1. Field of the Invention
This invention relates to intravascular implants for maintaining vascular patency in human blood vessels. More particularly, this invention relates to a radially expandable stent made from a fine wire formed into a serpentine ribbon wound into a cylindrical shape for introduction into a body vessel for balloon expansion therein in a radial fashion to support the wall of the vessel when in the expanded configuration. The stent includes an impermeable membrane that lies in the plane of the cylinder. This invention is particularly useful in transluminal implantation of a stent for use in the coronary angioplasty to prevent restenosis, and for the treatment of aneurysms or subintimal dissections.
2. Description of the Prior Art
The basic concept of stents has been known for a number of years. Various types of stents have been proposed and patented, including self-expanding spring types, compressed spring types, mechanically actuated expandable devices, heat actuated expandable devices, and the like. More recently, expandable sleeves have been proposed such as shown in Palmaz, U.S. Pat. No. 4,733,665. In this disclosure there is shown a sleeve having slots therethrough to form a permeable mesh. The sleeve is placed transluminally, and then expanded by a balloon catheter through the elastic limit of the metal so as to permanently deform the sleeve into supporting contact with the interior surface of a blood vessel. Other examples of expandable wire stents are shown in Hillstead, U.S. Pat. No. 4,865,516, and Wiktor, U.S. Pat. No. 4,886,062.
In my U.S. Pat. No. 5,217,483 (referred to hereinafter as the '483 Patent) I disclose the use of a fine platinum wire bent into a serpentine flat ribbon which is wound around a mandrel into a radially expandable cylindrical sleeve for mounting on a balloon catheter for transluminal intravascular placement. The expanded sleeve as disposed in a vessel possesses gaps or interstices which are believed to protect the vascular endothelium from contact therewith, and to promote endothelial proliferation and remodeling of the vascular intima about the sleeve. However in many cases the trauma of implantation causes microscopic or even macroscopic intimal tears, and exposes the subintimal space to the bloodstream. This is undesirable as further dissection of the vessel is possible. Furthermore tissue reactions, including thrombus formation, intimal fibroplasia, and cicatrization could result in restenosis of the vessel.
Permeable transluminally placed intravascular stents are suboptimum for the treatment of aneurysms. While the structure of the expanded mesh may reduce the pulsatile forces acting against a weakened arterial wall, this effect is doubtless incomplete. The art has long utilized grossly impermeable continuous structures such as Teflon grafts and implants for aneurysm repair in larger vessels by conventional open surgical techniques.