A type of endoprosthesis device, commonly referred to as a stent, is placed or implanted within a blood vessel for treating occlusions, stenoses, or aneurysms in the blood vessel. These devices are implanted within the vascular system to reinforce collapsing, partially occluded, weakened, or abnormally dilated sections of the blood vessel. Stents also have been successfully implanted in the urinary tract or the bile duct to reinforce those body vessels.
One of the drawbacks of conventional stents is that they are produced in a straight tubular configuration. The use of such a stent to treat disease at or near a branch or bifurcation of a blood vessel runs the risk of compromising the degree of patency of the primary vessel and/or its branches or bifurcation. This may occur as a result of several problems such as displacing diseased tissue, vessel spasm, dissection with or without intimal flaps, thrombosis, and embolism.
One common procedure for implanting the endoprosthesis or stent is to first open the region of the vessel with a balloon catheter and then place the stent in a position that bridges the weakened portion of the vessel.
Prior art patents refer to the construction and design of both the stent as well as the apparatus for positioning the stent within the vessel. One representative patent is U.S. Pat. No. 4,140,126 to Chaudhury which issued Feb. 20, 1979. This patent discloses a technique for positioning an elongated cylindrical stent at a region of an aneurysm to avoid catastrophic failure of the blood vessel wall. The '126 patent discloses a cylinder that expands to its implanted configuration after insertion with the aid of a catheter
A second prior art patent to Dotter U.S. Pat. No. 4,503,569 which issued Mar. 12, 1985 discloses a spring stent which expands to an implanted configuration with a change in temperature. The spring stent is implanted in a coiled orientation and heated to cause the spring to expand.
U.S. Pat. No. 4,733,665 to Palmaz which issued Mar. 29, 1988 discloses a number of stent configurations for implantation with the aid of a catheter. The catheter includes a mechanism for mounting and retaining the vascular prosthesis or stent, preferably on an inflatable portion of the catheter The stent is implanted by positioning it within the blood vessel and monitoring its position on a viewing monitor. Once the stent is properly positioned, the catheter is expanded and the stent separated from the catheter body. The catheter can then be withdrawn from the subject, leaving the stent in place within the blood vessel.
U.S. Pat. No. 4,413,989 to Schjeldahl et al. which issued Nov. 8, 1983 discloses a variety of balloon catheter constructions. FIG. 5 of this patent discloses a bifurcating expander for insertion into diverging branches of a subject blood vessel.
U.S. Pat. No. 3,993,078 to Bergentz et al. discloses an insert for use in vascular surgery. The embodiment of this insert disclosed in FIG. 2 forms a "Y" tube. A distingishing feature of the inserts disclosed in this patent is the ability to take apart the insert by pulling a free end of a thread that forms the insert. This insert is surgically placed within a subject and no mention is made concerning the non-surgical placement of such an insert within a vessel.
U.S. patent application Ser. No. 240,000 entitled "Radially Expandable Endoprosthesis and the Like" discloses a generally cylindrical stent formed from a wire that is bent into a series of tight bends and then spirally wound about a cylindrical mandrel to form the stent. If a radially outward force is applied to the stent the sharp bends in the wire tend to straighten and the stent diameter enlarges. One technique for implanting this stent uses a deflated balloon catheter to position the stent within a vessel. Once the stent is properly positioned the balloon is inflated to press the stent against the inner wall linings of the vessel. The balloon is then deflated and withdrawn from the vessel, leaving the stent in place.