Active fixation leads--long-term threshold reduction using a drug-infused ceramic collar.

Previous investigators, including our group, have reported the threshold reduction benefits of steroid-releasing leads. To date, all published literature has been for the passive fixation versions. The application of steroids should also enhance the performance of active fixation leads. We have developed and tested an atrial and a ventricular Accufix lead with a dexamethasone acetate-releasing, porous ceramic collar (DA DEC). A long-term sheep study has shown a significant reduction in thresholds (THR) when compared to standard Accufix leads without the collar (ACC) for atrial (ATR) and ventricular (VENT) versions (bipolar THR [0.5 msec] at 24 weeks: VENT DA DEC = 0.51 +/- 0.07, VENT ACC = 1.49 +/- 1.03; ATR DA DEC = 1.31 +/- 1.14, ATR ACC = 2.99 +/- 1.31). All other parameters tested, including pacing and sensing impedance as well as polarization overpotential, were similar for the two groups. The Accufix DEC leads therefore have excellent potential for low energy stimulation.

Drug-eluting collar--a new approach to reducing threshold.

This study evaluated the clinical performance of leads with a drug-eluting (less than 0.5 mg of dexamethasone sodium phosphate) collar (DEC) placed adjacent to a 4-mm2 Pt/Ir coated electrode (Telectronics model 030-368). Ten trailing tined ventricular silicone DEC leads and ten control leads (model 030-359) were implanted transvenously in patients of comparable age, sex, and indication for pacing. Early threshold rise, chronic thresholds (Vario), and lead impedances were monitored by pacer telemetry. The DEC lead had substantially lower thresholds in the first few weeks (P less than 0.0005) as well as chronically (P less than 0.025). The study has shown that a drug dose of less than 0.5 mg, released from a drug-eluting collar (DEC), is effective in reducing thresholds.

In vivo elution rate of drug eluting ceramic leads with a reduced dose of dexamethasone sodium phosphate.

We have evaluated the in vivo elution rate and the threshold voltage performance of a new lead incorporating a controlled delivery device based on a porous ceramic collar. The drug, dexamethasone sodium phosphate (DSP less than 0.2 mg), was contained within the pores of a ceramic collar that was positioned externally and adjacent to a 4 mm2 Pt/Ir coated electrode. Thirty-three leads comprising a porous ceramic drug eluting collar (DEC) were implanted in the right ventricle of 12 sheep. In vivo elution was determined by analyzing the drug remaining in the collar after 1, 3, 11, and 28 days. Voltage thresholds were measured at implant and then weekly for 28 days on three sheep. Results were compared to leads with identical electrodes but with silicone DEC (DSP less than 0.5 mg). The in vivo elution rate of the ceramic DEC leads was fast with approximately 50% of the drug content on the first day. Although the drug content and elution rates were different for the ceramic and silicone DEC leads, the threshold performance of the leads was similar. For ceramic and silicone DEC leads, threshold voltages at implant and at 4 weeks were 0.29 +/- 0.09 compared to 0.37 +/- 0.08 and 0.42 +/- 0.08 compared to 0.44 +/- 0.13, respectively. The results show that a relatively rapid release of a reduced dose of DSP from a DEC is still effective in reducing threshold peaking.

Composite electrode tips containing externally placed drug releasing collars.

We have developed a composite electrode tip based on a new concept whereby the electrode is combined with a polymeric collar containing dexamethasone sodium phosphate (DSP). The collar is positioned immediately adjacent to the electrode. Initial evaluation of this concept employed the Telectronics Laserpor electrode and a collar containing approximately 1.8 mg of DSP (LPD). Conventional Telectronics Laserpor (LP) electrodes were used as controls. Further evaluation was performed using a DSP (less than 0.5 mg) eluting collar and a new 4 mm2 mushroom shaped electrode with a high microsurface Pt/Ir coating (MD). Data for conventional Telectronics Laserdish (LD) electrodes were used for comparison. Unipolar ventricular leads were implanted transvenously in the right ventricular apex of sheep. Voltage thresholds, pacing (5 V, 0.5 ms) and sensing (50/100 mV RMS, 50 Hz) impedances were measured during the subchronic phase (less than 6 weeks) and in the case of LD and MD for 6 months. The steroid eluting electrodes were effective in eliminating (2 weeks vs. Impl., N.S.) the 2 week threshold peaking seen with the control leads (2 weeks vs. Impl., P less than 0.005). The small area MD electrode thresholds remained stable and low for up to 6 months (0.38 +/- 0.09 (10) c.f. 0.46 +/- 0.11(6); 14 and 180 days, respectively, N.S.). The composite electrode tips with steroid releasing collars thus show great potential for a substantial reduction in stimulation energy.

Characteristics of advanced porous and textured surface pacemaker electrodes.

Reduced stimulation thresholds, improved sensing and better attachment have been claimed for totally porous and porous surfaced electrodes. In this study, the potential for clinical use of two new types of porous electrodes and a non-porous, textured high microsurface area electrode, has been evaluated by comparison with equivalent sized, smooth non-porous controls. Eighteen sintered and seven laser drilled porous electrodes, seven-non-porous textured electrodes, and sixteen controls, were implanted singly in the right ventricles of sheep. Measurements of threshold, pacing, sensing and bulk impedances were taken at regular intervals for up 180 days. At sacrifice, only three of the thirteen non-porous controls were attached. All laser porous electrodes, apart from two which were dislodged, were attached, as were eleven of fifteen sintered porous, and five of seven textured non-porous electrodes. Tissue ingrowth was found for both porous electrode types. Stimulation thresholds were not statistically different for all electrode types (p less than 0.05). Pacing and bulk impedances of the two porous and surface textured electrodes were significantly higher (p less than 0.10, p less than 0.05, respectively) than those of controls. The three new electrodes exhibited similar chronic sensing impedance values, 30% less than equivalent non-porous electrodes. The similar sensing performance of the porous and high microsurface area non-porous electrodes indicates that the nature of the external surface, rather than internal porosity, determines sensing impedance. All three new electrode types showed improved attachment and sensing compared with similar smooth electrodes. The laser porous electrode, which permits fixation by tissue ingrowth and maintains simplicity of construction, is promising for routine clinical use.