Effects of local steroid elution on chronic pacing threshold and impedance of endocardial pacemaker leads

To study the effects of steroid elution on chronic pacing threshold and impedance, a 4-mm2 surface area lead with steroid (030-368, Telectronics; n = 9) was compared to the same lead without steroid (030-359, Telectronics; n = 9) 3 months after implantation. The pulse duration thresholds of the steroid lead were significantly lower at 0.8, 1.6, 2.5, and 5.0 V. Impedance measured by telemetry at 0.8, 1.6, 2.5, 5.0 and 8.0 V pulse amplitude, and 0.05, 0.25, 0.5 and 1.0 ms pulse duration was similar for the two leads. Mean impedance was about 650 omega and did not change from 0.8 to 8.0 V. The local steroid elution reduced the pacing threshold, but had no influence on the impedance. The stable impedance indicates that the impedance of this lead was not modified by pulse-dependent variables and, therefore, can also be correctly determined at pulse amplitudes below 5.0 V.