Endocardial silicone lead wear: description of tribological phenomena on the basis of microscopic examination of removed leads. Preliminary report.

BACKGROUND: The passage of a lead in tissues and in the cardiovascular system depends on the implantation technique. The structure of the leads, which is a combination of two or more materials, triggers their wear. Breakage of the external pacemaker (PM) lead insulation causes unsealing of the lead and exposure of its internal spaces, which can be the anchor of lead-dependent infective endocarditis (LDIE). In the case of implantable cardioverter-defibrillator (ICD) leads, damage to external insulation isthe cause of externalisation of the cable. AIM: To describe endocardial lead abrasion as a tribological phenomenon resulting from rubbing the leads against each other in the mechanism of polymer on polymer friction, and other mechanisms associated with lead structure i.e. polymer on metal friction. METHODS: Twenty-two leads were extracted from ten patients (three women) aged 66.5 ± 13.4 years. In all cases, the reason for lead removal was infection ­ in 80% LDIE. The PM (one ICD) two- and three-lead systems, all with silicone insulation, were aged 3­25, mean 8.3 years. The destroyed polymer insulation was examined by optical and scanning electron microscopy. The site of damage was defined as the length of the lead from its distal end. This lead segment motion was analysed on chest scopy performed prior to the removal procedure. In this way, three sites of lead damage were distinguished: intracardiac, intravenous, and intrapocket. Tribological wear was observed on the polymer-metal interface and between the leads. The following characteristics were recorded: the type of PM or ICD system in which the extracted leads worked, the lead dwell time,and the lead model. RESULTS: Scanning electron examinations showed that in all cases lead insulation had undergone tribological failure. In all samples, the image of fatigue wear was recorded. In all examined places, we found evidence that adhesive wear was present with the transfer of material to the edges of friction zones and/or to friction partners. In 80% of the patients with LDIE, a total breakage of insulation and abrasive wear was observed, especially when a lead cyclically bent and rubbed against another lead. Abrasive wear was the cause of lead unsealing at sites of strong lead bending, in the right atrium near the tricuspid valve. CONCLUSIONS: Acknowledging the tribological mechanism may connect the commonly known crush syndrome with lead abrasion in the cardiac implantable device pocket and in the heart cavity.

Analysis of wear of polyethylene hip joint cup related to its positioning in patient's body.

Polyethylene parts of endoprosthesis are the weakest parts of each medical implant. They can be worn out within several years. During this period, a patient can enjoy good physical efficiency until the wear of polyethylene part limits his/her mobility. Then the reoperation is necessary and positioning of all parts of endoprosthesis has an effect on future patient's mobility and durability of implant. Elements of endoprosthesis during exploitation are heavily loaded both by normal and tangential forces and moments. In this paper, the dependence of wear of polyethylene cup on its positioning in pelvis is the major problem. Wear of the cup is determined by two measures: the depth and volume of a material rubbed off from the contact surface. The sensitivity of the depth of rubbing off is evaluated relative to two angles of anteversion and abduction, and radii of the cup. Numerical results are obtained by using Abaqus FE system with data related to patient's activity identified on the basis of medical reports.