From the Laboratory Use of Stents Covered with Polytetra- fluoroethylene in Experimental Ab- dominal Aortic Aneurysm 1 Julio C. Palmaz, MD Fermin O. Tio, MD Jean Claude Laborde, MD Michael Clem, DVM Frank J. Rivera, MD Kenneth D. Murphy, MD Carlos E. Encarnacion, MD Index terms: Aneurysm, aortic, 89.73 • Aneurysm, therapy, 89.459, 981.1268' In- terventional procedures, experimental, 89.459,981.1268 • Stents and prostheses, 981.1268 JVIR 1995; 6:879-885 Abbreviations: AAA = abdominal aortic aneurysm, PTFE = polytetrafluoroethyl- ene PURPOSE: To establish the effectiveness of covered stents in the treatment of aortic aneurysms, to investigate the histopathologic healing patterns of the device, and to determine the long-term en- durance and integrity of modified polytetratluoroethylene (PTFE). MATERIALS AND METHODS: Experimental aneurysms were cre- ated in dogs by enlarging the aortic lumen with a patch of abdomi- nal fascia. After 5 months, eight animals underwent an endoluminal bypass. The bypass device consisted of a 6-cm-Iong stent covered with thin PTFE. After surgery, the animals were killed at 3, 6, and 12 months in groups of three, three, and two, respectively. Speci- mens were processed for luminal surface studies and cross-sec- tional histologic study. Explanted PTFE material was analyzed for its physical characteristics and performance and was compared with retained control samples. RESULTS: Before the animals were killed, aortography showed pat- ent bypass conduits in all animals, although two of eight had leaks into the aneurysmal sac. Endothelialized neointima largely covered the luminal surface of the PTFE stent. The percentage of prosthetic surface covered by tissue did not change from 3 months to 1 year. Physical testing of the explanted PTFE material showed no struc- tural deterioration and no change in the internodal distance. Thick- ness and axial tensile strength varied 12% and 17% from controls, respectively. CONCLUSION: Thin-walled PTFE seems to have physicochemical characteristics that make this material adequate for endovascular use. Though limited, this study supports the establishment of pre- liminary clinical evaluation of metallic stents combined with PTFE for the treatment of abdominal aortic aneurysm. I From the Section of Cardiovascular and Special Interventions (J.C.P., J.C.L., F.J.R., K.D.M., C.E.E.), the Department of Pathology (F.O.T.), and Laboratory Ani- mal Facilities (M.C.), University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78284-7800. Received March 6, 1995; revi- sion requested May 16; revision received June 7; accepted June 10. Address corre- spondence to J.C.P. © SCVIR, 1995 ENDOVASCULAR bypass of abdominal aortic aneurysms (AAA) is evolving as a promising form of therapy as the search for a more practical meth- od continues. To date, most clinical experience was gained with use of transluminal devices made of a thin- walled prosthetic conduit with self- expandable or balloon-expandable metallic stents affixed to the ends. Preliminary trials of endovascular bypass in patients (1-3) were chal- lenging due to the technical difficul- ties of attaining precise and secure placement of the device. Some of these difficulties were related to the large diameter ofthe introducer sys- tems and to the method ofintralu- minal anchoring employed in the by- pass procedure. The large size of some introducer sheaths has pre- cluded device placement in some pa- tients and has resulted in damage to the access vessel in others. Faulty or ineffective anchoring has resulted in displaced, kinked, or leaky intravas- cular bypass systems. In an attempt to reduce the size ofthe introducer and to improve the conformity and positional stability ofthe device, we designed a system consisting of a long balloon-expandable stent com- 879