Chronic threshold of stimulating electrodes: comparison of activated vitreous carbon with conventional platinum-iridium electrodes in animal tests.

Electrodes made of vitreous carbon are inert, corrosion-resistant, inactive to electrocatalytic reactions and are especially biocompatible. Upon activation, they attain a capacitance of 20 to 40 mF and become "non-polarizable". Therefore, they should be particularly suitable as stimulating and sensing electrodes for cardiac pacemakers. The connective tissue layer that develops around the electrode because of the foreign-body reaction is less than 100 micron thick. The threshold rise, through lower than that of conventional Pt-Ir or ELGILOY electrodes, cannot be attributed exclusively to the connective tissue layer that is formed. Under favourable conditions, the threshold in animal experiments remains below 525 mV. Blood-spaces adjoining the electrodes are found at higher chronic threshold values.