ELECTROACTIVE COATING OF STIMULATING ELECTRODES

Electrophysiologic examinations as well as the electrotherapy of heart diseases require electrodes which distinguish themselves by outstandi ng sensing and pacing performance. Both, the sensing and the stimulati on behaviour are determined by the interface between electrode and tis sue. To avoid energy losses and distortions of heart signals having co mponents down to 1 Hz, the interface's impedance has to be very small in the corresponding frequency range. Towards this goal a new coating has been developed: electrolytically deposited electroactive iridium o xide. On the electrode's surface iridium oxide forms a long-term stabl e reversible redox system which changes its oxidation state according to the applied potential. The decrease of impedance is demonstrated by impedance spectroscopy: the low-frequency limit is lowered by more th an three orders of magnitude to a value of 0.4 Hz. The reason is the e lectroactivity of this material which is caused by reversible proton i ncorporation into the coating, as is proven by cyclic voltammetry. Due to the low interface impedance well below 1 Hz, the coated electrodes fulfil the requirements for medical applications. Outstanding sensing behaviour was shown by measuring the monophasic action potential in d ogs, which is possible without any distortions.