Electroactive coating of stimulating electrodes

Abstract

Electrophysiologic examinations as well as the electrotherapy of heart diseases require electrodes which distinguish themselves by outstanding sensing and pacing performance. Both, the sensing and the stimulation behaviour are determined by the interface between electrode and tissue. To avoid energy losses and distortions of heart signals having components 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 oxide. On the electrode's surface iridium oxide forms a long-term stable reversible redox system which changes its oxidation state according to the applied potential. The decrease of impendance is demonstrated by impedance spectroscopy: the low-frequency limit is lowered by more than three orders of magnitude to a value of 0.4 Hz. The reason is the electroactivity of this material which is caused by reversible proton incorporation 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 dogs, which is possible without any distortions.