Apparatus for delivering endoluminal prostheses and methods of making and using them

An apparatus for delivering a stent into a blood vessel includes a sheath having a rounded bullet-shaped distal portion including a plurality of flexible leaflets integrally molded thereto. The stent is disposed in its contracted condition within a lumen of the sheath proximate the distal portion. A bumper is slidably disposed within the lumen that includes a helical compression coil, a bumper element attached to the helical coil including a blunt distal edge for abutting the stent, and an extension element extending distally from the bumper element through the stent and between the leaflets to facilitate introducing the apparatus over a guidewire. The sheath is formed by inserting a bullet into a blunt-ended tube, and inserting the tube into a bullet-shaped bore in a heated die until the tube material is softened and deforms into a rounded bullet shape. Slits are then cut into the distal portion to create the leaflets.

FIELD OF THE INVENTION

The present invention relates generally to apparatus and methods for delivering endoluminal prostheses within body lumens of a patient, and more particularly to apparatus for delivering tubular prostheses or “stents” within a patient's vasculature for treating stenoses or other lesions, for example, within the coronary and carotid arteries, and to methods of making and using such apparatus.

BACKGROUND

In recent years, a number of minimally invasive technologies have been developed for treating diseases, such as atherosclerosis, that result in narrowing of blood vessels, for example, within the coronary or carotid arteries. Tubular prostheses or “stents” have been developed for maintaining the patency of a blood vessel, for example, following angioplasty or other procedures used to treat a stenosis, occlusion, or other lesion within the blood vessel. The stent may be implanted across a treatment site to scaffold the site and prevent it from subsequently contracting or otherwise becoming obstructed.

Generally, the stent may be placed upon a catheter in a contracted condition, and the catheter advanced endoluminally to the treatment site until the stent is positioned across the stenosis. The stent may then be deployed and substantially anchored at the treatment site. The stent may be self-expanding, i.e., may be biased to expand to an enlarged condition upon release from the delivery catheter, thereby automatically substantially anchoring the stent at the treatment site. Alternatively, the stent may be plastically deformable, i.e., may be expanded with the aid of a balloon, which may underlie the stent on the catheter. The balloon may be inflated to expand the stent from the contracted condition to the enlarged condition wherein the stent substantially engages the wall of the treatment site. A balloon, for example, on a separate balloon catheter, may also be used to further expand and/or anchor a self-expanding stent.

Similarly, for ablation procedures and the like, a catheter including an array of electrodes, for example, on an expandable basket assembly, may be provided. The device may be introduced into a body lumen, e.g., through the patient's vasculature into the heart, to treat conditions, such as heart arrhythmia.

With any of these devices, a sheath may be provided over the catheter to protect the elements on the distal end of the catheter, such as a stent, a balloon, and/or an array of electrodes. The sheath may be advanced distally over the proximal end of the catheter until it covers the distal end and the element(s) thereon, or the distal end of the catheter may be introduced into the sheath, and advanced until it is proximate the distal end of the sheath. The distal end of the catheter, with the overlying sheath thereon, may then be introduced into a patient and positioned at a treatment site, whereupon the sheath may be retracted to expose the distal end of the catheter. After treatment, the sheath may be advanced back over the distal end of the catheter, and the entire device withdrawn from the patient.

One of the problems associated with these devices is that they may have substantially blunt distal ends that may scrape along the wall of a vessel during advancement therethrough, possibly damaging the wall and/or dislodging embolic material from the wall. To facilitate atraumatic advancement, particularly through tortuous anatomy, transition tips have been suggested for these devices.

For example, a conical or tapered nosepiece may be provided on the distal end of the catheter. A sheath may be disposed over the catheter, for example, to substantially cover the stent or other underlying element, such that the nosepiece extends distally from the end of the sheath, a distal edge of the sheath abutting the nosepiece. The nosepiece may facilitate advancement of the device through a narrow region of a blood vessel, although it may also risk catching on the wall of the vessel and/or dislodging embolic material, e.g., between the distal edge of the sheath and the nosepiece. Following delivery of a stent from the device, the nosepiece is generally positioned distal to the treated lesion. If the nosepiece is withdrawn directly, the proximal edge of the nosepiece may catch on the stent struts, resulting in the potential for trauma and embolic debris release. Alternatively, the sheath may be re-advanced across the treatment site to “recapture” the nosepiece, although in this approach the distal edge of the sheath may also catch on the stent struts.

As an alternative to a tapered nosepiece, a sheath having a rounded distal end has been suggested, as disclosed in U.S. Pat. No. 5,593,412 issued to Martinez et al. Weakened areas or slits are provided in the distal end, thereby defining sections that may be softened upon introduction of warm saline solution. Once the sections are softened, the sheath may be retracted from an underlying balloon catheter to expose and implant a stent mounted on the catheter. Introduction of saline or other liquids into a patient's vasculature, however, may be undesirable, but is necessary in order to soften the sections on the distal end of the sheath and allow the stent to be deployed from the sheath.

Another problem associated with such delivery systems is that the sheaths and/or catheters may buckle during insertion, because of the distal force applied from the proximal end to advance them through the patient's vasculature. In addition, because of their tubular nature, they may kink when advanced through tortuous anatomy, possibly damaging the device or an element within the device.

Accordingly, it is believed that delivery systems that facilitate delivery of a stent through a patient's vasculature and/or that overcome the problems discussed above would be considered useful.

SUMMARY OF THE INVENTION

The present invention is directed to apparatus for delivering treatment elements, such as tubular prostheses or “stents,” within a body lumen of a patient, for example, for treating stenoses or other lesions within the coronary arteries, the carotid arteries, or other blood vessels, and to methods of making and using such apparatus.

In accordance with one aspect of the present invention, an apparatus is provided for delivering a prosthesis into a blood vessel of a patient that includes an elongate tubular member having a proximal end, a distal end, and a lumen extending between the proximal and distal ends. The distal end has a size for endoluminal insertion into a blood vessel and terminates in a substantially atraumatic distal portion including a plurality of flexible leaflets integrally molded thereto.

The leaflets are deflectable from a closed position wherein the leaflets engage one another to an open position wherein the leaflets define an opening communicating with the lumen. Preferably, the leaflets define a substantially rounded bullet shape in the closed position, although alternatively, the leaflets may define a substantially conical shape in the closed position. The leaflets are preferably substantially flexible and independently deflectable at a temperature less than body temperature, and are biased towards the closed position, but are resiliently deflectable to the open position. Adjacent leaflets may be separated by a slit, or may be connected to one another by weakened regions, the weakened regions being tearable upon retraction of the tubular member with respect to the prosthesis to allow the leaflets to be deflected towards the open position.

In a preferred embodiment, a tubular prosthesis is disposed within the lumen proximate the distal portion. An elongate bumper member having a proximal end and a distal end is also provided, the bumper member being slidably disposed within the lumen of the sheath. The distal end of the bumper member has a blunt edge disposed adjacent to the proximal end of the prosthesis for preventing axial displacement of the prosthesis upon retraction of the tubular member with respect to the bumper member and/or the prosthesis.

Preferably, the prosthesis comprises a self-expanding stent, such as a coiled-sheet stent, the stent being biased to assume an expanded condition having a cross-section larger than the lumen of the tubular member, and being compressible to a contracted condition to facilitate insertion into the lumen.

In accordance with another aspect of the present invention, an apparatus for delivering a prosthesis into a blood vessel of a patient is provided that includes an elongate tubular member, such as that described above, having a proximal end, a distal end, and a lumen extending between the proximal and distal ends, the distal end having a size for endoluminal insertion into a blood vessel. A tubular prosthesis is disposed within the lumen proximate the distal end. An elongate bumper member is also provided that includes a helical coil having a proximal end and a distal end, the bumper member being slidably disposed within the lumen of the sheath. The distal end of the bumper member has a blunt distal edge disposed adjacent a proximal end of the prosthesis for preventing axial displacement of the prosthesis upon retraction of the tubular member with respect to the bumper member.

In a preferred embodiment, the bumper member includes a helical wire compression coil, preferably a solid height coil, extending between its proximal and distal ends. A plastic bumper element extends from a distal end of the helical coil, the bumper element including the blunt distal edge thereon. An extension element extends distally from the bumper element, the extension element having a cross-section substantially smaller than the bumper element, whereby the extension element may extend through the prosthesis disposed within the lumen of the tubular member. The helical coil, bumper element, and/or the extension element include a lumen extending axially therethrough for receiving a guidewire therethrough.

In accordance with yet another aspect of the present invention, a method for making a sheath for delivering a treatment element within a body lumen of a patient is provided. A tubular member is provided that is formed from a substantially flexible material, the tubular member having a proximal end, a distal end, and a lumen extending axially between the proximal and distal ends, the distal end having a size for endoluminal insertion into a body lumen. A die is provided having a bore therein, the bore having a tapered shape. The die is heated to a temperature in excess of a melting point of the flexible material from which the tubular member is formed. The distal end of the tubular member is inserted into the bore of the heated die until a distal portion of the tubular member is softened and deformed into a tapered shape substantially enclosing the distal end. One or more slits are then created in the distal portion of the tubular member after it is deformed into the tapered shape, the slits defining a plurality of leaflets. A treatment element may be inserted into the lumen of the tubular member until it is disposed proximate the distal portion.

In a preferred method, a bullet having a tapered shape distal end is inserted into the distal end of the tubular member before inserting the distal end of the tubular member into the bore. Preferably, the bullet and the bore have corresponding substantially rounded shapes defining a mold cavity therebetween when the distal end of the tubular member is inserted into the bore.

In another preferred method, the treatment element is a tubular prosthesis for implantation within a body lumen of a patient. Preferably, the prosthesis is a self-expanding stent biased to assume an expanded condition having a cross-section larger than the lumen, and compressible to a contracted condition before being inserted into the lumen of the tubular member. The prosthesis may be inserted into the lumen of the tubular member before inserting the distal end of the tubular member into the bore, e.g., inserted into the lumen from the distal end of the tubular membrane. Alternatively, the prosthesis may be inserted into the lumen from the proximal end of the tubular member, e.g., either before or after the leaflets are formed on the distal portion of the tubular member.

An elongate bumper member may be inserted into the lumen of the tubular member, the bumper member being slidably disposed within the lumen of the tubular member, the distal end having a blunt distal edge for abutting a proximal end of the prosthesis. To make the bumper member, an elongate helical coil may be provided having a proximal end and a distal end. A tubular bumper element may be attached to the distal end of the helical coil to provide the bumper member, the bumper element including the blunt distal edge of the bumper element. Preferably, the bumper element is formed from plastic, and is attached to the helical coil by heating the bumper element until it is softened, and then directing the softened bumper element over the distal end of the helical coil. A tubular extension element may be attached to the bumper element, the extension element having a cross-section substantially smaller than the bumper element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings,FIGS. 1A–2Bshow a preferred embodiment of an apparatus10for delivering a stent or other tubular prosthesis50into a blood vessel or other body lumen of a patient (not shown). Generally, the apparatus10includes an elongate tubular sheath12having a proximal end (not shown), a distal end14, and a lumen16extending generally therebetween. The tubular sheath12may be formed from a substantially flexible or semi-rigid material that may facilitate its advancement within a body lumen of a patient, preferably within the vasculature of a patient.

For example, the sheath12may be formed from a polymer, such as pebax, polyethylene, urethane, nylon, or other plastic material, that may be extruded or molded into elongate tubing of a desired length. Preferably, the tubing has a wall thickness of between about 0.003–0.006 inch (0.075–0.150 mm), and has a substantially uniform outer diameter appropriate for the size of the stent being implanted, for example, between about 1.5–2.5 mm. The sheath12may have a substantially uniform construction along its length, or the sheath12may include portions along its length having varying degrees of flexibility.

In a preferred embodiment, the sheath12includes a distal portion18formed entirely from a substantially flexible material, such as pebax, and an intermediate portion20formed from pebax including a stiffening element22therein. For for example, the intermediate portion20may include a braid or mesh, e.g., of stainless steel, laid over a teflon liner, with pebax tubing formed over the braid. Alternatively, the stiffening element22may be a helical wire coil and the like molded or otherwise formed in the tubing. The stiffening element22may enhance a rigidity of the intermediate portion20, for example, to reduce the risk of the intermediate portion20buckling or kinking, while still providing flexibility transverse to the longitudinal axis28, e.g., to accommodate advancement through tortuous anatomy. Preferably, the sheath12also includes a proximal portion (not shown) that is formed from a more rigid material, such as nylon tubing, that may include a stiffening element as described above. In a preferred embodiment, the distal portion18has a length of between about 10–20 cm, the intermediate portion20has a length of between about 20–30 cm, and the proximal portion has a length of between about 85–120 cm, more preferably about 100 cm or more.

The distal portion18of the sheath12preferably has a rounded bullet shape defined by a plurality of flexible leaflets24that are integrally formed thereon. The leaflets24are preferably deflectable from a closed position, wherein adjacent leaflets24abut one another, to an open position. In the closed position, the leaflets24substantially close the lumen16, as shown inFIG. 2A. Preferably, in the closed position, the leaflets24define a relatively small opening25where their apices meet. In the open position (the leaflets24are shown only partially open inFIG. 2B), the leaflets24are spread apart to define an opening26communicating with the lumen16. Preferably, in the open position, the leaflets24are oriented substantially axially such that the opening26has a cross-section similar to the lumen16. In the preferred embodiment shown inFIGS. 2A and 2B, three leaflets24are provided, although additional leaflets may be provided if desired.

As best seen inFIG. 1A, in the closed position, the leaflets24preferably define a substantially atraumatic distal portion18that may facilitate advancement of the sheath12endoluminally within a patient's vasculature with minimal risk of dislodging embolic material from and/or otherwise damaging the wall of a body lumen through which the sheath12is advanced. In the preferred embodiment shown, the leaflets24define a substantially rounded bullet shape in the closed position. Alternatively, leaflets24defining a substantially conical shape (not shown) in the closed position may be provided, with the leaflets24preferably biased to the closed position, as described below.

The leaflets24are substantially flexible and independently deflectable substantially independent of the temperature to which the leaflets24are exposed, e.g., at a temperature substantially less than body temperature. In a preferred embodiment, the leaflets24are biased towards the closed position, but are resiliently deflectable to the open position. This may ensure that the opening26remains substantially closed until time of deployment of an element, such as stent50, from within the lumen16, and/or that the leaflets24do not catch on anything and open inadvertently. This may be particularly important when the apparatus10is advanced through tortuous anatomy, as described further below. Alternatively, the leaflets24may be at least partially plastically deformed when they are deflected from the closed position to the open position. In this alternative, the leaflets24may not return completely to the closed position when released from the fully open position, e.g., after the stent50is deployed from the apparatus10.

Preferably, adjacent leaflets24are separated by a relatively narrow slit28, although alternatively, the leaflets24may partially overlap with one another in the closed position. In a further alternative, adjacent leaflets may be separated by a thin-walled or weakened region (not shown) that may be easily tearable upon retraction of the sheath12with respect to a stent or other element being deployed from within the lumen16. Once the weakened regions are torn, the leaflets may be freely deflected towards the open position as the element is being deployed.

In addition, the leaflets24may have a thickness that is substantially thinner than a wall thickness of the rest of the distal portion18, preferably tapering towards their distal tips24aas shown inFIGS. 1A and 1B, thereby enhancing the flexibility of the leaflets24. The tapering thickness may also ensure that the leaflets24are biased towards the closed position, yet may deflect easily to accommodate a guidewire (not shown), bumper extension element, and the like, as described further below.

Returning toFIG. 1B, in a preferred embodiment, the apparatus10also includes an elongate bumper member30that is slidably disposed within the sheath12. The bumper member30preferably includes a proximal end (not shown), a distal end32, and a lumen34that extends therebetween. The bumper member30preferably has a substantially uniform outer diameter slightly smaller than the interior lumen16of the sheath12, preferably by about 0.003–0.005 inch (0.075–0.125 mm) to create a close sliding, but not interfering, fit between the bumper member30and the sheath12. The lumen34has a diameter sufficiently large to accommodate a guidewire (not shown) therethrough, preferably between about 0.015–0.020 inch (0.375–0.500 mm), and more preferably about 0.016 inch (0.400 mm).

In a preferred form, the bumper member30is formed from a helical wire compression coil36, e.g., having adjacent turns that substantially abut one another. The coil36may be formed from flat or round wire, e.g., of stainless steel and the like, that is continuously helically wound along the length of the bumper member30, preferably a solid height coil. A relatively thin layer of teflon38and the like may be provided around the outside of the coil36to enhance a sliding relationship between the bumper member30and the sheath12. Because of the coil36, the bumper member30may be substantially resistant to buckling or kinking, while facilitating bending of the bumper member30transverse to the longitudinal axis28.

A substantially rigid tubular segment (not shown) may be attached to or otherwise extend from the proximal end of the coil36. Preferably, the tubular segment is a section of hypotube having an inner lumen (not shown) similar to the lumen34of the coil36, and more preferably a two-stage length of hypotube that has a greater outer diameter on its proximal-most end. The tubular segment may facilitate distal advancement of the bumper member30into the sheath12with minimal risk of buckling and/or may provide enhanced tactile perception of relative movement of the bumper member30and the sheath12. A valve or other seal (not shown), e.g., for accommodating a guidewire therethrough while maintaining a fluid-tight seal, may also be provided on the proximal end of the tubular segment.

The bumper member30also includes a tubular bumper element40on a distal end37of the coil36that includes a substantially blunt distal edge42. The bumper element40is preferably formed from pebax or other plastic material. A plastic bumper element40ensures no metal-to-metal contact, e.g., between the coil36of the bumper member30and the stent50that may lead to corrosion of the stent material. In addition, pebax and other substantially flexible materials may deform slightly, e.g., when the sheath12is retracted, to enhance contact between the blunt distal edge42of the bumper element40and the stent50. The bumper element40is preferably attached to the distal end37of the coil36, e.g., by heating the bumper element40to soften it and directing it over the distal end37, such that the bumper element is fused into the coils adjacent the distal end37.

The bumper member30may also include a radiopaque or other marker48thereon for identifying a location of the bumper member30using external imaging, such as fluoroscopy. Preferably, a platinum iridium ring48is provided on the bumper element40immediately adjacent the blunt distal edge42, thereby identifying a position of the proximal end52of the stent50. Alternatively, a marker (not shown) may be provided elsewhere on the apparatus10in addition to or instead of the marker48, such as on the sheath12or the stent50itself. Thus, the marker48may facilitate positioning of the apparatus10, and more particularly the stent50or other element therein, axially within a body lumen (not shown) before deploying the element from within the sheath12, as described further below.

The bumper member30may also include a tubular extension element44that is thermally bonded or otherwise attached to and extends distally from the bumper element40. The extension element44has an outer diameter that is substantially smaller than the bumper element40For example, the extension element44may be partially inserted into the bumper element40as it is thermally bonded thereto so as not to interfere with the blunt edge42of the bumper element40. Preferably, the extension element44has an outer diameter of about 0.66 mm (0.026 inch) to facilitate its insertion through the stent50, an inner diameter of about 0.41 mm (0.016 inch) to accommodate a guidewire therethrough, and a length of about 25 mm (1.0 inch). The extension element44may be appropriately sized larger or smaller to accommodate a guidewire, for example, between about 0.009–0.038 in (0.225–0.95 mm). The extension element44is preferably substantially flexible and has a substantially smooth outer surface to provide a low-friction, sliding contact with an element disposed within the sheath12.

In a preferred embodiment, a stent50or other tubular prosthesis or graft may be disposed within the lumen16of the sheath12proximate the distal portion18. The stent50preferably is expandable between a contracted condition that facilitates its loading into the lumen16of the sheath12, and an enlarged condition for engaging a wall of a blood vessel or other body lumen (not shown). In a preferred embodiment, the stent50is a coiled-sheet stent, such as that disclosed in U.S. Pat. No. 5,443,500 issued to Sigwart, and/or in co-pending application Ser. No. 09/347,845, filed Jul. 2, 1999, and Ser. No. 09/406,984, filed Sep. 28, 1999, the disclosures of which are incorporated herein by reference. The stent50may be self-expanding, i.e., may be biased to assume the enlarged condition, but may be compressed and constrained in the contracted condition, for example, by the lumen16of the sheath12. Alternatively, the stent50may be plastically deformable, i.e., may be substantially relaxed in the contracted condition, but may be forcibly expanded to the enlarged condition, for example, using a balloon catheter, as is known in the art.

Preferably, the apparatus10is provided pre-assembled with the stent50disposed within the lumen16of the sheath12adjacent the distal portion18of the sheath in its contracted condition. The bumper member30is also disposed within the lumen16such that the blunt edge42of the bumper element40is adjacent a proximal end52of the stent50. The extension element44preferably extends distally through the stent50and through the leaflets24, as best seen inFIGS. 1B and 2B. The extension element44may facilitate insertion of a guidewire (not shown) through the apparatus10, i.e., through the lumen16of the sheath12into the lumen34of the bumper member30to a to proximal end of the apparatus10. Preferably, the opening25at the apices of the leaflets24accommodates the extension element44therethrough without causing the leaflets24to partially buckle or bulge.

Alternatively, the extension element44may be eliminated, and a guidewire inserted directly between the leaflets24into the lumens16,34. The apparatus10may be used to implant the stent50within a body lumen, preferably within a carotid artery, a coronary artery, a cerebral artery, a renal artery, or other blood vessel, as described further below. In a further alternative, the apparatus10may incorporate “rapid exchange” configurations where a guidewire may exit from the lumens16,34of the sheath12and/or bumper member30through side ports (not shown) at a location along their lengths, i.e., at an intermediate location, rather than at their proximal ends, as is known to those skilled in the art. To accommodate a guidewire between the sheath12and the bumper member30during retraction, a longitudinal slot (not shown) may be provided in either the inner surface of the sheath or the outer surface of the bumper adjacent the side ports.

Turning toFIGS. 3A–3E, a method is shown for forming a rounded bullet-shaped distal portion18on a tubular sheath12and the like. A tubular sheath12is provided that is formed from substantially flexible plastic material, such as those described above, preferably pebax, and that has a lumen16therein extending from the distal end14towards the proximal end (not shown). The sheath12initially has a distal end14that terminates in a substantially blunt distal edge19(FIG. 3A).

In a preferred embodiment, the sheath12has a plurality of segments having varying degrees of flexibility, for example, including a distal portion18, an intermediate portion (not shown), and a proximal portion (also not shown). Preferably, the distal portion18is a predetermined length of pebax tubing that is thermal bonded, e.g., butt bonded to the intermediate portion, which is a predetermined length of pebax tubing reinforced by a stainless steel braid, such as the lengths described above. The intermediate portion, in turn, is thermally bonded to a predetermined length of nylon tubing. Alternatively, an adhesive, connectors, and the like may be used to attach two or more of the portions to one another.

Preferably, the sheath12is pre-assembled, i.e., with the distal, intermediate, and proximal portions bonded to one another before the distal portion18is formed into its bullet shape, as described below. Alternatively, the distal portion18may be formed into its bullet shape and/or other steps of the method performed before the distal portion18is attached to the intermediate portion.

A stent50or other prosthesis is disposed within the lumen16, preferably a predetermined distance from the distal end14of the sheath12. Preferably, the stent50is constrained in its contracted condition, and inserted into the distal end14of the sheath12before the distal portion18is formed into its bullet shape. Alternatively, the stent50may be provided in its contracted condition, and introduced into the lumen16from the proximal end of the sheath12, e.g., either before or after the distal portion18is formed into its bullet shape.

In a preferred embodiment, the stent50is a self-expanding tubular member formed from Nitinol having a transition temperature between ambient and body temperatures. The stent50may be formed into its enlarged condition in its austentic phase (e.g. by hand rolling for a coiled-sheet stent) and heat treated to set the enlarged condition in its shape memory. The stent50may then be chilled to its martensitic phase, e.g., at a temperature below ambient temperature, and preferably between about 0–10 degrees Celsius, for example, by blowing liquid Nitrogen onto the stent50. The stent50may then be pulled through one or more draw-down fixtures, i.e., tapered tubular dies (not shown), which may be chilled, to plastically compress the stent50into a contracted condition. In the contracted condition, the stent50preferably has a diameter substantially smaller than the lumen16of the sheath12. The stent50may then be pulled from the draw-down fixture into the lumen16of the sheath12. In a preferred method, a teflon tubular guide or sheath (not shown) may be used to facilitate sliding the stent50through one or more of the draw-down fixtures. The stent50may be pulled into the teflon guide as it enters a draw-down fixture, the teflon guide being split or otherwise removed from the stent50before it is pulled into the sheath12.

The bumper member30(not shown inFIGS. 3A–3C) may be inserted into the lumen16of the sheath12until the extension element44approaches, but does not extend from, the distal end14of the sheath12. For example, the blunt edge42of the bumper element40may abut the proximal end52of the stent50, with the extension element44extending therethrough. Alternatively, the bumper member30may not be extended distally to abut the stent50until after the distal portion18is formed into its bullet shape. In a further alternative, the bumper member30may not be introduced into the sheath12until after the distal portion18is formed into its bullet shape.

Returning toFIGS. 3A–3C, a die60, e.g., a spherically shaped “hot die,” is provided having a bore or other recess62therein. The bore62has an entry64with a cross-section substantially similar to the cross-section of the sheath12, a rounded inner end66having a tapered shape corresponding to the desired shape of the rounded distal portion18(FIG. 3C), and a relatively narrow aperture67extending distally from the inner end66through the die60. The die60may be coupled to a heating element in a conventional manner such that the die60may be heated to a desired temperature, as is well known in the art. In a preferred method, the die60is heated to a temperature in excess of a melting point of the material from which the distal portion18of the sheath12is formed, for example, between about 150–200 degrees Celsius (about 300–400 degrees Fahrenheit), and preferably about 160 degrees Celsius (320 degrees Fahrenheit).

As seen inFIG. 3A, a bullet70is inserted a predetermined distance into the distal end14of the sheath12, i.e., such that the bullet70does not contact the stent50(shown inFIG. 3B) but provides sufficient sheath material beyond a distal end72of the bullet70to form the bullet-shaped distal portion18. Preferably, a wire or other filament73is attached to the bullet70that extends distally from the distal end72of the bullet70. The bullet70and die60may be formed from like materials, preferably a hardened and polished tool steel. The distal end72of the bullet70has a predetermined curved shape corresponding to the rounded inner end66of the bore62in the die60.

In preparation for molding the distal portion18of the sheath12, the filament73is guided through the aperture67, maintaining sufficient tension to keep the filament73taut, but without pulling the bullet70from the tubular member12. As shown inFIG. 3B, the distal portion18of the tubular member12is inserted into the bore62of the heated die60until the distal portion18of the tubular member12is softened and deformed to fill the cavity defined between the distal end72of the bullet70and the rounded inner end66of the bore62. Thus, the distal portion18is molded into a rounded bullet shape, the molded shape being defined by the distal end72of the bullet70and the rounded inner end66of the bore62in the die60. Preferably, only slight pressure, e.g., mere hand pressure, preferably between about 1–2 pounds, is applied axially to the sheath12to fill the cavity defined by the bullet70and the bore62and ensure that there are no discontinuities in the resulting bullet shaped distal portion18. Because of the filament73, the resulting bullet shaped distal portion18includes the relatively small opening25(not shown inFIG. 3B) therethrough corresponding to the filament73for accommodating a guidewire or bumper extension element (not shown).

As shown inFIG. 3C, once the rounded bullet-shaped distal portion18is formed, the sheath12may be removed from the bore62of the die60, and allowed to cool for sufficient time to substantially solidify the sheath, i.e., to return to its flexible, but solid state.

One or more slits34are then formed in the tapered region22of the distal portion14. Preferably, a cutting device (not known) is used that includes three cutting wires or blades that are equally spaced radially about a central axis. The cutting device is aligned with the longitudinal axis28of the sheath12and forced into the enclosed distal portion18until the cutting device cuts completely through the material of the enclosed distal portion18. The cutting device is then withdrawn, thereby providing a plurality of substantially independently flexible leaflets24on the distal portion18. As shown inFIG. 3D, the bullet70may then be removed from the distal portion18, e.g., by pulling on the filament73to deflect the leaflets24and withdraw the bullet70through the opening26. The leaflets24preferably resiliently return to their closed position upon removal of the bullet70, as shown inFIG. 3E, thereby defining the opening25.

Alternatively, the filament73and aperture67may be eliminated from the bullet70and die60, and the bullet70withdrawn from the formed sheath12using other methods. For even numbers of slits, a cutting device including a single blade or wire (not shown) may be oriented substantially perpendicular to the longitudinal axis28of the sheath12, and a plurality of individual transverse slits may be cut into the distal portion18. In alternative methods, individual leaflets may be formed using a multi-cavity tool, and the leaflets may be shaped into a final position, as will be appreciated by those skilled in the art.

Once the leaflets24are formed, the bumper member30may be advanced further distally to push the stent50into a desired position within the lumen16of the sheath12, i.e., proximate the bullet-shaped distal portion18, and/or to direct the extension element44through the opening25. To facilitate this pre-loading stage, it may b desirable to form the distal portion18of the sheath12from a substantially transparent material, thereby facilitating visual monitoring of the stent50and/or the bumper member30. The apparatus10is then ready to be used to introduce and implant the stent50within a body lumen of a patient, as described further below.

In an alternative method, the stent50may be inserted into the sheath12from its proximal end after distal portion18is formed into its bullet shape. For example, the stent50may be constrained in its contracted condition, and advancing it through the lumen16of the tubular member12to the distal portion18. The stent may be released, i.e., unconstrained, once introduced into the lumen16, whereupon the stent may partially expand to engage the wall of the lumen16. Preferably, the stent remains slidable within the lumen16such that the stent50may be advanced to a location proximate the distal portion18and/or easily deployed through the opening26. The bumper member30may be inserted into the proximal end of the sheath12and directed distally to advance the stent50to the desired position.

Turning toFIGS. 4A and 4B, the apparatus10may be used to implant the stent50or other prosthesis within a body lumen100of a patient, such as within a coronary, carotid, cerebral, renal artery, or other blood vessel. The apparatus10is percutaneously introduced into the patient's vasculature and advanced distally to a target treatment region102. Preferably, the apparatus10is advanced over a guidewire104already placed across the treatment region102using conventional methods. The guidewire104may be backloaded through the extension element44, and through the bumper member30to its proximal end (not shown).

The rounded distal portion18of the sheath12substantially protects the stent50during advancement and/or allows atraumatic advancement of the apparatus10. Preferably, as explained above, the leaflets24are resiliently flexible and biased to the closed position, causing the leaflets24to hug the guidewire104during advancement, particularly through tortuous anatomy. For example, if the leaflets24are flexible and biased to the closed position, the leaflet(s)24on the outside of a sharp bend may hug the guidewire104, rather than deflecting away from the guidewire104and risking catching on the wall of the vessel, and possibly damaging the wall and/or dislodging embolic material from the wall. In addition, the rounded distal portion18may facilitate advancement of the apparatus10through the treatment region100.

Once the apparatus10is advanced into the body lumen100, the stent50is positioned across the treatment region102, as shown inFIG. 4A, for example, by monitoring the marker48using fluoroscopy and the like. Preferably, the treatment region102is a stenotic or occluded region of a blood vessel, although other lesions or damaged vessel segments may be treated, as will be appreciated by those skilled in the art. Once the stent50is properly positioned, the bumper member30is held stationary, and the sheath12withdrawn to deploy the stent50from the lumen16, as shown inFIG. 4B. Because of their flexible nature, the leaflets24easily deflect outward to allow the stent50to be deployed through the opening26, and slide over the stent50and/or over the bumper member30. Once the stent50is deployed, the apparatus10may be withdrawn from the body lumen100and from the patient (not shown). Preferably, the sheath12remains in its retracted position without requiring advancement back over the bumper element40and/or the extension element44before removal of the apparatus10. The leaflets24preferably hug the outside of the bumper member30, thereby facilitating substantially atraumatic withdrawal of the apparatus10.

Preferably, the stent50is self-expanding, and therefore automatically expands upon deployment to engage the body lumen100at the treatment location102. The stent50may trap embolic material between itself and the body lumen100and/or may dilate and hold the body lumen100open. If desired to further expand the stent50, an expansion device, such as a catheter (not shown) may be introduced into the body lumen100, e.g., upon removal of the apparatus10, and positioned within the stent50. A balloon or other expandable member on the catheter may be expanded to engage and further expand the stent50to a predetermined diameter, e.g., corresponding substantially to the unobstructed diameter of the body lumen100.

In an alternative embodiment (not shown), the stent50may be plastically expandable, and may be mounted onto a catheter that is inserted into a sheath12in accordance with the present invention. The catheter may include a balloon or other expandable member over which the stent may be mounted. Once the sheath is retracted to deploy the stent, for example, at a target treatment region, the expandable member may be expanded, e.g., by inflating the balloon, to plastically deform the stent and expand it to engage the body lumen at the treatment region. Once the stent has been expanded to a desired size, the expandable member may be deflated, and the apparatus withdrawn from the body lumen and the patient.

In further alternatives, other deployable devices may be provided within a sheath in accordance with the present invention, such as an electrode device, e.g., an array of electrodes on an expandable basket assembly and the like. Once a desired location is reached, such as a chamber of a heart, the sheath may be retracted with respect to the underlying device, until one or more elements on the device are deployed from the sheath. A procedure may be completed at the location, e.g., an ablation procedure, and then the sheath and device may be withdrawn from the location.