Rotational Atherectomy Device with a System of Eccentric Abrading Heads

CROSS-REFERENCE TO RELATED 333ion serial number 13/621 ,398 filed September 17, 2012, which is incorporated herein by reference.

INVENTORS

Matthew D. Cambronne, a citizen of the United States resident in Mounds View, Minnesota

Robert E. Kohler, a citizen of the United States resident in Lake Elmo, Minnesota BACKGROUND OF THE INVENTION [001] Field of the Invention

[002] The invention relates to devices and methods for removing tissue from body passageways, such as removal of atherosclerotic plaque from arteries, utilizing a highspeed rotational atherectomy device.

[003] Description of the Related Art

[004] 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's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very 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, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.

[005] Rotational atherectomy procedures have become a common technique for removing such stenotic material. Such procedures are used most frequently to initiate the opening of calcified lesions in coronary arteries. Most often the rotational

atherectomy procedure is not used alone, but is followed by a balloon angioplasty procedure, which, in turn, is very frequently followed by placement of a stent to assist in maintaining patency of the opened artery. For non-calcified lesions, balloon angioplasty most often is used alone to open the artery, and stents often are placed to maintain patency of the opened artery. Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience stent restenosis-i.e., blockage of the stent which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. In such situations an atherectomy procedure is the preferred procedure to remove the excessive scar tissue from the stent (balloon angioplasty being not very effective within the stent), thereby restoring the patency of the artery.

[006] Several kinds of rotational atherectomy devices have been developed for attempting to remove stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990, 134 (Auth), a burr covered with an abrasive abrading material such as diamond particles is carried at the distal end of a flexible drive shaft. The burr is rotated at high speeds (typically, e.g., in the range of about 150,000-190,000 rpm) while it is advanced across the stenosis. As the burr is removing stenotic tissue, however, it blocks blood flow. Once the burr has been 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. Frequently more than one size burr must be utilized to open an artery to the desired diameter.

[007] 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 surface 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. The disclosure of US Pat 5,314,438 is hereby incorporated by reference in its entirety.

[008] U.S. Pat No. 5,681 ,336 (Clement) provides an eccentric tissue removing burr with a coating of abrasive particles secured to a portion of its outer surface by a suitable binding material. This construction is limited, however because, as Clement explains at Col. 3, lines 53-55, that the asymmetrical burr is rotated at "lower speeds than are used with high speed ablation devices, to compensate for heat or imbalance." That is, given both the size and mass of the solid burr, it is infeasible to rotate the burr at the high speeds used during atherectomy procedures, i.e., 20,000-200,000 rpm. Essentially, in this prior art device, the center of mass offset from the rotational axis of the drive shaft would result in development of significant centrifugal force, exerting too much pressure on the wall of the artery and creating too much heat and excessively large particles.

[009] U.S. Patent 5,584,843 (Wulfman) discloses one or more ellipsoidal burrs or cuffs attached to a flexible drive shaft. The drive shaft is placed over a preformed shaped guidewire so that the drive shaft and burrs conform to the shape and profile of the guide wire, i.e., a gentle "S" or "cork-screw" shape. Wulfman, however, requires the preformed guidewire to achieve the non-linear shaping of the drive shaft, a deformed shaping state that is, therefore, present when the device is not rotated. Thus,

Wulfman's burrs comprise a sweeping diameter that is limited to, and by, the guidewire shaping. In addition, each of Wulfman's burrs are elliptical and symmetric about the rotational axis of the drive shaft with each center of mass for the burrs being on the drive shaft's rotational axis. Thus, the sweeping diameter of Wulfman is not induced by rotational speed and, therefore, cannot be controlled other than by the guidewire's shaping. Difficulties in positioning the shaped, undeformed, guidewire without damaging the patient's vasculature are also present.

[010] The present invention overcomes these deficiencies. [011] BRIEF SUMMARY OF THE INVENTION

[012] The invention provides a rotational atherectomy device having, in various embodiments, a flexible, elongated, rotatable drive shaft with a system of eccentric abrading heads attached thereto. At least part of the eccentric enlarged abrading heads in the system have a tissue removing surface-typically an abrasive surface. In certain embodiments, the abrading heads may be at least partially hollow. Preferably the eccentric enlarged abrading heads have centers of mass spaced radially from the rotational axis of the drive shaft, facilitating the ability of the system of eccentric abrading heads to work together to open the stenotic lesion to a diameter substantially larger than the outer resting diameter of the enlarged abrading heads when operated at high speeds. Therefore, certain embodiments comprise a system having unbalanced centers of mass to not only stimulate greater rotational diameters but also arranged in a manner whereby a debris-removing augering effect occurs. Alternatively, other embodiments may comprise systems having abrading heads with balanced centers of mass.

[013] The figures and the detailed description which follow more particularly exemplify these and other embodiments of the invention.

[014] BRIEF DESCRIPTION OF THE DRAWINGS

[015] The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, which are as follows.

[016] FIG. 1 is a perspective view of one embodiment of the present invention;

[017] FIG. 2 is a side and partial cutaway view of one embodiment of the present invention;

[018] FIG. 3A is an end view of one embodiment of the present invention; [019] FIG. 3B is an end view of one embodiment of the present invention;

[020] FIG. 4A is a schematic chart illustrating possible rotational angle separations of the present invention;

[021] FIG. 4B is a side and cutaway view of one embodiment of the present invention;

[022] FIG. 5 is a perspective and cutaway view of one embodiment of the present invention;

[023] FIG. 6 is a side cutaway view of one embodiment of the present invention;

[024] FIG. 7 is a side cutaway view of one embodiment of the present invention;

[025] FIG. 8A is a perspective view of one embodiment of the present invention;

[026] FIG. 8B is a bottom view of one embodiment of the present invention;

[027] FIG. 8C is a side cutaway view of one embodiment of the present invention;

[028] FIG. 9 is a cutaway view of one embodiment of the present invention;

[029] FIG. 10 is a schematic view illustrating of one embodiment of the present invention.

[030] FIG. 11 is a cross-sectional drawing of an eccentric abrasive element, an eccentric proximal counterweight and an eccentric distal counterweight.

[031] FIG. 12 is a cross-sectional drawing of an eccentric abrasive element, an eccentric proximal counterweight and a concentric distal counterweight.

[032] FIG. 13 is a cross-sectional drawing of an eccentric abrasive element, a concentric proximal counterweight and an eccentric distal counterweight. [033] FIG. 14 is a cross-sectional drawing of an eccentric abrasive element, a concentric proximal counterweight and a concentric distal counterweight.

[034] FIG. 15 is a cross-sectional drawing of a concentric abrasive element, an eccentric proximal counterweight and an eccentric distal counterweight.

[035] FIG. 16 is a cross-sectional drawing of a concentric abrasive element, an eccentric proximal counterweight and a concentric distal counterweight.

[036] FIG. 17 is a cross-sectional drawing of a concentric abrasive element, a concentric proximal counterweight and an eccentric distal counterweight.

[037] FIG. 18 is a cross-sectional drawing of a concentric abrasive element, a concentric proximal counterweight and a concentric distal counterweight.

[038] FIG. 19 is a schematic drawing of the abrasive element and counterweights, with a distance D1 between the centers of mass of proximal counterweight and abrasive element, and a distance D2 between the centers of mass of distal counterweight and abrasive element.

[039] DETAILED DESCRIPTION OF THE INVENTION, INCLUDING THE BEST MODE

[040] While the invention is amenable to various modifications and alternative forms, specifics thereof are shown by way of example in the drawings and described in detail herein. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[041] FIG. 1 illustrates one embodiment of a rotational atherectomy device according to the present invention. The device includes a handle portion 10, an elongated, flexible

- 8 - drive shaft 20 having a system of eccentric abrading heads 27 comprising, in the illustrated embodiment and without limitation, a proximal eccentric enlarged abrading head 28, a distal eccentric enlarged abrading head or abrasive element 29, and an elongated catheter 13 extending distally from the handle portion 10. The drive shaft 20 is constructed from helically coiled wire as is known in the art and the exemplary system 27 comprising the proximal abrading head 28 and distal abrading head 29 are fixedly attached thereto. The catheter 13 has a lumen in which most of the length of the drive shaft 20 is disposed, except for the enlarged proximal and distal abrading heads 28, 29 and a short section distal to the distal enlarged abrading head 29. The drive shaft 20 also contains an inner lumen, permitting the drive shaft 20 to be advanced and rotated over a guide wire 15. A fluid supply line 17 may be provided for introducing a cooling and lubricating solution (typically saline or another biocompatible fluid) into the catheter 13.

[042] The handle 10 desirably contains a turbine (or similar rotational drive

mechanism) for rotating the drive shaft 20 at high speeds. The handle 10 typically may be connected to a power source, such as compressed air delivered through a tube 16. A pair of fiber optic cables 25, alternatively a single fiber optic cable may be used, may also be provided for monitoring the speed of rotation of the turbine and drive shaft 20, details regarding such handles and associated instrumentation are well known in the industry. The handle 10 also desirably includes a control knob 1 1 for advancing and retracting the turbine and drive shaft 20 with respect to the catheter 13 and the body of the handle.

[043] Proximal eccentric abrading head 28 and distal eccentric abrading head 29 of the illustrative system 27 are attached or otherwise disposed on or integrated with or formed from the drive shaft. Proximal abrading head 28 is located at a more proximal position in relation to the distal abrading head 29, i.e., the distal abrading head 29 is closest to the distal end of drive shaft 20. A distance or spacing separates the proximal and distal abrading heads 28, 29 from each other along drive shaft 20. Moreover, proximal and distal abrading heads 28, 29 each comprise a resting diameter D and D', respectively. The present invention requires that the resting diameter D of proximal abrading head 28 is larger than the resting diameter D' of distal abrading head 29.

Further, the present invention is not limited to a system 27 comprising two abrading heads and, therefore, may comprise more than one abrading head. In all cases, however, the resting diameter of the most distal abrading head, e.g., 29, will be the smallest diameter abrading head, with each successively more proximal abrading head, e.g., 28, comprising a larger resting diameter than the adjacent distal head, e.g., 29. Stated differently, the abrading heads will increase in resting diameter moving from the distal end of the drive shaft 20 to a more proximal position on the drive shaft, with the most distal abrading head comprising the smallest resting diameter of all abrading heads.

[044] The preferred embodiment comprises two abrading heads, i.e., 28, 29, as illustrated. An exemplary resting diameter D for the proximal abrading head may be in the range of 2 mm to 3 mm while the distal abrading head may comprise a resting diameter D' range of 1.25 to 5 mm. As discussed above, however, in each

embodiment, the most distal abrading head has the smallest resting diameter in the system 27, with successively more proximal abrading head(s) comprising successively larger resting diameters.

[045] Thus, one of the purposes of the primary invention is to provide a system of abrading heads 27 comprising a smaller resting diameter distal eccentric abrading head 29 in conjunction with at least one larger resting diameter proximal eccentric abrading head 28. The small diameter of the distal eccentric abrading head 29 may therefore be positioned within a small hole in the occlusive material in the patient's vasculature prior to high speed rotation therein. Initiation of rotation of the drive shaft 20 causes the system comprising drive shaft 20 with abrading heads 28, 29 mounted thereon, to begin to generate centrifugal forces as will be described in more detail herein. The result is, among other things, orbital motion of the abrading heads 28, 29, wherein the abrading heads 28, 29 begin to trace out paths that comprise working diameters that are, e.g., two to three times larger than the respective resting diameters D, D'. [046] Figures 2, 3A and 3B provide illustration of the arrangement of certain embodiments of the system 27. Thus, Figures 2 and 3A illustrate an unbalanced system of abrading heads 27 comprising a proximal abrading head 28 and a distal abrading head 29 attached to the drive shaft 20, separated by a distance and wherein the centers of mass of both abrading heads 28, 29 are radially offset from the axis of rotation A of the drive shaft 20 in the same direction and in the same plane as illustrated by the dashed line in Fig 3A. Stated differently, the offset of the center of mass of the entire system of abrading heads 27 is maximized in one radially offset direction, e.g., along the dashed line of Fig 3A. A balanced embodiment would comprise, e.g., the centers of mass of the proximal abrading head 28 and the distal abrading head 29 to be separated rotationally by 180 degrees, whereby the centers of mass of the abrading heads 28, 29 would be on dashed line of Fig 3A, but on opposing sides of the rotational axis of the drive shaft 20. Alternatively, an even number, e.g., four, of eccentric abrading heads could be provided, with rotational separation of equivalent rotational angle between each of the exemplary four eccentric abrading heads being equivalent, e.g., 45 degrees or 90 degrees or the like to achieve a balanced system. In this balanced embodiment, a preferred arrangement provides the centers of mass of the eccentric abrading heads being roughly equivalent in mass, though the resting diameters decrease successively moving from most proximal to most distal eccentric abrading head.

[047] Figure 3B illustrates an alternate embodiment of an unbalanced system of abrading heads 27. In this illustrative embodiment, the proximal and distal abrading heads 28, 29 are affixed or mounted on or formed from the drive shaft 20 and separated by a distance as in the embodiment of Figures 2 and 3A. However, the embodiment of 3B comprises the centers of mass of the proximal and distal abrading heads 28, 29 being radially offset from the axis of rotation of the drive shaft in different directions and different planes. Thus, as shown, the center of mass of distal abrading head 29 is substantially aligned with the rotational axis of the drive shaft 20 in a vertical direction, as illustrated by vertical dashed line. However, the center of mass of the proximal abrading head 28 is not on that vertical dashed line and is, in fact, provided in an approximately 100 degrees rotation from the vertical dashed line representing the plane comprising the center of mass of the distal abrading head 29. As a result, the system of abrading heads 27 comprises an unbalanced weight which, as with the system 27 of Fig 3A, will tend to result in centrifugal forces generated during high speed rotation of the drive shaft 20 and orbital motion of the abrading heads 28, 29.

[048] The primary difference between the embodiment of Fig 3A and that of Fig 3B comprises the influencing of fluid flow distally along the drive shaft 20 within the system of abrading heads 27 during high speed rotation and orbital motion of the heads 28, 29. Figure 3A will generate a turbulence without a regular pattern of the surrounding fluid, comprising not only blood but also the debris abraded from the occlusion during high speed rotation.

[049] Figure 3B, in contrast, provides a generally spiral profile moving down the drive shaft 20 from a point proximal to the proximal abrading head 28 distally to a point distal to the distal abrading head 29. This spiraling profile is a result of the rotational spacing of the centers of mass of the abrading heads 28, 29, in the illustrated case

approximately 100 degrees. In the illustrated case, the radial offset of the centers of mass is achieved by an eccentricity of the abrading heads 28, 29 provided by a geometric eccentricity. Stated differently, the geometric longitudinal profile of the abrading heads 28, 29 is eccentric. As a consequence, the profile of the system 27 comprises a spiral channel as described above along which fluid flow occurs. The result of this spiral profile during high speed rotation is that the fluid comprising blood and debris will tend to move along the spiral in a distal direction, from the larger diameter proximal abrading head 28 distally toward and beyond the smaller distal abrading head 29. Thus, the debris generated by the atherectomy procedure by system 27 is channeled away from the occlusion along the spiral channel of the system 27 in a controlled fashion.

[050] The spiral channel of system 27 is further illustrated in Figure 4A which provides a longitudinal cross sectional view of drive shaft 20 with axis of rotation A with a rotational angle grid superimposed thereon. The rotational angle grid is broken into exemplary 45 degree sections around the drive shaft 20. Creation of the spirai channel and profile thereof may be achieved by rotationally separating the geometric centers, and centers of mass, of the eccentric abrading heads of the system 27. By way of example, an eccentric proximal abrading head 28 may comprise a geometric center, and a center of mass, located rotationally within the 0 degree to 45 degree rotational section as illustrated. A distal eccentric abrading head 29 may then be disposed so that its geometric center, and center of mass, is rotationally located within the rotational section comprising 45 degrees to 90 degrees. If, in certain embodiments, more than two abrading heads comprise the system 27, then, as illustrated, a third eccentric abrading head may be disposed with its geometric center and center of mass is rotationally located within the rotational section comprising 90 degrees to 135 degrees. If additional eccentric abrading heads, e.g., a fourth eccentric abrading head etc., are in system 27, their geometric centers and centers of mass will preferably be located in rotational sections greater than 135 degrees using the same logical progression.

[051] The rotational sections illustrated are exemplary only and the skilled artisan will recognize that sections may be larger and/or smaller. Further, the skilled artisan will recognize that, e.g., proximal eccentric abrading head 28 may be separated more than 45 degrees from the distal eccentric abrading head 29.

[052] The net effect of this rotational progression moving longitudinally along drive shaft 20 within system 27 is provision of a spiral channel as illustrated in Fig 4B, with the fluid flow, including blood, cooling solution and debris, along the fluid flow line between the peaks of the successively mounted, and rotationally separated, abrading heads of system 27. The channeled spiraling of the fluid is enhanced and aided by the abrading head peaks engaging the occlusion.

[053] The abrading heads of the system of abrading heads 27 may comprise one or more types of abrading heads.

[054] For example, Figures 5 and 6 illustrate an abrading head which may be used for one, or more, of the abrading heads, e.g., proximal and distal abrading heads 28, 29, of the present invention. This embodiment comprises an eccentric enlarged diameter abrading section 28A of a drive shaft 20A. Note that this embodiment is designated as 28A for instructive purposes only, this designation does not limit the illustrated

embodiment to a proximal abrading head position on the drive shaft. The drive shaft 20A comprises one or more helically wound wires 18 which define a guide wire lumen 19A and a hollow cavity 25A within the enlarged abrading section 28A. Except for the guide wire 15 traversing the hollow cavity 25A, the hollow cavity 25A is substantially empty. The eccentric enlarged diameter abrading section 28A includes, relative to the location of the stenosis, proximal 30A, intermediate 35A and distal 40A portions. Wire turns 31 of the proximal portion 30A of the eccentric enlarged diameter section 28A preferably have diameters that progressively increase distally at a generally constant rate, thereby forming generally the shape of a cone. Wire turns 41 of the distal portion 40A preferably have diameters that progressively decrease distally at a generally constant rate, thereby forming generally the shape of a cone. Wire turns 36 of the intermediate portion 35A are provided with gradually changing diameters to provide a generally convex outer surface which is shaped to provide a smooth transition between the proximal and distal conical portions of the enlarged eccentric diameter section 28A of the drive shaft 20A. In this abrading head embodiment, the center of mass is located radially offset from the drive shaft axis of rotation A.

[055] Further, at least part of the eccentric enlarged diameter abrading section of the drive shaft 28A (preferably the intermediate portion 35A) comprises an external surface capable of removing tissue. A tissue removing surface 37 comprising a coating of an abrasive material 24A to define a tissue removing segment of the drive shaft 20A is shown attached directly to the wire turns of the drive shaft 20A by a suitable binder 26A.

[056] Figs 5 and 6 thus illustrate one embodiment of the enlarged diameter abrading section disclosed in commonly assigned U.S. Pat. No. 6,494,890 (Shturman) wherein at least a segment of this enlarged section is covered with an abrasive material and which may be used in present invention's system 27. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery. The device is capable of opening an artery to a diameter that is larger than the resting diameter of the enlarged eccentric section due, in part, to the orbital rotational motion during high speed operation. Since the enlarged eccentric section comprises drive shaft wires that are not bound together, the enlarged eccentric section of the drive shaft may flex during placement within the stenosis or during high speed operation. This flexion allows for a larger diameter opening during high speed operation. The disclosure of U.S. Pat. No. 6,494,890 is hereby incorporated by reference in its entirety.

[057] Turning now to Figures 7 and 8A-8C, another embodiment of a possible abrading head comprising system of eccentric abrading heads 27 of the present invention will be discussed. As with the embodiment of Figs 4 and 5, the instant embodiment may be used for one, or more, of the abrading heads of the system of eccentric abrading heads 27. By way of non-limiting example, the instant embodiment may comprise one or both of the proximal and/or distal abrading heads 28, 29. Alternatively, the instant

embodiment may be combined with another type of abrading head, e.g., that

embodiment illustrated in Figs 5 and 6 to comprise system 27. Thus, the instant embodiment may comprise the proximal abrading head 28 and the embodiment of Figs 5 and 6 may comprise the distal abrading head 29 to form system 27. Many other equivalent variations and combinations present themselves readily to the skilled artisan, each such combination is within the scope of the present invention.

[058] As discussed above, the drive shaft 20 has a rotational axis A which is coaxial with the guide wire 15, the guide wire 15 being disposed within the lumen 19 of the drive shaft 20. With particular reference to Figs 7 and 8A-8C, the proximal portion 30S of the eccentric enlarged abrading head 28S has an outer surface which is substantially defined by the lateral surface of a frustum of a cone, the cone having an axis 32 which intersects the rotational axis 21 of the drive shaft 20 at a relatively shallow angle β. Similarly, the distal portion 40S of the enlarged abrading head 28S has an outer surface which is substantially defined by the lateral surface of a frustum of a cone, the cone having an axis 42 which also intersects the rotational axis 21 of the drive shaft 20 at a relatively shallow angle β. The cone axis 32 of the proximal portion SOS and the cone axis 42 of the distal portion 40S intersect each other and are coplanar with the longitudinal rotational axis A of the drive shaft.

[059] The opposing sides of the cones generally should be at an angle a of between about 10° and about 30° with respect to each other; preferably the angle a is between about 20° and about 24°, and most preferably the angle a is about 22°. Also, the cone axis 32 of the proximal portion 30S and the cone axis 42 of the distal portion 40S normally intersect the rotational axis 21 of the drive shaft 20 at an angle β of between about 20° and about 8°. Preferably the angle β is between about 3° and about 6°.

Although in the preferred embodiment shown in the drawings the angles a of the distal and proximal portions of the enlarged abrading head 28S are generally equal, they need not be equal. The same is true for the angles β.

[060] In an alternate embodiment, the intermediate portion 35S may comprise a diameter that gradually increases from the intersection with the distal portion 40 to the intersection of the proximal portion 30. In this embodiment, angle a, as illustrated in Fig. 7, may be larger in the proximal portion 30S than the distal portion 40S, or vice versa. Further alternate embodiments comprise the intermediate portion 35S having a surface that is convex, wherein the intermediate portion outer surface may be shaped to provide a smooth transition between the proximal and distal outer surfaces of the proximal and distal portions.

[061] The abrading head 28S may comprise at least one tissue removing surface 37 on the external surface(s) of the intermediate portion 35S, the distal portion 40S and/or the proximal portion 30S to facilitate abrasion of the stenosis during high speed rotation. The tissue removing surface 37 may comprise a coating of an abrasive material 24 bound to the external surface(s) of the intermediate portion 35S, the distal portion 40S and/or the proximal portion 30S of abrading head 28S. The abrasive material may be any suitable material, such as 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 tissue removing surface(s) by a suitable binder-such attachment may be achieved using well known techniques, such as conventional electroplating or fusion technologies (see, e.g., U.S. Pat. No. 4,018,576). Alternately the external tissue removing surface may comprise mechanically or chemically roughening the external surface(s) of the intermediate portion 35S, the distal portion 40S and/or the proximal portion 30S to provide a suitable abrasive tissue removing surface 37. In yet another variation, the external surface may be etched or cut (e.g., with a laser) to provide small but effective abrading surfaces. Other similar techniques may also be utilized to provide a suitable tissue removing surface 37.

[062] As best illustrated in Figs. 8A-8C, an at least partially enclosed lumen or slot 23 may be provided longitudinally through the enlarged abrading head 28S along the rotational axis 21 of the drive shaft 20 for securing the abrading head 28 to the drive shaft 20 in a manner well known to those skilled in the art. In the embodiment shown, a hollowed section 26 is provided to lessen the mass of the abrading head 28S to facilitate atraumatic abrasion and improve predictability of control of the orbital pathway of the abrading head 28S during high speed, i.e., 20,000 to 200,000 rpm, operation. In this embodiment, the abrading head 28S may be fixedly attached to the drive shaft 20, wherein the drive shaft comprises one single unit. Alternatively, the drive shaft 20 may comprise two separate pieces, wherein the enlarged eccentric abrading head 28S is fixedly attached to both drive shaft 20 pieces, with a gap therebetween. This two-piece drive shaft construction technique may, in combination with hollowed section 26, allow further manipulation of the placement of the center of mass of the abrading head 28S. The size and shape of the hollowed section 26 in all embodiments may be modified to optimize the orbital rotational path of the abrading head 28S for particularly desirable rotational speeds. It is understood that hollow section 26 is illustrated as symmetrical in all planes, though this is certainly not a limiting example. Hollowed section 26 may be asymmetric longitudinally and/or radially in order to move the center of mass of the abrading head 28S to the desired location. Those skilled in the art will readily recognize the various possible configurations, each of which is within the scope of the present invention. [063] Further, the embodiment of Figs 7, 8A-8C illustrates the proximal portion 30S and distal portion 40S of symmetrical shape and length. Alternate embodiments may increase the length of either the proximal portion 30S or the distal portion 40S, to create an asymmetrical profile.

[064] Because the cone axes 32 and 42 intersect the rotational axis 21 of the drive shaft 20 at an angle β the eccentric enlarged abrading head 28S has a center of mass that is spaced radially away from the longitudinal rotational axis 21 of the drive shaft 20. As will be described in greater detail below, offsetting the center of mass from the drive shaft's axis of rotation 21 provides the enlarged abrading head 28S with an eccentricity that permits it to open an artery to a diameter substantially larger, than the nominal diameter of the enlarged eccentric abrading head 28S, preferably the opened diameter is at least twice as large as the nominal resting diameter of the enlarged eccentric abrading head 28S.

[065] It is understood that, as used herein, the word "eccentric" is defined and used herein to refer to either a difference in location between the geometric center of the enlarged abrading head 28S and the rotational axis 21 of the drive shaft 20, or to a difference in location between the center of mass of system 27 components exemplary enlarged abrading head 28S and/or eccentric abrading head 28A and the rotational axis 21 of the drive shaft 20. Either such difference, at the proper rotational speeds, will enable the system 27 components eccentric enlarged abrading head 28S, 28A to open a stenosis to a diameter substantially greater than the nominal diameter of the eccentric enlarged abrading head 28S, 28A. Moreover, for an eccentric enlarged abrading head 28S, 28A having a shape that is not a regular geometric shape, the concept of

"geometric center" can be approximated by locating the mid-point of the longest chord which is drawn through the rotational axis 21 of the drive shaft 28 and connects two points on a perimeter of a transverse cross-section taken at a position where the perimeter of the eccentric enlarged abrading head 28S, 28A has its maximum length.

[066] The abrading head 28S and/or 28A of the rotational atherectomy device of the invention may be constructed of stainless steel, tungsten or similar material. The abrading head 28 may be a single piece unitary construction or, alternatively, may be an assembly of two or more abrading head components fitted and fixed together to achieve the objects of the present invention.

[067] The extent to which a stenosis in an artery can be opened to a diameter larger than the nominal diameter of the eccentric enlarged abrading head of the present invention depends on several parameters, including the shape of the eccentric enlarged abrading head, the mass of the eccentric enlarged abrading head, the distribution of that mass and, therefore, the location of the center of mass within the abrading head with respect to the rotational axis of the drive shaft, and the speed of rotation.

[068] The speed of rotation is a significant factor in determining the centrifugal force with which the tissue removing surface of the enlarged abrading head is pressed against the stenotic tissue, thereby permitting the operator to control the rate of tissue removal. Control of the rotational speed also allows, to some extent, control over the maximum diameter to which the device will open a stenosis. Applicants have also found that the ability to reliably control the force with which the tissue removing surface is pressed against the stenotic tissue not only permits the operator to better control the rate of tissue removal but also provides better control of the size of the particles being removed.

[069] FIG. 9 illustrates the generally spiral orbital path taken by various embodiments of an exemplary system 27 eccentric abrading heads comprising 28S and/or 28A of the present invention, the abrading head 28 shown relative to the guide wire 15 over which the abrading head 28A and/or 28S has been advanced. The pitch of the spiral path in FIG. 9 is exaggerated for illustrative purposes-in reality, each spiral path of the system 27 comprising eccentric enlarged abrading heads 28A and/or 28S removes only a very thin layer of tissue via the tissue removing surface 37, and many, many such spiral passes are made by the system 27 as the device is repeatedly moved forward and backward across the stenosis to fully open the stenosis. FIG. 10 shows schematically three different rotational positions of the eccentric enlarged abrading head 28S and/or 28A of a rotational atherectomy device of the invention. At each position the abrasive surface of the eccentric enlarged abrading head 28S and/or 28A contacts the plaque "P" to be removed-the three positions are identified by three different points of contact with the plaque "P", those points being designated in the drawing as points B1 , B2, and B3. Notice that at each point it is generally the same portion of the abrasive surface of the eccentric enlarged abrading head 28S and/or 28A that contacts the tissue-the portion of the tissue removing surface 37 that is radially most distant from the rotational axis of the drive shaft.

[070] Although not wishing to be constrained to any particular theory of operation, applicants believe that offsetting the center of mass from the axis of rotation produces an "orbital" movement of the enlarged abrading head, the diameter of the "orbit" being controllable by varying, inter alia, the rotational speed of the drive shaft. Applicants have empirically demonstrated that by varying the rotational speed of the drive shaft one can control the centrifugal force urging the tissue removing surface of the eccentric enlarged abrading head 28S and/or 28A against the surface of the stenosis. The centrifugal force can be determined according to the formula:

[071] F _c =m Ax (π n/30) ²

[072] Where F _c is the centrifugal force, m is the mass of the eccentric enlarged abrading head, Δχ is the distance between the center of mass of the eccentric enlarged abrading head and the rotational axis of the drive shaft, and n is the rotational speed in revolutions per minute (rpm). Controlling this force F _c provides control over the rapidity with which tissue is removed, control over the maximum diameter to which the device will open a stenosis, and improved control over the particle size of the tissue being removed.

[073] The abrading head 28S and/or 28A of the present invention comprises more mass than prior art high speed atherectomy abrading devices. As a result, a larger orbit may be achieved during high speed rotation which, in turn, allows for use of a smaller abrading head than with prior art devices. In addition to allowing for the creation of pilot holes in completely or substantially blocked arteries and the like, using a smaller abrading head will allow for greater ease of access and less trauma during insertion,

[074] Operationally, using the rotational atherectomy device of the invention the eccentric enlarged abrading head 28S and/or 28A is repeatedly moved distally and proximally through the stenosis. By changing the rotational speed of the device he or she is able to control the force with which the tissue removal surface is pressed against the stenotic tissue, thereby being able to better control the speed of the plaque removal as well as the particle size of tissue removed. In addition, the successively increasing (from distal to proximal) resting diameters of the more than one eccentric abrading heads of the system 27 enables opening the stenosis to a diameter larger than the resting diameter of the enlarged eccentric abrading head, e.g., 28S and/or 28A. In addition, in the unbalanced embodiment described above wherein a spiral channel is formed around the eccentric abrading heads of system 27, the cooling solution and blood are able to constantly flow around the enlarged abrading heads. Such constant flow of blood and cooling solution constantly flushes away removed tissue particles down the spiral channel, thus providing uniform release of removed particles, once the abrading head has passed through the lesion once.

[075] The eccentric enlarged abrading head 28S and/or 28A may comprise a maximum cross-sectional diameter ranging between about 1.0 mm to about 3.0 mm. Thus, the eccentric enlarged abrading head may comprise cross-sectional diameters including, but not limited to: 1 .0 mm, 1 .25 mm, 1 .50 mm, 1 .75 mm, 2.0 mm, 2.25 mm, 2.50 mm, 2.75 mm, and 3.0 mm. Those skilled in the art will readily recognize that the incremental increases of 0.25 mm within the above-listing of cross-sectional diameter are exemplary only, the present invention is not limited by the exemplary listing and, as a result, other incremental increases in cross-sectional diameter are possible and within the scope of the present invention.

[076] Because, as described above, the eccentricity of the enlarged abrading head 28S and/or 28A is dependent on a number of parameters, applicants have found that the following design parameters may be considered regarding the distance between the rotational axis 21 of the drive shaft 20 and the geometric center of a face of a transverse cross-section, taken at a position of maximum cross-sectional diameter of the eccentric enlarged abrading head: for a device having an eccentric enlarged abrading head with a maximum cross-sectional diameter between about 1.0 mm and about 1 .5 mm, desirably the geometric center should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.02 mm, and preferably by a distance of at least about 0.035 mm; for a device having an eccentric enlarged abrading head with a maximum cross-sectional diameter between about 1.5 mm and about 1.75 mm, desirably the geometric center should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.05 mm, preferably by a distance of at least about 0.07 mm, and most preferably by a distance of at least about 0.09 mm; for a device having an eccentric enlarged abrading head with a maximum cross-sectional diameter between about 1.75 mm and about 2.0 mm, desirably the geometric center should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.1 mm, preferably by a distance of at least about 0.15 mm, and most preferably by a distance of at least about 0.2 mm; and for a device having an eccentric enlarged abrading head with a maximum cross-sectional diameter above 2.0 mm, desirably the geometric center should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.15 mm, preferably by a distance of at least about 0.25 mm, and most preferably by a distance of at least about 0.3 mm.

[077] Design parameters can also be based on the location of the center of mass. For a device having an eccentric enlarged abrading head 28S and/or 28A with a maximum cross-sectional diameter between about 1 .0 mm and about 1.5 mm, desirably the center of mass should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.013 mm, and preferably by a distance of at least about 0.02 mm; for a device having an eccentric enlarged abrading head 28S and/or 28A with a maximum cross-sectional diameter between about 1.5 mm and about 1.75 mm, desirably the center of mass should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.03 mm, and preferably by a distance of at least about 0.05 mm; for a device having an eccentric enlarged abrading head with a maximum cross- sectional diameter between about 1 .75 mm and about 2.0 mm, desirably the center of mass should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.06 mm, and preferably by a distance of at least about 0.1 mm; and for a device having an eccentric enlarged abrading head with a maximum cross-sectional diameter above 2.0 mm, desirably the center of mass should be spaced away from the rotational axis of the drive shaft by a distance of at least about 0.1 mm, and preferably by a distance of at least about 0.16 mm.

[078] Further this application may comprise at least one counterweight located on, and fixedly attached to, the drive shaft to stimulate orbital motion of an abrasive element, wherein the abrasive element may be either concentric or eccentric. One such at least one counterweight may be located proximal to the abrasive section, while another at least one counterweight may be located distal to the abrasive section. The at least one counterweight may further comprise abrasive thereon, thereby forming an at least one abrasive counterweight.

[079] Counterweight is defined herein as an element located on the drive shaft, either proximal or distal to an abrasive element which may be concentric, i.e., comprising a center of mass located on the rotational axis of the drive shaft or may alternatively be eccentric, i.e., comprising a center of mass radially offset from the rotational axis of the drive shaft. The counterweight(s) may also be eccentric or concentric. Thus, counterweight is further defined as comprising a center of mass that is radially offset from the positioning of the abrasive element's center of mass. A wide variety of possibilities will now readily present to the skilled artisan. In each case, there is an unbalanced system, wherein the location of the center of mass of at least one of the at least one counterweights is offset radially from the center of mass of the abrasive element. Counterweight is further defined in a system of an abrasive element with two or more counterweights wherein the distances between each counterweight and the abrasive element are not equal. Thus, even though the centers of mass for the abrasive element and the at least one counterweight may be located on the rotational axis of the drive shaft, a proximal counterweight located at distance D1 from the abrasive element and a distal counterweight located at distance D2 from the abrasive element, wherein D1 is greater than D2 will provide a counterweighing effect.

[080] Thus, FIGS. 1 1-17 are cross-section schematic drawings of a portion of a drive shaft 120 that includes an abrasive element 121 C, 121 E with an abrasive portion 122 on it, a proximal counterweight 123C, 123E and a distal counterweight 124C, 124E. The rotational axis 125 extends through the center of the drive shaft 120. For simplicity, the individual coils of the drive shaft 120 are not shown. The elements 121 C, 121 E, 123C, 123E, 124C and 124E are shown merely as circular in these figures, but it will be understood that any or all of the elements may be an abrasive burr, a mass of any geometry, and further including but not limited to a change in the size and/or shape of the drive shaft coils, or anything else that is distinguishable from the generally

featureless drive shaft 120. The centers of mass for each element in Figures 10 through 18 are marked with "x" and provided with further reference to the rotational axis 25 of the drive shaft 120 to provide illustration of the radial offset therefrom, if any.

[081] FIG. 1 1 illustrates an eccentric abrasive element 121 E, an eccentric proximal counterweight 123E and an eccentric distal counterweight 124E mounted on a rotational drive shaft 120. FIG. 12 shows an eccentric abrasive element 121 E, an eccentric proximal counterweight 123E and a concentric distal counterweight 124C. FIG. 13 shows an eccentric abrasive element 121 E, a concentric proximal counterweight 123C and an eccentric distal counterweight 124E. FIG. 14 shows an eccentric abrasive element 121 E, a concentric proximal counterweight 123C and a concentric distal counterweight 124C. FIG. 15 shows a concentric abrasive element 121 C, an eccentric proximal counterweight 123E and an eccentric distal counterweight 124E. FIG. 16 shows a concentric abrasive element 121 C, an eccentric proximal counterweight 123E and a concentric distal counterweight 124C. FIG. 17 shows a concentric abrasive element 121 C, a concentric proximal counterweight 123C and an eccentric distal counterweight 124E. FIG. 18 shows a concentric abrasive element 121 C, a concentric proximal counterweight 123C and a concentric distal counterweight 124C. [082] Note that Figures 1 1 -17 ail illustrate a proximal and a distal counterweight, it is understood that a single counterweight is also within the scope of the invention described herein, so long as the single counterweight comprises a located center of mass that is radially offset from the location of the center of mass of the associated abrasive element.

[083] FIG. 19 is a schematic drawing of the abrasive element 121 and counterweights 123 and 124, with a distance D1 between the centers of mass of proximal

counterweight 123 and abrasive element 121 , and a distance D2 between the centers of mass of distal counterweight 24 and abrasive element 121. In some cases, D1 equals D2. In other cases, D1 is different from D2. Note that D1 and D2 are shown in FIG. 18 as being the distances between the centers of mass of the various elements;

alternatively, D1 and D2 may denote the longitudinal distances along the rotational axis of the drive shaft.

[084] For example, one or both of the proximal and distal counterweights 100, 102 may comprise enlarged diameter sections of the drive shaft, formed in similar fashion as the enlarged eccentric diameter abrasive section 28A. In this application, the

counterweights 100, 102 are essentially hollow, enlarged wire turns of the drive shaft 20, formed by use of a mandrel during the wire turn winding process. In the case where only one, either the proximal 102 or the distal 100, counterweight is an enlarged eccentric diameter abrasive section of the drive shaft 20, the remaining counterweight may be either concentric, i.e., center of mass collinear with the drive shaft's axis of rotation and comprising an enlarged diameter section of the drive shaft, a solid crown or at least partially hollow crown, or may be eccentric and comprising a solid burr or an at least partially hollow crown or abrading head.

[085] Alternatively, one or both of the proximal and distal counterweights 100, 102 may be solid, as illustrated in FIG. 6 and attached to the wire turns of the drive shaft 20 by means well known to those skilled in the art. More alternatively, the proximal and distal counterweights may be at least partially hollow. [086] Still more alternatively, one or both of the at least one counterweights may comprise differential combination of materials, wherein one side of at least one of the counterweights 100, 102 comprises a more massive or denser material than the other side, which creates eccentricity as defined herein. As those skilled in the art will recognize, creation of eccentricity by differential use of materials within the at least one counterweights, a center of mass offset from the drive shaft's rotational axis, is applicable to any configuration of the counterweights whether concentric, eccentric, solid burr, partially hollow crown or abrading head or an enlarged section of the drive shaft, or the equivalent.

[087] Still further, in one application, the proximal and distal counterweights are substantially equivalent in overall mass, with each counterweight being roughly one half the overall mass of the abrasive element, wherein the proximal and distal

counterweights are equidistant from the abrasive section, wherein the proximal and distal counterweights comprise centers of mass that are equidistant from the axis of rotation of the drive shaft and wherein the proximal and distal counterweights comprise centers of mass are equidistant from the center of mass of the abrasive element.

Alternative and equivalent mass distributions between the abrasive element and the counterweight(s) for use in manipulating the orbital rotational diameter of the abrasive element during high-speed rotation will present themselves readily to those skilled in the art.

[088] Alternatively, one of the at least one counterweights may be eccentric, i.e., one configuration may comprise the counterweights (proximal and/or distal) having a center of mass spaced radially from the rotational axis of the drive shaft and aligned within the same longitudinal plane as the center of mass of an eccentric abrasive element. The radial spacing of the centers of mass of the counterweights may be achieved by spacing the geometric center of each counterweight away from the rotational axis of the drive shaft, wherein the proximal counterweight and the distal counterweight each have a center of mass separated from the abrasive element's center of mass by a rotational angle of 180 degrees. The centers of mass of the proximal and/or distal counterweight(s) discussed herein may either stimulate, i.e., increase the rotational diameter, or dampen, i.e., decrease the rotational diameter, the orbital motion of the abrasive element.

[089] Significantly, the present application may allow use of a smaller diameter abrasive element, in conjunction with proximal and/or distal counterweights while opening a lumen having a swept diameter equivalent to that of larger diameter abrasive element of the known references that do not comprise counterweights as described herein.

[090] Those skilled in the art will recognize any number of combinations and

permutations of these parameters for a given rotational speed of the drive shaft. The skilled artisan will recognize that modification of any of these parameters will either increase or decrease/dampen the diameter of the orbital path taken by the abrasive section. As such, the diameter of the orbital path may be customized for individual lumens.

[091] In one application wherein the abrasive section 28 is concentric, the proximal and distal counterweights 100, 102 are substantially equivalent in overall mass, with each counterweight 100, 102 being roughly one half the overall mass of the concentric abrasive section 28, wherein the proximal 102 and distal 00 counterweights are equidistant from the concentric abrasive section 100, wherein the proximal and distal centers of mass are equidistant from the axis of rotation of the drive shaft 20 and wherein the proximal and distal centers of mass are equidistant from the center of mass of the concentric abrasive section 28.

[092] The proximal and/or counterweight(s) may be concentric, i.e., spherical or ellipsoidal in profile or other concentric shape, with the counterweight(s) having a center of mass that is substantially on the axis of rotation of the drive shaft.

[093] Preferably in this application comprising a concentric abrasive element, the proximal and/or distal counterweights are eccentric, i.e., the proximal and/or distal counterweights may have a center of mass spaced radially from the rotational axis of the drive shaft as in e.g., Figure 15, wherein each counterweight comprises a center of mass offset within the same longitudinal plane and within the same longitudinal plane as the center of mass of the concentric abrasive section which is collinear with the axis of rotation. Moreover, the proximal and/or distal counterweights' centers of mass may both be either above the axis of rotation or below the axis of rotation of the drive shaft, while both centers of mass are aligned within the same longitudinal plane, creating an "offset" between the center of mass of the abrasive element and the centers of mass of the proximal and/or distal counterweights. The centers of mass of the proximal and/or distal counterweights may be offset 180 degrees, or other degree of offset as will be readily recognized by those skilled in the art, from each other around the axis of rotation of the drive shaft as may be seen by reference to Figure 4A.

[094] As with the eccentric abrasive section case, the concentric abrasive section case may achieve the radial spacing of the centers of mass of the eccentric case of the proximal and/or counterweights by spacing the geometric center of each counterweight away from the rotational axis of the drive shaft, wherein the proximal counterweight and the distal counterweight each have a center of mass separated from the concentric abrasive section's center of mass and within the same longitudinal plane. This counterweighting case stimulates orbital motion by the abrasive element and facilitates the ability of the abrasive element to sweep and open the stenotic lesion to a diameter substantially larger than the outer diameter of the resting concentric abrasive element. As above, the present application may allow use of a smaller diameter abrasive element, in conjunction with proximal and/or counterweights, while opening a lumen having a swept diameter equivalent to that of larger diameter concentric abrasive element of the known references.

[095] It should be understood that, as used herein, the word "eccentric" is defined herein to mean either a difference in location between the geometric center of the abrasive element comprising eccentric enlarged diameter section of the drive shaft, or an eccentric solid burr, or an eccentric at least partially hollow crown or abrading head, or the eccentric counterweight(s) and the rotational axis of the drive shaft, or to a difference in location between the center of mass of the eccentric abrasive element comprising an eccentric enlarged diameter section, an eccentric solid burr, and eccentric and at least partially hollow crown or abrading head 28C, or the proximal and/or distal eccentric counterweights and the rotational axis of the drive shaft. Either such difference, at the proper rotational speeds, will enable the abrasive element to open a stenosis to a diameter substantially greater than the nominal diameter of the abrasive element. Moreover, for an eccentric abrasive element having a shape that is not a regular geometric shape, the concept of "geometric center" can be approximated by locating the mid-point of the longest chord which is drawn through the rotational axis of the drive shaft and connects two points on a perimeter of a transverse cross-section taken at a position where the perimeter of the eccentric enlarged diameter section has its maximum length. Moreover, those skilled in the art will recognize that eccentricity as defined may be designed into an abrasive element having a substantially concentric profile, but with one aspect of the profile being more massive than the rest by, e.g., hollowing out a portion of one side of the abrasive element.

[096] Moreover, it should also be understood that concentric as used herein, is defined to mean an abrasive element and/or proximal and/or distal counterweight(s) that comprises a center of mass that is on, i.e., collinear with, the axis of rotation of the drive shaft and a profile that is substantially symmetrical as shown in Figure 18.

[097] As used herein, the term "element" may be used to denote any feature along the drive shaft, such as an abrasive burr, a mass, a weight, a counterweight, a change in the size and/or shape of the drive shaft coils, or anything else that is distinguishable from the generally featureless drive shaft.

[098] In general, the drive shaft may include at least one helically-wound coil that surrounds the guide wire, so that the guide wire may be translated longitudinally with respect to the drive shaft. In other words, the guide wire may be advanced and retracted longitudinally with respect to the drive shaft, and/or the drive shaft may be advanced and retracted longitudinally with respect to the guide wire. This advancing and/or retracting may be performed at any suitable time before, during and/or after the stenosis is removed.

[099] When the atherectomy device includes only a single element, such as a single abrasive burr, or a single portion of the drive shaft that has enlarged coils, there may be instability during operation. For instance, when the single element is rotated rapidly around the rotational axis of the drive shaft, the single element may be deflected rather easily, leading to an irregular orbital motion of the element, and possible damage to the inside of the vessel being cleaned.

[0100] In order to increase stability, one may be tempted to merely increase the mass of the single element. This increased mass may provide an increased resistance to deflection, but if the element is eccentric (having its center of mass laterally displaced from the rotational axis of the drive shaft), then the increase in mass may reduce the stability of the orbital motion itself, simply by having too much mass too far off axis. This increase in eccentric mass may lead to damage of the drive shaft and/or the guide wire at high rotational velocities.

[0101] An improvement over simply increasing the mass of a single element is to provide one or more counterweights to the element, longitudinally separated from the element along the drive shaft. Taken as a whole, the increase in mass does increase stability during operation, but having the mass increased at locations proximally and/or distally, with respect to the single element, may increase the stability without

deteriorating the orbital motion of the single element.

[0102] In some cases, the increase in mass may be a proximal counterweight and a distal counterweight, which are disposed longitudinally along the drive shaft on either side of an abrasive element. The following paragraphs describe various configurations for these counterweights. [0103] In some cases, the abrasive element may be located halfway between the proximal and distal counterweights. In other applications, the abrasive element may be closer to one counterweight than to the other.

[0104] In some cases, the proximal and distal counterweights may have equal masses. In some cases, the proximal and distal counterweights may both have masses equal to half that of the abrasive element. In some cases, the proximal and distal counterweights may both have masses equal to half that of the abrasive element, and the abrasive element may be longitudinally located halfway between the counterweights.

[0105] in some cases, the abrasive element may be eccentric. In some cases, the abrasive element may be eccentric, with both counterweights being eccentric. In other applications, the abrasive element may be eccentric, with one counterweight being eccentric and the other counterweight being concentric. In some of these applications, the counterweights and abrasive element may have a combined center of mass that is coincident with the rotational axis of the drive shaft. In other of these applications, the counterweights and abrasive element may have a combined center of mass that is laterally displaced from the rotational axis of the drive shaft.

[0106] In some cases, the abrasive element may be concentric. In some cases, the abrasive element may be concentric, with both counterweights being concentric. In other applications, the abrasive element may be concentric, with both counterweights being concentric but on opposite sides of the drive shaft so that their combined center of mass is generally coincident with the rotational axis of the drive shaft. In still other applications, the abrasive element may be concentric, with both counterweights being concentric but on the same side of the drive shaft so that their combined center of mass is generally laterally displaced away from the rotational axis of the drive shaft.

[0107] In some cases, there may be more than one proximal counterweight, and/or more than one distal counterweight. In some cases, adjacent counterweights may be eccentric, with lateral displacements being on opposite sides of the drive shaft from each other so that their combined center of mass is roughly coincident with the rotational axis of the drive shaft.

[0108] In some cases, at least one counterweight may be generally round in shape, with a generally smooth exterior surface. This may help reduce any unwanted damage to the inside of the vessel during use.

[0109] In some cases, the guide wire may remain extended throughout the interior of the drive shaft during use, and may even extend out to the distal end of the drive shaft or beyond. This may increase the stability of the overall atherectomy device, because the local stiffness of the guide wire may be greater than that of the drive shaft, but may reduce the amplitude of the orbital motion of any eccentric elements on the drive shaft. However, the guide wire may experience unwanted flexional stress under these conditions.

[0110] In other applications, the guide wire may be partially or fully retracted from the distal end of the drive shaft prior to (or during) use. Without the locally stiff guide wire inside, the drive shaft is free to flex more as it is rotated under the influence of centrifugal force, compared with when the guide wire remains inside. As a result, for a given rotational speed and element size, an eccentric element without a guide wire therethrough may extend farther away from the rotational axis during high speed rotation and may therefore produce a desirably larger cutting diameter. Depending on the stiffnesses, flexions and/or flexibility of the materials involved, this increase in cutting diameter may be up to a factor of four or more.

[0111]This retraction of the guide wire may be advantageous in several ways. For instance, if one of the design goals is to achieve a particular cutting diameter for a given rotation speed, then the rest diameter of the eccentric abrasive element may be reduced if the guide wire is retracted, compared to when the guide wire is left extended throughout the drive shaft during use. In other words, a smaller abrasive element may achieve the desired cutting diameter if the guide wire is retracted prior to (or during) use, all other things being equal. Having a smaller abrasive element may be advantageous in that it may be easier to feed such a smaller element through the vasculature of the patient, in that it is less easily blocked, is more easily maneuvered, and may cause less incidental damage to the inside of the vessel before and after use.

[0112] In addition, the guide wire, being retracted, will experience less flexional stress and therefore may be less susceptible to breakage, thereby further reducing the risk of damage to the inside of the vessel being cleaned.

[0113] In some cases, the guide wire extends to the distal end, or beyond the distal end, of the drive shaft during use. In some cases, the guide wire may be retracted to the distal counterweight prior to, or during, use. In some cases, the guide wire may be retracted to the abrasive element prior to, or during, use. In some cases, the guide wire may be retracted to the proximal counterweight prior to, or during, use. In some cases, the guide wire may be retracted beyond the proximal counterweight prior to, or during, use.

[0114] The present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present specification.