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Figure 1. Local impedance in action
A) Electric fish use sensors on their sides to feel the expansion and compression of the field lines created between their head and tail. In open ocean the field lines spread uniformly, but when an object enters the field the field compresses. If that object’s resistivity decreases due to heat, the field expands proportional to volume heating. B) A local electrical field (~) is created by driving non-stimulatory current from the tip of the catheter to the proximal ring electrode, while voltage (V) is measured from the tip to distal ring electrode. This allows the catheter to sense changes in volumetric dielectric properties surrounding the tip electrode. C) In this bench study, temperature profiles at varying depths were correlated with the local impedance measured during RF lesion creation. Thermocouples were placed into the tissue at the surface, at 2 mm depth, and at 4 mm depth. The local impedance drop was seen to dynamically follow the rate of intramural temperature rise at both low and high powers.