WO2002049518A2

WO2002049518A2 - Atherectomy burr with micro-engineered cutting surfaces

Info

Publication number: WO2002049518A2
Application number: PCT/US2001/043497
Authority: WO
Inventors: Thomas D. Kadavy; Eric W. Baker
Original assignee: Scimed Life Systems, Inc.
Priority date: 2000-12-18
Filing date: 2001-11-14
Publication date: 2002-06-27
Also published as: WO2002049518A3; AU2002225680A1

Abstract

A burr (100) for rotational ablation atherectomy devices having micro-engineered cutting features. The burr includes a plurality of stacked cutting disks (120) that are attached to a back support element (110). The back support element is rotationally coupled to a drive shaft (22) of the atherectomy device. The stacked cutting disks include a keyed center hole, and a plurality of outwardly-oriented cutting teeth. The cutting disks (120) are varying outer diameter and are arranged to produce the desired burr shape. In one embodiment, a center mandrel (130) having a body portion slidably engages the keyed center holes of the stack of cutting disks, and connects to the back portion (110), thereby locking the cutting disks in place. In one disclosed embodiment, spacing disks are inserted between pairs of adjacent cutting disks (120). The spacing disks have a diameter less than the diameter of the adjacent cutting disks, thereby cooperatively with the adjacent cutting disks forming a circumferential channel in the burr. It is empasized that this abstract is intended to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope of meaning of the claims pursuant to 37 C.F. R. 1 72 (b).

Description

ATHERECTOMY BURR WITH MICRO-ENGINEERED CUTTING SURFACE

Field of the Invention The present invention relates to medical devices in general and, in particular, to atherectomy devices for removing occluding material from a patient's vessels.

Background of the Invention

A number of vascular diseases, such as arteriosclerosis, are characterized by the buildup of deposits (atheromas) or growths in the intimal layer of a patient's blood vessels. Such occlusions in a person's vascular system can impede the flow of blood to the effected portion of the person's body. If the occlusion is not removed or otherwise ameliorated, enlargement of the occlusion can result in the complete stoppage of blood flow to the effected region. This can be particularly serious if the, of course, if the occlusion occurs in a portion of the vasculature that supplies vital organs with blood or other necessary fluids. To treat such diseases, many invasive and noninvasive techniques and therapies have been developed. For example, cardiac bypass, surgery is now a commonly performed procedure whereby an occluded cardiac artery is bypassed with a segment of a healthy blood vessel that is obtained from elsewhere in the body. While this procedure is generally successful, it is traumatic to the patient because the entire chest cavity must be opened to access the site of the occluded vessel. Because of the trauma and substantial risks associated with cardiac bypass surgery, the procedure may not be a viable option for certain patients, particularly for elderly or relatively frail patients.

As an alternative to cardiac bypass surgery, numerous atherectomy (atheroma removal) devices have been developed for removing such deposits in a less invasive manner. One such device that is particularly suited to removing calcified atherosclerotic plaque is an ablative rotational atherectomy device, such as that disclosed in U.S. Patents No. 4,990,134 and 5,314,407, both to Auth. Auth teaches using a small burr covered, or partially covered, with an abrasive cutting material, such as diamond grit. The burr is attached to the distal end of a flexible, rotatable drive shaft that can be slidably inserted over a guide wire that is inserted through the vasculature of a patient to the site of an occlusion. A rotational atherectomy device practicing the Auth invention is sold by the assignee of the present invention under the trademark Rotablator® and is described below.

Refer now to FIGURE 1, depicting the Rotablator® ablative rotational atherectomy device 10. This prior art device utilizes a guide wire 26 that is inserted through the patient's vasculature approximately to the location of the deposit that is to be treated. A hollow, flexible drive shaft 22 having an ablative burr 24 at its distal end is then inserted over the guide wire 26, and advanced to a location just proximal to the deposit. The drive shaft 22 is covered with a lumen or catheter 20 along most of its length to minimize the impact to surrounding tissue when the drive shaft 22 is rotatably engaged. The drive shaft 22 is connected to a compressed-air driven drive assembly 16 having a turbine (not shown) that can rotate the drive shaft 22 at relatively high rotational speeds. The drive assembly 16 is slidably mounted in an advancer housing 12 on a track, allowing a surgeon using the Rotablator® device 10 to move the drive assembly 16 transversely, and hence move the drive shaft 22 and burr 24 forward and backward to impact and ablate the atheroma.

The ablative surface on conventional prior art atherectomy burrs are created by embedding, or otherwise affixing, abrasive particles, such as fine diamond particles, onto a portion of the surface of a burr body. Although this technique successfully produces an ablative surface, the cutting edges of the ablative surface (i.e., the abrasive particle edges) are randomly oriented on the surface, and have varying sizes and shapes. More precise control of the size, shape, and orientation of the cutting elements on an atherectomy burr would permit the burr to be engineered to improve cutting efficiency. Moreover, micro- engineering the burr geometry would permit the burr to be tailored for specific applications. There is a need for a rotational atherectomy burr with a cutting or ablative surface that is precisely engineered and manufactured.

Summary of the Invention The present invention provides an atherectomy burr for rotational ablation atherectomy procedures have a cutting surface that is micro-machined to produce improved cutting properties.

In a preferred embodiment, a back or proximal portion of the burr is fixedly attachable to the flexible drive shaft and is adapted to receive a locking mandrel. A plurality of stacked, axially aligned, cutting disks are coupled to the back portion, each cutting disk having a keyed center hole and a plurality of teeth extending radially outward therefrom. A mandrel couples the stacked cutting disks to the back portion, the mandrel adapted to extend through the keyed center holes in the cutting disks, and slidably engage the back portion.

In an aspect of the present invention, the cutting disks have different outer diameters, and are arranged on the stack to produce the desired burr shape.

In a second preferred embodiment, a plurality of spacing disks is inserted between at least some of the cutting disks. In an aspect of the second embodiment, the spacing disks have a diameter that is less than adjacent cutting disks, such that the spacing disk, cooperatively with adjacent cutting disks, forms a circumferential channel in the burr.

Brief Description of the Drawings The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a perspective view of the prior art Rotablator® rotational atherectomy device described above; FIGURE 2 is a side view of a first embodiment of an atherectomy burr according to the present invention;

FIGURE 3 is a side cross-sectional view of the atherectomy burr shown in FIGURE 2.

FIGURE 4 is a partially exploded view of the atherectomy burr shown in FIGURE 2.

FIGURE 5 is a side view of a second embodiment of an atherectomy burr according to the present invention;

FIGURE 6 is a front view of a spacer portion of the atherectomy burr shown in FIGURE 4. FIGURE 7 is a front view of a cutter plate portion of an atherectomy burr according to the present invention, showing an alternative keyed center hole. FIGURE 8 is a fractional close-up view of the cutter teeth of the cutter plate shown in FIGURE 7.

FIGURE 9 is a fractional close-up view of an alternative configuration for the cutter teeth for the cutter plate shown in FIGURE 7.

Detailed Description of the Preferred Embodiment The contents of U.S. Patent No. 6,015,420, entitled Atherectomy Device for Reducing Damage to Vessels and/or In- Vivo Stents, which issued to Wulfman et al. and is assigned to the assignee of the present application, is hereby incoiporated by reference. The present invention relates to atherectomy burrs suitable for use in rotational atherectomy devices such as prior art the Rotablator® device illustrated in FIGURE 1 and described above. FIGURE 2 shows a side view of a first preferred embodiment of an atherectomy burr in accordance with the present invention. The atherectomy burr 100 is shown attached to a flexible drive shaft 22, and having a guide wire 26 passing therethrough.

The atherectomy burr 100 includes a half-ovoid back or proximal portion 110 having a first end 112 fixedly attached to the flexible drive shaft 22, and a larger diameter second end 114. As seen most clearly in FIGURE 3, which shows a side cross-sectional view of atherectomy burr 100, the back portion 110 includes a first recess 113 at the first end 112 that is adapted to receive an end of the flexible drive shaft 22. The back portion 110 is fixed, or rotatably coupled, to the flexible drive shaft 22, for example, by a press fit, a screw-on coupling, chemical bonding, welding, or any other suitable coupling method, as are well known in the art. Similarly, a second recess 115 is provided at the second end 114 of the back portion 110, generally coaxial with the first recess 113. The first recess 113 and second recess 115 are joined with a small axial hole 111 thereby cooperatively with the first and second recess 113, 115 providing an axial channel that is sized to slidably receive a guide wire 26. The second recess 115 is preferably keyed, i.e., non-circular, to match center holes 124 in the cutting disks 120, discussed below.

As seen most clearly in the exploded view shown in FIGURE 4, a plurality of thin cutting disks 120 are provided, generally coaxially oriented with the back portion 110 and stacked adjacent the second end 114 thereof. In this first preferred embodiment, the plurality of cutting disks 120 are disposed in a coaxially aligned, stacked configuration. The cutting disks 120 are of varying diameter, and preferably arranged in order of decreasing diameter such that the stacked cutting disks 120 collectively form a forward buιτ body having a desired outer profile. The individual cutting disks 120 are generally circular in shape, with outwardly-disposed serrations, or cutting teeth 122. One possible embodiment for a cutting disk 120 is shown in FIGURE 7. A keyed, i.e., non-circular, center hole 124 is provided in each disk 120.

The plurality of cutting disks 120 is coupled to the burr back portion 110 with a mandrel 130 having an elongate, tubular body portion 132, and a larger diameter head portion 134 at its distal end. The tubular body portion 132 is shaped to be slidably inserted through the center holes 124 of the cutting disks 120 and into the second recess 115 of the back portion 110. In the preferred embodiment, the proximal end 136 of the mandrel 130 is adapted to tightly engage the second recess 115 of the back portion 110, forming a friction, or press, fit. The length of the tubular body portion 132 is selected such that the plurality of disks 120 is held tightly together when the mandrel 130 is fully inserted into the back portion 110. The mandrel 130 includes an axial passage therethrough 121, providing a channel for the guide wire 26. It is contemplated that the head portion 134 of the mandrel may be provided with an abrasive forward surface, for example, by affixing abrasive particles such as diamond grit to the surface. The abrasive forward surface may facilitate pushing the burr 100 through deposits, particularly in situations wherein the deposit is occluding a significant portion of the vessel cross- section.

In one embodiment of the invention the cutting teeth 122 on the cutting disk 120 (as shown in FIGURE 8) are generally triangular, and disposed adjacent each other around the perimeter of the cutting disk 120. However, other cutting tooth shapes are possible, and contemplated by this invention. For example, the teeth may be curved with the point disposed tangentially, to reduce irritation of healthy tissue near the treated occlusion. Also, circumferential spacing may be provided between the teeth, as depicted in FIGURE 9, thereby reducing the number of cutting edges. A reduced number of cutting teeth may lessen any tendency of the cutting disks to become clogged with foreign matter. It is contemplated that the precise shape and spacing of the teeth may be engineered to optimize the burr to specific applications. For example, the optimal tooth geometry for removing hardened deposits within a stent may be significantly different from the optimal tooth geometry for removing softer occlusions, or occlusions in an non- stented vessel.

Further flexibility in the burr design may be realized by varying the geometry of the cutting disks on a single burr, for example, placing more closely spaced teeth on the smaller cutting disks, and more widely spaced teeth an the larger cutting disks, thereby keeping the number of teeth approximately constant along the length of the burr. Similarly, the keyed center hole 124 of the cutting disks 120 may be oriented to produce a desired alignment between the cutting teeth 122 of adjacent cutting disks 120. For example, by properly orienting the center holes 124, the cutting teeth 122 of adjacent disks 120 can be staggered, to increase the cutting efficiency of the burr. It will be appreciated that an advantage of the present invention is that the same overall bun^* design can be used to produce burrs with much different cutting characteristics by simply modifying the specific shape of the cutting disks.

The cutting disks may be made from any suitably hard and machinable (or appropriately manufacturable) material, such as stainless steel. A number of manufacturing methods well known in the art may be used to produce the toothed cutting disks 120. For example, the photo-etching techniques, or injection molding from a mold made from a mask-and-etch construction processes may be used to produce the very small cutting disks 120. By way of another non-limiting example, a micro electro- discharge machining method may be employed. Micro electro-discharge machining (EDM) is a material removal method for conductive materials that is well known in the art, and in general employs an electrode that is used to melt a section of the work opposite that electrode tool by sparking between the work piece and the electrode.

It is also contemplated that the cutting disk 120 may be provided with a coating to improve the performance of the atherectomy burr 100. For example, a diamond or diamond-like carbon coating may be applied to increase the hardness of the surface of the cutting disks 120. In the disclosed embodiments, the individual cutting disks 120 are preferably between 0.0002 - 0.005 inch thick, and more preferably between 0.0005 - 0.001 inch thick. However, the optimal thickness of the cutting disks will depend on the specific material that is used, and thinner or thicker disks could also be used. The thickness of the cutting disks should be selected to be able to withstand the forces imposed on the burr during the atherectomy procedure without destroying the cutting disks, while being thin enough to produce a burr with the desired shape and cutting properties.

A related alternate embodiment also contemplated by this invention includes a mandrel that engages the flexible drive shaft 22 directly, thereby obviating the need for a back portion 110 that is coupled to the drive shaft 22. For example, a mandrel, substantially similar to the mandrel 130 shown in FIGURE 2, with a proximal end adapted to couple directly to the drive shaft 22, extends through the cutting disks 120 to the flexible drive shaft 22. The mandrel may be insertable into, or fit around, the drive shaft 22, or otherwise couple directly to the drive, for example by screwing onto a suitably adapted drive shaft. In this alternate embodiment the rear portion of the burr may be omitted, or may comprise one or more disks, such as toothed disks similar to the cutting disks 120. Conversely, if an generally half-ovoid rear portion is retained, the rear portion need not be rotatably coupled directly to the drive shaft 22.

In a second preferred embodiment of an atherectomy burr 150 in accordance with the present invention, as shown in FIGURE 5, the individual cutting disks 120 are spaced apart using spacing disks 140 disposed between the cutting disks 120. In one embodiment, the spacing disks 140 are smaller in diameter than adjacent cutting disks 120 and therefore do not interfere with the cutting function of the cutting disks. The spacing disks 140 cooperate with the cutting disks 120 to form a channel between pairs of cutting disks 120. These channels provide a flow path for fluids and other particulate debris that are generated during the atherectomy procedure, thereby reducing the tendency for the burr to become clogged with foreign matter. The disks may also establish a desired cutting depth for the cutting disks 120. In a preferred embodiment, as shown in FIGURE 6, the spacing disks 140 are generally circular, with a keyed center hole 144 matching the keyed center holes 124 of the cutting disks 120. The spacing disks may be made from any suitable material, including for example, stainless steel. It is also contemplated that the spacing disks might have a diameter equal to the diameter of adjacent cutting disks, or even a slightly greater diameter, thereby limiting the cutting aggressiveness of the cutting disks. It will be appreciated that although the invention is described with reference to presently preferred embodiments, many variations to the disclosed embodiments are also contemplated by this invention. For example, although the preferred embodiments utilize a central mandrel that is slidably inserted through keyed holes in the cutting disks, the cutting plates could be attached to the back portion by other means. For example, one or more aligned, non-centered holes could be provided in the cutting disks, and a pin inserted through the cutting disks to engage the back portion, thereby holding the disks in the desired position in a manner similar to the disclosed mandrel. Alternatively, the cutting disks might be bonded or welded together to form the desired burr shape without a mandrel. Similarly, the cutting disks may be produced with surface locking features, such as ridges and grooves that prevent relative rotation between the disks maintaining them in the desired orientation. It is also contemplated that the cutting disks might be produced in integral sets, rather than individually. That is, a single piece of material could be machined or otherwise produced in the shape of a plurality of stacked cutting disks. Similarly, in an embodiment wherein the cutting disks are axially spaced, a cutting disk and spacer disk may be manufactured as an integral piece. While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that other 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 thereof.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An atherectomy bun- adapted to be rotationally coupled to a flexible drive shaft, the atherectomy burr comprising: a plurality of stacked, axially aligned, cutting disks, each cutting disk having a keyed center hole and a plurality of cutting teeth; a mandrel having a first end that is larger than the keyed center holes in the cutting disks, a cylindrical body insertable through and engaging the keyed center holes of the cutting disks, and a second end; and a back portion fixedly attachable to the flexible drive shaft and adapted to receive the second end of the mandrel.

2. The atherectomy burr of Claim 1 further comprising at least one spacer disk disposed between two adjacent cutting disks, the spacer disk having a smaller diameter than the adjacent cutting disks whereby the spacer disk cooperatively with the adjacent cutting disks forms a circumferential channel in the burr.

3. The atherectomy burr of Claim 1, wherein the cutting disks are made from a hard metal.

4. The atherectomy burr of Claim 1, wherein the cutting disks are made from stainless steel.

5. The atherectomy burr of Claim 1, wherein the cutting disks have varying maximum diameters wherein the cutting disks are arranged on the mandrel to produce a desired burr shape.

6. The atherectomy burr of Claim 1, wherein the cutting disks have varying maximum diameters and the plurality of teeth on each cutting disks are variably spaced such that each cutting disk has the same number of teeth.

7. The atherectomy burr of Claim 1, wherein the plurality of teeth on each cutting disk are generally triangular in shape.

8. The atherectomy burr of Claim 1, wherein the cutting disks are coated with a diamond-like carbon coating.

9. An atherectomy burr comprising: a disk support; a plurality of stacked cutting disks adapted to be attached to the disk support; and means for coupling the plurality of cutting disks to the disk support whereby rotation of the back support will cause rotation of the plurality of cutting disks.

10. The atherectomy burr of Claim 9 further comprising at least one spacer disk disposed between two adjacent cutting disks.

11. The atherectomy burr of Claim 10 wherein the spacer disk has a smaller diameter than the adjacent cutting disks whereby the spacer disk cooperatively with the adjacent cutting disks forms a circumferential channel in the burr.

12. The atherectomy device of Claim 10 wherein the cutting disks and the spacer disks are made from a hard metal.

13. An atherectomy device for removing an occlusion in a patient's blood vessel, comprising: a flexible drive shaft; and a burr having a plurality of stacked, axially aligned, cutting disks, each cutting disk having a keyed center hole and a plurality of teeth extending radially therefrom, and a mandrel having an elongate body adapted to slidably receive the cutting disks, a first end adapted to retain the cutting disks and a second end that can be coupled to the flexible drive shaft.

14. The atherectomy device of Claim 13 further comprising at least one spacer disk disposed between two adjacent cutting disks, the spacer disk having a diameter not greater than the adjacent cutting disks.

15. An atherectomy burr having selectable cutting properties, the burr comprising a plurality of thin cutting disks, each cutting disk having a plurality of outwardly-extending teeth, the cutting disks being disposed in axial alignment and retained by an elongate member, wherein the selectable cutting properties are controlled by the selection of the size, shape and spacing of the outwardly-extending teeth.

16. The atherectomy burr of Claim 15 further comprising a plurality of spacer disks, each spacer disk disposed between adjacent cutting disks.

17. The atherectomy burr of Claim 15 wherein the cutting disks comprise a fist set of cutting disks having less aggressive cutting properties and a second set of cutting disks having more aggressive cutting properties.

18. The atherectomy burr of Claim 17 wherein the first set of cutting disks is disposed forwardly of the second set of cutting disks.

19. The atherectomy burr of Claim 17 wherein the cutting disks further comprise one or more additional sets of cutting disks having intermediately aggressive cutting properties.

20. A method for performing an atherectomy procedure, the method comprising: advancing a guide wire through a patients vasculature to the site of an occlusion; advancing an atherectomy burr that is coupled to a flexible drive shaft over the guide wire to the site of the occlusion, the atherectomy burr of the type having a disk support that is adapted to be axially connectable to the drive shaft, a plurality of stacked cutting disks having a toothed outer diameter and a keyed center hole, and a mandrel disposed through the keyed center holes of the cutting disks and coupled to the disk support; and rotating the atherectomy burr while transversely moving the burr through the site of the occlusion such that at least of portion of the occlusion is removed.

21. The method of Claim 20 wherein the atherectomy burr disk support comprises a half-ovoid back portion.