Modeling Cardiac Ventricular Activation

We describe the microscopic and macroscopic level modeling of the cardiac activation in the realistic three-dimensional ventricles of the human heart. At the microscopic level, the subthreshold behaviour of the excitable elements (cells) is governed by a reaction-diffusion equation derived from the bidomain theory, while in the suprathreshold state the elements obey cellular automata rules. Each cell is assigned a principal fiber direction according to the fiber architecture in the human heart. At the macroscopic level, the excitation of the ventricles is controlled by a model of the conduction system based on reports on the anatomy and physiology of the human heart. In the simulations, the activation was allowed to propagate from the His bundle to Purkinje-myocardial junction sites and through the ventricular myocardium. After careful evaluation of primary activation areas and balancing the activation timing between the right and the left ventricle, the final simulated activation sequence agreed with isochrones obtained from an isolated human heart. The calculated body surface potential and magnetocardiographic maps during the QRS complex correlated well with our clinical recordings on normal subjects. Furthermore, the vectorcardiogram produced by the simulated activation showed a correct pattern, although some minor discrepancies were observed in the morphology of the 12-lead electrocardiogram. K eywords: Bidomain theory, hybrid model, anisotropy, ventricles, conduction system, human