Compressive stent and delivery system

United States Patent [19]

Wolff et al.

[ii] Patent Number: 4,830,003 [45] Date of Patent: May 16, 1989

[54] COMPRESSIVE STENT AND DELIVERY SYSTEM

[76] Inventors: Rodney G. Wolff, 468 W. Eagle Lake Dr., Maple Grove, Minn. 55369; Creg W. Dance, 812 Benton St., Anoka, Minn. 55303; Brice Letac, 134 rue du Renard, 76.000 Roven, France; Alain Cribier, 76150 Maromme, Maromme, France

[21] Appl. No.: 208,252

[22] Filed: Jun. 17,1988

[51] Int. CI.* A61M 29/00

[52] U.S. CI 128/343; 623/1

[58] Field of Search 623/1; 600/37; 128/343,

128/334 R, 335

[56] References Cited

U.S. PATENT DOCUMENTS

4,503,569 3/1985 Dotter 128/303

4,553,545 11/1985 Maass et al 128/341

4,580,568 4/1986 Gianturco 128/348

4,647,416 3/1987 Seller 623/1

4,649,922 3/1987 Wiktor 128/344

4,655,771 4/1987 Wallsten 128/343

4,733,665 3/1988 Palmaz 128/343

OTHER PUBLICATIONS

Palmaz et al., Expandable Intraluminal Vascular Graft:
A Feasibility Study, Feb., 1986, Surgery, pp. 199-205.
Palmaz et al., Expandable Intraluminal Graft: A Prelim-
inary Study, 1985, Radiology, pp. 73-77.
Palmaz et al., Atherosclerotic Rabbit Aortas: Expand-
able Intraluminal Grafting, 1986, Radiology, pp.
723-726.

Primary Examiner—Richard J. Apley
Assistant Examiner—James Prizant

[57] ABSTRACT

A cylindrical shaped stent to prevent arterial acute closure and subsequent restenosis formed of longitudinal wires of biocompatible metal. The wires are welded together in pairs at alternate ends with each pair of wires bent into a V-section. The wires are all formed into a cylinder welded closed to form the stent. The stent is compressed and loaded into an outer catheter by a special tool. The stent is positioned and released for self expansion in situ by an inner catheter. A guide wire through both assists in threading the catheters through blood vessels.

10 Claims, 2 Drawing Sheets

COMPRESSIVE STENT AND DELIVERY SYSTEM

TECHNICAL FIELD

The present invention relates to an intravascular stent 5 which can be applied within the peripheral or coronary arteries of a living animal or human being to maintain patency after a balloon angioplasty, either a percutaneous transluminal coronary angioplasty (PCTA) or a percutaneous transluminal angioplasty (PTA) proce- 10 dure. The stent comprises a tubular shaped structure made up of individual wires welded together which can be compressed along the axis to a smaller tubular diameter to fit within an outer catheter to hold the stent compressed, which is used along with an inner catheter to 15 release the stent and a guide wire which are used after a balloon angioplasty to insert, position and fix the stent permanently at the angioplasty site to prevent acute reocclusion and subsequent restenosis. The construction of the stent is such that the dimensions and material of 20 the device can be selected to provide a given radial force against the interior of the artery adequate to maintain the shape of the vessel against any force tending to close it. These closure forces include not only acute reclosure due to intimal dissections, flaps and spasm but 25 also plaque restenosis. The latter is prevented or slowed by neo-intimal overgrowth on the stent itself. The length of the stent can also be varied or more than one stent can be used at a single location to accommodate curvature and other unusual arterial characteristics. 30 Radiopaque marker material on the end of the inner and outer catheters permits locating the stent at the desired site by external monitoring or the stent itself can be made of radiopaque material.

BACKGROUND ART 35

In U.S. Pat. No. 4,553,545 a device which can be expanded after insertion in a blood vessel by rotating a wire coil about its length to reduce the number of turns and thereby increase the diameter is disclosed. In U.S. 40 Pat. No. 4,503,569 a helically wound coil is formed of a memory Nitinol alloy which has a transition temperature in the range of 115 degrees to 125 degrees Farenheit. After placement in the vessel this coil is heated to regain its original larger shape. These approaches re- 45 quire either heat or mechanical forces to be applied to the apparatus, in order to expand the stent at the site, with the resulting trauma to the body.

In U.S. Pat. No. 4,580,568 a stent is formed of stainless steel wire of 0.018 inches diameter arranged in a 50 closed zig-zag pattern. The stent is compressed to reduce its size in order to position it within a sheath, which is used to locate the stent within the vascular system. A flat-ended catheter is used through the sheath to hold the stent in place in the passageway while the 55 sheath is withdrawn, allowing the stent to expand into its original shape to hold the passageway open and enlarged. According to the specifications the only energy stored in this stent to restore it to its original shape is stored in the bends. 60

This device and delivery system suffers from a number of severe limitations and problems. Fashioning the stent from a continuous wire folded in a zig-zag fashion requires a sharp bend in the wire at each end of the stent to form this shape. A wire can only be bent at a ratio 65 which is some multiple of the wire diameter. The exact multiple will vary according to the property of the material. The example cited in the patent as claimed

uses a wire of 0.018 inches in diameter which is equivalent to 0.04572 centimeters and a bend ratio of no more than 0.2 centimeters. This is a ratio of approximately 1 to 4.37. Since the wire is bent to form the zig-zag shape there must be some angle formed between adjacent legs which limits the minimum spacing between these legs. A large amount of force is necessary to compress the stent when the stent is short since energy is only stored in the bends. If the stent is made relatively short in length with respect to the diameter then the amount of force necessary to bend the wires in order to compress the stent becomes large. This again is because the bends are the only place that energy is stored. Only if the stent is made relatively long with respect to the diameter is the force required to hold a vascular vessel open reduced. The claims specified stents of specific sizes 5.5 cm long X 4 cm diameter fully expanded and 3.0 cm long X 2.5 cm diameter fully expanded. This relatively long length and diameter results in forces which are compatible with the vascular system but can obviously only be used in very large peripheral arteries and veins. Another effect is the absolute minimum size to which the stent can be compressed. As mentioned earlier the angular relationship between adjacent wires at the ends limits the minimum spacing between adjacent wires which in turn limits the minimum diameter of the stent to a size which is incompatible with coronary arteries and like sized vessels.

In addition, since the diameter of the wire and the material composition is continuous throughout its length, these parameters are not varied to provide different characteristics at the bends vs. the straight section of the zig-zag. Since only the material in the bends themselves are involved in storing energy the characteristics of the bends versus the straight sections are not necessarily compatible for all of these requirements in particular when the additional necessity for utilizing a bio-compatible material is added. Further, to complete and close the zig-zag pattern made up of a single wire a sleeve must be placed over the two ends to connect them together which results in an anomoly at that point.

We have taken an entirely different approach to the problem to avoid these inherent limitations of the previous system by using individual parts welded together to avoid the necessity for a bend in the material completely. This overcomes all of the limitations and restrictions enumerated above. Our stent is adaptable for use in coronary arteries with their extremely small diameter where the other approach because of the bend diameters results in a stent which cannot be reduced to the required coronary size, unless a far fewer number of wires are used. If far fewer numbers of wires are used, this greatly limits both the force applied to and the surface coverage of the vessel wall.

The delivery system has no means of locating the position of the stent relative to the stenosis site from the exterior of the body. No guide wire is used and in use the stent is inserted from the proximal end of the catheter.

SUMMARY OF THE INVENTION

The present invention is characterized by a prothesis stent which is useful in conjunction with a balloon angioplasty, either a percutaneous transluminal coronary angioplasty (PCTA) or a percutaneous transluminal angioplasty (PTA) of diseased coronary arteries or any other larger arteries to prevent acute reclosure or reste