Spatial potential and current distributions along transvenous defibrillation electrodes: variation of electrode characteristics.

The therapeutic efficacy of an endocardial defibrillation lead system can be improved by controlling the profile of current delivery through a suitable choice of electrode characteristics, which include the length, radius, number of conductor elements, electrode resistance, and point of connection to the voltage source. Such control will minimize tissue and lead damage during long-term use. In this study, a semianalytical model was developed to study cylindrical electrodes of different constructions in an idealized electrolytic medium. Simulations were performed to investigate the effects of varying the electrode characteristics on the spatial voltage and current distributions and interelectrode resistance for cylindrical electrodes of different constructions. The results show that, for transvenous electrodes of realistic dimensions, the current distributions are determined largely by the edge effects. The edge effects increase as the aspect ratio of the electrode (length/radius) decrease. The multiple edges resulting from wrapping conductor elements over a nonconducting base are found to increase the nonuniformity and the current density over the conductor-covered surface. The model is used to demonstrate two techniques of controlling the current distribution. The first method involve modifying the electrode resistivity profile and point of connection. In the second approach, the electrode surface is covered with a thin film having a model-computed resistance profile. By using either methods to produce isocurrent electrodes, the interelectrode resistance is found to increase.