Morphologic and immunohistochemical observations of tissues surrounding retrieved transvenous pacemaker leads

Immunohistochemical and morphologic techniques were employed to evaluate the tissue response around chronically implanted pacing leads. Seventeen leads were retrieved from 12 patients. Leads were extracted by direct manual traction (1), extraction with sheaths and locking stylets (1), or with by a combination of mechanical tools and Excimer laser sheaths (15). Mean lead implantation time was 5.6 years (range 1-8 years). Frozen sections, 6-8 microm thick, were incubated with antibodies against HLA-DR antigen, endothelial cells, macrophages, T cells, plasma cells, fibrinogen, and interleukin-1beta. Prominent morphologic observations were fibrous encapsulations of the leads. Immunohistochemical analysis revealed a tissue generally devoid of inflammatory and immune cells. The fibrous capsule surrounding the lead was partially or completely covered with a monolayer of CD34 expressing endothelial cells. The results from this study provide useful information in design and material selection for pacemaker leads. Endothelialization of the fibrous encapsulation indicates a functionalization of blood-contacting surfaces around pacemaker materials, thus providing a mechanism for long-term persistence of foreign materials in the blood. The laser method allowed an efficient extraction of pacemaker leads without damage to the studied tissues, as suggested by the presence of immunolabeled cells close to the cut surfaces.