Parametrization strategies for matching activation sequences in models of ventricular electrophysiology

Driven by recent advances in medical imaging, image segmentation and numerical techniques computer models of ventricular electrophysiology account for increasingly finer levels of anatomical and biophysical detail. However, considering the large number of model parameters involved parametrization poses a major challenge. A minimum requirement in combined experimental and modeling studies which aim at making specific predictions on a case by case basis is to achieve good agreement in activation and repolarization sequences between model and experiment or patient data. In this study we propose basic techniques which aide in determining bidomain parameters to match ventricular activation sequences. Two specific aspects will be considered. First, conduction velocity in the ventricles is orthotropic and varies in space. An iterative parametrization algorithm is implemented which determines appropriate conductivities which yield prescribed velocities. Secondly, impulse propagation in the ventricles is initiated subendocardially at Purkinje-ventricular junctions, the terminal endings of Purkinje system (PS), and, thus, the PS plays a key role in determining the shape of activation wave fronts as reflected in the QRS complex of the electro-cardiogram (ECG). While ventricular models equipped with generic PS topologies match well with experimental observation in terms of epicardial breakthrough sites, predicted ECGs match poorly with known key ECG characteristics.