System for implanting a replacement valve

[0001] This invention relates to a system for the percutaneous implantation of a biological venous valvular replacement for a human valve.

[0002] There exists a need in the medical field for an improved system for carrying out the percutaneous implantation of biological venous valvular replacements for human valves and in particular cardiac valves. Up until recently, many valves such as heart valves had to be replaced surgically. Accordingly, the patients were exposed to all the potential dangers of major surgery.

[0003] Recently, procedures have been devised for implanting biological valves harvested from animals percutaneously into humans to replace damaged or malfunctioning valves. Andersen et al. in U.S. Pat. No. 5,840,081 describes a system for carrying out such a procedure. In Andersen et al., a biological cardiac valve is mounted upon the expandable stent of a catheter. The assembly is crimped onto the balloon section of the catheter and a protective cap is placed over the package. The catheter is then passed through a body lumen into a predetermined site within the heart. The package is then moved out of the cap and is positioned in the implantation site using well known positioning techniques. The balloon is inflated causing the stent with the replacement valve attached thereto to expand thus implanting the valve within the desire site.

[0004] The Andersen et al. type system works well in practice in that it can be carried out in a relatively short period of time when compared to surgical procedures and the risk to the patient is considerably reduced. However, the biological prosthesis that include the venous valvular replacement and the stent tends to be relatively bulky and thick even when tightly compressed against the deflated balloon and thus sometimes difficult to move through the body lumen into the implantation site. Most catheters in present day use can not deliver the necessary torque to guide the prosthesis through the body lumen, particularly where there is a relatively tight bend in the path of travel. In addition, most of the catheters that are equipped with protective caps do not possess the rigidity needed to hold the prosthesis in the desired location as the balloon is cleared for inflation.

[0005] It is therefore an object of the present invention to improve percutaneous deliver systems for placing a biological venous valvular replacement for a defective valve within an implantation site.

[0006] A further object of the present invention is to improve the steerability of a balloon catheter used to implant a biological valve percutaneously in a patient.

[0007] A still further object of the present invention is to more accurately place a biological valve prosthesis with a desired implantation site.

[0008] Another object of the present invention is to provide a more compact system for percutaneously inserting a biological replacement valve into an implantation site.

[0009] These and other objects of the present invention are attained by a system for percutaneously inserting a biological venous valvular replacement for a defective valve within a patient through a body lumen. The system includes a balloon catheter upon which a collapsable stent containing a venous valvular replacement is mounted in a collapsed condition upon the deflated balloon. A protective shield is placed over the balloon and the replacement valve unit. The shield is movable from a closed position over the balloon to a fully opened position without having to axially displace the balloon so that the balloon can be inflated to expand the stent and accurately implant the replacement valve. A central lumen formed of a stainless steel tube passes through the catheter to provide a one to one torque ratio between the proximal end of the catheter and its distal end. The wall thickness of the venous valvular replacement is reduced from its original size by between 50% and 90% to provide for a more compact replacement package when the package is collapsed upon the uninflated balloon.

[0010] For a better understanding of these and other objects of the invention, reference will be made to the following detailed description of the invention which is to be read in association with the accompanying drawing, wherein:

[0011] FIG. 1 is a perspective view illustrating a delivery system embodying the teachings of the present invention for the percutaneous insertion and implantation of a biological replacement valve within a patient;

[0012] FIG. 2. is a partial perspective view illustrating the distal end of the system shown in FIG. 1 with its protective shield moved back away from the balloon section of the system;

[0013] FIG. 3 is an enlarged side elevation of an expanded stent used in the practice of the present invention;

[0014] FIG. 4 is a perspective view of the stent with a biological replacement valve unit mounted inside the stent;

[0015] FIG. 5 is an enlarged section taken along lines 4-4 in FIG. 2; and

[0016] FIG. 6 is a side elevation illustrating a biological replacement valve suitable for use in the present invention as the wall thickness of the vein which supports the valve is being reduced.

[0017] FIGS. 1 and 2 illustrate a system, generally referenced 10, for percutaneous insertion and implantation of a biological venous valvular replacement for a defective or malfunctioning valve. The system includes an elongated balloon catheter 12 having an inflatable balloon 13 joined to the distal end of the catheter. The balloon is connected in fluid flow communication with a lumen 15 through which the balloon is inflated or deflated in a manner well known in the art. Preferably the balloon is inflated using a radio-opaque fluid. Although a single balloon is shown in the present embodiment of the invention, it should be obvious to one skilled in the art that a plurality of balloons in various configurations may be employed in the practice of the present invention.

[0018] The catheter further includes a centrally located lumen 17 that passes through the entire length of the catheter from its proximal end to its distal end. The central lumen, unlike other catheter lumens employed in the prior art, is formed from a length of stainless steel tubing. A pointed nose cone 20 is affixed to the distal end of the tubing and the rear section 21 of the nose cone is secured to the front part of the balloon. The distal end of the central lumen 17 opens to the surrounding ambient at one end through the front of the nose cone and at the other end through the rear section of the catheter as illustrated in FIG. 1.

[0019] A thin guide wire 24 passes through the central lumen which is used in a conventional manner to guide the catheter into the implantation site.

[0020] It has been found that when a stent containing a biological valve is mounted upon the balloon of a catheter, the package tends to become overly large and clumsy to maneuver. Accordingly, maneuvering of the catheter through a vein or artery to the implantation site becomes difficult, particularly where the catheter has to be conducted through a number of bends along the intended path of travel. Conventional catheters and the lumens running there-through are fabricated from plastic materials that tend to twist when a torque is applied to the proximal or steering end of the device. This twisting adversely effects the steering control at the distal end of the catheter making it difficult to direct the catheter around any bends in the intended path of travel and accurately place the replacement package in the implantation region. The stainless steel tube running down the center of the present catheter is designed to provide the catheter with a 1 to 1 torque ratio between the proximal end of the catheter and its distal end. This in turn, enhances the steerability of the catheter as well as providing the user with the ability to more easily push the catheter along the desired path of travel. It has been found that a stainless steel tube having an inside diameter of about 0.039 will provide the above noted desired properties while at the same time providing the catheter with sufficient flexibility to pass readily through bent regions along the path of travel. This, along with the contoured nose cone, enables the user to rapidly guide the catheter into a desired implantation site and thus considerably shorten the implantation procedure when compared to similar systems used in the art.

[0021] An elongated sheath 30 is placed over the catheter. A close running fit is provided between the sheath and the catheter so that the sheath can slide easily over the body of the catheter. A protective shield 31 is attached to the distal end of the sheath so that the shield can be repositioned by simply moving the sheath over the catheter. In assembly, the shield is movable between a fully closed position as illustrated in FIG. 1 wherein the balloon and the replacement package are protectively enclosed and a fully opened position as illustrated in FIG. 2 wherein the balloon is cleared for inflation. An annular stop 33 is mounted on the catheter adjacent to the back edge of the balloon section. The stop is arranged to arrest the forward motion of the sheath once the shield reaches a fully closed position insuring that the shield will not ride over the nose cone.

[0022] The proximal end of the sheath contains a cylindrical flange 34 by which aids the operator to manually slide the sheath over the catheter body to open or close the protective shield. The distal end 35 of the catheter passes out of the sheath through the flange and extend back a distance that is greater than the axial length of the shield. Indicator marks 36 and 37 are placed on the extended length of the catheter for informing the operator when the shield is located in either the open or the closed position.

[0023] A cylindrical fluid barrier 40 is slidably mounted upon the proximal end of the sheath. The barrier includes a tubular body section 41 and a radially extended end flange 42. The outside diameter of the body section is about equal to that of the protective shield. In practice, once the balloon shield has passed into the body lumen through the physician's incision, the body of the fluid barrier is passed into the body lumen through the incision and the flange is placed in contact against the incision opening. Once inserted, the barrier restricts the flow of body fluid through the incision opening while, at the same time, allowing the sheath and the catheter to be advanced and maneuvered within the body lumen into the implantation site.

[0024] As will be further explained below, the prosthetic device made up of an expandable stent and a biological venous valvular replacement is mounted in a collapsed state upon the balloon section of the catheter. The replacement is preferably has been harvested from the jugular vein of an animal, such as a cow, and is secured to the inside of the stent. Initially, the sheath is pulled back along the catheter to expose the collapsed balloon and the prosthetic device is passed over the balloon and crimped tightly onto the balloon to establish a compact low profile package. The sheath is then moved forward along the catheter to place the shield over the package to protect it during insertion. Once the package is positioned within the insertion site the shield again is moved back over the stationary body of the catheter as explained above and the balloon is inflated to implant the biological replacement within the site.

[0025] Turning more specifically to FIGS. 2-5, there is illustrated a stent 50 that is particularly well suited for use in the present system. A biological venous valvular replacement 51 for a defective valve is carried inside of the stent. Although the present valve replacement is ideally suited for percutaneous implantation of a pulmonary valve, it should clear that the present system can be used in a number of similar applications without departing from the teachings of the invention. As illustrated in FIG. 3, the biological replacement unit 51 includes a section of vein 55 that contain a valve 56. As will be explained below in further detail the venous valvular replacement is attached to the stent by means of sutures 58.

[0026] The present expandable stent includes a series of fine wire ribbon sections, each designated 60 that are joined together to create a tubular or cylindrical member. The wire stand 59 of each section is fabricated of a soft, highly malleable metal alloy that has been fully annealed to remove as much of its spring memory as possible. Preferably the wire material is fabricated of an alloy consisting of about 90% platinum and 10% iridium that has a tensile strength of between 150,000 psi and 175,000 psi. Although a platinum iridium wire is preferred for use in the present stent, other alloys having similar properties such as a gold nickle alloy may also be employed. Prior to winding the wire ribbon sections into a cylindrical shape, each section is formed so that it contains a series of alternating sinusoidal bends 61. The sections are formed by winding the strand of wire between rows of vertical pins projecting from the surface of a flat substrate. The strand is then wound about the pins in alternate rows to create a sinusoidal shaped ribbon section having a desired number of bends and a free length of wire is located at each end of the ribbon section.

[0027] Each ribbon section is next wound into a cylinder and the cylinders are then placed in axial alignment so that the apex of each bend section is located in close proximity with the apex of a bend section on an adjacent ribbon section. The adjacent bends are then welded together to cojoin the ribbon section in assembly. Although not shown, the free ends of the adjacent cylindrical ribbon sections, in turn, are bent into parallel overlapping alignment and are cojoined using similar welds.

[0028] Referring to FIG. 5, there is illustrated a typical weld joint 64 used in the practice of the present invention. Each weld is formed so that it lies inside the boundaries of the cylindrical stent as described by the inside diameter and outside diameter of the stent. Accordingly, the welds do not protrude beyond the boundaries of the wire cylinder into regions where rough edges of the welds might come in contact with the tissue of the biological valve replacement thereby preventing the tissue from becoming damaged during insertion and implantation.

[0029] A stent of the construction and configuration as herein describe has extremely good flexibility, dimensional stability, very smooth surfaces, a low profile when collapsed and an immunity to fatigue and corrosion. As should be evident the length of the stent can be varied by varying the number of ribbon sections that are utilized. By the same token, the working range of the stent between its fully collapsed condition and it fully expanded condition can also be varied by varying the number of bends in each of the ribbon sections. As can be seen each stent can be tailored for insertion into a particular body site to provide for the most effective implantation of the biological valve which is attached to the stent.

[0030] Because of the stent construction there is very little or no axial deformation of the stent as it is radially expanded or collapsed. Another feature of the present stent is its ability to be reconfigured even after implantation without adversely effecting the stents performance. This feature is important in cases where a valve has been implanted in a growing child. Rather than replacing a valve periodically during the growth period, the supporting stent can be simply reconfigured to accommodate for growth using a percutaneously introduced balloon catheter for re-engaging the stent to reconfigure the stent so that it will conform to the changes in the implantation site produced by growth.

[0031] As illustrated in FIG. 4, the stent is initially expanded to a desired diameter which generally conforms to the body vessel configuration at the implantation site. Next, as illustrated in FIG. 6, the vein section of the valve is trimmed to a desired length conforming to the length of the stent with the valve 56 being located in about the mid-region of the stent. In addition, the wall of the vein 56 is reduced in thickness to between 50% to 90% of its original thickness to considerably reduce the size of the valve package when the stent is collapsed over the balloon prior to insertion. It has been found that the jugular vein of a bovine animal is formed by layers of tissue that can be readily peeled back using a sharp instrument 75. The layers can be removed without destroying the integrity of the vein structure or its ability to function in a replacement prosthesis. The wall of the vein is trimmed so that its outside diameter about matches the inside diameter of the expanded stent. The vein is then passed into the expanded stent and the vein sutured to the stent as illustrated in FIG. 3. The sutures are arranged to support the vein in a fully opened circular configuration within the expanded stent.

[0032] Once the prosthesis has been sutured in place, it is passed over the balloon section of the catheter and the stent is collapsed tightly against the balloon to provide a more compact than normal package that can more easily be delivered through a body lumen into an implantation site when compared to similar devices employing bovine or eqvine biological valves replacements.

[0033] While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.