Abstract:
A terminal guide for a helically wound drive shaft for use in an rotational atherectomy device. The terminal guide is atraumatic to prevent perforation of the arterial wall or the embedding of the device into the arterial wall. The terminal guide may be pre-machined, cast, molded or formed in any manner that maintains the required dimensions and tolerances and may be fabricated from any biocompatible material and coated with radiopaque material to more accurately position the rotational atherectomy device without going past the distal end of the pre-positioned guide wire.

Description:
BACKGROUND OF THE INVENTION  
     FIELD OF THE INVENTION  
       [0001]     The present invention relates to medical devices, more particularly, devices and methods for removing tissue from a body lumen, such as removal of atherosclerotic plaque from arteries, utilizing a rotational atherectomy device.  
       SUMMARY OF THE INVENTION  
       [0002]     A terminal guide for a helically wound drive shaft for use in a rotational atherectomy device. The terminal guide is atraumatic to prevent perforation of the arterial wall or the embedding of the device into the arterial wall. The terminal guide may be pre-machined, cast, molded or formed in any manner that maintains the required dimensions and tolerances. The terminal guide may be fabricated from any biocompatible material and coated or formed with radiopaque material to more accurately position the rotational atherectomy device without going past the distal end of the pre-positioned guide wire.  
         [0003]     An object and advantage of the present invention is to provide an atraumatic terminal guide for the drive shaft of a rotating atherectomy device.  
         [0004]     Another object and advantage of the present invention is to provide an atraumatic terminal guide for a rotating atherectomy device that minimizes or eliminates the possibility that the device&#39;s drive shaft is advanced past the distal end of the pre-positioned guide wire.  
         [0005]     Another object and advantage of the present invention is to provide an atraumatic terminal guide for a rotating atherectomy device that minimizes or eliminates the unwanted eccentric motion of the drive shaft distal end.  
         [0006]     Yet another object and advantage of the present invention is to provide an atraumatic terminal guide for a rotating atherectomy device that reduces surface erosion of the guide wire as a consequence of unwanted eccentric motion of the drive shaft and frictional welding of the drive shaft to the guide wire, while increasing the useful life of both the drive shaft and the guide wire.  
         [0007]     The foregoing objects and advantages of the invention will become apparent to those skilled in the art when the following detailed description of the invention is read in conjunction with the accompanying drawings and claims. Throughout the drawings, like numerals refer to similar or identical parts.  
       DISCUSSION OF THE RELATED ART  
       [0008]     A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient&#39;s arteries. Atherosclerosis is characterized by the buildup of fatty deposits in a patient&#39;s blood vessels. Often, over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, with the blocking material referred to as stenotic material.  
         [0009]     Orbital atherectomy procedures have become common for removing such stenotic material. Such procedures are used most frequently to initiate the opening of calcified lesions in coronary arteries.  
         [0010]     Several kinds of rotational atherectomy devices have been developed for removal of stenotic materials. In one type of device, such as that disclosed in U.S. Pat. No. 4,990,134 (Auth), a nickel-plated burr covered with an abrasive cutting material such as diamond particles is carried at the distal end of a flexible drive shaft. The burr rotates at high speeds (typically in the range of about 80,000-200,000 rpm) while it is advanced across the stenosis. As the burr is removing stenotic material, however, it also blocks blood flow. Further, once the burr has advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr. Moreover, fluoroscopy is typically utilized to assist the physician in placing the nickel-plated Auth-type burr in the general location of a stenosis in an artery. However, since the nickel-plated burr is not radiopaque, the ability of the physician to monitor, in real time, the actual removal of stenotic tissue is significantly hampered. In addition, this has an adverse effect on the ability of the physician to manage the risk of perforating the arterial wall while ensuring that the stenotic tissue is completely removed.  
         [0011]     Moreover, the Auth-type burr uses a multi-step, electrochemical deposition process to plate the nickel on the distal tip of the burr. A secondary process requires hand work to remove any sharp edges and to drill a center shaft through the deposited nickel, leaving the distal tip with a profile resembling that of a drill bit with a hole through the center. The difficulties with the known process are that it is costly, time-consuming and it is extremely difficult to control. The results of the uncontrolled hand fluting of the distal tip is that it creates potential for misalignment of the central bore through the burr with the guide wire. This creates undesirable eccentric motion of the distal end which, in turn, may create surface erosion of the guide wire as the drive shaft rubs against it, friction welding of the drive shaft to the guide wire and, ultimately premature failure of the drive shaft and/or the guide wire may ensue. Finally, because the distal ends of the Auth-type burr have a fluted profile, during the procedure the rotating flutes are capable of either embedding into or perforating the arterial wall of the drive shaft is deployed beyond the end of the guide wire.  
         [0012]     U.S. Pat. No. 5,314,438 (Shturman) discloses another atherectomy device having a drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged diameter being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery. While this atherectomy device possesses several advantages over the Auth device due to its flexibility, it also is capable of only opening an artery to a diameter about equal to the diameter of the enlarged diameter section of the drive shaft. In addition, though this device permits use of intravascular ultrasound imaging to monitor the removal of stenotic tissue, thus reducing the risk of perforation of the tissue removing surface during the procedure, the device may remain susceptible to the problem of perforation due to the advancement of the device beyond the end of the guide wire which may result in perforation.  
         [0013]     U.S. Pat. No. 6,494,890 (Shturman) discloses an atherectomy device having a drive shaft with a section of the drive shaft having an eccentric enlarged diameter, at least a segment of this enlarged eccentric diameter being covered with an abrasive material. When rotated at high speeds and placed within an artery against stenotic tissue, the eccentric nature of the enlarged diameter section cause the section to rotate in such a fashion as to open the stenotic lesion to a diameter substantially larger than the outer diameter of the enlarged diameter section. This device does permit use of intravascular ultrasound imagine to monitor the removal of stenotic tissue, thus reducing the risk of perforation of the tissue removing surface during the procedure. However, the device may remain susceptible to the problem of perforation due to the difficulties in monitoring the advancement of the device beyond the end of the guide wire which may result in perforation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a perspective view of a rotational atherectomy device of the invention.  
         [0015]      FIG. 2  is a perspective, broken-away view of an enlarged diameter section of the drive shaft of a rotational atherectomy device of the invention.  
         [0016]      FIG. 3A  is a broken away, longitudinal cross-sectional view of the eccentric embodiment of the enlarged diameter section of the drive shaft of the invention.  
         [0017]      FIG. 3B  is similar to  FIG. 3A , with the addition of an external tissue removing member.  
         [0018]      FIG. 4A  is a broken away, longitudinal cross-sectional view of the concentric embodiment of the enlarged diameter section of the atherectomy device of the invention.  
         [0019]      FIG. 4B  is a detail of  FIG. 4A  in the circled area, showing the terminal guide of the present invention.  
         [0020]      FIG. 5  is a broken away, longitudinal cross-sectional view of the terminal guide.  
         [0021]      FIG. 6  is a broken away, longitudinal cross-sectional view of the terminal guide with radiused or chamfered edges.  
         [0022]      FIGS. 7A and 7B  are broken away, longitudinal cross-sectional views of the terminal guide with radiused or chamfered edges and a radioopaque jacket. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     With reference to the Figures, the present inventive design incorporates a radiopaque atraumatic terminal guide at the distal end of the drive shaft. Specifically, with reference to  FIG. 1 , a typical rotational atherectomy device is illustrated. The device includes a handle portion  10 , an elongated, flexible drive shaft  12 , having an enlarged diameter section  14 , and an elongated catheter  16  extending distally from the handle portion  10 . The drive shaft  12  and its enlarged diameter section  14  are constructed from helically coiled wire. The catheter  16  has a lumen in which most of the length of the drive shaft  12  is disposed, except for the enlarged diameter section  14  and a short section distal  13  to the enlarged diameter section  14 . The drive shaft  12  also contains an inner lumen  30 , permitting the drive shaft  12  to be advanced, retracted and rotated over a guide wire  28 . A fluid supply line  20  may be provided for introducing cooling and lubricating fluid, typically saline or other biocompatible solution, into the catheter  16 .  
         [0024]     The handle  10  generally contains a turbine (or similar rotational drive mechanism) for rotating the drive shaft  12  at high speeds. The handle and turbine typically may be connected to a power source, such as compressed air delivered through a tube  22 . A pair of fiber optic cables  24  may also be provided for monitoring the speed of rotation of the turbine and drive shaft  12 . The handle also desirably includes a control knob  26  for advancing and retracting the turbine and drive shaft  12  with respect to the catheter  16  and the body of the handle  10 .  
         [0025]     The enlarged diameter section  14  may be concentric or eccentric in profile.  FIGS. 2 and 4  illustrate details of the concentric embodiment of the enlarged diameter section  14  while  FIG. 3  illustrates an alternate eccentric embodiment. It should be understood that, as used herein, the term “eccentric” is intended to refer to either a difference in location between the geometric center of the enlarged diameter section  14  and the rotational axis of the drive shaft  12 , and/or to a difference in location between the center of mass of the enlarged diameter section  14  and the rotational axis of the drive shaft  12 . Either difference, at the proper rotational speeds, will enable the eccentric embodiment of the enlarge diameter section  14  to open a stenosis to a diameter substantially greater than the nominal diameter of the eccentric embodiment of the enlarged diameter section  14 .  
         [0026]     Continuing with reference to  FIGS. 1-4 , the drive shaft  12  is comprised of one or more helically wound wires  128  defining a guide wire lumen  30  and a hollow cavity  32  within the enlarged diameter section  14 . The hollow cavity is substantially empty, except for the guide wire  28  traversing the hollow cavity  32 . The enlarged diameter section  14  includes proximal  34 , intermediate  36  and distal  38  portions in both the concentric and eccentric embodiments. Wire turns  40  of the proximal portion  34  preferably have diameters that progressively increase distally at a generally constant rate, thereby forming generally the shape of a cone. Wire turns  42  of the distal portion  38  preferably have diameters that progressively decrease distally at a generally constant rate, thereby forming generally the shape of a cone. Wire turns  44  of the intermediate portion  36  are provided with gradually changing diameters to provide a generally convex outer surface shaped to provide a smooth transition between the proximal and distal conical portions of the enlarged diameter section  14  of the drive shaft  12 . The elongated drive shaft  12  is illustrated with a distal section  13  and a proximal section  11 , located respectively distally and proximally of the enlarged diameter section  14 .  
         [0027]     Turning to  FIGS. 2 and 3 A, at least part of the enlarged diameter section  14  includes an external surface capable of removing tissue. In the preferred embodiment, the tissue removal surface is disposed on the intermediate portion  36  of the enlarged diameter section  14 . Preferably the tissue removing surface  45  comprises a coating of an abrasive material  46  to define a tissue removing segment  48  of the drive shaft  12 . The abrasive material may be any suitable material, e.g., diamond powder, fused silica, titanium nitride, tungsten carbide, aluminum oxide, boron carbide, or other ceramic materials. Preferably, the abrasive material is comprised of diamond chips, or diamond dust particles, attached directly to the wire turns of the drive shaft  12  by a suitable binder  50 . Such attachment may be achieved using well known techniques such as conventional electroplating or fusion technologies. (See, e.g., U.S. Pat. No. 4,028,576). Alternatively, the external tissue removing surface  45  may simply be a section of the wire turns that has been roughened to provide a suitably abrasive surface. In another embodiment, the external surface may be etched or cut, perhaps with a laser, to provide small but sharp cutting surfaces. One skilled in the art will recognize that other equivalent techniques may be utilized to provide a suitable tissue removal surface.  
         [0028]      FIG. 3B  illustrates another embodiment, in which an external abrading member or crown  49 A is attached to the wire turns  44  by some suitable method such as brazing. The external abrading member  49 A may, for example but only illustratively, be a stainless steel hoop. An abrading surface  49 B, such as diamond chips, diamond powder, fused silica, titanium nitride, tungsten carbide, aluminum oxide, boron carbide, or other ceramic material, is coated onto the external abrading member  49 A. Preferably, the wire turns  44  in this embodiment are caused during manufacturing to follow a flat plane  44 A.  
         [0029]     With reference to the Figures, the inventive drive shaft terminal guide will now be described. The terminal guide  15  ( FIGS. 4A and 4B ) is attached to the distal end  13  of the helically wound drive shaft  12 . The terminal guide  15  is attached using bonding material  54  or any other method known in the art. The terminal guide  15  has a reduced outer diameter proximal surface  56  and an enlarged outer diameter distal surface  58  to facilitate attachment to the helically wound drive shaft. Those skilled in the art will readily recognize equivalent alternative profiles that will allow and facilitate attachment of the terminal guide to the drive shaft. The distal end  13  of the helically wound drive shaft  12  is adjacent and attached to the proximal surface  56  and abuts and is attached to the distal surface  58 . The terminal guide  15  may thus be inserted inside the distal end  13  of the helically wound drive shaft  12  and secured in place by bonding matter  54  or other methods well known in the art.  
         [0030]     The terminal guide  15  has a central orifice  60  therethrough sufficient in diameter to allow the guide wire  18  to pass through. The central orifice  60  has a proximal edge  62  and a distal edge  64 . Referring now to  FIG. 6 , the terminal guide is illustrated having the proximal edge  62  radiused or chamfered to facilitate advancement and retraction of the drive shaft, and the terminal guide  15 , over the guide wire  18 . Similarly, the distal edge  64  is radiused or chamfered to facilitate advancement and retraction of the drive shaft  12 , and the terminal guide  15 , over the guide wire  18 . In addition, radiusing or chamfering the distal edge  64  of the terminal guide  15  reduces any trauma that the otherwise sharp edges may cause to the arterial wall.  
         [0031]     An interface  66  is formed between the guide wire  18  and the central orifice  60  of the terminal guide when the drive shaft  12  is deployed over the pre-positioned guide wire  18 . In addition to the precision manufacturing of the terminal guide  15 , further reduction of the possibility that the drive shaft  12 , or the central orifice  60 , will erode the guide wire  18  or become frictionally welded to the drive shaft  12  or central orifice  60  is obtained by introduction of a lubricating, cooling fluid flow within the interface  66 . The fluid, typically saline or other biocompatible solution, may be introduced through a fluid supply line  20 , as seen in  FIG. 1 .  
         [0032]     The terminal guide  15  greatly reduces loading on the guide wire  18  from the drive shaft  12 . As the drive shaft  12  rotates, a force is developed substantially normal to the axis of the guide wire  18 . The present invention distributes the load from this force into the terminal guide  15  instead of onto the drive shaft  12 . In conjunction with the lubricated bearing effect of lubricating, cooling fluid flowing within the interface  66 , this substantially eliminates any gouging of the guide wire.  
         [0033]     The terminal guide  15  may further be manufactured using radiopaque material either embedded throughout the terminal guide  15  or bands of radiopaque material may be interspersed along the terminal guide  15  to facilitate locating the terminal guide during the atherectomy procedure and to reduce or eliminate the possibility that the distal end  13  of the drive shaft  12  is advanced beyond the distal end  19  of the guide wire  18 . Alternatively, the terminal guide may be coated with a radiopaque material. The radiopaque material thus reduces the possibility that healthy arterial tissue will be damaged or that the arterial wall will be perforated.  
         [0034]      FIG. 7A  illustrates an alternate embodiment. Here, a radiopaque jacket  68  is bonded to circumferentially surround the helically wound drive shaft  12  in the area of the reduced outer diameter of the proximal surface of the terminal guide  56 . The radiopaque jacket  68  is attached to the enlarged outer diameter of the distal surface  58  of the terminal guide  15  by any known method such as bonding. In this embodiment, the outer diameter of the radiopaque jacket  68  is substantially equivalent to the outer diameter of the distal surface of the terminal guide  58  to provide a substantially smooth terminal guide outer diameter  70 . To increase visibility of the terminal guide  15  during the atherectomy procedure, the jacket  68  may have radiopaque material embedded throughout the terminal guide or bands of radiopaque material may be interspersed substantially throughout the jacket  68 . Alternatively, the jacket  68  may simply be coated with radiopaque material.  
         [0035]      FIG. 7B  shows another embodiment. Here, rather than having the jacket  68  attached to the enlarged outer diameter of the distal surface  58  of the terminal guide, the jacket  68  is applied to the terminal guide as a coating or tube, so that it extends outside the outer diameter of the distal surface  58  of the terminal guide  15 .  
         [0036]     The terminal guide  15  requires relatively high precision dimensional tolerances to prevent misalignment of the distal end  13  of the drive shaft  12  with respect to the pre-positioned guide wire  18 . The impact of such misalignment is typically an unwanted eccentric motion which, in turn, may produce frictional surface erosion of the guide wire  18 , frictional welding of the drive shaft  12  to the guide wire  18 , and ultimately may produce premature failure of the drive shaft  12  and/or the guide wire  18 . The required precision to prevent such misalignment in the present invention is preferably obtained by machining, casting, molding or otherwise precision forming by methods well known in the art so that the terminal guide precisely fits the distal end  13  of the drive shaft  12 .  
         [0037]     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar to or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety to the extent allowed by applicable law and regulations. In case of conflict, the present specification, including definitions, will control.  
         [0038]     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.