Abstract:
A plaque-modifying balloon and method for use in an endovascular procedure includes an elongated balloon that defines a longitudinal axis and is inflatable from a first deflated configuration to a second radially expanded configuration. One or more plaque-modifying elements are mounted on the outside of the inflatable balloon. Optionally, a compressible sheath made of a relatively low durometer, flexible material is mounted on the balloon to cover the elements during transit of the plaque-modifying balloon to and from the treatment site.

Description:
The invention pertains generally to endovascular devices and methods and more particularly to plaque-modifying balloon catheters for treating vessels in the arterial vasculature. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     Percutaneous transluminal angioplasty (PTA) procedures can treat arterial disease. In such endovascular procedures, cutting balloons are sometimes considered as a treatment option for opening blocked coronary and peripheral vessels. Such balloons are sometimes configured so that balloon pressure is communicated to one or more cutting elements. Those elements may selectively cut stenosed vessel walls. In the hands of a skilled interventionist, PTA atherectomy procedures have sometimes reduced vessel recoil, lessened vessel tears and may have improved outcomes in comparison to traditional PTCA procedures. 
     Severing elements used in such balloons can for analysis be said to include an effective surface feature (e.g., an edge) that is capable of incising or scoring vessel walls with which they come into contact. But if suitable precautions are not taken, the incising elements can tear, cut or perforate the thin, fragile inflation balloon during assembly, handling or use. It is also possible that an unintended balloon rupture could damage the arterial wall. This may result in loss of inflation fluid into the patient&#39;s vasculature. Another problem may arise if an inadvertent or unwanted cutting occurs of adjacent perhaps healthy tissue as the cutting balloon is being positioned or withdrawn from the vasculature. 
     (2) Description of Related Art 
     A device with a cutting edge which is covered within the pleats of an expandable clover leaf-shaped tube is disclosed by Shiber in U.S. Publication No. US 2002/0151924. However, such designs may fail to protect a fragile balloon during installation of the cutting edges, even before the device is used in situ. In addition, because the blades are situated within the balloon folds, creased portions of the balloon may be exposed to the blades when the device is navigated by twisting, turning and bending through narrow tortuous vasculature passageways. 
     The following references, among others, were considered before filing this application: U.S. Pat. Nos. 7,686,824; 7,799,043; and 7,691,080. 
     BRIEF SUMMARY OF THE INVENTION 
     Against this background, it would be advantageous to provide an assembly of plaque-modifying elements that are urged into contact with stenosed vessel walls and weaken those hardened portions as well as calcific plaques by creating and propagating localized fissures. 
     Yet other desires include providing a catheter system with an assembly of plaque-modifying elements that extend from an inflatable balloon which is easy to use by surgeons of varying skill levels, is straightforward to make and is comparatively cost-effective. 
     One aspect of the invention focuses on a plaque-modifying catheter system that includes an inflatable balloon which is provided with plaque-modifying elements that alter the surface and sub-surface characteristics of stenotic tissue at a treatment site in a vessel of a patient. For discussion and analysis, an embodiment of a catheter system falling within the scope of the present disclosure has an elongated balloon that defines a longitudinal axis. The balloon is inflatable from a first deflated configuration through intermediate second configurations to a third radially expanded configuration. 
     In some embodiments, the balloon includes one or more stiff pedestals or footpads (“plaque-modifying elements”) that are brought into contact with plaque on vessel walls during inflation. For example, the pedestals could be considered as a punch or tool with a head that is circular, rounded (“domed”), x-shaped, star-shaped, polygonal, and the like. Its constituent material may include a hardened polymer. In some embodiments, the array of plaque-modifying elements is oriented longitudinally and mounted on the outside of the inflatable balloon. 
     When the inflatable balloon is in the radially expanded configuration, at least some of the pedestals are urged outwardly radially by the inflatable balloon so that they are capable of fracturing hardened tissue (soft plaque, as well as calcific plaques). 
     The balloon may further include on its outer surface one or more mounting pads that secure the pedestals to the balloons. For example, some of the pedestals may extend from an associated mounting pad that is affixed to the outer surface of the inflatable balloon. 
     Optionally, the plaque-modifying balloon system includes one or more sheaths that are made of a relatively low durometer, flexible material. Functionally, if used, each sheath protects the vasculature from an operative surface feature of a plaque-modifying element during transit of the balloon to and from the treatment site. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a simplified, longitudinal cross sectional schematic view of a catheter system having an array of plaque-modifying elements operatively positioned in the body of a patient; 
         FIG. 2  is a perspective view of one embodiment of the catheter system (without a covering sheath); 
         FIG. 3  is perspective partially sectioned view of the embodiment of a plaque-modifying balloon system depicted in  FIG. 2 ; 
         FIG. 4  is a cross sectional view of the balloon system of  FIGS. 1-3  shown after the balloon has been inflated to urge plaque-modifying elements radially outwardly before sheath removal; 
         FIG. 5  illustrates method steps that exemplify how the catheter system is used. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring initially to  FIG. 1 , a plaque-modifying catheter system  10  is shown with an expansible balloon  12  that supports plaque-modifying elements  32 . The system  10  enables a surgeon to perform an endovascular procedure in which a catheter with a deflated balloon surrounding it is inserted percutaneously into a blood vessel (e.g., a femoral artery) to treat vascular disease. 
     More specifically, the catheter system  10  is depicted as being positioned to treat a lesion  14  in an artery  16  such as but not limited to a coronary, renal, popliteal or femoral artery, the aorta or other artery. But those skilled in the art will recognize that the use of the catheter system  10  as herein described is not limited to treatment of a specific artery. Instead it can be deployed in vascular conduits and other ductal systems throughout the human body. 
     In  FIGS. 1-4 , there is depicted one embodiment of a plaque-modifying catheter system  10  with an open inner lumen  18 . In that embodiment, the system  10  has a catheter (tube)  20  with a proximal end  22  and a distal end  24 . As used herein, “proximal” is used in relation to the surgeon. The inner lumen  18  extends between the proximal  22  and distal  24  ends so that a medical device or fluid may pass through the lumen  18  without interruption or interference. If desired, the disclosed invention could be used as a blood perfusion balloon catheter such as that disclosed in U.S. Pat. No. 5,370,617. Such catheters can be used in administering treatments to relieve stenotic regions within a body lumen while maintaining blood flow past the dilation balloons. Perfusion ports in one example can be provided in both a guide wire lumen and in a bypass lumen in order to provide increased blood flow. Abstract, &#39;617 patent. 
     Thus, the plaque-modifying balloon  12  includes an expandable balloon  26  ( FIG. 4 ) that is located proximate to and circumscribes at least the distal end region  22  of the catheter  20 . The expandable balloon  26  encapsulates a pressurizing fluid (such as a saline solution or nitrous oxide) in a chamber  28  formed between the catheter  20  and the balloon  26 , which causes the balloon  26  to inflate. The balloon  26  has an outer surface  30  which may optionally at least partially have a dry coating. The pressurizing fluid is delivered by means for pressurizing, maintaining and deflating the chamber  28  formed between the catheter and the balloon (such as a pump in communication with an activator for imparting a rapid rise in pressure). 
     An assembly of plaque-modifying elements  32  is mounted on at least a part of the outer surface  30  of the balloon  26 . Without being bound to any theory of operation, the modifying elements  32  are thought to break collagen and distend elastin in the intima and media of a vessel wall  16 , thereby weakening the intima and media and superimposing (by, for example “stamping” or “embossing” or “fracturing”) a pattern of weakened areas in the vessel wall  16 . Such weakened areas may allow the vessel wall  16  to become more flexible, to bend and to distend radially. 
     In one treatment protocol, it is envisioned that the step of pressurizing the balloon is completed in about 1-5 seconds and the step of depressurizing the balloon is completed in a similar time. Optionally the step of contacting the balloon with a vessel wall to be treated is completed over a dwell time of about 1-5 minutes or longer if desired. 
     In one embodiment, at least some of the modifying elements  32  are supported from a base  34  extending from the outer surface  30  of the balloon  26 . Extending outwardly from the base  34  is a shaft  36 . A plaque-modifying tip  38  is situated atop the shaft  36 . The plaque-modifying tip  38  has a cross section geometry selected from the group consisting of a polygon, an oval, a circle, a dome, an ellipse, an “x” shape, a star shape and a “y” shape. 
     In an embodiment, optionally, a retractable sheath  40  at least partially covers the modifying elements  32  as the catheter system  10  is maneuvered through a tortuous vasculature. The sheath  40  can be retracted to expose at least a part of the plaque-modifying assembly  32  when the assembly  32  is juxtaposed with a site to be treated. If desired, the sheath  40  can be repositioned to cover the plaque-modifying assembly  32  before the catheter system  10  is withdrawn. 
     Not shown in communication with the balloon  26  are one or more conventional fluid ports for pressurization and relief of the chamber  28  between the catheter  20  and the balloon  26 . It will be appreciated that the proximal portion  22  of the catheter  20  is connected to the distal end  26  of an inflation mechanism or the means for inflation  42  ( FIG. 1 ). Typically, the inflatable balloon  26  is made of a polymeric material such as polyethylene terephthalate (PET) or nylon and its outside diameter is about 6-8 French. 
     As best seen in  FIG. 4 , the inflatable balloon  26  can be thought of as having an outer surface  30  and an opposed inner surface  46  that surrounds an inflation volume or chamber  28  that can be infused with a medical grade fluid to expand the inflatable balloon  26 . It will be appreciated that an inflation device  42  (not shown) may include a syringe that can be activated to pump the medical grade fluid (such as a saline solution) to expand the inflatable balloon  26 . 
     In  FIGS. 1-4 , the plaque-modifying elements  32  may assume various alternative forms. These include tips  38  that are circular, rounded (“domed”), x-shaped, star-shaped, polygonal, and the like in a variety of configurations, e.g., an array of longitudinally or laterally spaced or aligned sets, as shown in  FIGS. 2-3 . As seen in  FIG. 4 , in one embodiment, the modifying elements  32  are distributed around the circumference  30  of an operative section of the inflatable balloon  26 . Typically, at least some of the modifying elements  32  are made of a medical grade material such as a hard plastic like polytetrafluoroethylene (PTFE). 
     As best seen in  FIG. 4 , a portion of at least some of the modifying elements  32  extend from associated mounting pads or bases  34  that are secured to an outside surface  30  of the balloon  26 . Typically, each mounting pad  34  is made of a relatively flexible polymeric material such as polyurethane and is bonded (e.g. heat bonded or adhesively bonded) to the outer surface  30  of the inflatable balloon  12 . It can further be seen that each element  32  extends from its associated mounting pad  34  to an operative tip  38  that is capable of modifying the plaque with which it is urged into contact upon balloon inflation. The process is analogous to fracturing the plaque and causing a modified surface that in some cases may resemble the fractured windshield of an automobile. 
     It can be further seen that the tip  38  of each plaque-modifying element  32  extends in a radial direction (“height”) which on average amounts to a distance “X” from the outer surface  30  of the balloon  26 . The rise and fall (“pulse”) during balloon compression and decompression occurs over an average distance “x”. For the embodiment shown in  FIGS. 3 and 4 , the plaque-modifying elements  32  are preferably bonded to the inflatable balloon  26 . This structure limits the amount of a given element that can sink into ambient plaque, by analogy to a depth gauge. 
     Regardless of whether a sheath is deployed, it is sometimes preferable that the plaque modifying elements  32  closer to the distal end  24  of the balloon  26  are closer to the balloon surface elements  32  that lie closer to the proximal end  22  of the balloon  12  to facilitate insertion of the catheter system  10  into the vasculature. 
     In alternate embodiments, the plaque-modifying elements  32  are not too tightly located and are spaced apart. In some embodiments the average spacing between adjacent elements is at least 3 times the height of the tip above the outer surface of the balloon. This geometry permits navigation of the catheter system  10  around abrupt turns in the vasculature without adjacent elements  32  interfering with each other. 
     The plaque-modifying elements are optionally aligned in longitudinally oriented rows on an outside surface of the balloon. In some embodiments, the plaque-modifying elements are aligned in laterally oriented rows on an outside surface of the balloon. Alternatively, the plaque-modifying elements are staggered so that an element in a row lies longitudinally between adjacent elements in a neighboring lateral row. 
     The functionality of one sheath embodiment  40  can be appreciated with reference to  FIG. 4 . As shown, the optional sheath  40 , if deployed, protects the effective tips  38  of plaque-modifying elements  32  during transit of the balloon  26  and plaque-modifying elements  32  to the treatment site. After the system  10  is positioned at the treatment site and before the balloon  26  is expanded, the sheath  40  (if present) is withdrawn. The plaque-modifying elements  32  make their first contact with the tissue  14  (see  FIG. 1 ). Once contact has been established between the tissue  14  and the plaque-modifying elements  32 , further pressurization over a short period of time of the inflatable balloon  26  causes the elements  32  to pulse outwardly radially for tissue modification. Plaque modification arises from localized weakening by fracture of for example calcified areas. Not only does fracture engender fissure formation (thereby weakening the fissured area), but it also reduces the stiffness of plaque-lined vessel walls while augmenting the surface area over which chemical reaction occurs if a pharmaceutically effective drug is delivered thereto. If desired, pressure can be applied quickly once, like a single hammer blow to a sheet of ice. Alternatively, pressure can be administered pulsatingly, like a jack hammer. Optionally the means for pressurizing  42  includes a control mechanism that allows the surgeon to administer either or both modes of pressure application. 
       FIG. 5  illustrates a series of method steps that can be followed in practicing one aspect of the disclosed endovascular protocol. 
     The steps include: 
     A. Prepare a catheter subassembly. This step involves connecting a catheter which is covered at least partially somewhere but not necessarily completely between its intermediate region and distal end by an expansible balloon to an external source of fluid pressure. The source may optionally be provided with a pulsating means so that balloon expansion can be controlled and (if desired) affected rapidly, thereby creating a pulsating or hammer-like impact to a stenosed region. Optionally, pressure could be increased more slowly and stopped. 
     B. Optionally cover the catheter subassembly with a sheath to form a catheter assembly. When used, the sheath protects potentially healthy vessel walls from abrasion by unprotected plaque-modifying elements. 
     C. Insert the assembly into the vasculature. One insertion site is the femoral artery, although other sites may be used. Following insertion, the assembly is carefully pushed along the tortuous vascular passageways until it is juxtaposed with an anatomical site to be treated. 
     D. If present, the sheath may then be removed, thereby exposing the plaque-modifying elements. 
     E. The balloon is then expanded by the application of fluid pressure. If used, a saline solution or nitrous oxide, for example, can be first used to flood a chamber between the outside of the catheter and the inside of the balloon, thereby expanding it. If desired, a shockwave can be propagated through the relatively incompressible fluid so that a punching effect on the stenosed vessel wall can be created by rapidly moving plaque-modifying elements. Optionally:
         1. pharmaceutical agent may be delivered by microchannels extending through the plaque-modifying elements to the stenosed region either before or after fracture; or   2. the drug may be bonded to the balloon wall and by contiguity eluted into the vessel (e.g., Paclitaxel is lipophilic and rapidly reacts within 60 seconds with the vessel wall).       

     F. The balloon may then be deflated by evacuating the pressurizing fluid before the deflated balloon is covered with the sheath. The assembly may then be withdrawn in such a way that the plaque-modifying elements do not interfere with potentially healthy regions of the vasculature. 
     It will be appreciated that plaque-lined vessel walls following treatment become more compliant and therefore can bend, thereby responding to rather than resisting pulsating blood pressure. 
     Without being bound by a particular theory of operation, the Applicant anticipates that effective deployment of the disclosed system may usefully smoothen the arterial walls without leaving scars. Rather, the modified surface tends to be compliant, by analogy to perforated paper that extends rather than tears upon being subjected to stretching forces. 
     Preferably, the depth of plaque-modification should not exceed about one-half of the thickness of the vessel wall. Flexibility is thereby provided to a plaque-lined arterial wall which can open in response to blood pressure and flow. 
     Thus, there has been disclosed a plaque-modifying catheter system which can be used effectively upon single insertion and single delivery. 
     While the particular plaque-modifying elements  32  as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE NUMERALS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 Catheter system 
               
               
                 12 
                 Balloon 
               
               
                 14 
                 Lesion 
               
               
                 16 
                 Artery 
               
               
                 18 
                 Inner lumen (of 20) 
               
               
                 20 
                 Catheter (tube) 
               
               
                 22 
                 Proximal end (of 20) 
               
               
                 24 
                 Distal end 
               
               
                 26 
                 Balloon 
               
               
                 28 
                 Pressurizing fluid 
               
               
                 30 
                 Outer surface (of 26) 
               
               
                 32 
                 Assembly of plaque - modifying elements 
               
               
                 34 
                 Base (of 32) 
               
               
                 36 
                 Shaft 
               
               
                 38 
                 Tip 
               
               
                 40 
                 Sheath 
               
               
                 42 
                 Inflation device 
               
               
                 46 
                 Inner surface (of 26) 
               
               
                   
               
             
          
         
       
     
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.