Effect of tissue damage on virtual electrode polarization pattern

The virtual electrode polarization (VEP) effect is believed to play the key role in pacing and defibrillation. However, under certain conditions, including clinical, its existence and importance remain unknown. We investigated how tissue damage under the pacing electrode might affect the VEP on the basis of a 2D passive bidomain model with tissue damage represented as a local increase of intracellular conductivity (cell uncoupling) and/or electroporation. The model predictions were compared to experiments. 10 ms stimuli of increasing strength were applied to the ventricular surface of a rabbit heart; VEP patterns were recorded by a fluorescent mapping setup and tissue damage under the electrode was estimated from the micrographs of the pacing site. The bidomain simulations showed that local decrease in either transmembrane resistance or intracellular conductance lead to fainting and subsequent elimination of the characteristic "dog-bone" pattern of VEP. The experiments confirmed that tissue damage around the pacing electrode could obscure theoretically predicted VEP pattern. In conclusion, the study demonstrates that VEP pattern is strongly modulated by the tissue damage.