Abstract:
A deformable sheath is attached to a catheter and introduced intravascularly to be expanded against an arterial wall and entrap plaque therebetween. A stent is subsequently deployed within the expanded sheath and the sheath is then withdrawn from within the vasculature to leave the stent expanded against the arterial wall with the plaque entrapped therebetween.

Description:
This application is a divisional of application Ser. No. 09/439,692, filed Nov. 15, 1999, now U.S. Pat. No. 6,264,671. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to angioplasty procedures, and more particularly to a device and method to prevent arterial plaque from being dislodged from the arterial wall in procedures such as, for example, percutaneous transluminal coronary angioplasty (PTCA) or percutaneous transluminal angioplasty (PTA), especially carotid PTA, and migrating into the patient&#39;s vasculature. 
     In typical carotid PTA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the common carotid artery. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient&#39;s carotid vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient&#39;s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty. 
     In angioplasty procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent is crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient&#39;s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter. The stent also may be of the self-expanding type. 
     A danger always present during any intravascular procedure is the potential for particles of the atherosclerotic plaque, which can be extremely friable, breaking away from the arterial wall. These emboli can subsequently migrate through the patient&#39;s vasculature to sensitive organs such as the brain, where they may induce trauma. 
     2. Description of the Prior Art 
     The majority of devices that have been proposed to prevent the problem of emboli generated during an angioplasty procedure fall into either of two broad categories: devices that simply intercept emboli flowing within the patient&#39;s blood stream, and devices that intercept as well as remove such emboli from within the patient&#39;s body. A device typical of the first category is described by Goldberg in U.S. Pat. No. 5,152,777 and consists of a filter comprised of a plurality of resilient, stainless steel wire arms joined at one end so as to form a conical surface, and having rounded tips at their other ends to prevent damage to the vessel walls. Alternatively, the filter may be attached to a catheter through which lysing agents can be introduced to dissolve any trapped emboli. Most devices of this type are intended for permanent deployment within the patient&#39;s body, and thus pose the risk of trapping sufficient emboli to adversely affect the flow of blood within the vessel in which they are deployed. Furthermore, any foreign object in the body tends to provoke a response from the immune system and over time can lead to endothelial cell formation. 
     Devices that remove emboli from the blood stream are similar to the filter devices described above and are typically connected to a deployment device such as a catheter that permits their withdrawal from the vasculature. U.S. Pat. No. 4,969,891 to Gewertz, for example, discloses a removable vascular filter permanently attached to a wire sufficiently long to extend out of the patient when the filter is deployed within. The filter is comprised of a bundle of wires secured together and having end portions that flare outwards to form the actual filter element. The filter is introduced through a catheter and the filter wires expand on their own once released from the catheter to obstruct the vessel and strain the blood flowing therethrough. This device, and others like it, are not adapted for permanent deployment within the body and can only be used for limited periods of time, limiting their efficacy. 
     In light of the above, it becomes apparent that there remains a need for a device or method that will prevent friable plaque from breaking away from arterial walls during intravascular procedures and forming emboli in the bloodstream, that is easy and safe to deploy, and that may be easily removed or alternatively employed over extended periods of time with minimal adverse impact or immunological response. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above mentioned need by providing a sheath at the distal tip of a catheter to be expanded against an arterial wall and trap plaque therebetween. A stent or other intravascular graft subsequently can be partially deployed distally of the plaque, the sheath then can be removed, and the stent fully expanded to trap the arterial plaque and any emboli between the stent and the arterial wall. 
     Thus, in one aspect, it is an object of the present invention to provide a device for trapping plaque against a vascular wall comprising an expandable sheath mounted to the distal end of an elongated tube such as a catheter, the sheath to be expanded by a balloon against a mass of atherosclerotic plaque site lining the intima of a body vessel. In another aspect of the present invention, the expandable sheath is reinforced by an expandable element embedded within it. 
     In yet another aspect of the present invention, an assembly is provided for trapping plaque against a vascular wall comprising an expandable sheath mounted to the distal end of an elongated tube such as a perfusion catheter, a delivery catheter axially slidably disposed within the perfusion catheter, a self-expanding intravascular device such as a stent disposed within the distal tip of the delivery catheter, and a pusher rod axially slidably disposed within the delivery catheter. 
     It is a further object of the present invention to provide a method for trapping plaque against a vascular wall comprising the steps of expanding a sheath mounted to the distal end of an elongated tube such as a perfusion catheter against the plaque, inserting within the perfusion catheter a delivery catheter with a self-expanding intravascular device such as a stent or intravascular graft disposed within its distal end and a pusher rod disposed adjacent the intravascular device, positioning the delivery catheter distal tip within the expanded sheath, partially withdrawing the delivery catheter to allow the distal portion of the intravascular device to expand against the vessel wall at a location distal of the plaque, withdrawing the expanded sheath, and withdrawing the delivery catheter to expose the rest of the intravascular device and thus allow it to fully expand and trap the plaque against the vessel wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  depicts a cross-sectional side view of an expandable sheath device according to the present invention inserted into a body vessel at an atherosclerotic plaque site; 
     FIG. 1 b  depicts a cross-sectional side view of the device shown in FIG. 1 a  with the sheath in an expanded configuration; 
     FIG. 2 a  depicts a side view, partially in cross-section, of the device shown in FIG. 1 a with a balloon catheter inserted therethrough; 
     FIG. 2 b  depicts a side view, partially in cross-section, of the device shown in FIG. 2 a  with the sheath expanded by the catheter balloon and the plaque shown in FIG. 1 partially compressed against the vascular wall; 
     FIG. 2 c  depicts a side view, partially in cross-section, of the device shown in FIG. 2 b  with the sheath in an expanded configuration after the balloon catheter has been deflated and withdrawn; 
     FIG. 2 d  depicts a side view, partially in cross-section, of the device shown in FIG. 2 c  with a delivery catheter inserted therethrough and a self-expanding stent disposed within the delivery catheter in a compressed state; 
     FIG. 2 e  depicts a side view, partially in cross-section, of the device shown in FIG. 2 d  with the delivery catheter partially withdrawn and the exposed distal portion of the self-expanding stent in an expanded state contacting the vessel wall at a location distal of the partially compressed plaque; 
     FIG. 2 f  depicts a side view, partially in cross-section, of the device shown in FIG. 2 e  with the sheath withdrawn proximally from contact with the plaque to expose the distal tip portion of the delivery catheter; 
     FIG. 2 g  depicts a side view, partially in cross-section, of the device shown in FIG. 2 f  with the delivery catheter fully withdrawn and the self-expanding stent in a fully expanded state against the vascular wall to compress and trap the plaque therebetween; 
     FIG. 3 depicts a side view, partially in cross-section, of the device shown in FIG. 1 a with a coil embedded within the sheath; 
     FIG. 4 a  depicts a side view of the expandable sheath device shown in FIG. 1 a  with a stent embedded in the sheath; and 
     FIG. 4 b  depicts a side view of the device shown in FIG. 4 a  with the sheath and the stent embedded therein expanded against the plaque on the vascular wall. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1 a , wherein a preferred embodiment of the catheter assembly and expandable sheath device of the present invention is depicted in its operating environment, expandable sheath  100  is comprised of a tubular wall  102  with a proximal end  104  and a distal end  106 , and defining an inner lumen  108  extending therebetween. Sheath  100  as depicted in FIG. 1 a  is in its unexpanded configuration. 
     With continued reference to FIG. 1 a , sheath  100  preferably is connected to a delivery/deployment device  120  that can introduce the sheath into a patient&#39;s body lumen  110  and advance it to the desired deployment site. Insertion device  120  is preferably an elongated tubular member such as catheter  130  depicted in FIG. 1 a , with catheter wall  131  defining inner lumen  132  which extends from distal end  134  to a proximal end [not shown] that remains outside of the patient&#39;s body. Radiopaque marker  136  is disposed at distal end  134  to enable a physician to precisely position the catheter and sheath with the aid of fluoroscopy. 
     In a preferred embodiment, catheter  130  is a perfusion catheter provided with perfusion holes  138  formed near distal end  134 . Perfusion holes  138  extend from the outside of catheter  130  through catheter wall  131  to inner lumen  132  to allow blood or any other fluid flowing through body lumen  110  to pass between the outside of the catheter and the inner lumen. This feature allows the sheath of the present invention and its associated delivery device to be deployed within a patient&#39;s vasculature for extended periods of time without blocking the patient&#39;s blood flow. In a preferred embodiment, blood flow through the perfusion holes will be somewhat less than normal blood flow which will lessen the chance of dislodging particles, and if particles are dislodged, the emboli will move more slowly in the reduced blood flow and will be easier to trap in sheath  100 . 
     Sheath  100  is formed from a permanently deformable material, preferably a polymeric material such as a low or medium molecular weight polyolefin, examples of which include PE, EVAc, EVA, and Ionomers. Any other plastically deformable material or blend of materials, including cross-linked materials and composites, may be suitable. The material, once formed into sheath  100 , should preferably display a plastic yield strength of between 50 psi and 300 psi, and a tensile break strength of over 2,000 psi. The catheter is of conventional construction with an inner diameter of preferably no less than 8 French in size. Sheath  100  may be attached to distal end  134  of catheter  130  by any known means, such as adhesives or thermoplastics, or may be formed integrally as one piece with the catheter wall  131  through any known extrusion, drawing, rolling, or similar process. 
     With reference now to FIG. 1 b , when formed from a material such as described above, sheath  100  is plastically deformable by a typical angioplasty balloon. When expanded by such a balloon, sheath  100  assumes the expanded configuration depicted in FIG. 1 b , wherein the sheath is deployed against vascular wall  112  and any arterial plaque  114  deposited thereon, thus compressing and trapping the plaque against the vascular wall. 
     In keeping with the invention, as shown in FIG. 2 a , in a preferred method of use of the device of the present invention, guidewire  200  is first inserted percutaneously in a conventional manner and advanced through a guide catheter [not shown] and then the patient&#39;s body lumen  110  until its distal end lies distal of the arterial plaque  114 . Perfusion catheter  130  with sheath  100  attached to its distal end  134  is next inserted into the guide catheter and advanced therethrough over guidewire  200  until the sheath is positioned adjacent to arterial plaque  114  in the patient&#39;s body lumen. Radiopaque marker  136  on distal end  134  of perfusion catheter  130  aids the operating physician in accurately placing the catheter and sheath  100  within body lumen  110  by tracking the progress of the radiopaque marker on an x-ray or similar visualization apparatus. 
     Once perfusion catheter  130  has been properly positioned with sheath  100  adjacent to arterial plaque  114 , guidewire  200  may optionally be withdrawn. Conventional balloon catheter  210  next is inserted within inner lumen  132  of perfusion catheter  130  and advanced over guidewire  200  until balloon  212  on the distal end of the balloon catheter is positioned within sheath  100  with the distal end of the balloon extending past the distal end of the sheath. It is understood that the type of balloon catheter that is employed is dictated by whether guidewire  200  remains within perfusion catheter  130  throughout the procedure or is withdrawn following placement of perfusion catheter  130  and sheath  100 . Balloon catheter  210  will typically also have a radiopaque marker  214  to aid the physician in accurately placing balloon  212 . Optionally, balloon catheter  210  may also be a perfusion catheter with perfusion holes  218  provided distally and proximally of the balloon  212 , which allow uninterrupted blood flow to the brain throughout the entire procedure. 
     Referring now to FIG. 2 b , once properly positioned within sheath  100 , balloon  212  is inflated to a predetermined pressure. Sheath  100  is expanded by balloon  212  as the balloon is inflated, and therefore the balloon must be inflated with fluid of sufficient pressure to overcome the plastic yield strength of the sheath and thus plastically, or permanently, expand the sheath. Balloon  212  is inflated to a size sufficient to expand sheath  100  against vascular wall  112  and thus compress arterial plaque  114  and trap the plaque against the vascular wall. In this manner any portions of arterial plaque  114  that may have become loose are prevented by sheath  100  from breaking away from vascular wall  112  and embolizing in the blood stream of the patient. 
     With reference to FIG. 2 c , after sheath  100  has been expanded and has trapped arterial plaque  114  against vascular wall  112 , balloon  212  is deflated and allowed to regress to its folded configuration, following which balloon catheter  210  is withdrawn from within perfusion catheter  130 . At this point perfusion catheter  130  is still located within body lumen  110  to maintain expanded sheath  100  in position to retain arterial plaque  114  against vascular wall  112 . At this time perfusion holes  138  allow blood to flow uninterrupted through body lumen  110  by providing a flow channel between proximal end  104  and distal end  106  of sheath  100 . Blood thus flows from the outside of perfusion catheter  130  on the proximal side of sheath  100  through perfusion holes  138 , into sheath inner lumen  108 , out through expanded sheath distal end  106 , and on into body lumen  110  on the distal end of the sheath. Providing perfusion holes  138  in perfusion catheter  130  therefore enables use of the device of the present invention over extended periods of time with no adverse effects that may otherwise be induced by throttling off the patient&#39;s normal blood flow. This is especially important in applications to the carotid artery, which supplies blood to the brain and which could trigger a stroke or seizure if starved of blood. 
     In the next step, as depicted in FIG. 2 d , delivery catheter  310  is inserted into interior lumen  132  of perfusion catheter  130 . Delivery catheter  310  is of conventional construction and may include perfusion holes  312  to allow blood flow therethrough. Self-expanding stent  320  is disposed within the distal end of delivery catheter  310 , which further includes pusher rod  316  disposed within it and adjacent to the stent. Pusher rod  316  is formed with pusher plate  318  mounted at its distal end, and the pusher rod is disposed within delivery catheter  310  such that the pusher plate is adjacent to and in contact with the proximal end of stent  320 . If guidewire  200  is utilized to advance delivery catheter  310 , then pusher plate  318  and optionally pusher rod  316  must be formed with an appropriately sized lumen [not shown] to permit the guidewire to pass through. 
     Self-expanding stent  320  can be formed from any number of materials, including metals, metal alloys, and polymeric materials. Preferably, the stents are formed from metal alloys such as stainless steel, tantalum, or the so-called heat-sensitive metal alloys such as nickel titanium (NiTi). When formed from shape-memory alloys such as NiTi, stent  320  will remain passive in its martensitic state when it is kept at a temperature below the transition temperature. In this case, the transition temperature will be below the normal body temperature, or about 98.6° F., and in a preferred embodiment the stent self expands at room temperature. When the NiTi is exposed to normal body temperature upon insertion of delivery catheter  310  into perfusion catheter  130 , it will attempt to return to its austenitic state and, if not constrained, will rapidly expand radially outwardly to assume its preformed, expanded state. Alternative shape-memory materials that may be used to form stent  320  include stress-induced martensite (SIM) alloys, which transform into martensite upon the application of stress such as a compressive load, and return to their austenitic, preformed state when the stress is removed. 
     Stent  320  is thus restrained by delivery catheter  310  from assuming its expanded state, and the delivery catheter wall must be of sufficient thickness to withstand the radially outward expansive forces exerted by the stent upon it. Delivery catheter  310  typically is provided with radiopaque marker  314  to aid the physician in accurately positioning its distal tip relative to sheath  100 . The radiopacity of stent  320  also further enhances the visualization of delivery catheter  310  via fluoroscopy. With continued reference to FIG. 2 d , upon insertion into interior lumen  132 , delivery catheter  310  is advanced through perfusion catheter  130  until it is placed so as to position the distal end of stent  320  outside distal end  106  of sheath  100 , and thus distally of plaque  114 . 
     Referring now to FIG. 2 e , the preferred method of deployment entails disposing the distal portion of stent  320  distally of distal end  106  of sheath  100 , and thus distally of arterial plaque  114 , and then partially retracting delivery catheter  310  proximally to expose the distal portion of the stent. While retracting delivery catheter  310  proximally, pusher rod  316  is immobilized so as to ensure that stent  320  does not travel proximally along with the delivery catheter due to any frictional forces applied by the wall of the delivery catheter as it slides over the stent. Thus, as delivery catheter  310  is retracted proximally, the stent will likely be urged proximally along with it by the friction between the delivery catheter wall and the stent outer surface, but the progress of the stent will be halted by pusher plate  318 , which will ensure that the stent remains located at the position initially selected by the physician for deployment. 
     With continued reference to FIG. 2 e , as delivery catheter  310  is retracted, the distal portion of self-expanding stent  320  becomes exposed and, because the restraint applied by the delivery catheter is thereby removed, the radially outward expansive forces exhibited by the stent urge the distal portion of the stent to assume its expanded state, with the distal end of the stent thus expanding to contact the vessel wall  112  at a location distal of the arterial plaque  114 . At this point stent  320 , although only partially deployed, is in position to intercept any plaque that may come loose and break off from vascular wall  112 . 
     To be able to intercept and retain plaque that may break off, the stent must be designed such that, when in its expanded state, the apertures in the stent wall are no larger than about 200 microns, more preferably no larger than about 50 to 100 microns, and in a preferred embodiment no larger than 25 microns. Thus, the stent may be an expandable tube with slots or other shaped apertures cut therein, or a wire mesh, or a wire coil, or any other practicable self-expanding device. Co-owned U.S. Pat. No. 5,514,154 to Lau et al., U.S. Pat. No. 5,569,295 to Lam, U.S. Pat. No. 5,591,197 to Orth et al., U.S. Pat. No. 5,603,721 to Lau et al., U.S. Pat. No. 5,649,952 to Lam, U.S. Pat. No. 5,728,158 to Lau et al., and U.S. Pat. No. 5,735,893 to Lau et al. describe suitable stents, and these patents are hereby incorporated herein in their entirety by reference thereto. The device of the present invention may also be used in conjunction with other expandable intravascular devices, such as grafts or fine mesh filters that may have a completely or substantially closed outer surface. 
     In the next step, as depicted in FIG. 2 f , perfusion catheter  130  is withdrawn proximally to retract sheath  100  from contact with plaque  114  and expose the distal tip of delivery catheter  310  to the plaque. This step presents the potential for portions of plaque  114  breaking off due to the frictional forces between the sliding sheath and the plaque, but because the distal end of stent  320  is deployed against vascular wall  112 , any dislodged plaque will be safely intercepted and retained by the stent. The remaining, restricted length of stent  320 , which is still disposed within delivery catheter  310 , can now be deployed directly against plaque  114 . 
     Therefore, as shown in FIG. 2 g , in the next step delivery catheter  310  is retracted to expose the entire length of stent  320  and thereby allow the rest of the stent to fully expand against vascular wall  112  and thus further compress and trap arterial plaque  114  therebetween. At this time plaque  114  is safely stabilized against vascular wall  112 , the cross-section of the body lumen  110  has been largely restored to about its nominal size, and the procedure is almost completed. In the following steps [not shown in the Figures], guidewire  200 , delivery catheter  310 , and perfusion catheter  130  are withdrawn from the body lumen, either sequentially or as one unit, and the entry wound into the patient&#39;s body is closed. Optionally, prior to withdrawing perfusion catheter  130 , the physician may choose to insert a balloon catheter into the perfusion catheter and further expand stent  320  with the balloon to ensure that plaque  114  is sufficiently compressed and/or lumen  110  has been sufficiently expanded. 
     Referring once again to FIG. 2 e , in an alternative embodiment the assembly of the present invention may additionally comprise outer sheath  350 , which overlies perfusion catheter  130  and is sized so that when in its expanded state, sheath  100  may be retracted into outer sheath. The principal purpose of outer sheath  350  is to scrape off any plaque that may be adhering to the outer surface of sheath  100 , and thus the outer sheath is preferably sized so that, as shown in FIG. 2 f , expanded sheath  100  contacts the outer sheath as the expanded sheath is drawn into the outer sheath and thereby dislodges any plaque adhering to the expanded sheath. It would therefore be advantageous if outer sheath is formed of a relatively flexible, compliant material such as PTFE that will expand to accommodate expanded outer sheath  100  as it is drawn into the outer sheath, and thus allow the physician to expand sheath  100  to any desired size during the procedure with no limitations imposed on the maximum expandable size of sheath  100  by outer sheath  350 . To further aid the process, proximal end  104  of sheath  100  may be formed with an angled configuration that will more easily slide into outer sheath  350 . 
     In an alternative embodiment of the device of the present invention, as depicted in FIG. 3, sheath  100  comprises an expandable support element such as helical coil  400  embedded within tubular wall  102 . The purpose of coil  400  is to impart additional structural strength and crush resistance to sheath  100 , and thus enable the sheath to better support body lumen  110  while a stent or graft is being deployed. An alternative embodiment of an expandable support element is depicted in FIG. 4 a , wherein stent  500  is embedded in tubular wall  102 . FIG. 4 b  depicts sheath  100  with stent  500  in an expanded configuration. Such reinforced sheaths may be used to expand body lumen  110  to  100  percent or more of its nominal, unconstricted size. 
     With continued reference to FIGS. 3 and 4, in an alternative embodiment of the device of the present invention, the expandable support element such as illustrated by coil  400  and stent  500  may comprise materials exhibiting shape memory properties, such as spring steel, Nitinol, superelastic or shape memory nickel-titanium alloys, and resilient engineering plastics such as polysulfones, PEEK, polysulfides, LCPs, etc. In such an embodiment, the expandable support element would be formed to exhibit a radially outward expansive force that is weaker than the force required for plastic deformation of sheath  100  and, preferably, the resistance to elastic deformation of the sheath would be between one and five percent greater than the expansive force exhibited by the support element. The sheath would thus remain in its unexpanded configuration until expanded by a balloon or similar expansion device, as detailed elsewhere in the specification, but would require a lessened degree of expansive force (e.g., a lower balloon inflation pressure) to be deployed into its expanded configuration due to the aiding outward force exhibited by the expandable support element. These embodiments could also be used in conjunction with outer sheath  350 , as discussed previously in conjunction with FIGS. 2 e  &amp;  2   f.    
     In view of the foregoing, it is apparent that the device and method of the present invention enhance substantially the safety of angioplasty procedures by significantly reducing the risk associated with friable plaque deposits breaking away from the vascular wall and migrating into the patient&#39;s blood stream to form emboli and potentially cause injury. Further modifications and improvements may additionally be made to the device and method disclosed herein without departing from the scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.