The widespread usage of chronic implantable sensors in cardiac device systems has been hampered by both sensor technology issues and the lack of surface passivations with chronic antithrombogenic capabilities. In this study, dummy pacing leads with six types of passivations were implanted for 17 weeks in 36 dogs to assess thrombogenic character, degree of tissue growth and encapulation, and general performance in providing optically clear windows into the blood or body tissues. Asceptic surgical procedures were used and complete blood work-up was performed every two weeks postop. Two dogs served as surgical shams to monitor system artifacts. At explant the devices fairly clearly divided themselves into two groups based on the percent of exposed surface area covered by gross macroscopic tissue accumulations. There were three passivated types in each group. Scanning electron microscopy (SEM) and energy dispersive analysis of x-rays (EDAX) techniques were used to investigate further the samples from the three passivation types that performed "better" based on percent surface area analysis. Issues that became prominent were substrate surface finish and topography, and some mineralization phenomena. Some of the evidence raises the possibility that processes that provide chronic antithrombogenic performance might also enhance mineralization or propensity toward natural breakdown processes. These questions are now being more closely addressed in follow-up studies now in progress.
