Abstract:
A method for deploying an expandable implant ( 100 ) in a body passage ( 302 ) of varying diameter includes selecting a balloon ( 200 ) having a radial dimension that varies, when the balloon is inflated, in accordance with the varying diameter of the body passage. The balloon is inserted, in a deflated state, into the body passage, with the expandable implant fitted radially around the balloon. The balloon is inflated so as to cause the implant to open, responsively to the varying radial dimension of the balloon, into an expanded shape that approximately matches the varying diameter of the body passage, thus anchoring the implant in the body passage.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to implantable therapeutic devices, and specifically to varying-diameter intravascular implants.  
       BACKGROUND OF THE INVENTION  
       [0002]     Stent implants are commonly used in treating arterial stenoses and other unwanted constrictions of body passages. Stents typically comprise a metal coil or mesh. An arterial stent, for example, is threaded through the vascular system to the point of stenosis in an artery. When the stent is in place, it is expanded to force the artery open to the desired diameter. Typically, the stent comprises a plastic material, which is inserted using a balloon catheter into the point of stenosis in a compressed state. The stent is then expanded by inflating the balloon. An apparatus and method for securing a stent to a balloon catheter is described, for example, in U.S. Pat. No. 6,364,870, whose disclosure is incorporated herein by reference.  
         [0003]     On the other hand, there are some procedures in which stent implants are required to constrict the diameter of a blood vessel. For example, Ruiz describes an endoluminal stent having adjustable constriction in U.S. Pat. No. 6,120,534, whose disclosure is incorporated herein by reference. The stent comprises a deformable mesh having a conical portion and a constricted region, which forms a flow-limiting constriction. The stent is delivered and deployed inside a blood vessel. The constricted region of the mesh is then selectively enlarged to adjust the flow impedance in the vessel. Ruiz describes particularly the use of his stent to reduce blood flow in the pulmonary artery, as a palliative treatment for infants having complex congenital cardiac malformations.  
         [0004]     Other types of constricting stents and applications of such stents are described by Shalev et al. in PCT Patent Publication WO 01/72239, whose disclosure is incorporated herein by reference. In particular, this publication describes the use of a flow-reducing implant in the coronary sinus, in order to promote angiogenesis in the heart tissues. The implant is inserted by catheter through a central vein, such as the jugular vein, and brought into the coronary sinus. Alternatively, the implant may be installed in one or more of the coronary veins. Once the implant is in place, it is allowed to elastically expand or it is plastically expanded using a balloon.  
         [0005]     Examples of high-pressure balloons, traditionally used in angioplasty, and recent balloon design development, are described in an article entitled, “Applications of High-Pressure Balloons for Medical Device Industry,”  Medical Device and Diagnostic Industry Magazine  (September 2000), whose disclosure is incorporated herein by reference. Recent improvements in materials, balloon shape design, and fabrication technology include, inter alia, additional lengths, ultra thin walls (for minimal invasiveness and a smaller profile), varying diameters throughout the balloon length, custom shapes, and tapered ends and angles.  
         [0006]     The specific shape of a high-pressure balloon may be demanded by the peculiarities of an anatomical site and/or the requirements of the treatment process. For example, a dog bone shaped balloon may be used to localize delivery of medication to avoid systemic intravenous administration. The ends of the balloon can be of equal or different sizes, depending on the shape of the cavity or vessel. When inflated, the ends seal off the area to be treated, and the medication is infused through a hole or series of holes in the narrower center section of the balloon. High-pressure balloons are also used to position diagnostic devices inside vessels or body cavities for ultrasound imaging and other techniques. Rather than having a complicated steering or positioning mechanism on the end of a catheter, a high-pressure balloon can be used to either center or offset the device, precisely positioning it as required.  
       SUMMARY OF THE INVENTION  
       [0007]     Embodiments of the present invention provide novel devices and methods for deploying an implant in a body passage, such as the coronary sinus, that varies in diameter over its length. In implantation of stents known in the art, a balloon whose diameter is roughly uniform over its length is typically used. Therefore, if the diameter of the body passage varies over the length of the stent, the end of the stent in the wider area of the passage may be insufficiently expanded, so that the stent is not securely anchored. Alternatively, the opposite end of the stent, in the narrower area of the body passage, may be expanded substantially beyond the natural diameter of the passage, causing strain on the tissue.  
         [0008]     In embodiments of the present invention, on the other hand, the balloon that is used to expand the implant has a diameter that varies over its length, in such a way as to roughly match the varying diameter of the body passage. When the implant is in place within the body passage, the balloon is inflated to plastically expand the implant, so that the expanded diameter of the implant roughly matches the full diameter of the body passage at two or more points, typically at both ends of the implant. (In the case of a constricting implant, as may be used in the cardiac sinus in order to partially constrict the flow of blood therethrough, a part of the implant, typically a central part, may remain unexpanded.) As a result, the implant is anchored securely in place, without undue strain on the walls of the body passage.  
         [0009]     The implant and balloon and method of inserting them described herein are particularly useful for restricting blood flow in the coronary sinus, as described in the above-mentioned PCT publication and in U.S. patent application Ser. No. 09/534,968, which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference. The principles of the present invention, however, may be similarly used in deploying implants within other varying-diameter veins and arteries, as well as in other medical applications.  
         [0010]     There is therefore provided, in accordance with an embodiment of the present invention, a method for deploying an expandable implant in a body passage of varying diameter, including: 
        selecting a balloon having a radial dimension that varies, when the balloon is inflated, in accordance with the varying diameter of the body passage;     inserting the balloon, in a deflated state, into the body passage, with the expandable implant fitted radially around the balloon; and     inflating the balloon so as to cause the implant to open, responsively to the varying radial dimension of the balloon, into an expanded shape that approximately matches the varying diameter of the body passage, thus anchoring the implant in the body passage.        
 
         [0014]     Typically, the method includes attaching the balloon to a catheter and passing the balloon into the body passage using the catheter.  
         [0015]     In one embodiment, the body passage is a coronary sinus of a patient, and passing the balloon includes: 
        guiding the catheter through a vascular path into a right atrium of the patient; and     steering the catheter within the right atrium so as to position the balloon and the implant in the coronary sinus.        
 
         [0018]     Typically, the selected balloon has distal and proximal ends, and the radial dimension of the distal end is substantially smaller than the radial dimension of the proximal end. In one embodiment, the selected balloon has a generally conical profile.  
         [0019]     In other embodiments, the selected balloon includes a proximal segment having a first diameter and a distal segment having a second diameter, which is substantially smaller than the first diameter. In one of these embodiments, at least one of the segments terminates in a bulb, having a third diameter that is greater than the diameter of the at least one of the segments. In another embodiment, the selected balloon includes a neck intermediate the proximal and distal segments, the neck having a third diameter that is less than the second diameter.  
         [0020]     In a further embodiment, the method includes deflating the balloon after the implant has opened, drawing the deflated balloon in a distal direction into a tubular accessory, and withdrawing the accessory, containing the balloon, from the body passage. Drawing the deflated balloon in the distal direction may include widening a distal end of the tubular accessory in order to receive the balloon.  
         [0021]     Additionally or alternatively, selecting the balloon may include measuring the diameter of the body passage at multiple points along the passage, and choosing the balloon from among a selection of available balloons, so as to fit the radial dimension of the balloon to the measured diameter of the body passage.  
         [0022]     In one embodiment, in which the body passage is a coronary sinus of a patient, choosing the balloon includes fitting the balloon to a widening region of the coronary sinus adjacent to a right atrium of the patient. Typically, the implant includes a constriction, and inflating the balloon includes expanding the implant to match the varying diameter of the coronary sinus except at the constriction, so as to inhibit a flow of blood through the coronary sinus.  
         [0023]     There is also provided, in accordance with an embodiment of the present invention, apparatus for treatment of a body passage of varying diameter, including: 
        a balloon having a radial dimension that varies, when the balloon is inflated, in accordance with the varying diameter of the body passage; and     an expandable implant, fitted radially around the balloon, so that when the balloon is inflated within the body passage, the implant opens, responsively to the varying radial dimension of the balloon, into an expanded shape that approximately matches the varying diameter of the body passage, thus anchoring the implant in the body passage. Typically, the apparatus includes a catheter, which is adapted to deploy the balloon and implant in the body passage.        
 
         [0026]     Typically, the balloon is one of a plurality of balloons having different radial dimensions, which are selectable for insertion into the body passage depending upon a measured diameter of the body passage at multiple points along the passage.  
         [0027]     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1A  is a schematic, pictorial view of an exemplary implantable device, in a non-expanded position, in accordance with an embodiment of the present invention;  
         [0029]      FIG. 1B  is a schematic, pictorial view of the exemplary implantable device shown in  FIG. 1A , in an expanded position;  
         [0030]      FIG. 2  is a schematic, pictorial view of an exemplary stent balloon, in accordance with an embodiment of the present invention;  
         [0031]      FIG. 3  is a schematic view of the vascular path to a human heart having a coronary sinus;  
         [0032]      FIG. 4  is a detailed schematic view of the coronary sinus following expansion of an implantable device by the balloon shown in  FIG. 2 , in accordance with an embodiment of the present invention;  
         [0033]      FIGS. 5 and 6  are schematic, pictorial views of exemplary stent balloons, in accordance with alternative embodiments of the present invention;  
         [0034]      FIGS. 7A-7D  are schematic, pictorial views of exemplary stent balloons, in accordance with further embodiments of the present invention;  
         [0035]      FIG. 8  is a schematic, pictorial view of a deflated balloon inside a stent and an accessory used in removing the deflated balloon from the stent, in accordance with an embodiment of the present invention; and  
         [0036]      FIGS. 9A and 9B  are schematic, detail views showing steps in a process of removing a deflated balloon from a stent, in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0037]     Reference is now made to  FIGS. 1A and 1B , which are schematic, pictorial views of an exemplary implantable device  100 , in a constricted state and an expanded state, respectively, in accordance with an embodiment of the present invention. Device  100  is adapted for use particularly in restricting blood flow through the coronary sinus, as described in the above-mentioned PCT Publication WO 01/72239 and U.S. patent application Ser. No. 09/534,968. Alternatively, devices in accordance with the principles of the present invention may be implanted elsewhere in the vascular system, as well as in other body passages. For the sake of simplicity and clarity, however, and not limitation, embodiments of the present invention are described hereinbelow with reference to implantation of flow-constricting devices in blood vessels of varying diameter, such as the coronary sinus.  
         [0038]     Device  100  is of general tubular construction with two expandable ends  110  and a central section  120 . Further alternatively or additionally, device  100  may comprise a mesh or coil, as is known in the art. Device  100  comprises a deformable material, such as a suitable metal or plastic, as is known in the art of implantable devices, which is sufficiently flexible to be expanded by inflation of a balloon (shown in  FIG. 2 ), but strong enough to hold its shape when it is deployed and expanded within a body passage, in the manner of stents known in the art. Furthermore, the shape of device  100 , combined with its flexibility, enables the device to be deployed in compact form, as shown in  FIG. 1A , and subsequently expanded, as shown in  FIG. 1B , either partially or completely, within the coronary sinus. A non-expandable constricting element  125  may attached around a central section  120  of device  100 , in order to ensure that the central section remains constricted, as shown in  FIG. 1B .  
         [0039]     A flexible sleeve (not shown) may be fixed around or within device  100 , in order to prevent blood from flowing through the openings in the sides of the device when it is implanted, so that substantially all the blood flows through central section  120 . Typically, the sleeve comprises a biocompatible fabric such as Gore-Tex or Dacron, which is stitched or otherwise fastened to device  100 . Alternatively, other sleeve materials may be used, such as thin plastic or rubber materials. Constricting element  125  is fitted around the sleeve, over central section  120 . As can be seen in  FIG. 1B , the effect of the constricting element is to maintain a predetermined reduced diameter of device  100  in the region of central section  120 , defining a lumen with a constricted central section diameter. Constricting element  125  may comprise a closed ring, made of metal or plastic, or it may alternatively comprise a thread.  
         [0040]     Reference is now made to  FIG. 2 , which is a schematic pictorial view of an exemplary high pressure stent balloon  200 , used to expand device  100 , in accordance with an embodiment of the present invention. Balloon  200  has a generally conical shape, having a blunt, narrowed distal end  210  and a widened proximal end  220 . The balloon terminates in a taper  225 , which forms a continuation of the channel portion of a catheter (shown in  FIG. 4 ), through which the balloon is inflated and deflated. Balloon  200  typically comprises a high-pressure, non-elastic material, as is known in the art, which is designed to apply an outward radial force when inflated, as described in the above-mentioned article from  Medical Device  &amp;  Diagnostic Industry Magazine . Generally, device  100  is deployed into a body passage with deflated balloon  200  contained concentrically within it. The shape of balloon  200  is adapted so that when balloon inflates, it expands device  100  and positions it within a preselected varying-diameter body passage, as is discussed hereinbelow.  
         [0041]     Balloon  200  is typically fabricated from materials such as polyethlylene tererphthalate (PET) or nylon. Some considerations for fabricating balloon  200  using these materials include: high tensile strength, allowing high operating pressures; thin balloon wall formation, allowing precise balloon shape and low profile; and low elongation (otherwise known as “low compliance”). The latter consideration ensures that balloon  200 , when fully pressurized, exhibits relatively unchanging dimensions, ensuring that device  100  is not uncontrollably over-expanded in a body passage. Low elongation also means that balloon  200  will not over-expand at either end of device  100  and that the expansion force of the balloon is directed generally radially to expand device  100  substantially against the walls of the body passage.  
         [0042]     Reference is now made to  FIG. 3 , which is a schematic view of vascular paths to a human heart  300  having a coronary sinus  302 . Coronary sinus  302  comprises a junction of three major cardiac veins (not shown), and becomes progressively wider as it empties into a right atrium  306 . The diameter of coronary sinus  302  increases as it opens out into right atrium  306 .  
         [0043]     To implant device  100 , the device is passed through the vascular system to a preselected position in coronary sinus  302 , using a suitable percutaneous catheter (shown in  FIG. 4 ). Suitable methods of catheterization for this purpose are known in the art. During the insertion procedure, device  100  is maintained in the non-expanded configuration shown in  FIG. 1A , so that its outer diameter is substantially smaller than the blood vessels through which it must pass, allowing the physician operating the catheter to pass the device through the blood vessels. Typically, the physician inserts the catheter through a jugular vein  310  or a subclavian vein  312 , and then guides the catheter into a right atrium  306  via a superior vena cava  308 . Another insertion point is through a femoral vein  322 , and the catheter is then guided to an inferior vena cava  324  and into right atrium  306 . Once in right atrium  306 , the physician steers the catheter through a sharp bend in order to guide device  100  into coronary sinus  302 .  
         [0044]     Reference is now made to  FIG. 4 , which is a detailed schematic view of coronary sinus  302  following expansion of device  100  by balloon  200 , in accordance with an embodiment of the present invention. A catheter  410  is used, as described hereinabove, to position the device and balloon in coronary sinus  302  via right atrium  306 . Balloon  200  is then inflated, via catheter  410 , and assumes a general shape as shown in the figure. The physician may choose the shape of balloon  200  in advance, so as to optimally match the given dimensions of the coronary sinus of the patient in question. These dimensions may be determined, for example, by taking fluoroscopic images while injecting a contrast agent into the coronary sinus, as is known in the art.  
         [0045]     When balloon  200  is inflated, it applies a radial force to plastically expand device  100  against the walls of coronary sinus  302 . As shown in the figure, due to the varying diameter of balloon  200 , the distal end of device  100  is only partially expanded, whereas the proximal end of device  100  is more completely expanded, reflecting the varying diameter of coronary sinus  302 . As previously noted, balloon  200  does not over-expand at either end of device  100 . Distal end  210  of balloon may protrude slightly from the distal end of device  100 . In a similar fashion, widened proximal end  220  and the taper  225  of balloon  200  may protrude from the proximal end of device  100 . Because the shape of device  100  is fit to the natural shape of the coronary sinus, both the distal and proximal ends of the device press outward against the wall of the coronary sinus with approximately equal force. Thus, device  100  is securely anchored in place, without exerting excessive pressure against the wall of the coronary sinus at any point. Central section  120 , however, remains constricted due to the presence of constricting element  125  or other means provided for this purpose.  
         [0046]     Once device  100  is satisfactorily positioned and expanded, balloon  200  is deflated and withdrawn from device  100 . Catheter  410  and balloon  200  are then withdrawn from the body. Device  100  remains in place to restrict the flow of blood through coronary sinus  302 . As noted above, this flow restriction increases the blood pressure in the coronary veins, thereby fostering angiogenesis. Device  100  may be left in place indefinitely, in substantially the form shown in  FIG. 4 . Alternatively, it may be desirable in some cases to eliminate the flow restriction caused by the device. In such cases, a catheter with a suitable cutting tool may be inserted percutaneously to the location of the device, and the cutting tool may then be used to cut constricting element  125  or central section  120 . A balloon, such as balloon  200 , may then be reinserted via catheter into device  100  and the balloon may then be inflated in order to open section  120 .  
         [0047]     Although in the embodiments described above, device  100  and balloon  200  are shown to have certain particular shapes, alternative shapes and forms of these elements, which will be apparent to those skilled in the art, are considered to be within the scope of the present invention. Similarly, balloons of the general type described above may be used to deliver not only device  100 , but also other implantable devices for implantation in other body passages of variable diameter, as are otherwise known in the art. Furthermore, although the catheter shown here provides a convenient means for delivering implantable devices in accordance with the present invention, balloons in accordance with the present invention may also be used in conjunction with other means for implant deployment, including both minimally invasive (typically percutaneous) and invasive (i.e., surgical) types.  
         [0048]     For example,  FIGS. 5 and 6  are schematic, pictorial views of balloons  500  and  600 , which may be used in place of balloon  200 , in accordance with alternative embodiments of the present invention. Instead of the generally conical profile of balloon  200 , these alternative balloons comprise a broad proximal segment  510  and a narrow distal segment  520 . The proximal and distal segments are generally cylindrical, and have different, respective diameters. Alternatively, the proximal and distal segments may have trapezoidal profiles. For stent implantation in the coronary sinus, these balloons are typically about 30 mm long, and have diameters of about 10 mm in the broad segment and 7 mm in the narrow segment. Alternatively, larger or smaller dimensions may be used, depending on application requirements and physiological characteristics of the patient.  
         [0049]     In balloon  600 , narrow segment  520  terminates distally in a bulb  610 , which is broader than the narrow segment. For example, if narrow segment  520  is 7 mm in diameter, bulb  610  may have a diameter of about 8 mm. The bulb helps to open the upstream end  110  of the stent in order to anchor the stent more securely in the coronary sinus (or other body passage). Additionally or alternatively, broad segment  510  may terminate proximally in a similar sort of a bulb.  
         [0050]      FIGS. 7A-7D  are schematic, pictorial views of balloons  700 ,  720 ,  730  and  740 , in accordance with further embodiments of the present invention. Each of these balloons comprises a narrow neck  710  between segments  510  and  520 . Typically, the neck is about 3 mm in diameter, although smaller or larger dimensions may also be used. Neck  710  fits inside central section  120  of stent  100  during inflation of the stent. It thus prevents the balloon from exerting pressure against non-expandable constricting element  125 , and is also useful in facilitating removal of the balloon from the stent after completion of the stent implantation procedure.  
         [0051]     The walls of segments  510  and  520  may be parallel to the axis of the balloon, as shown in  FIG. 7A , or they may be sloped relative to the axis in order to better fit the shape of the coronary sinus. As shown in  FIGS. 7B, 7C  and  7 D, either one or both of segments  510  and  520  may be sloped in this manner.  
         [0052]      FIG. 8  is a schematic, pictorial illustration showing the use of a tubular accessory  820  in removing balloon  200  from the body, in accordance with an embodiment of the present invention. In this embodiment, an operator, typically a physician, has inserted a guide wire  800  through a patient&#39;s vascular system into the coronary sinus, using techniques known in the art. Stent  100  and balloon  200  have been passed over wire  800  into the coronary sinus, and balloon  200  has been inflated in order to expand the stent to the proper dimensions. The balloon has an annular cross-section, in order to fit over wire  800 , and is inflated and deflated via an annular tube  810 . At the stage of the procedure pictured in  FIG. 8 , balloon  200  has been deflated (likewise via tube  810 ), and is now to be withdrawn over wire  800  from the patient&#39;s body by pulling tube  810  in the proximal direction, out of the body.  
         [0053]     The inventors have found that under these circumstances, it is sometimes difficult to extract balloon  200  from stent  100  and through the vascular system. Therefore, to facilitate extraction of the balloon, the operator inserts accessory  820  over wire  800  to a position just proximal of balloon  200 , and then draws the balloon in the proximal direction into the accessory. Once the balloon is held inside accessory  820 , the accessory containing the balloon can be withdrawn easily from the body. Similar sorts of accessories and methods may be used for inserting and extracting a balloon over other sorts of guides, such as a “monorail” guide, as is known in the art.  
         [0054]     For these purposes, accessory  820  typically comprises a tube of small diameter, for example, about 2.8 mm, with a length of about 500 mm. The tube should be flexible enough to pass through the vascular system, but stiff enough so as not to deform significantly when balloon  200  is pulled inside it. Accessory  820  may comprise, for example, polyurethane or another biocompatible plastic material, with a wall thickness of about 0.4 mm. An additional catheter or other insertion tube (not shown in the figures) may be attached to the proximal end of accessory  820 , for use in advancing the accessory into place adjacent to balloon  200 , and then pulling the accessory and balloon out of the body.  
         [0055]     Similar techniques and accessories may be used in inserting and removing balloons of other shapes, such as those shown in  FIGS. 5-7 .  
         [0056]      FIGS. 9A and 9B  schematically show details of the distal end of accessory  820  and its use in capturing balloon  200 , in accordance with an embodiment of the present invention. In this embodiment, the distal end of accessory  820  is scored or perforated along score lines  900 . The score lines are designed to rip open under sufficient outward radial force. A stiffening ring  910  limits the extent of the rip to a predetermined length from the distal end of the accessory, typically about 3.5 mm. Ring  910  may comprise metal or another radiopaque material, so that the location of accessory  820  is visible under X-ray imaging.  
         [0057]     In operation, accessory  820  is advanced in the distal direction, as shown by an arrow  915  in  FIG. 9A , until the scored, distal end of the accessory slides inside the expanded proximal end of stent  100 . If balloon  200  is sufficiently flaccid at this point, it will be possible to draw the balloon into accessory  820  simply by pulling tube  810  in the proximal direction, as indicated by an arrow  930  in  FIG. 9B . If there is residual pressure in the balloon, however, or inherent stiffness of the balloon material, the balloon may tear score lines  900 , causing the distal end of accessory  820  to widen by opening into multiple flaps  920 . These flaps widen out to create a funnel structure at the distal end of the accessory. This structure may be supported radially by stent  100 , as shown in the figure. The funnel aids in compressing the balloon gradually as it is pulled in the direction of arrow  930 , so that the balloon slides smoothly into accessory  820 . Other means for widening the distal end of accessory  820  may alternatively be provided, as will be apparent to those skilled in the art.  
         [0058]     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.