Clinical Experience with Steroid‐Eluting Unipolar Electrodes

In continuing search of low chronic threshold leads, a new concept of electrode design which is capable of delivering corticosteroids at the myocardial tissue interface has been made available by Medtronic. Twenty-three patients, 17 females and 6 males, were either implanted with 4003 (n = 21) or 5023 (n - 2) steroid-eluting electrodes in the ventricular chamber. Pacing modes utilized were WIM (n = 13) or DDD (n = 10). Pulse generators used were Medtronic (7005. 8317, 8329) Pacesetter (285) and Intermedics (283). Thresholds at the time of implantation at 0.50 msec pulse width were 0.40 ± 0.02 volts at 0.66 ± 0.05 milliamps. Resistance and R wave measured were 565.43 ± 22.07 ohms and 9.24 ± 1.06 mv, respectively. Chronic thresholds were checked on routine follow-up visits by either decreasing pulse width and for pulse amplitude. Data is being reported between 1 and 88 (23.22 ± 4.35) weeks. Pulse width threshold at 2.5 volts were 0.10 msec (n = n) and 0.05 msec or lower (n = 12). At 5.0 volts no loss of capture was seen at 0.05 msec (n = 22) except in one patient at 0.10 msec. Pulse width thresholds in the first 24 weeks were lower than 0.20 msec at 2.5 volts (n = 15) and less than 0.70 msec, at 0.8 volts (n = 6). No loss of sensing was seen by electrocardiographic analysis at the time of threshold checks with the pulse generator at standard setting of the R wave. Thus, in this initial report, the steroid-eluting electrodes have demonstrated very low thresholds both in the early and chronic follow-up phase. Demonstration of consistently low thresholds, avoiding initial peaking, will permit routine low output setting without compromising safety and thus prolong the life of the pulse generators.