SYSTEM FOR REMOVABLY SECURING A STENT ON A CATHETER ASSEMBLY AND METHOD OF USE

Abstract: A catheter system for removably securing a stent which generally includes an inner tubular member and an outer tubular member with an expandable member disposed about the inner tubular member. A deformable material is disposed between the expandable member and the inner tubular member. An expandable stent is crimped onto the expandable member and is retained in place by compressing the deformable material. Used with a stent delivery systems, the catheter system is inserted into a body lumen such as an artery. The stent is secured in place while advancing the system through tortuous body lumen passages. The stent is advanced to the desired location in the body lumen and implanted by inflating the expandable member and thereby expanding the stent into the body lumen. The stent is released from the system by deflating the expandable member and withdrawing the catheter system from the body.

Description: SYSTEM FOR REMOVABLY SECURING A STENT ON A CATHETER ASSEMBLY AND METHOD OF USE BACKGROUND OF THE INVENTION This invention relates to devices for the treatment of heart disease and particularly to endo-arterial prosthesis, which are commonly called stents. More particularly, the invention relates to catheter assemblies for removably securing the stent to the catheter during delivery through a body lumen. Several interventional treatment modalities are presently used for heart disease including balloon and laser angioplasty, atherectomy and by-pass surgery. In typical balloon angioplasty procedures, a guiding catheter having a pre-formed distal tip is percutaneously introduced through the femoral artery into the cardiovascular system of a patient in a conventional Seldinger technique and is advanced within the cardiovascular system until the distal tip of the guiding catheter is seated in the ostium. A guidewire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire first is advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guidewire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once in position across the lesion, the balloon, which is made of relatively inelastic materials, is inflated to a predetermined size with radiopaque liquid at relatively high pressure (e.g., greater than 4 atmospheres) to compress the arterioscl erotic plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon then is deflated so that blood flow can be resumed through the dilated artery and the dilatation catheter can be removed therefrom. Further details of dilatation catheters, guidewires, and devices associated therewith for angioplasty procedures can be found in U.S. Patent No. 4,323,071 (Simpson-Robert); U.S. Patent No. 4,439,185 (Lindquist); U.S. Patent No. 4,516,972 (Samson); U.S. Patent No. 4,538,622 (Samson, et al.); U.S. Patent No. 4,554,929 (Samson, et al.); U.S. Patent No. 4,616,652 (Simpson); U.S. Patent No. 4,638,805 (Powell); U.S. Patent No. 4,748,982 (Horzewski, et al.); U.S. Patent No. 5,507,768 (Lau, et al.); U.S. Patent No. 5,451,233 (Yock); and U.S. Patent No. 5,458,651 (Klemm, et al.). One problem which can occur during balloon angioplasty procedures is the formation of intimal flaps which can collapse and occlude the artery when the balloon is deflated at the end of the angioplasty procedure. Another problem characteristic of ballo angioplasty procedures is the large number of patients who are subject to restenosis in the treated artery. In the case of restenosis, the treated artery again may be subjected to balloon angioplasty, or to other treatments such as by-pass surgery if additional balloon angioplasty procedures are not warranted. However, in the event of a partial or total occlusion of a coronary artery by the collapse of a dissected arterial lining after the balloon is deflated, the patient may require immediate medical attention, particularly in the coronary arteries. A focus of recent development work in the treatment of heart disease has been directed to endoprosthetic devices called stents. Stents are generally cylindrically shaped intravascular devices which are placed within an artery to hold it open. The device can be used to prevent restenosis and to maintain the patency of a blood vessel immediately after intravascular treatments. In some circumstances, stents also can be used as the primary treatment device where they are expanded to dilate a stenosis and then left in place. One method and system developed for delivering stents to desired locations within the patient's body lumen involves crimping a stent about an expandable member, such as a balloon on the distal end of a catheter, advancing the catheter through the patient's vascular system until the stent is in the desired location within a blood vessel, and then inflating the expandable member on the catheter to expand the stent within the blood vessel. The expandable member then is deflated and the catheter withdrawn, leaving the expanded stent within the blood vessel, holding open the passageway thereof. However, retaining the position of the stent in the proper location on the expandable member while advancing the catheter through the body lumen has been found to be difficult. If the stent is dislodged from or moved on the expandable member the system will not correctly deliver the stent into the body lumen. This would require repeating the procedure. This delays insertion of the stent into the body lumen and lengthens the time of the stenting procedure. Different methods have been attempted to maintain the position of the stent on the expandable member. One such method involves a protective sheath surrounding the catheter and stent assembly, which is retracted prior to inflation of the expandable member. The use of the sheath, however, increases the profile of the catheter assembly which must traverse narrow vessels and the sheath reduces the flexibility of the distal end of the delivery catheter. It would be an improvement to use a technique which does not increase the overall profile of the catheter assembly and maintains the flexibility of the delivery catheter. Another method has been to remove the friction-reducing coating on the expandable member in the location of the stent thereby allowing the pre-coated surface of the catheter assembly to hold the stent in frictional contact. This method has not proven highly efficient in maintaining the stent in the desired location. What has been needed and heretofore unavailable is a highly efficient means of maintaining a stent in a desired location on a stent delivery system without increasing the overall profile of the catheter assembly or compromising the flexibility. The present invention satisfies this need. SUMMARY OF THE INVENTION This invention is directed to an improvement in stent delivery systems for removably securing a stent onto an expandable member. Securing the stent is accomplished by tightly crimping the stent onto the balloon portion of a catheter wherein a deformable material has been disposed. By compressing the deformable material the stent is secured due to the increased frictional contact and interference between the stent and the compressed catheter assembly. Stent delivery systems typically are composed of an elongated tubular member, or catheter, encompassed by an expandable member such as an inflatable balloon. The stent is located about the expandable member so that the two can be expanded together. The improvement of this invention includes introducing a deformable material into the space between the tube member and the expandable member. The deformable material may be adhered to the elongated tube member, the expandable member, or injected into the space therebetween. The stent then is crimped onto the expandable member so that the deformable material is compressed. The deformable material may be compressed with sufficient force to form pockets of material within the deformable material corresponding to gaps within the structure of the stent. The deformable material also may extend beyond one or both of the longitudinal ends of the stent so that sufficient crimping force can be applied on the expandable stent to form ridges in the deformable material located beyond the ends of the stent. This invention can be used with the known configurations of stent delivery catheter assemblies including over-the-wire (OTW) intravascular catheters and rapid exchange (RX) intravascular catheters. The deformable material may be composed of elastomeric or silastic material. The deformable material also may contain a viscid surface to aid in holding down the expandable member and to avoid bunching. Further, the deformable material may be cured into shape after being compressed. The present invention results in a simplified method of inserting the stent into the body lumen. The catheter assembly is inserted into the body lumen without further steps being taken to secure the stent. The expandable member is inflated at the desired location expanding and implanting the stent within the body lumen. When the expandable member then is deflated, the stent is released and the remainder of the catheter assembly may be withdrawn leaving the stent implanted within the body lumen. Other features and advantages of the invention will be come apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a partial cross-sectional view depicting a stent delivery system depicting elements of the invention prior to crimping. FIG. 2 is a cross-sectional view taken along lines 2-2 in FIG. 1. FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 1. FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 1. FIG. 5 is a cross-sectional view of the corresponding area in FIG. 1 after crimping the stent onto the expandable member of the catheter. FIG. 6 is a cross-sectional view taken along lines 6-6 in FIG. 5. FIG. 7 is a partial cross-sectional view depicting a stent delivery system configured as a rapid exchange catheter incorporating the invention. FIG. 8 is a cross-sectional view taken along lines 8-8 in FIG. 7. FIG. 9 is a cross-sectional view taken along lines 9-9 in FIG. 7. FIG. 10 is a cross-sectional view taken along the lines 10-10 shown in FIG. 7. FIG. 11 is a plan view of a stent delivery system having a rapid exchange configuration and including elements of the invention. FIG. 12 is a longitudinal cross-sectional view of a body lumen depicting an elevational view of a partially inserted stent delivery system. FIG. 13 depicts a longitudinal cross-sectional view of a body lumen and an elevational view of a stent delivery system where the stent has been expanded. FIG. 14 is a cross-sectional view taken along lines 14-14 in FIG. 13. FIG. 15 is a cross-sectional view depicting a partially withdrawn stent delivery system. DET AILED DESCRIPTION OF PREFERRED EMBODIMENTS FIGS. 1 through 6 illustrate a catheter assembly with a removably secured stent which embodies the features of the invention. Generally, the catheter assembly 8 includes an inner tubular member 10 and an outer tubular member 11 aligned about the inner tubular member. The outer tubular member has an expandable member 16 incorporated within it, located adjacent the distal end of the inner tubular member. The inner tubular member and the expandable member define an annular space 22 between them. A deformable material 24 is located in the annular space 22, preferably connected to the outer surface 12 of the inner tubular member 10. An expandable stent 26 is positioned around the expandable member 16. When the stent 26 is tightly crimped about the outer surface 20 of the expandable member 16, the inner surface 18 of the expandable member will compress the deformable material 24. This configuration secures the expandable stent 26 in the proper location while the stent is inserted into a body lumen by increasing the frictional contact between the expandable stent and the outer surface 20 of the expandable member due to the compression of the deformable material 24. This configuration presents an improvement to stent delivery systems by increasing the efficiency of delivering and implanting the stent in the body lumen. Stent delivery systems typically are composed of an inner tubular member 10 and an outer tubular member 11 with an inflatable means, such as expandable members, attached to the distal end. The expandable member 16 preferably is attached to or is one piece and formed from the outer member, and is aligned about the inner tubular member, thereby defining an annular space 22 between the two. This allows the introduction of inflation fluid to inflate the expandable member. Crimping the expandable stent 26 about the expandable member allows the two to be expanded together. The improvement of this invention is to removably retain the stent onto the expandable member by applying deformable material within the annular space. Expandable stents 26 generally are composed of a lattice configuration which defines gaps 28 within the body of the stent. In one embodiment of the invention, the expandable stent 26 is crimped about the expandable member 16 and the deformable material 24 with sufficient force to cause pockets of material 30 to form in the deformable material and which correspond with the gaps 28 in the stent. This pocketing further enhances the retention of the expandable stent by increasing the interference between the stent and the combination of the expandable member and the deformable material. This configuration is most clearly illustrated in FIG. 6. Another embodiment of the invention includes extending the deformable material 24 within the annular space beyond the location at which one or both of the longitudinal ends 42,44 of the expandable stent 26 will be located on the outer surface 20 of the expandable member 16. The expandable stent then is crimped about the expandable member and the deformable material with sufficient force to cause ridges 46,48 to be formed beyond one or both ends of the stent. These ridges 46,48 further enhance the retention of the expandable stent by increasing the interference between the stent and the combination of the expandable member and the deformable material. Another advantage to this embodiment is that the diameter of the expandable member is increased distal to the stent. The increased diameter just distal to the stent helps to hold the stent on the expandable member as the delivery catheter is advanced through sometimes tortuous body lumens. This stent delivery catheter assembly can be configured by modifying commonly known stent delivery systems. On many of these systems, the expandable member 16 is an inflatable balloon. FIGS. 1 through 6 show the catheter assembly configured as an over-the-wire (OTW) intravascular catheter 34. FIGS. 7 through 10 and FIGS. 11 through 15 show the catheter assembly configured as a rapid exchange (RX) intravascular catheter 36. The RX configuration typically requires the fluid inflation lumen 40 to be positioned within the inner tubular member 10, which allows inflation fluid access into the annular space 22, through a port 60 for inflation of the expandable member 16. The deformable material 24 may be attached to the outer surface 12 of the inner tubular member 10 as shown in the figures. Another embodiment, not shown in the figures, is realized by injecting the deformable material into the annular space 22 without attaching the deformable member to any surface. Another embodiment, not shown in the figures, is realized by attaching the deformable material onto the inner surface 18 of the expandable member 16. When the catheter assembly is configured as an RX intravascular catheter 36 and the deformable material is attached to the outer surface 12 of the inner tubular member 10, the deformable material is configured so as not to obscure the port 60 or the fluid communication between the annular space 22 and the fluid inflation lumen 40 of the inner tubular member 10. The deformable material 24 may be formed from generally available materials including elastomeric and silastic materials. In a preferred embodiment, an elastomeric material commercially available as C-FLEX is used, which is a trademark of Consolidated Polymer Technologies Corporation. This material can be pre-formed into a thin- walled cylinder (about 0.13mm (.005 inch) wall thickness) and then heat- shrunk over the inner tubular member 10. This cylinder can be trimmed to the same length or to a length that is slightly longer than the length of the stent (approximately 20 mm for a 20 mm stent). Polyurethane is another possible material which has a viscid surface. Silastic, or silicon rubber materials have the advantage of being sufficiently deformable to flow into the annular space to form the deformable material. The invention also may use a deformable material 24 which is cured after the stent has been crimped onto the catheter assembly. Several materials may be used as curable deformable materials. Depending on what material is used, the curable deformable material preferably may be cured using, for example, heat cures, time cures or ultraviolet cures. Another embodiment uses the adhesive commercially available as LOCTITE 33-11, a trademark of the Lotite Corporation. This material uses an ultraviolet cure. Using a curable material has the advantage that the deformable material maintains its shape after curing and during stent delivery. FIGS. 1 through 6 further illustrate a method for configuring a catheter assembly with a removably secured expandable stent 26. FIG. 3 shows the inner tubular member 10 having the outer surface of the expandable member 20 aligned about it, thereby defining an annular space 22 therebetween. The first step in the method is to provide the deformable material 24 within the annular space 22. A preferred method involves attaching the deformable material to the outer surface 12 of the inner tubular member 10. Further, a preferred method involves extending the deformable material beyond the location where one or both of the ends 42,44 of the expandable stent 26 will be mounted. The next step is to crimp the expandable stent onto the outer surface 20 of the expandable member 16 so that the inner surface 18 of the expandable member 16 compresses the deformable material 24. FIGS. 5 and 6 most clearly illustrate the results of this step. A preferred method includes crimping the expandable stent with sufficient force to produce pockets of material 30 in the deformable material 24 which correspond to gaps 28 in the stent. Further, it is preferable to crimp the expandable stent with sufficient force to produce ridges 46,48 in the deformable material which extend beyond one or both ends of the stent. When using a curable material, the additional step of curing the deformable material 24 is required after crimping the expandable stent 26 and compressing the deformable material. Curing the deformable material may comprise an ultraviolet, heat or time cure, which is commonly known. The curing technique used is dependent on the deformable material chosen and known to persons of ordinary skill in the art. This step results in the deformable material maintaining its shape after being compressed. The present invention catheter assembly with a removably secured stent can be used for delivering and implanting a stent into a body lumen when used in combination with stent delivery systems. These systems include modified over-the- wire (OTW) catheters 34 and rapid exchange (RX) catheters 36. FIGS. 11 through 15 illustrate one use of the invention using an RX catheter. The catheter assembly 36 with the expandable stent 26 crimped firmly in place on the expandable member 16 is inserted into a body lumen, e.g., a coronary artery. FIGS. 12 through 15 illustrate a typical situation in which the invention is used after an intravascular procedure has damaged a patient's arterial lining to such an extent that the lining needs support to prevent it from collapsing into the arterial passageway and obstructing blood flow through the artery. In these situations, as others, the stent can be delivered to, and implanted into, the location requiring support without the use of further means to secure the stent. The catheter assembly 36 is advanced along the guidewire 52, which is already in position distal to the location requiring support. As illustrated in FIG. 13, the expandable member 16 is inflated thereby expanding the stent 26. This may be accomplished, for example, by injecting fluid into the annular space 22 under substantial pressure (4 to 10 atm is preferred). The expandable member 16 then is deflated leaving the expandable stent 26 expanded and implanted in the desired location of the body lumen. The remainder of the catheter assembly, with the expandable member deflated and no longer in frictional contact with the expandable stent, then is withdrawn from the body lumen. The dimensions of the intravascular catheter will generally follow the dimensions of intravascular catheters used in angioplasty procedures in the same arterial location. Typically, the length of a catheter for use in the coronary arteries is about 150 cm, the outer diameter of the catheter shaft is about 0.89 mm (about 0.035 inch), the length of the balloon typically is about 20 mm and the inflated diameter about 1 to about 8 mm. The materials of construction for the inner tubular member and expandable member may be selected from those used in conventional balloon angioplasty catheters, such as those described in the patents identified above herein. While the present invention has been described herein in terms of delivering an expandable stent to a desired location within a patient's blood vessel, the delivery system can be employed to deliver stents to locations within other body lumens so that the stents can be expanded to maintain the patency of those body lumens. This invention also may be used to deliver and implant other intravascular prostheses, such as tube grafts to treat abdominal aortic aneurisms. Various changes and improvements also may be made to the invention without departing from the scope thereof.

Claims: WHAT IS CLAIMED IS: 1. A catheter assembly for removably securing an expandable stent during stent delivery and implanting within a body lumen, comprising: the catheter assembly having an outer tubular member and an inner tubular member, the outer tubular member having a proximal end and a distal end; the inner tubular member having a proximal end and a distal end and having an outer surface and including at least one inner lumen; an expandable member associated with the outer tubular member and adjacent to the outer tubular member distal end, the expandable member having an inner surface and an outer surface with the inner surface of the expandable member and the outer surface of the inner tubular member defining an annular space therebetween; and a deformable material located within the annular space, whereby an expandable stent is tightly crimped onto the outer surface of the expandable member thereby compressing the expandable member and the deformable material. 2. The catheter assembly of claim 1, wherein the expandable stent comprises a lattice configuration defining gaps in the stent so that as the stent is crimped onto the outer surface of the expandable member the deformable material deforms into pockets corresponding to the gaps in the stent. 3. The catheter assembly of claim 2, wherein the deformable material forms pockets corresponding to less than all of the gaps in the stent. 4. The catheter assembly of claim 1, wherein the expandable stent includes a distal end and a proximal end and the deformable material extends proximal to at least the proximal end forming a ridge in the deformable material proximal to the proximal end of the stent as a result of the stent being crimped on the expandable member thereby compressing the deformable material. 5. The catheter assembly of claim 1, wherein the expandable stent includes a distal end and a proximal end, the deformable material extending distal of at least the distal end forming a ridge in the deformable material distal to the distal end of the stent as a result of the stent being crimped on the expandable member thereby compressing the deformable material. 6. The catheter assembly of claim 1, wherein the expandable stent includes a distal end and a proximal end and the deformable material extends beyond the ends forming a first ridge in the deformable material distal to the distal end of the stent, and a second ridge in the deformable material proximal to the proximal end of the stent as a result of the stent being crimped on the expandable member thereby compressing the deformable material. 7. The catheter assembly of claim 1, wherein the expandable member is an inflatable balloon. 8. The catheter assembly of claim 1, further comprising means for delivering the stent through a body lumen. 9. The catheter assembly of claim 8, wherein the delivery means includes an over-the-wire intravascular catheter. 10. The catheter assembly of claim 8, wherein the delivery means includes a rapid exchange intravascular catheter. 11. The catheter assembly of claim 8, wherein the inner tubular member also includes a fluid inflation lumen having a port in fluid communication with the annular space. 12. The catheter assembly of claim 1, wherein the deformable material is attached to the outer surface of the inner tubular member within the annular space. 13. The catheter assembly of claim 1, wherein the deformable material is attached to the inner surface of the expandable member within the annular space. 14. The catheter assembly of claim 13, wherein the deformable material has a viscid surface for holding the expandable member when the expandable member is compressed onto the viscid surface. 15. The catheter assembly of claim 11, wherein the deformable material is attached to the outer surface of the inner tubular member within the annular space, so that the port and the fluid inflation lumen are not obstructed. 16. The catheter assembly of claim 1, wherein the deformable material is formed from an elastomeric material. 17. The catheter assembly of claim 1 , wherein the deformable material is formed from a silastic material. 18. A method for removably securing an expandable stent on a catheter assembly, the method comprising: providing an assembly comprising; an outer tubular member having a proximal end and a distal end, an inner tubular member having a proximal end and a distal end and having an outer surface, an expandable member associated with the outer tubular member and adjacent to the outer tubular member distal end, the expandable member having an inner surface and outer surface wherein the inner surface of the expandable member and the outer surface of the inner tubular member define an annular space therebetween, and an expandable stent for mounting onto the expandable member; providing a deformable material within the annular space; and crimping the expandable stent onto the expandable member thereby compressing the expandable member and the deformable material. 19. The method of claim 18, further comprising the step of curing the deformable material after crimping the expandable stent onto the expandable member. 20. The method of claim 18, wherein introducing the deformable material into the annular space includes attaching the deformable material to the outer surface of the inner tubular member. 21. The method of claim 18, wherein introducing the deformable material into the annular space includes attaching the deformable material to the inner surface of the expandable member. 22. The method of claim 18, wherein introducing the deformable material into the annular space includes, forming a cylinder of elastomeric material, placing the cylinder around the outer surface of the inner tubular member, and heat- shrinking the cylinder onto the inner member. 23. The method of claim 18, wherein the expandable stent provided is formed of a lattice configuration defining gaps in the stent, and the step of crimping the stent onto the expandable member includes crimping with sufficient force thereby compressing the deformable material and forming pockets in the deformable material corresponding to the gaps in the stent. 24. The method of claim 18, wherein the expandable stent includes a distal end and a proximal end, the deformable material extending distal of the distal end, and the step of crimping the stent onto the expandable member includes crimping with sufficient force to form a ridge in the deformable material that extends distal to the distal end. 25. The method of claim 18, wherein the expandable stent includes a distal end and a proximal end and the deformable material extends proximal to the proximal end, and the step of crimping the stent onto the expandable member includes crimping with sufficient force to form a ridge in the deformable material that extends proximal to the proximal end. 26. The method of claim 18, wherein the expandable stent includes a distal end and a proximal end and the expandable material extends beyond the distal end and the proximal end, and the step of crimping the deformable stent onto the expandable member includes crimping with sufficient force to form a first ridge distal to the distal end and a second ridge proximal to the proximal end. 27. A method of delivering and implanting a removably secured expandable stent to a desired location within a body lumen, the method comprising: providing a catheter assembly comprising an outer tubular member having a distal end and a proximal end and an inner tubular member having a distal end and a proximal end and having an outer surface, and at least one internal lumen extending within the inner tubular member; an expandable member aligned about the inner tubular member and attached adjacent to the outer tubular member distal end, the expandable member having an inner surface and an outer surface wherein the inner surface of the expandable member and the outer surface of the inner tubular member define an annular space therebetween; a deformable material disposed within the annular space; and an expandable stent tightly crimped onto the expandable member so that frictional contact between the expandable stent and the expandable member is enhanced by the resultant contact between the expandable member and the deformable material thereby removably retaining the expandable stent in place during delivery of the stent through the body lumen; advancing the catheter assembly through the body lumen to the desired location; inflating the expandable member thereby expanding and implanting the stent at the desired location; deflating the expandable member so that the expandable stent is no longer in contact with the catheter assembly; withdrawing the catheter assembly from the body lumen.

Inventors: FOREMAN PHILIP C, LIMON TIMOTHY A, SAUNDERS RICHARD J, SVENSSON BJORN G, TEABY GREGG, FOREMAN, PHILIP, C., LIMON, TIMOTHY, A., SAUNDERS, RICHARD, J., SVENSSON, BJORN, G., TEABY, GREGG
Applicants: ADVANCED CARDIOVASCULAR SYSTEM, ADVANCED CARDIOVASCULAR SYSTEMS, INC.
Application year: 2000
Main classification: A61F2
IPC codes: A61F2