Electrical current distribution under transthoracic defibrillation and pacing electrodes.

The known effect of high current density under the perimeter of defibrillation electrodes, leading to skin damage and even severe burns in some cases, has been considered by many investigators. Two main approaches for improvement were proposed: (i) interfacing with layers of varying and high resistivity and (ii) lengthening and shaping the perimeter line. Using finite element and physical modelling, it is shown that the second approach does not yield significant improvement in the distribution uniformity. Moreover, the application of high resistivity layers is unacceptable in dibrillation. The use of a low resistance layer with a diameter covering and extending over the metal plate by at least 2.5 mm results in better uniformity. A similar effect can be obtained by recessing the metal plate in an isolating support--an approach adopted from implantable neurostimulation electrodes. These two versions can be applied in combination.