Models of the electrical activity of the heart and computer simulation of the electrocardiogram

This paper reviews models of the electrical activity of the heart and their use for simulations of the surface electrocardiogram. As such, it focuses on the forward problem of electrocardiography. The paper starts with an overview of the biophysical background that forms the underpinning of most heart models and surface potential computations. The basic volume-conductor equations and the different techniques used to solve them, the bidomain characterization of the myocardium, propagation in cardiac tissue, and equivalent source formulations for the electrical activity of the heart are all reviewed. Following this, a review of heart models conceived for cardiac rhythm simulations is presented. These models do not represent the heart geometry accurately, and hence ECG simulations with such models are, at best, first approximations. Next, realistic-geometry heart models, but without propagation, are described. Since the activation isochrones in such models are fixed, they are essentially suited only for the study of normal activation or for ischemia and infarction simulations. Finally, realistic-geometry models which use element-to-element propagation are described. Because of their ability to alter activation patterns, such models may also be used to study conduction disturbances and arrhythmias. Surface potential simulations realized with both types of realistic-geometry models are also reviewed. The paper concludes with a section on heart models of the future.