Histological Reactions of Porous Tip Endocardial Electrodes Implanted in Sheep

The tissue reaction caused by a sintered tip electrode is compared with that of a platinum-iridium tip electrode in a work which employs implantation in sheep and follow-up of the implant for up to 90 days. Clinical tests and anatomo-pathological examination of the histological sections were performed.

The results show a remarkably rapid fixation to the heart for the porous electrode with formation of limited inflammatory process, a thin fibrous capsule and modest alteration of the endocardial tissue. Conversely, the platinum-iridium electrode does not fix even in long periods and therefore continously rubs the endocardial surface.

Chronic inflammation and formation of remarkably thick connective capsule results, under which the heart seems mode deeply altered.

“Are the Differences between ‘High Performance’ Pacing Leads Clinically Significant? A Comparison of Sintered Platinum and Activated Carbon”

A retrospective assessment was performed of the acute implantation characteristics of two pacing leads, one with a sintered platinum (S 80-T) electrode and the other with an activated vitreous carbon (412-S) electrode in 124 patients. The S80-T lead had a significantly lower implantation threshold. The differences between the two leads in sensing properties, in current flow at threshold voltage and at the output of the generator were not significant at implantation. The 412-S lead had a higher impedance measurement than the S-80-T at implantation but this was mainly due to the resistance differences of the conductors rather than to electrode-patient interactions.

A subgroup of 20 patients had chronic threshold measurements. The S 80-T lead had a significantly lower chronic voltage threshold.

However because the acute and chronic differences are small we conclude that, although these differences are statistically significant, they are not clinically significant.

Both can justifiably be termed ‘high-performance’ leads.

Do electrode and lead design differences for permanent cardiac pacing translate into clinically demonstrable differences? (Comparison of sintered platinum and activated vitreous and porous carbon electrodes)

A randomized prospective study was undertaken to compare the electrical performances of three permanent, endocardial, tined pacing leads with different electrode designs--sintered platinum, vitreous carbon, and porous carbon. Ninety-nine patients received one of the leads (S80 31; 423S 32; S100 36). Acute R wave amplitude and ST elevation of the native endocardial electrogram, voltage threshold, impedance, and current flow at four pulse durations (0.25-1.0 msec) were measured. Voltage thresholds were measured noninvasively at each of four pulse durations at 2 days and 1, 3, and 6 months after implantation. No significant differences were found in sensing properties, or current flow at threshold at 0.5 msec pulse duration. The 423S lead had a significantly higher impedance at threshold and both a higher impedance and lower current flow at 5 V. No significant differences in threshold voltages were found between the three leads at any pulse duration, at any of the assessed times after implantation. Six-month thresholds for the S80, 423S, and S100 leads were 1.18 +/- 0.35, 1.17 +/- 0.29, and 1.06 +/- 0.38 V respectively at 0.5 msec pulse duration. Differences between 'high performance' pacing leads need to be of a greater order of magnitude before they can be exploited to give any real clinical advantage to patients.

Effects of dexamethasone elution on tissue reaction around stimulating electrodes of endocardial pacing leads in dogs

A pair of endocardial pacemaker leads, identical except for the presence or absence of dexamethasone elution from the distal stimulating electrode, was implanted into the right ventricle of each of 12 dogs for either 3 weeks (n = six pairs) or 6 weeks (n = six pairs). Fibrous connective tissue sheaths (0.04 to 0.20 mm thick) formed around the distal porous-surfaced stimulating electrodes because of proliferation of endocardial connective tissue and adherence and organization of thrombus. Connective tissue sheaths were composed of fibroblasts within an abundant collagen matrix and contained scattered macrophages, lymphocytes, plasma cells, and mast cells. Connective tissue sheaths around dexamethasone-eluting leads were thinner (p less than 0.03), less cellular (p less than 0.10), and had fewer mast cells (p less than 0.10) than corresponding nonsteroid leads. There was mild multifocal interstitial fibrosis, myofiber atrophy, and myofibrillar lysis in the adjacent myocardium. Thresholds for electrical stimulation of the myocardium were consistently lower for pacing leads with dexamethasone-eluting stimulating electrodes than for leads without dexamethasone.

Porous electrodes: concept, technology and results

Porous electrodes were designed and implanted to optimize sensing and pacing performance of the cardiac pacemaker. These electrodes were manufactured to create an effective, atraumatic endocardial interface in order to (1) decrease chronic stimulation thresholds and pacemaker current drain; (2) facilitate fibrous protein tissue ingrowth for reduced electrode displacement; and (3) to create a large electrolytic surface area of contact for reduced polarization voltage, thus improving impulse and electrogram transmission. Thus far, clinical results demonstrate reduced long-term threshold and decreased current drain. Long-term advantages of porous electrodes remain to be determined.