A New Low Threshold Platinized Epicardial Pacing Electrode: Comparative Evaluation in Immature Canines

Abstract

A prospective comparison of pacing and sensing capabilities between the conventional Medtronic Model 4951 platinum-iridium epicardial pacing electrode and a new modified "platinized" version of the same electrode was performed in immature canines to determine if the new electrode design improves pacing in the immature myocardium. The conventional electrode was modified by electroplating platinum black particles onto the surface to increase the effective or true microscopic surface area, yet essentially maintain the same overall geometric electrode size. Both epicardial electrodes were inserted into the right ventricular myocardium with the lead pad sutured to the epicardium, and externalized to the scruff in five puppies (age 3 months). An additional left ventricular lead was implanted to permit chronic pacing following epicardially-induced atrioventricular block. Acute and chronic sensing and pacing capabilities of each externalized electrode were performed at implant and weekly up to 4 months. Histologic examination of each electrode implant site was performed at the end of the study period. At implant, both electrodes exhibited comparable values for sensed R waves, lead impedances, and pacing thresholds. During the study, the platinized electrode exhibited lower pacing thresholds. Analysis of all postimplant data demonstrated this threshold difference to be significantly lower (P less than .01) for the platinized version. Lead impedance and sensing capabilities remained comparable between the two designs. Histologic study demonstrated less fibrotic infiltration at the platinized electrode site. This preliminary evaluation indicates that for the duration of the postimplant study period, the platinized epicardial electrode design was associated with significantly lower thresholds and less fibrosis as a function of time compared to the conventional smooth electrode surface design. The new platinized electrode limits exit block in the developing immature myocardium and permits safe pacing at lower pulse widths and voltages to increase battery life.

The Electrode‐Tissue Interface: The Revolutionary Role of Steroid‐Elution

“…For example, it has long been known that a perfectly clean electrode will produce a lower stimulation threshold than one contaminated with dust, fiber, glove powder, or other contaminants collected during the lead's manufacture or implantation. Thoroughly cleaned platinized platinum epicardial leads have demonstrated superior stimulation thresholds and reduced fibrotic tissue encapsulation in immature canines . A variation of the clean electrode concept was the Nafion® copolymer ion‐exchange membrane (DuPont, Wilmington, DE, USA), which allows a free flow of current.…”

Long‐Term Performance of Transvenous, Steroid‐Eluting, High Impedance, Passive‐Fixation Ventricular Pacing Leads

“…Pacing impedance varies as a function of the geometric surface area of electrode, however, the source impedance varies as a function of the microscopic surface area of the electrode 3 . Several designs have been developed to create a large microscopic surface area: a porous electrode was made by coiled wire mesh with a basket screen (groups I and III) while the platinized electrode was made by a microporous surface (group II) 1–3 . These designs have resulted in a small geometric surface area, high impedance, steroid‐eluting electrode with a larger electrode‐tissue contact area to improve sensing and to facilitate tissue ingrowth for prevention of electrode dislodgement.…”

“…It appeared that the electrode tissue interface reaction play an important role during long‐term electrical performance, as the changes during long‐term follow‐up were similar in groups with same electrode material (groups I and III) regardless of tip electrode geometric surface area. Previous canine histological study has demonstrated that the inflammatory response could be minimized by modification of the electrode surface to an ultrasmall particulate surface, resulting in a thinner fibrotic capsule and lower chronic threshold 2 …”

“…However, a decrease in the geometric surface area of the pacing electrode may result in an unfavorable sensing and an increase in pacing threshold. The porous surface or platinized electrode with enlarged microscopic electrode‐tissue contact area and improved sensing input impedance was designed to resolve problems related to a small electrode 1–3 . The steroid elution technique is expected to improve chronic pacing threshold with alteration of tissue reaction pattern surrounding the electrode 4 .…”