atrial node activation and atrial excitation and propagation. It offers an improved representation of the electrotonic interactions between heterogenous cell types and is able to reproduce the transition in action potential morphology between different regions. This tissue based optimization approach is a contribution to the development of realistic electro-anatomical cardiac models based on experimental data.