LOW POLARIZATION PACING LEAD FOR DETECTING THE VENTRICULAR-EVOKED RESPONSE

The cardiac response to a pacing pulse is potentially useful for rate adaptive pacemakers and threshold tracking systems. However, until now capture recognition of the ventricular-evoked response by the use of a single electrode for stimulation as well as detection was limited by the electrode polarization. Electronic measures against the stimulus polarization artifact have not been successful due to the variability of the after potential or the requirement of additional battery power. Following the idea of Lewin, Myers and Parsonnet [1], who introduced the idea of a non-polarizable porous electrode for physiological stimu lation, titanium nitride (TiN) and iridium (Ir) coatings with fractal surface structure have been developed with high electro-chemical activ e surface areas and Helmholtz double-layer capacities of up to 50.000 mu F/cm(2), thus reducing the polarization artifact significantly. Two types of endocardial leads (10 with a fractal TiN coating and 5 with a fractal Ir coating) were implanted in the apex of the right ventricl e and the polarization artifact, as well as the evoked response, was m easured. Both types of pacing leads show a 90% reduction in the polari zation artifact in comparison to conventional leads. If an autoshort o f approximately 20 to 50 ms is applied after the pacing pulse, the pol arization artifact of these leads is negligible, thus enabling reliabl e detection of at least the repolarization phase of the ventricular-ev oked response, which is fully sufficient: for capture recognition. Add itionally, due to their low polarization losses, TiN- or Ir-coated ele ctrodes with fractal surface structure have a unique stimulation and d etection performance.