Abstract:
This invention provides prosthesis delivery systems with tips constructed to permit both easier advance into the body and easier removal from the body after expanding the prosthesis. The tip includes a distal taper that can gently widen a lumen during advance in instances where the lumen is narrower than the tip and a proximal taper that can gently widen the lumen on retraction in instances where the prosthesis does not immediately expand the lumen to provide clearance for the larger diameter tip.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of an application entitled “Prosthesis Delivery System” by George T. Roberts, Darin Wilson, Erik Andersen and Hans-Peter Strohband, filed Apr. 13, 1993, the entire contents of which is hereby incorporated by reference.  
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to systems for delivering prostheses into the body.  
         BACKGROUND OF THE INVENTION  
         [0003]    Prostheses, such as stents, grafts, and the like, are placed within the body to improve the function of a body lumen. For example, stents with substantial elasticity can be used to exert a radial force on a constricted portion of a lumen wall to open the lumen to near normal size.  
           [0004]    These stents can be delivered into the lumen using a system which includes a catheter, with the stent supported near its distal end, and a sheath, positioned coaxially about the catheter and over the stent, to prevent abrasion between the stent and body wall as the catheter is directed through torturous body pathways. The catheter may have an enlarged tip adjacent the distal end of the stent that also helps to atraumatically advance the system and protects the stent.  
           [0005]    Once the stent is located at the constricted portion of the lumen, the sheath is removed to expose the stent, which is expanded so it contacts the lumen wall. The catheter is subsequently removed from the body by pulling it in the proximal direction, through the larger lumen diameter created by the expanded prosthesis, which is left in the body.  
         SUMMARY OF THE INVENTION  
         [0006]    This invention provides prosthesis delivery systems with tips constructed to permit both easier advance into the body and easier removal from the body after expanding the prosthesis. The tip includes a distal taper that can gently widen a lumen during advance in instances where the lumen is narrower than the tip and a proximal taper that can gently widen the lumen on retraction in instances where the prosthesis does not immediately expand the lumen to provide clearance for the larger diameter tip. The features of the following aspects can be combined in various ways.  
           [0007]    In a one aspect the invention features a system for delivering a prosthesis into the body of a patient. The system includes an elongated catheter having a proximal end that remains outside the body, a distal end, and a supporting portion supporting a prosthesis in a radially compacted form for delivery of the prosthesis to a desired location inside the body, and an dilating tip distal of the prosthesis. The tip has a maximum diameter about equal to or greater than the radially compacted prosthesis and is shaped to include a distal portion that smoothly extends distally to smaller diameters, and a proximal portion that smoothly extends proximally to smaller diameters for enhancing withdrawal after expanding the stent.  
           [0008]    Various aspects may also include one or more of the following features. The distal and proximal portions of the tip include tapers to smaller diameter. The tip is formed with a proximal taper an angle of 20 degrees or less. The tip is smoothly shaped in the proximal portion without abrupt edges. The prosthesis is expandable to diameters less than the maximum diameter of the tip and the proximal portion of the tip engages the prosthesis during withdrawing the catheter proximally to widen the passage through the prosthesis for removing the catheter. The proximal portion includes taper of about 20° or less. The tip has a maximum diameter of about 8 mm. The proximal and distal portions have an axial length greater than the maximum diameter of the tip. The tip has transition regions between portions of different diameter and the transition regions are smoothly formed, without abrupt edges. The prosthesis is self-expanding. The system has a retractable protective sheath over the prosthesis, that engages the tip to form a seal that protects the prosthesis from exposure to body fluids during delivery into the body. The protective sheath engages the tip at a step region, which has smooth transitions to to different diameters. The sheath has a flexible proximal portion with a smaller diameter than a distal protion positioned over the sheath during delivery into the body.  
           [0009]    In another aspect, the invention features a method for delivering a prosthesis into the body of a patient that includes, providing an elongated catheter having a proximal end that remains outside the body, a distal end, and a supporting portion supporting a prosthesis in a radially compacted form, the catheter further including a dilating tip distal of the supporting portion and having a diameter about equal to or greater than the radially compacted prosthesis, and being shaped to include a distal portion that smoothly extends distally to smaller diameters, and a proximal portion that smoothly extends proximally to smaller diameters for enhancing withdrawal after expanding the stent. The method also includes placing the catheter into a body lumen and positioning the prosthesis at a desired location, expanding the prosthesis to a diameter no larger than the maximum diameter of the tip, withdrawing the catheter to engage the proximal portion of the tip and the prosthesis, and continuing to withdraw the catheter so the tip widens the passage through the prosthesis so the catheter can be removed from the body.  
           [0010]    Various aspects of the invention may also include one or more of the following features. The method includes selecting a self-expanding prosthesis to provide axial force to the interior of the lumen to fully expand the lumen after an extended period of time, and withdrawing the catheter prior to fully expanding the prosthesis. The method includes crossing a region of a lumen consticted to a diameter smaller than the maximum diameter of the tip by urging the distal or proximal portion of the tip against the region to widen the region.  
           [0011]    The inventions have many advantages. For example, since the catheter can be easily removed from the body, the physician does not have to wait until the prosthesis expands to a radial dimension larger than the tip or use a separate dilatation catheter to expand the lumen so that the catheter can be removed. With systems according to the invention, the physician can even select a prosthesis that will produce a predetermined slow expansion of the lumen, over a period of hours or even days, which can have therapeutic benefits such as avoiding rupture of a lumen wall that has been weakened by a tumor. The catheter can be removed from the body immediately after release of the slow-expanding prosthesis. The system, since it can be used to widen the lumen while advancing it into the lumen, also may reduce the need for predilating the lumen with other devices.  
           [0012]    Further features and advantages follow.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    We first briefly describe the drawings.  
         [0014]    [0014]FIG. 1 is a cross-sectional side view of a system according to the invention configured for delivery into the body, while FIG. 1 a  is a similar view of the system in an alternate configuration,  
         [0015]    [0015]FIG. 2 is a detailed side view of a dilating tip; and  
         [0016]    FIGS.  3 - 3   h  illustrate positioning a stent in the esophagus of a patient with a system according to the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    Structure  
         [0018]    Referring to FIGS. 1 and 1 a , a delivery system  2  according to the invention for operation in the esophagus includes a catheter  4  with a stent  14  positioned near the distal end. The system also includes sheath  20 , with a reduced diameter portion  24  proximal of a portion  22  for covering the stent  14  during entry into the body (FIG. 1). The sheath  20  can be retracted (arrow  17 ) to expose and expand (arrows  19 ) the stent (FIG. 1 a ). A dilating tip  26 , permanently attached to the catheter, has a distal taper  28  to smaller diameter for atraumatic entry of the device into the body, and a proximal taper  29  which can engage the prosthesis and lumen to atraumatically widen the lumen during withdrawal.  
         [0019]    The catheter  4  has an overall length, L 1 , about 100 cm, with a constant outer diameter of about 3.4 mm. The catheter  4  (Pebax, 70 durometer, Atochem, Philedelphia, Pa.) includes a handle  12  (nylon) on the proximal end, an inner lumen  6  (phantom), of about 1.1 mm inner diameter, for tracking over a guidewire (e.g., 0.038 inch). The catheter  4  may include a stainless steel hypotube (not shown) along the wall of its internal lumen and a permanently attached flexible distal end  8 , of length, L 2 , about 3 cm, formed of a soft polymer (Pebax, 40 durometer, Atochem) that flexes easily when challenged by a lumen wall, for atraumatic advance.  
         [0020]    The catheter  4  includes a supporting portion  10 , of length L 3 , about 15 cm, for supporting the stent  14  in a radially compacted form during delivery into the body. The stent  14  is preferably a self-expanding knitted stent formed of a highly elastic material such as a nitinol-type material (Strecker Stent, Boston Scientific, Watertown, Mass.). Knitted stents are discussed in detail in Strecker, U.S. Pat. No. 4,922,905 and U.S. patent application Ser. No. 07/960,584, filed Oct. 13, 1992, the entire contents of these cases being hereby incorporated by reference. The stent has a maximum expanded diameter of about 20 mm. As mentioned, a stent may be selected to apply a constant, rather gentle radial force to the lumen wall that expands the wall to near normal diameter over an extended period, for example, 24 or 48 hours. The stent is radially compacted by wrapping it about the portion  10  and fixing it in this form using a body-fluid degradable gelatin material (DFG STOESS, Deutsch Gelatin Fabriken AG, Germany). The stent in the compacted form has an outer diameter of about 6.5 mm. Compacting the stent by wrapping it onto a catheter and holding it with gelatin is discussed in allowed U.S. application Ser. No. 07/773,847, filed Oct. 9, 1991, the entire contents of which is also hereby incorporated by reference. Dissolvable polymers are also discussed in U.S. Pat. No. 5,049,138, which is also incorporated herein by reference.  
         [0021]    The supporting portion  10  includes radiopaque markers  16 ,  16 ′ which mark the location of the proximal and distal ends of the stent in the compacted form. The portion  10  also includes radiopaque markers  18 ,  18 ′ which indicate the ends of the stent  14  in the expanded state.  
         [0022]    Positioned coaxially about the catheter  4 , and extending over the stent  14  during delivery into the body (FIG. 1), is protective sheath  20 . The sheath  20  has an overall length L 4 , about 70 cm, is formed of a single piece of extruded flexible polymer (extruded Pebax, 70 durometer, available from Atochem) and has a constant wall thickness of about 0.5 mm. The sheath includes a distal portion  22  having a length, L 5 , about 17 cm, which corresponds approximately to the length of the stent in compacted form with some extension on either end. The outer diameter of the distal portion  22  of the sheath is about 8 mm and the inner diameter is slightly larger than the diameter of the stent  14  in its compacted form, to provide a clearance of about 0.5 mm between the inner wall of the sheath and the compacted stent. The sheath  20  further includes a tapered portion of length, L 6 , about 7-9 cm, from the larger diameter of the distal portion  22  to the smaller diameter, about 5 mm, of a proximal portion  24  which has a length, L 7 , about 53 cm. A handle  25  (nylon) allows the sheath to be retracted from the proximal end (arrow  17 ) to expose the stent so that it can be expanded (arrows  19 ). (The distance between the handle  25  on the sheath, and handle  12 , on the catheter, corresponds approximately to the length of the compacted stent.) A safety sleeve  27  with a slit  29  and pull tab  32  is positioned between the handles during delivery to prevent inadvertent exposure of the stent (FIG. 1). The sleeve  27  is stripped from the catheter once the system is properly placed so the sheath can be retracted to expose the stent (FIG. 1 a ). The diameter of the proximal portion  24  is selected to conform closely to the outer diameter of the catheter body  4 . The clearance between the outer diameter of the catheter body  4  and the inner diameter of the proximal portion  24  of the sheath  20  is about 1.5 mm.  
         [0023]    The sheath, having variable radial dimension along its length, is a particular feature of the invention which enhances positioning of a large stent with large delivery systems for use in a lumens having torturous pathways. Since the outer diameter of the proximal portion of the sheath is small, the flexibility is enhanced. It flexes more easily around torturous channels because there is less strain on the outside curved wall and less compaction on the inside curved wall. Since all portions of the sheath conform more closely to the outer diameter of the components within the sheath, kinking along the length is reduced. The gap between the outer diameter of the catheter and inner diameter of the sheath is small, so the catheter tends to support the relatively thin-walled sheath when the system is bent around a curve. In the distal portion of the sheath, the larger radial dimension is supported by the larger radial dimension of the stent, which is positioned around the catheter. Minimizing kinking is an important feature, since severe kinking can cause friction between the sheath and the catheter that can prevent the sheath from being retracted. In many body lumens, such as the esophagus, the most torturous portion of the lumen is near the point of entry of the body. The present system improves operation by enhancing flexibility and reducing kinking particularly in the proximal portions of the device typically located along a torturous bend. The sheath of the system described does not kink in the proximal portions when bent 90 degrees over a radius of about 6.35 cm, which is typical of the esophagus. Moreover, a sheath with reduced size in proximal portions presents a smaller inner surface area, which reduces friction against the catheter, and therefore makes operation smoother.  
         [0024]    Referring particularly to FIG. 2, the system further includes a dilating tip  26  which is generally designed to contact the body lumen atraumatically and also can perform the additional function of dilating the lumen so the catheter can be urged through a narrow stricture, smaller than the tip, to widen and cross a lesion. After expanding the stent, the tip allows dilating the lumen and/or the passage through the stent during withdrawal of the catheter. The tip  26  has a length, L 8 , about 28 mm, and a maximum outer diameter, d 1 , about 8 mm. The maximum outer diameter of the tip  26  substantially corresponds to the maximum outer diameter of the distal portion  22  of the sheath  20  (phantom). The tip  26  includes a distal taper portion  28  of length, L 9 , about 12.5 mm, at an angle θ 1 , about 10 degrees, to present a gradual increase in diameter when the system is moved axially distally. The distal taper tapers to a diameter, d 2 , about 4.5 mm at its end  35 , which has atraumatic rounded edges as shown. The tip  26  also provides a gradual profile to smaller diameters in the proxial direction. The tip includes a proximal taper  29  at an angle, θ 2 , about 20° (smaller angles can be used) that aids smooth engagement of the tip with portions of the the stent and/or lumen and gentle expansion when removing the catheter during withdrawal. The proximal taper  29  has a length, L 12 , about 4 mm, and tapers to a diameter, d 3 , about 4.0 mm at the end  37  of the taper. The tip, generally, is elongated compared to its maximum diameter and, in particular, the proximal region is elongated compared to the maximum diameter for providing a gradual transition. The most proximal portion  39  of the tip is rounded to the outer diameter of the catheter  4  (phantom). The distal portion of the sheath meets the tip  26  along a step portion  30  of length, L 11 , about 7 mm and diameter, d 4 , about 6.8 mm. The step portion  30  also includes a slight taper  31 , at an angle of less than 20 degrees, for example, around 10 degrees, with length L 10 , about 4 mm, to the maximum diameter d 1 . The transitions between all of the portions of the tip of different diameter, especially those in the proximal parts of the tip, are smooth or rounded for gradual, atraumatic movement and to avoid any sharp edges that could hang up when engaging a partially expanded stent or body lumen wall, especially during withdrawal. The smooth profile and rounded surfaces without blunt ends or abrupt edges substantially aviods the tip hanging up on the stent as the catheter is withdrawn. This feature is paricularly important with knit-type stents formed of successive rows of loops. The length of the regions proximal and distal of the maximum diameter are relatively long compared to the maximum diameter to provide a gentle, gradual engagement and widening of the lumen during withdrawal. The step portion  30  of the tip  26  and the sheath  20  (phantom) form a seal that isolates the stent from body fluids during delivery into the body to avoid dissolving the gelatin prior to withdrawal of the sheath, which could cause premature expansion of the stent.  
         [0025]    The tip  26  can be formed of a nondissolvable relatively noncompressible polymer (Nylon, Vestamid, Hulls, Germany) and can be securely attached to the catheter by insert molding the tip onto the catheter. A compressible silicon O-ring  67 , about 1 mm diameter, may be fitted into a groove (about 0.85 mm deep) in the step portion  30  to enhance the seal with the sheath. The tip may also be polyethylene.  
         [0026]    Use  
         [0027]    The following procedure may be used for treating a patient with a tumor in the esophagus. The patient is prepared on an endoscopic table. The physician passes an endoscope, which has a diameter of approximately 12 mm, through the patient&#39;s mouth into the esophagus to view both the proximal and distal portions of the tumor to determine its morphology and character. If the endoscope will not cross through the tumor, the physician will dilate the lumen with a rigid dilator tracked over a guidewire or a balloon dilator which tracks through the endoscope. The endoscope is then passed retroflex so it looks back on itself and up at the most distal portion of the tumor to view its makeup. The physician measures the length of the tumor using graduated centimeter markings on the endoscope and/or makes a notation of the patient&#39;s incisor as to the most distal segment of the tumor. The physician then withdraws the endoscope partially and finds the most proximal segment of the tumor and makes a similar notation to determine the length of the tumor. Generally, the length of the stent is selected so that it extends about 2 cm beyond each end of the tumor. As discussed, the tip  26  may also be used to widen the lumen in some cases, either initally or after the esophageal wall rebounds after dilatation by other means.  
         [0028]    Referring to the series of FIGS.  3 - 3   h , placement of a stent in the esophagus of a patient is illustrated. Referring to FIG. 3, the patient  50  having a tumor  52  in the esophagus  54 , normally about 20 mm lumen diameter, but constricted to 8-12 mm by the tumor is treated by positioning a guidewire  56  through the throat into the esophagus to a position distal of the tumor  52 , usually into the stomach.  
         [0029]    Referring to FIG. 3 a , the delivery system  2  is delivered over the guidewire by sliding the proximal portion of the guidewire through the guidewire lumen in the catheter. A lubricant, K-Y jelly, may be applied to the distal end  8  of the catheter and the tip  26 . The physician then observes the placement with a fluoroscopic device using the radiopaque markers. As illustrated, the esophagus includes a highly torturous portion just distal of the throat including a 90 degree bend over a radius of about 6.35 cm. The distal end of the system, including the enlarged portion  22  of the sheath covering the stent, has sufficient strength to follow the contour of the wire without excessive kinking, which is enhanced by the support of the underlying stent. It should be appreciated that in this case, even if some kinking of the distal portion  22  of the sheath should occur as it passes the torturous bend, the kinks do not substantially impede the operation since the stent has not been located at a position at which the sheath would be withdrawn. As illustrated, the tip  26  provides a gradual increase in diameter, providing an atraumatic advance of the system into the esophagus.  
         [0030]    Referring to FIGS. 3 b  and  3   c  (an enlarged view of the area in circle c) the distal portion of the system, corresponding to the position of the stent and the enlarged portion  22  of the sheath, is located across the constriction caused by the tumor  52 . In this position, the portions of the system including the reduced diameter portions  24  of the sheath are easily bent around the initial curve. The tip  26 , with the gradual transition to larger diameter, aids in crossing the constricted region. As discussed, the tip may also be used to urge open the region.  
         [0031]    Referring to FIGS. 3 d  to  3   h , enlarged views of the constricted region are shown to further illustrate the operation. Referring particularly to FIG. 3 d , with the stent properly located about the constriction, the sheath is slid axially proximally to expose the stent to the body lumen. The gelatin holding the stent in compacted form is dissolved by body fluids and the stent self-expands to larger diameter. As illustrated, in many instances, the stent initially expands the constriction to a small degree with a waist-shaped constriction still providing a rather narrow passageway with radial dimension somewhat smaller than the maximum radial dimension of the tip  26 . The initial opening through the constriction may be formed, as mentioned, by a dilating means, so the opening is initially large enough to allow the system to cross with some clearance. However, the opening can be reduced somewhat after the system has crossed by a rebounding of the esophageal wall. In some cases, the system, with the atraumatic tip may be used to widen the constricted portion slightly so that the system can pass. Further, the stent, upon release from the catheter unwraps partially, leaving fold portions  58  that occlude the lumen partially. All of these conditions can create situations in which the tip is of a larger diameter than the constricted region of the lumen.  
         [0032]    Referring to FIG. 3 e , under these conditions, upon withdrawing the catheter, the the proximal portion of the tip  26  engages the stent in the region of the constriction. The smooth gradual profile to larger diameters and rounded transitions keep the tip from hanging up or catching on the stent as the tip is drawn proximally.  
         [0033]    Referring to FIG. 3 f , as withdrawal of the catheter continues, the the proximal portion of the tip gradually enlarges the passage throught the constricted area by either or a combination of expanding the body lumen (arrow  61 ) and the stent or gently pushing the folds of the stent out of the way to form a larger passageway, allowing the tip to pass through and the catheter to be withdrawn.  
         [0034]    Referring to FIGS. 3 g  and  3   h , after a short time, about 4 hours, the tip  26  dissolves and/or is passed through the body. In time, the radial force provided by the stent, further widens the esophagus providing a large open lumen that facilitates swallowing.  
         [0035]    Other Embodiments  
         [0036]    Many other embodiments are possible. For example, the maximum diameter of the tip may be slected to be much larger than the diameter of the stent in the compacted form so the tip dilates the lume to a desired diameter before expanding the stent. The sheath may be modified to enhance pushability or pullablity when the tip is used to widen lumens. The tip may be formed integrally with the catheter. The delivery systems can be sized and configured for use in various body lumens, the prostate, urethra or the biliary tree including the common bile duct, pancreatic duct and left and right hepatic ducts, and with particular benefit in alimentary tract lumens, such as the esophagus, stomach, pilorus, small intestine, colon or rectum. As will be appreciated, most of the latter applications involve relatively large lumens, about 1 to 1.5 cm or more, with torturous bends requiring relatively large stents to be delivered with large flexible delivery systems that resist kinking. As mentioned above, aspects of this invention provide particular advantages for delivering large stents, greater than about 10 mm expanded diameter, using larger delivery systems, greater than 6 mm maximum diameter. Like the esophagus, most of these lumens also have an extreme curvature near the entry point of the delivery system, such as the rectal sigmoid area in the colon. In the structure discussed in detail above, the stent is self-expanding and held compacted using a gelatin, but other embodiments uses a sheath that holds the stent in compacted form, without use of the gelatin. For example, the sheath may be constructed to hold the stent in compacted form by having a thicker wall in the distal portions and a thinner wall in proximal portions. The sheath may be formed in various ways, such as from polyethylene shrink tubing, which is reduced in diameter in proximal portions by heat application. In such cases, the wall thickness of the tubing is increased in the proximal portions, which can enhance the strength. The advantages of the invention can also be realized with stents that are not self-expanding, such as balloon expandable stents. A fluid, such as saline can be flowed into the lumen to more rapidly dissolve body-fluid dissolving portions.  
         [0037]    Still further embodiments are within the following claims.