The effect of nonporous PTFE-covered stents on intimal hyperplasia following balloon arterial injury in minipigs

Purpose: To report an experimental study investigating the ability of nonporous polytetrafluoroethylene (PTFE) covering on a metallic stent to retard the development of neointimal hyperplasia (NIH). Methods: Three groups of Hanford miniature swine underwent standardized balloon injury to both external lilac arteries. Group I animals (control) received balloon injuries only. Group II had the site of balloon injury supported by a properly sized, balloon-expandable Palmaz stent placed directly over the injury site. Group III animals received a Palmaz stent covered with PTFE graft. All animals underwent arteriography immediately after intervention and again prior to sacrifice and specimen harvest at 4 weeks. The specimens were examined grossly and histologically at the proximal, middle, and distal segments for NIH development. Results: Uncovered stents developed significantly more NIH (p < 0.0001) and greater luminal narrowing (p < 0.001) than the controls. PTFE-covered stents (group III) exhibited less NIH (p < 0.001) and luminal reduction (p < 0.01) than bare stents (group II) at the middle portion of the stent-graft, but the PTFE cover had no effect on NIH and lumen reduction at the proximal or distal ends of the prosthesis. Conclusions: PTFE-covered stents retarded NIH at 4 weeks, but only at the midportion of the devices; the covering did not prevent neointimal pannus ingrowth at the proximal and distal ends.