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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 3–25, 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.