Investigation of Wear Mechanisms in Silicone Sleeved Implantable Cardiac Device Leads using an In Vitro Approach

Cardiac implantable electronic devices (CIED), such as pacemakers and defibrillators, have a titanium casing which holds the electronics, connected to insulated leads which deliver therapeutic pulses to regulate heart activity. CIED lifetimes are often limited by wear of their polymer components, as on the surface of the elastomeric insulation of the leads, which is frequently silicone. Insulation wear during regular activity can yield patient discomfort or surgical complications upon replacement. Little is known about the wear mechanisms of these silicone materials in situ, but it is known that wear occurs between the leads and either the titanium casing, other leads, or bodily tissue. This study investigated titanium-on-silicone wear of lead insulation used in CIEDs. Surgically retrieved silicone insulated leads showed unusual wear scars that were polished and smooth. The goal of this study was twofold: replicate the unique wear scar with a testing apparatus, and determine wear mechanisms of the silicone insulation. Silicone cardiac leads were obtained from the manufacturer and an apparatus was constructed to simulate in-body conditions while accelerating the wear process. Three key parameters were chosen to investigate the wear mechanisms of this system: load, environmental fluid, and third-body abrasive. A factorial matrix with two replications was used to test these variables. Wear scars were examined using white light profilometry, optical microscopy, and scanning electron microscopy (SEM). An analysis-of-variance (ANOVA) showed that all test factors did not significantly affect the size and depth of the wear scars, but revealed key mechanisms that could affect other known wear configurations such as lead-on-lead wear.