Michael Samuel Hirshorn

Screening of Solid and Porous Materials for Pacemaker Electrodes

Several different materials, including one which was porous, were studied to assess their properties as pacemaker electrode tips. Leads were implanted in sheep for periods up to one year. Electrical measurements were made during the implant period and histopathological examination performed after sacrifice. Although titanium vapor‐deposited carbon, and silver did not lower the chronic stimulation threshold below that of platinum, their electrical characteristics were within generally acceptable limits. Zinc evoked a severe tissue reaction and a high threshold. Porous titanium alloy electrodes demonstrated reduced dislodgement, more frequent attachment and a lower sensing impedance than other electrodes.

Characteristles of Advanced Porous and Textured Surface Pacemaker Electrodes

Reduced stimulation thresholds, improved sensing and betler 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 equivalenf 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 fhe right ventricles of sheep. Measurements of threshold, pacing, sensing and bulk impedances were taken at regular intervals for up to 180 days. At sacrifice, only three of the thirteen non‐porous confrols were attached. AU laser porous electrodes, apart from two which were dislodged, were attached, as were eieven of fifteen sintered porous, and five of seven textured non‐porous electrodes. Tissue ingrowth was found for both porous electrode types. Stimulation threshoJds were not statistically different for all electrode types (p < 0.05). Pacing and bulk impedances of the two porous and surface textured electrodes were significantly higher (p < 0.10, p < 0.05, respectively) than those of controls. The three new electrodes exhibited similar chronic sensing impedance vaJues, 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 eJectrodes. The laser porous electrode, which permits fixation by tissue ingrowth and maintainssimplicity of construction, is promising for routine clinical use.

Effect of Pore Size on Threshold and Impedance of Pacemaker Electrodes

The effect of pore size on threshold and pacing impedance of two sintered porous platinum electrodes was evaluated using non porous electrodes as controls.