How epicardial electrodes influence the transmembrane potential during a strong shock.

This paper analyzes a possible artifact that may corrupt experiments studying defibrillation of the heart. Our hypothesis is that surface recording electrodes can influence the transmembrane potential during a shock. In the vicinity of an electrode, current leaves the intracellular space to take advantage of the low resistance of the extracellular path, thereby depolarizing the tissue. We calculate the transmembrane potential induced around a circular electrode when exposed to a uniform electric field. The bidomain model represents the electrical behavior of the cardiac tissue, and we account for electrode polarization impedance. Our results show that adjacent regions of depolarization and hyperpolarization exist around the electrode, and that the induced depolarization is greater than 100 mV for a 0.5 mm radius silver-silver chloride electrode in a 500 V/m electric field. We conclude that surface electrodes may produce artifacts during experiments designed to study defibrillation-strength electrical shocks.