Effects of the tissue-bath interface on the induced transmembrane potential: a modeling study in cardiac stimulation

During the initial stages of cardiac stimulation or defibrillation, the distribution of transmembrane potential generated in the myocardium by the external stimulus is determined by the local interactions between fibrous tissue organization and applied electric field. We hypothesize that the pattern of induced transmembrane potential is different, depending on whether the tissue is in insulator, such as air, or in contact with a low-resistance volume conductor, such as blood or perfuseate. The goal of this study is to evaluate the impact of the volume conductor bordering the myocardium on the pattern of stimulus-induced transmembrane potential. Presented here are computer simulations of the steady-state response of model tissue-bath preparations to extracellular current stimuli. Transmembrane potential distributions for various tissue and bath sizes, as well as locations of the stimulation electrodes, are examined. The results indicate that when the external stimuli are located in close proximity to or at the tissue-bath interface, both the magnitude and the distribution of transmembrane potential are significantly altered, compared with the case of an insulated preparation. Thus, the volume conductor seems to be another possible factor contributing to the pattern of membrane hyper- and depolarization in the myocardium. Its influence is, however, modulated by the promixity of the stimuli sites to the tissue-bath interface.