[High impedance electrodes]. / Hochohm-Elektroden.

The concept of small surface high impedance pacing electrodes is based on three major arguments: 1) tip size reduction increases the field strength at the electrode surface; 2) a micro-porous coating allows for downsizing the geometric surface area to about 1 mm(2) without increasing the voltage pacing threshold; and 3) small electrodes exhibit high pacing impedance hence reduce the charge transfer from the battery through the electrode-tissue interface. This design does not compromise sensing if the input impedance of the amplifier used is adequate (>30kΩ). In the long term (2 up to 5 years post-implant), typical impedance values range between 900 and 1200Ω, pacing thresholds are below 1.0V @ 0.5 ms, and the minimum charge delivered per pulse is around 0.2µC. Careful implantation is a prerequisite of good long term performance and does not bear additional risks of myocardial perforation or excessive threshold rise as compared to the normal (5.8 mm(2)) electrode size. The benefit in terms of battery drain is maximum with nominal output parameters (≥2.5 volt); when pacing below the battery voltage, however, the difference in pacemaker longevity is marginal between normal and high impedance "low threshold electrodes". This energy balance may change in favor of high impedance leads if the current drain of the circuitry will be lowered in next generation pacing devices.