as explained in further detail below , the present invention is an atherectomy device having an ablation burr that can be compressed to a smaller diameter to facilitate insertion and removal of the ablation burr , but will expand to a fixed diameter during the atherectomy procedure . referring now to the drawings , the compressible atherectomy burr of the present invention will be described . fig1 a , 1 b , and 1 c illustrate a first embodiment of an atherectomy burr according to the present invention , wherein the burr 100 is attached to the end of a flexible drive shaft 90 that is disposed within a guide catheter 80 . the burr 100 has a nose portion 102 with an abrasive leading surface 104 . the abrasive leading surface 104 may be formed by affixing abrasive particles to the nose portion 102 or by making the nose portion 102 from a hard material , such as stainless steel , and machining or otherwise affecting an abrasive topography onto the surface of a hard material . at least one annular flexible disk 110 is located behind or proximal to the nose portion 102 . three flexible disks 110 are shown in the preferred embodiment . the flexible disks 110 are made of polyurethane or other tough , flexible polymer , and have a center hole 112 that is approximately equal in diameter to the diameter of the drive shaft 90 , and the flexible disks 110 slidably engage the drive shaft 90 . a plurality of cylindrical spacers 106 are slidably inserted between the flexible disks 110 , maintaining them in the desired spaced - apart relation . the flexible disks 110 are fixedly connected to the drive shaft 90 such that rotation of the drive shaft 90 will cause the flexible disks 110 to rotate correspondingly . the details of the connection between the flexible disks 110 and the drive shaft 90 are not critical to the present invention , and may be accomplished in a variety of ways . for example , the flexible disks 110 can be welded , brazed or glued to the drive shaft 90 , or attached to the cylindrical spacers 106 , which are then affixed to the drive shaft . alternatively , the end portion of the drive shaft 90 could be provided with a keyed ( noncircular ) shape , and the center hole 112 made to match the keyed shape . other methods of rotationally coupling the flexible disks 110 to the drive shaft 90 are well known in the art , and within the scope of the present invention . the flexible disks 110 include a forward surface 114 having an abrasive portion 116 that preferably extends generally to the outer edge of the flexible disks 110 . the abrasive portion 116 may be formed , for example , by affixing abrasive particles , such as diamond particles , to selected portions of the forward surface 114 . diamond particles may be attached to the forward surface 114 with an adhesive or a plating process , for example . in the preferred embodiment , the flexible disks 110 include a plurality of radial slots 118 that extend from the outer edge of the disks 110 part way to the center hole 112 . the radial slots 118 divide the outer portion of the flexible disks 110 into a number of disk segments 120 . the radial slots 118 may optionally terminate with a small hole 122 , the small hole relieving the stress at the end of the slot 118 and decreasing the force required to bend the disk segments 120 . as seen most clearly in fig1 b , the flexible disks 110 are intended to deform , or fold over , to be slidably insertable into the guide catheter 80 . the guide catheter 80 may include an expanded or fluted portion 85 at its distal end to accommodate the burr 100 with the folded flexible disks 110 . the burr 100 can then be inserted to the location of the occlusion that is to be treated using a guide catheter 80 having a diameter that is smaller than the diameter of the unfolded burr 100 . the catheter 80 can then be pulled back ( or the drive shaft 90 pushed forward ), releasing the burr 100 and permitting the flexible disks 110 to unfold to their full diameter . it will be appreciated that the flexible disks 110 have a well - defined maximum diameter that will not be significantly effected by spinning the drive shaft 90 at high rotation speeds . after the atherectomy procedure is completed , the drive shaft 90 can be pulled back into the distal end of the guide catheter 80 to fold the flexible disks 110 in order to remove the burr 100 from the patient &# 39 ; s vasculature . it may be desirable to coat the back surfaces 115 of the flexible disks 110 and / or an inner surface 83 of the guide catheter 80 with a hydrophilic coating , such as hydropass ™, available from boston scientific and described in u . s . pat . no . 5 , 702 , 754 . the hydrophilic coating attracts water molecules , thereby making the surfaces slippery , facilitating insertion and removal of the burr 100 into the catheter 80 . in addition , the hydrophilic coating may be beneficial during ablation since less torque may be transferred to a vessel wall if the burr stalls . in addition , the differential cutting ability of the burr may be enhanced due to the increased ability of the burr to slide over soft tissues . it will be appreciated that in addition to the advantages associated with insertion and removal of the burr 100 , there may be further advantages of the flexible disks 100 during the atherectomy procedure . for example , the abrasive portions 116 are nominally oriented forwardly in the treated vessel , avoiding or minimizing undesirable contact between the abrasive portion 116 and the vessel wall . as the abrasive disks 110 encounter hardened occlusions in the vessel , forward motion of the flexible drive shaft 90 will cause the flexible disks 110 to bend backwardly , rotating the abrasive portions 116 toward the occlusion , thereby naturally enhancing the ablative action at the location of the hardened occlusion . although this embodiment has been described and illustrated with three flexible disks 110 , it will be appreciated that more or fewer flexible disks 110 may be used to accommodate the needs of a particular application , and would be within the scope of the present invention . it will also be appreciated that the flexible disk 110 could be made without the radial slots 118 , thereby increasing the stiffness of the flexible disk 110 , while still permitting it to deform into a folded condition for insertion and removal . a second embodiment of a compressible burr according to the present invention is shown in fig2 a and 2b . the burr 200 includes a centrally located cylindrical portion 210 that is fixedly and generally coaxially connected to a drive shaft 90 such that rotation of the drive shaft 90 will cause the burr 200 to rotate . the drive shaft 90 is covered over a substantial portion of its length with a guide catheter 80 , which , in the preferred embodiment , includes a fluted portion 85 . although other attachment mechanisms are possible , in the preferred embodiment the central cylindrical portion 210 includes a center hole ( not shown ) through which the drive shaft 90 is inserted and fixedly attached using any suitable adhesive . a thin panel of flap portion 220 extends radially outward from the central cylindrical portion 210 to form a generally circular cylindrical shell that partially surrounds the center cylindrical portion 210 . the outer edge 224 of the panel portion 220 is disposed radially away from the center cylindrical portion 210 to form an elongate gap 226 between the outer edge 224 and the center cylindrical portion 210 . the panel portion 220 is formed from a semi - rigid material , selected such that the panel portion 220 can be elastically compressed to close the gap 226 , thereby decreasing the diameter of the burr 200 . the panel portion 220 includes a forward segment 230 that has a constant axial cross section , and a back segment 232 that tapers radially inward . the taper of the back segment 232 provides a ramp such that when the drive shaft 90 is retracted into the catheter 80 , the tapered back segment 232 will slidably engage the lumen of catheter 80 . as the drive shaft 90 is pulled further back into the catheter 80 , the panel portion 220 will elastically compress thereby reducing the diameter of the burr 200 as it is pulled into the catheter 80 , for easier insertion and extraction of the burr 200 . the forward segment 230 of the panel portion 220 includes one or more abrasive sections 228 on its exterior surface , providing an ablative surface for the atherectomy procedure . the abrasive portion 228 may be formed , for example , by affixing abrasive particles , such as diamond particles , to selected portions of the outer surface . it may be desirable to coat the back segment 232 of the panel portion 220 and / or the inner surface 83 of the fluted portion 85 of the guide catheter 80 with a hydrophilic coating to facilitate the retraction of the burr 200 into the catheter 80 . as will be appreciated , the burr 200 is rotated such that the edge 224 trails the movement of the burr . in the embodiment shown in fig2 b , the burr 200 is always rotated clockwise . however , the burr could also be constructed to rotate counterclockwise as desired . it is contemplated that this second embodiment of a burr 200 might also incorporate features of other atherectomy burrs described herein . for example , a smaller , forwardly facing nose portion , such as the nose portion 102 shown in fig1 a , could be added to the front of the burr 200 to produce a guide hole . moreover , the panel portion 220 could include a tapered forwardmost segment ( not shown ) similar to the back segment 232 , but facing forwardly , to facilitate engagement of the occlusion . in particular , a tapered forwardmost segment could taper to generally meet the widest portion of a nose portion , to produce a substantially continuous , increasing diameter , ablative surface . alternatively , the burr could have a forward nose not contiguous with the flap . a third embodiment of a compressible burr according to the present invention is shown in fig3 a and 3b . the burr 300 includes a rear hub 310 that is fixedly connected to a drive shaft 90 such that rotation of the drive shaft 90 will cause the burr 300 to rotate . the drive shaft 90 is covered over a substantial portion of its length with a guide catheter 80 , that optionally includes a fluted portion at its distal end . the burr 300 includes a plurality of flexible struts 320 , each strut having a back portion 322 that is fixedly attached to the rear hub 310 , a forward portion 324 that extends forwardly from the back portion 322 , and a folded back portion 326 , that extends backwardly from the distal end 325 of the forward portion 324 . the plurality of flexible struts 320 are equally spaced around the perimeter of the hub 310 , cooperatively defining a volume therebetween . as seen most clearly in fig3 c , which shows a side view of an individual strut 320 , the back portion 322 is preferably longitudinally convex and includes a proximally extending tab portion 323 for attachment to the drive shaft 90 . the forward portion 324 is preferably longitudinally concave . the outer surface of the forward portion 324 is coated with diamond particles 327 to provide an abrasive surface . a compressible body 330 , such as a hollow elastomeric bladder , is provided within the volume defined by the interior of the flexible struts 320 . the flexible struts 320 are preferably attached to the compressible body 330 , such that the compressible body 330 will generally maintain the flexible struts 320 in a spaced - apart configuration , while also permitting longitudinal flexure of the struts 320 . the burr 300 can be fabricated , for example , by stamping or wire electro - discharge machining , the flexible struts 320 from a suitable metal , then welding the flexible struts 320 at a proximal end 321 to the rear hub 310 . a liquid injection molding process can then be used to create the compressible body 330 from silicone , or some other suitable material . finally , any particulate abrasive , such as diamond particles can be attached to the forward portion 324 of the flexible struts 320 . it will be appreciated that the burr 300 can be deformed to a compressed state , as shown in fig3 b . the compressed state has a smaller maximum diameter than the relaxed , expanded state ( shown in fig3 a ). for example , a “ pull - in ” sheath 340 can be provided that slidably fits within the guide of catheter 80 . when the drive shaft 90 is pulled backwardly , the burr 300 will be pulled against the pull - in sheath 340 , such that the back portion 322 of the flexible struts 320 engage the sheath 340 . pulling the drive shaft 90 further will result in an inward force on the compressible body 330 from the back portions 322 of the struts 320 , thereby permitting the sheath 340 , and burr 300 to be retracted into the guide catheter 80 . it will be appreciated that other means of compressing and retracting the burr 300 are also possible , including the use of a fluted catheter , as discussed above . a fourth embodiment of a compressible burr according to the present invention is shown in fig4 a , 4 b , and 4 c . the burr 400 is fixedly connected to a drive shaft 90 such that rotation of the drive shaft 90 will cause the burr 400 to rotate . fig4 a shows a side view of the burr 400 connected to a drive shaft 90 , and fig4 b shows a cross - sectional view of the burr 400 , taken along a axial center plane . the drive shaft 90 is covered over a substantial portion of its length with a guide catheter 80 that optionally includes a fluted portion at its distal end . the burr 400 includes a plurality of elongate flexible members or wires 410 ( four shown in fig4 c ), each wire 410 having a distal end 412 that is attached to the drive shaft 90 , and a proximal end 414 extending proximally from the distal end 412 that is also attached to the drive shaft 90 . the wires 410 are preferably equally spaced around the perimeter of the drive shaft 90 , and may attach directly to the drive shaft 90 or attach through an intermediate hub ( not shown ) that connects to the drive shaft 90 . a resilient sheath 420 , having a generally football shape or ellipsoidal shape , encloses the wires 410 . the resilient sheath 420 is attached to the drive shaft 90 , and may optionally also be attached to one or more of the wires 410 . the sheath 420 is thin and sufficiently flexible to collapse , or fold in on itself , and strong enough to provide the working surface for the burr 400 . an abrasive coating 430 , such as a coating including diamond particles , is applied to the forward portion of the sheath 420 in the manner described below . the sheath 420 may be attached to the wires 410 , for example , by use of an appropriate adhesive inside the sheath 420 . the burr 400 may be spun while the adhesive is drying , to keep the adhesive at the outer surface for bonding the wires 410 to the sheath 420 . the plurality of wires 410 provide a support for the sheath 420 , maintaining it in an uncompressed configuration , as shown in fig4 a , during the atherectomy procedure . to facilitate insertion and removal of the burr 400 through the vasculature of the patient , the burr 400 can be compressed by bending the wires 410 inwardly , as shown in fig4 d . the burr 400 can then be inserted through the guide catheter 80 to the site of the occlusion . the wires 410 are selected to have sufficient flexibility that upon spin - up of the burr for the ablation procedure , the wires 410 are forced outwardly by centrifugal forces , returning the burr 400 to the uncompressed configuration . alternatively , the wires 410 may be made from a resilient elastically deformable material formed to maintain the burr in the desired shape ( which may or may not be ellipsoidal ), the elastically deformable material being able to elastically compress sufficiently to allow the burr 400 to be inserted through the guide catheter 80 , then elastically springing out to the desired shape when it is no longer constrained by the guide catheter 80 . another alternative is to use a so - called shape memory alloy , such as niti , for the wires 410 . a shape memory alloy wire 410 is deformable to allow the burr to be compressed , but has a selectable preferred shape to which it will return ( generally upon being heated ). two variations of a fifth embodiment of a compressible burr according to the present invention are shown in fig5 a and 5c . the burr 500 a , 500 b is rotatably coupled to a drive shaft 90 such that rotation of the drive shaft 90 will cause the burr 500 a , 500 b to rotate . the burrs 500 a , 500 b include nose portions 510 a , 510 b having abrasive leading surfaces 512 a , 512 b that taper in the distal direction . the abrasive leading surface may be formed , for example , by affixing an abrasive material such as diamond particles to the leading surfaces 512 a , 512 b or by machining or otherwise roughing the leading surfaces 512 a , 512 b to create an abrasive topography . a resilient shell 520 a , 520 b is attached to back surfaces 514 a , 514 b of the nose , for example , by use of an adhesive . each resilient shell 520 a , 520 b is shown most clearly in fig5 b and 5c . a shell 520 a , 520 b is generally axisymmetric , and includes a collapsible center portion 524 a , 524 b that , in its uncollapsed state , has a greater outer diameter than the nose portion 510 a , 510 b . the shells 520 a , 520 b may be made from any appropriate resilient material . in the preferred embodiment , a polyurethane polymer is used that having a low elasticity , so that the center portion 524 a , 524 b will not stretch when the burr is rotated at high speeds . the center portion 524 a , 524 b is provided with an abrasive outer surface 525 a , 525 b , at least over the forward part of the center portion 524 a , 524 b . the abrasive outer surface may be formed by affixing diamond particles , or other abrasive particles , to the center portion 524 a , 524 b as described below . in the first variation of the burr 500 a , shown in fig5 a and 5b , the shell 520 a includes a generally cylindrical proximal portion 522 a extending backwardly from the center portion 524 a , that is disposed coaxially around the drive shaft 90 . the proximal portion 522 a is preferably not affixed to the drive shaft 90 , so that it can slide proximally or distally , to facilitate compression of the center portion 524 a . a distal portion 526 a of the shell 520 a extends forwardly from the center portion 524 a and is fixedly attached to the back surface 514 a of the nose portion 510 a . the nose portion 510 a is attached to the drive shaft 90 such that rotation of the drive shaft will cause a corresponding rotation of the nose portion 510 a . the distal portion 526 a may optionally also have an abrasive outer surface . the resilient center portion 524 a can be collapsed into the guide catheter ( not shown ) for easier insertion and removal of the burr 500 a , and will expand to its uncompressed state as it is released from the guide catheter . in the second variation of the burr 500 b , shown in fig5 c and 5d , the shell 520 b is formed in two parts . a proximal portion 522 b is made from a hard material such as stainless steel . the proximal portion 522 b includes a generally cylindrical back section 521 b that is fixedly connected to the drive shaft 90 , and a smaller - diameter , elongate forward section 523 b that extends coaxially forward . the nose portion 510 b is attached to the distal end of the elongate forward section 523 b . the nose portion may include an abrasive outer surface , similar to that described above . the resilient center portion 524 b is attached to the back surface 514 b of the nose portion 510 b . the resilient center portion 524 b has a maximum diameter that is greater than the diameter of the nose portion 510 b that can be collapsed into the guide catheter ( not shown ) for easier insertion and removal of the burr 500 b . it will appreciated that collapsing these burrs 500 a , 500 b aids in insertion and removal of the burrs into the patient &# 39 ; s vasculature by permitting the use of a guide catheter having a smaller diameter than the working diameter of the burrs 500 a , 500 b . additionally , during the atherectomy procedure , as the burrs are rotated in the proximity of an occlusion , the resilient center portions 524 a , 524 b will flex to accommodate restricted passageways in the patient &# 39 ; s vessels that are causes by the occlusion . the resilient center portions 524 a , 524 b and , in particular , the abrasive surfaces 525 a , 525 b will provide a gentle , outward pressure on the occlusion , facilitating the ablative removal of the occlusion during the procedure , and the burrs 500 a , 500 b will expand to the desired , predetermined maximum radius as the occlusion is removed . in the various embodiments of the preferred embodiment described above , where abrasive particles are to be affixed to a polymeric burr element , any suitable method of affixing the particles may be used . for example , in the preferred embodiments , the abrasive is secured to the polymeric member by creating a thin base layer of silver using vacuum deposition techniques such as are well known in the art . metalization of polymeric materials is discussed , for example , in u . s . pat . no . 5 , 468 , 562 to farivar , et al ., and in the references cited therein . once the silver base layer is applied to the polymeric member , a layer of metal such as nickel having a slurry of diamond particles disposed therein can be plated to the base layer using an electro - or electroless - plating method as is done with conventional burrs . in some instances , it may be desirable to etch or mask a portion of the polymeric member with a patter of dots or other shapes so that the base layer does not completely surround the polymeric member . if the abrasive is only plated to the etched pattern , it may allow the polymeric member to more easily expand , collapse , or otherwise flex , and also enhance the adhesive stability of the abrasive coating . in the preferred embodiments , abrasive dots or pads having a diameter of approximately 0 . 010 to 0 . 015 inches are used . in addition to electroplating , it is believed that other techniques could be used to secure the abrasive to the balloon , such as by using an adhesive or chemically bonding sites on the outer surface of the polymeric balloon to which metal ions such as copper , silver , gold , or nickel may bond . these sites may be bonded to the polymeric member using a high - vacuum plasma system or by incorporating chemicals ( such as carbon , silver , etc .) with the polymer prior to fabrication of the polymeric member . alternatively , it is believed that pulse cathode arc ion deposition could be used to incorporate bonding sites on the surface of the elastomer . while the preferred embodiment of the invention has been illustrated and described , it will be appreciated that various changes can be made therein without departing from the scope of the invention . it is therefore intended that the scope of the invention be determined from the following claims and equivalents thereto .
a rotational ablation atherectomy device including a flexible drive shaft and a compressible burr that may be inserted and extracted from a patient using a catheter having a diameter that is smaller than the operational diameter of the burr . in one embodiment , the burr includes a nose portion coupled to the drive shaft and one or more flexible abrasive disks disposed rearwardly from the nose portion . the flexible disks are foldable to be slidably received within a catheter . in another embodiment , the burr includes a support member coupled to the drive shaft , the support member having a resilient panel that spirals outwardly , forming a generally cylindrical ablation surface . the flexible panel can be elastically urged toward the support member and slidably inserted into the catheter . in a third embodiment , the burr includes a plurality of struts that are coupled to the drive shaft . an elastically compressible body disposed between the struts permits the struts to flex inwardly to reduce the burr diameter . in another embodiment , the burr includes a plurality of flexible wires attached at proximal and distal ends to the drive shaft . an abrasive sheath is disposed over the wires . the wires can be bent inwardly to compress the burr and re - expanded by rotation of the burr . in another embodiment , the burr comprises a nose portion and a resilient shell having a compressible , larger diameter abrasive section disposed at the proximal end of the nose portion .