Atherectomy cutter with a positive attack angle

Abstract: A rotatable atherectomy cutter (10) is provided with a body (26) and a pair of blade elements (28a,b). The blade elements are mounted on the periphery of the body and extend distally therefrom in a linearly convergent manner. Each blade element has a flat planar outer face (46a) with two linear longitudinally-exposed edges (50,52), one of which is defined as the cutting edge and the other of which is defined as the trailing edge. The cutting and trailing edges are positioned at a maximum radial distance from the axis relative to the remainder of the blade element to define the outermost rotation surface of the blade element. Accordingly, contact between the blade element and the stenosis is limited to the edges during rotational operation of the cutter, while a clearance is maintained between the stenosis and the outer face. The clearance defines a positive attack angle that enables the cutting edge to more effectively cut away the plaque of the stenosis.

Description: FIELD OF THE INVENTION The present invention relates generally to devices which remove stenoses from blood vessels. More particularly, the present invention relates to atherectomy devices. The present invention particularly, though not exclusively, relates to cutters for atherectomy devices which cut a bore through atherosclerotic plaque. BACKGROUND OF THE INVENTION Blockage of human arteries is a widespread malady and, as such, represents a significant health concern. Blockages reducing blood flow through the coronary arteries to the heart can cause heart attacks, while blockages reducing blood flow through the arteries to the brain can cause strokes. Similarly, arterial blockages reducing blood flow through arteries to other parts of the body can produce grave consequences in an affected organ or limb. The build-up of atherosclerotic plaque is a chief cause of blockages reducing arterial blood flow. Consequently, several methods have been introduced to alleviate the effects of plaque build-up restricing the arterial lumen. One such method is a procedure termed angioplasty, which uses an inflatable device positioned in the artery to dilate the lumen at the stenosis. A typical angioplasty device is disclosed in U.S. Patent No. 4,896,669 to Bhate et al. The angioplasty device of Bhate et al includes an inflatable balloon which is attached to the distal end of a hollow catheter. The proximal end of the catheter is attached to a fluid source, providing fluid communication between the balloon and the fluid source. To treat an arterial stenosis, the Bhate et al balloon is introduced into the artery in a deflated state and guided through the artery over a guide wire to a position adjacent the stenosis. Fluid from the fluid source is then infused into the balloon via the catheter to inflate the balloon. As the balloon expands, it dilates the lumen of the artery. The balloon is then deflated and removed from the artery. While effective for dilating the lumen at the stenosis, angioplasty devices such as the Bhate et al device do not remove the plaque from the artery. Consequently, the residual plaque fragments either remain in place at the point of the stenosis or break off and migrate to other locations in the blood stream. In either case the plaque remains a continuing threat to create blockages in the circulatory system. To address the shortcomings of angioplasty, a procedure termed atherectomy has been devised which cuts a stenosis and removes the plaque fragments comprising the stenosis from the blood vessel. An atherectomy procedure typically includes inserting a guide wire into the affected artery and advancing a hollow cutting device over the wire until the cutting device is positioned adjacent the stenosis. The cutting device is then advanced into the stenosis to cut a channel through the plaque, thereby increasing blood flow through the artery. The resulting plaque fragments are removed from the blood stream by drawing them into the hollow cutting device. A number of atherectomy devices capable of performing this procedure are known in the art. U.S. Patent No. 4,887,613 to Farr et al, which is assigned to the same assignee as the present invention and is incorporated herein by reference, discloses an atherectomy device having a frustum-shaped cutter which is attached to the distal end of a hollow catheter. The cutter has a plurality of openings that define cutting blades. The cutter is directed through the artery and rotated as it advances into the stenosis, thereby cutting the plaque. Excised plaque enters the openings of the cutter and is subsequently removed through the hollow catheter. While the Farr et al device is at least somewhat effective for its intended purpose, due to the configuration of the cutter blades, the orientation of the blades relative to the surface of the plaque being cut is less than optimal. This encumbers the cutting procedure and may result in unacceptable amounts of plaque remaining in the artery which can ultimately lead to a restenosis of the affected artery. Accordingly, the present invention recognizes a need to provide an atherectomy device which more effectively cuts a smooth channel through a stenosis than known devices. It is therefore an object of the present invention to provide an atherectomy cutter that can cut a channel through a stenosis in an artery of a living being. Another object of the present invention is to provide an atherectomy cutter that cuts a relatively smooth and wide channel through the arterial stenosis. Yet another object of the present invention is to provide an atherectomy cutter that minimizes the residual plaque remaining in the artery as the channel is cut. Finally, it is an object of the present invention to provide an atherectomy cutter which is relatively easy to use and cost-effective to manufacture. The present invention is defined in the accompanying claims with the features known from EP-A-348573 in the precharacterising portion. intersect at the longitudinal axis of the cutter. The blade elements are fixably connected to one another at their point of intersection to define a hub. The hub has an opening extending through it which enables positioning of the cutter on a guide wire. Each blade element of the cutter is a relatively rigid band having an outer face that is characterized as a flat planar surface facing away from the longitudinal axis of the cutter. The outer face has two linear and substantially longitudinal edges, extending between the proximal and distal ends of the blade element. One edge defines the cutting edge of the blade element and the other defines the trailing edge. As the blade element is rotated about the longitudinal axis of the cutter, the leading edge is termed the cutting edge while the edge following the cutting edge in the direction of rotation is termed the trailing edge. According to one embodiment of the cutter, the outer face of the blade element is oriented relative to the longitudinal axis of the cutter such that, for any given point on the axis, the radial distance from the axis to the cutting edge and the radial distance from the axis to the trailing edge are substantially equal. Further, the outer face is oriented such that the radial distance from the axis to the cutting or trailing edge is greater than the radial distance from the axis to any other longitudinally corresponding point lying on the outer face of the blade element. Stated differently, rotationally sweeping the cutting and trailing edges of the blade element about the longitudinal axis of the cutter defines a continuous frustum-shaped cutting surface which is the maximum or outermost rotation surface of the blade element. According to another embodiment of the cutter, the blade element of the previous embodiment is reoriented by rotating it slightly about its own longitudinal axis to a new position relative to the longitudinal axis of the cutter. As a result, for any given point on the longitudinal axis of the cutter, there is only one maximum radial point on the outer face of the blade element and this point lies on the cutting edge. The trailing edge, in distinction contains the minimum radial point on the outer face. Thus, the cutting edge exclusively defines the outermost rotation surface of the blade element. According to either embodiment of the cutter described above, the proximal end of the cutter is attachable to the distal end of a hollow catheter. By engaging a rotational drive motor with the proximal end of the catheter, the catheter can be rotated. As is apparent, rotation of the catheter is translated into rotation of the cutter. Coupling of the cutter and associated catheter also provides a continuous passageway for cuttings in a proximal direction away from the blade elements. The cutter of the present invention is operated by positioning it on the distal end of the catheter and inserting it through the skin of a patient into a stenotic artery to be treated. The cutter is guided through the artery, typically along a guide wire previously inserted into the artery, to the stenosis. The cutter is then urged into the stenosis while rotating the catheter and cutter. The rotating cutter is driven through the entire stenosis, cutting a smooth wide channel therethrough which preferably extends to the artery wall. Because of the blade element configurations described above, contact between the blade elements and the plaque making up the stenosis is primarily limited to those portions of each blade element which are at a maximum radial distance from the longitudinal axis of the cutter, i.e., either the cutting edge alone, or the cutting and trailing edges simultaneously. A clearance is maintained between the stenosis and the remaining portions of the outer face which are interior to the edges. The degree of clearance between the stenosis and the outer face of the blade element interior to the edges can be characterized by what is termed the attack angle, i.e., the angle between the outer face and the stenotic surface behind the cutting edge of the blade element. In general increasing the attack angle increases the clearance, thereby enabling the cutting edge to more aggressively attack and cut the plaque making up the stenosis. This effect can be attributed to the fact that a clearance prevents the outer face from diminishing the force of the cutting edge on the plaque. As the plaque is cut away from the stenosis, the cuttings can be collected in the distal end of the hollow catheter and proximally displaced therethrough. When a satisfactory channel is completed through the stenosis, the cutter and catheter containing the cuttings are withdrawn back out through the artery, after which the patient is allowed to recover. The features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawing, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of the atherectomy cutter of the present invention in its intended operational environment. Figure 2 is a perspective view of the atherectomy cutter of the present invention. Figure 3A is a cross-sectional view of the atherectomy cutter of the present invention as seen along line 3-3 in Figure 2 showing the blade elements. Figure 3B is a cross-sectional view of the atherectomy cutter of the present invention showing a further embodiment of the blade elements. Figure 3C is a cross-sectional view of the atherectomy cutter of the present invention showing another embodiment of the blade elements. Figure 3D is a cross-sectional view of the atherectomy cutter of the present invention showing yet another embodiment of the blade elements. Figure 4 is a schematic cross-sectional view of a prior art atherectomy cutter in the operational environment of an arterial stenosis. Figure 5 is a schematic cross-sectional view of the atherectomy cutter of the present invention in the operational environment of an arterial stenosis. DESCRIPTION OF PREFERRED EMBODIMENTS Referring initially to Figure 1, an atherectomy cutter generally designated 10 is shown cutting a substantially smooth channel through a stenosis 12 that is formed on the interior wall of an artery 14 . As shown, the proximal end 16 of cutter 10 is attached to a hollow rotatable catheter 18 at its distal end 20 . Catheter 18 is any suitable tubular structure which can transmit torque, e.g., in the direction indicated by clockwise arrow 22 , from a motor (not shown) to cutter 10 . Cutter 10 can be steered by an operator to the stenosis 12 within artery 14 over a flexible guide wire 24 that extends through torque tube 18 and atherectomy cutter 10 . The materials of atherectomy cutter assembly 10 are preferably lightweight and strong, as well as chemically inert with the tissue of artery 14 . For example, atherectomy cutter 10 can be made of 400 series stainless steel. Similarly, guide wire 24 can be a flexible yet strong stainless steel wire. The details of atherectomy cutter 10 are best seen with cross-reference to Figures 1 and 2. Cutter 10 comprises a body 26 and a pair of opposing blade elements 28a , 28b integral therewith. Body 26 is hollow and has a proximal opening 30 and a distal opening 32 . Body 26 is substantially cylindrical in shape to enable coupling with catheter 18 as shown in Figure 1. With body 26 coaxially positioned in an interference fit with catheter 18 , body 26 provides a continuous passageway from blade elements 28a , 28b into catheter 18 . If desired, catheter 18 and body 26 can further be epoxy-bonded or spot welded together. As shown in Figure 1, cuttings 34 from stenosis 12 , are permitted to flow through the passageway formed by body 26 and through catheter 18 for withdrawal from artery 14 . Passage of cuttings 34 through catheter 18 may be facilitated by providing a suction means (not shown) at the proximal end of catheter 18 in a manner known to one skilled in the art. Returning to Figure 2, proximal ends 36a , 36b of blade elements 28a , 28b are peripherally and opposingly mounted around distal opening 32 . Blade elements 28a , 28b extend along a linear pathway from body 26 . The direction of extension has both a distally longitudinal and an inwardly radial component causing convergence of blade elements 28a , 28b at their distal ends 38a , 38b on the longitudinal axis 40 of cutter 10 . Thus, blade elements 28a , 28b are obliquely aligned relative to axis 40 . The intersection of distal ends 38a , 38b defines a hub 42 , at which blade elements 28a , 28b are attached to one another. Hub 42 has an opening 44 formed through it to receive guide wire 24 . Blade elements 28a , 28b are substantially identical in configuration. Accordingly both will be described hereafter with reference to a single blade element 28a , it being understood that the description applies likewise to blade element 28b . Blade element 28a is configured as a straight band that preferably is relatively rigid. As such, blade element 28a has an outer face 46a that is a flat trapezoidal-shaped outer planar surface facing away from the longitudinal axis 40 of cutter 10 . The flat surface of outer face 46a can be continuous with body 26 , thereby providing flattened portions 48a , 48b on substantially cylindrical body 26 . Blade element 28a further has an inner face 46b shown in Figure 3A that is a flat trapezoidal-shaped inner planar surface facing toward the longitudinal axis 40 of cutter 10 . Inner face 46b and outer face 46a are aligned parallel to one another, and inner face 46b has a width less than outer face 46a . First and second side surfaces 47a , 47b are positioned between inner and outer faces 46a , 46b respectively. The intersection of outer face 46a with first and second side surfaces 47a , 47b defines two linear edges 50 , 52 , respectively which are longitudinally exposed and aligned in an oblique direction corresponding to the extension of blade element 28a . When cutter 10 is operated in the clockwise direction of rotation, edge 50 is the cutting edge of blade element 28a and edge 52 is the trailing edge. The function of edges 50 , 52 can be reversed in a manner apparent to the skilled artisan, if cutter 10 is desired to be operable in the counterclockwise direction of rotation. The specific orientation of outer face 46a relative to the longitudinal axis 40 of cutter 10 is best seen with reference to Figures 3A-3D and Figure 5. Referring initially to Figure 3A, the longitudinal axis 40 of cutter 10 is shown in cross-section as a single central point within cutter 10 . It is apparent that the radial distance from axis 40 to cutting edge 50 and the radial distance from axis 40 to trailing edge 52 are equal, and further that this distance is a maximum, i.e., greater than the radial distance from axis 40 to any other longitudinally corresponding point lying on outer face 46a of blade element 28a , e.g., point 54 . Consequently, cutting edge 50 and trailing edge 52 define the maximum or outermost rotation surface of blade element 28a . As is further apparent from Figure 3A, blade element 28a has the configuration of a trapezoidal solid, wherein outer face 46a forms the base of the trapezoidal solid. It is apparent, however, from Figures 3B and 3C that the blade element can have alternate configurations and fall within the scope of the present invention. In Figure 3B, blade elements 56a , 56b have the configuration of a triangular solid and in Figure 3C blade elements 58a , 58b have the configuration of a semi-cylindrical solid. The blade element configurations shown in Figures 3B and 3C both satisfy the requirement that the radial distance from the longitudinal axis to the cutting and trailing edges is greater than the radial distance from the axis to any other longitudinally corresponding point lying on the outer face of the blade element. Consequently, as in Figure 3A, the blade elements embodied in Figures 3B and 3C have cutting and trailing edges that define the outermost rotation surface of the blade elements. Figure 3D shows an embodiment of cutter 10 , wherein blade elements 60a , 60b have a similar configuration to blade elements 28a , 28b of Figure 3A, but are rotated somewhat about their own longitudinal axes, thereby displacing cutting edge 50 away from the longitudinal axis 40 of cutter 10 while displacing trailing edge 52 toward axis 40 . Consequently, the radial distance from longitudinal axis 40 to any longitudinally corresponding point on outer face 46a is a maximum at cutting edge 50 and a minimum at trailing edge 52 , and cutting edge 50 alone defines the outermost rotation surface of blade elements 60a , 60b . It is understood that blade elements 56a , 56b and 58a , 58b of Figures 3B and 3C respectively, can be rotated in a manner similar to that shown in Figure 3D, and that such embodiments fall within the scope of the present invention. OPERATION In the operation of atherectomy cutter 10 , reference is initially made to Figure 1. In accordance with well-known surgical techniques, guide wire 24 is positioned within artery 14 . Catheter 18 having atherectomy cutter 10 attached thereto is advanced over wire 24 until cutter 10 is positioned adjacent stenosis 12 . Catheter 18 is then rotated causing cutter 10 to rotate. As cutter 10 rotates, it is advanced into stenosis 12 where plaque is encountered. Accordingly, cutter 10 progresses forward to cut a wide and substantially smooth channel therethrough. Plaque cuttings 34 which are excised are drawn into catheter 18 by applying a vacuum thereto. Upon completion of the channel, cutter 10 is withdrawn back out through artery 14 . The enhanced plaque cutting ability of cutter 10 is best demonstrated by comparing the operation of cutter 10 with a prior art cutter configuration. Referring to Figure 4, a pair of prior art blade elements 62a , 62b , such as those defined by the frustum-shaped cutter of U.S. Patent No. 4,887,613, are shown in schematic operation within stenosis 12 . For purposes of illustration, only one blade element 62a is described below since blade elements 62a and 62b are substantially identical. It is understood that the description of blade element 62a applies likewise to blade element 62b . Blade element 62a is rotated in a clockwise direction designated by arrow 64 , which differentiates cutting edge 66 from trailing edge 68 , edges 66 , 68 being separated by a curved outer face 70 . When blade element 62a enters stenosis 12 as shown, the entire outer face 70 contacts stenosis 12 , not just edges 66 , 68 . Upon such contact, stenosis 12 is compressed both ahead and behind cutting edge 66 due to the curvature of outer face 70 and the elastic nature of the plaque. The attack angle between blade element 62a and stenosis 12 is essentially zero. Consequently, stenosis 12 is only partially exposed ahead of cutting edge 66 for cutting thereby. As blade element 62a is withdrawn from stenosis 12 , however, the compression force on stenosis 12 by outer face 70 diminishes, and stenosis 12 undesireably returns to an expanded diameter. Thus, it is apparent that removal of a stenosis with blade elements lacking a positive attack angle is less effective because much of the stenosis remains in place after treatment. Referring to Figure 5, the schematic operation of blade elements 28a , 28b , as previously shown in Figure 2, is demonstrated in accordance with the present invention. Contact between blade elements 28a , 28b and stenosis 12 is essentially limited to cutting edges 50 and trailing edges 52 , while a clearance 72 is maintained between stenosis 12 and the remainder of outer face 46a . Clearance 72 is characterized by attack angle  which is the angle between outer face 46a and the tangent to the stenotic surface behind cutting edge 50 . As shown,  has a positive value typically on the order of about 45°. The positive attack angle avoids compression of stenosis 12 by outer face 46a and fully exposes stenosis 12 to cutting edge 50 , thereby enabling effective cutting of a wide smooth channel through stenosis 12 . While the particular atherectomy cutter as herein shown and disclosed in detail is capable of obtaining the objects and providing the advantages hereinbefore stated, it is understood that this particular cutter is merely illustrative of presently preferred embodiments of the invention. It is further understood that the present invention is not intended to be so limited and that other embodiments are further possible within the scope of the present invention. For example, although the cutter of the present invention has been described above with reference to a pair of blade elements, it is understood that the present invention may also apply to a cutter having any number of blade elements, such as can be constructed by the skilled artisan employing the teaching set forth herein.

Claims: A rotatable atherectomy cutter (10) having a longitudinal axis and positionable within an artery for removing a stenosis therefrom, said cutter comprising: a body (26) having a proximal end (16) and a distal end; at least one rigid blade element (28a,28b) having a proximal end (36a,36b) and a distal end (38a,38b), said proximal end (36a,36b) of said blade element (28a,28b) peripherally mounted on said distal end of said body (26) and linearly extending from said body (26) in a distal direction convergent with the longitudinal axis (40) of said cutter (10) said blade element (28a,28b) further has an outer face (46a) directed away from the longitudinal axis (40) of said cutter (10) and bounded on opposite sides by a first cutting edge (50) and a second edge (52) extending between said proximal (36a,36b) and distal ends (38a,38b) of said blade element (28a,28b); said blade element (28a,28b) further having a first flat side surface (47a) and a second flat side surface (47b) characterised in that: said blade element (28a,28b) has a flat planar outer face and said flat side surfaces (47a,47b) extend respectively from said first (50) and second (52) edges toward said longitudinal axis (40), each of said side surfaces (47a,47b) forming an acute angle between said side surface (47a,47b) and said planar outer face (46a), with the result that the radial distance from the longitudinal axis (40) and the first edge (50) is greater than the radial distance from the longitudinal axis (40) to any other longitudinally corresponding point lying on the outer face (46a), so said first cutting edge (50) establishes a positive attack angle between said planar outer face (46a) and a surface of said stenosis during rotation of said cutter (10). A rotatable atherectomy cutter (10) according to Claim 1 further comprising a plurality of said blade elements (28a,28b). A rotatable atherectomy cutter (10) according to Claim 1 or 2 wherein said body (26) is substantially cylindrical and hollow, having proximal and distal openings (30,32), and further wherein said proximal end (36a,36b) of said blade element (28a,28b) is diametrically mounted at said distal opening (32). A rotatable atherectomy cutter (10) according to Claim 2 comprising a pair of blade elements (28a,28b) peripherally and opposingly mounted around said distal opening (32). A rotatable atherectomy cutter (10) according to Claim 4 wherein the distal ends (38a,38b) of the blade elements (28a,28b) are fixably connected to each other at the longitudinal axis (40) of the cutter (10). A rotatable atherectomy cutter (10) according to any one of the preceding claims wherein said proximal end (16) of said body engages a hollow rotatable catheter (18). A rotatable atherectomy cutter (10) according to Claim 6 wherein said body (26) forms a continuous passageway from said blade element (28a,28b) to said hollow catheter (18). A rotatable atherectomy cutter (10) according to any one of the preceding claims wherein said first edge (50) and said second edge (52) are substantially parallel. A rotatable atherectomy cutter (10) according to any one of the preceding claims wherein said blade element (28a,28b) has a trapezoidal cross-section with said outer face (46a) defining the base of said trapezoidal cross-section and said first and second edges (50,52) defining the corners of said base. A rotatable atherectomy cutter (10) according to any one of the preceding claims wherein said first and second edges (50,52) are radially equidistant from the longitudinal axis (40) of said cutter (10). A rotatable atherectomy cutter (10) according to Claim 10 wherein second edge (52) follows said maximum rotation surface upon rotation of said blade element (28a,28b) about the longitudinal axis (40) of said cutter (10). A rotatable atherectomy cutter (10) according to Claim 10 wherein the radial distance from the longitudinal axis (40) of said cutter (10) to said first and second edges (50,52) is greater than the radial distance from said longitudinal axis (40) to any other longitudinally corresponding point on said outer face (46a). A cutting element for use with an atherectomy system to remove plaque from a stenotic segment in an artery which comprises: a blade element (28a,28b) having a proximal end (36a,36b), a distal end (38a,38b); said blade element (28a,28b) being connected to a body (26) having an axis of rotation (40); characterised by: said blade element (28a,28b) having a trapezoidal shaped cross section being defined by outer and inner flat planar surfaces (46a,46b) with first (47a) and second (47b) flat planar side surfaces therebetween, said inner surface (46b) being of less width than said outer surface (46a) and being oriented relative to said outer surface (46a) to establish a first cutting edge (50) where said first side surface (47a) intersects said outer surface (46a), with the result that the radial distance from the longitudinal axis (40) to the first edge (50) is greater than the radial distance from the longitudinal axis (40) to any other longitudinally corresponding point lying on the outer face (46a); and means for holding said blade element (28a,28b) to position said inner surface (46b) between said outer surface (46a) and said axis of rotation, and to incline said blade element (28a,28b) with said distal end (38a,38b) nearer said axis of rotation than said proximal end (36a,36b).

Inventors: RADISCH HERBERT R JR, RADISCH, HERBERT R., JR.
Applicants: INTERVENTIONAL TECHNOLOGIES, INTERVENTIONAL TECHNOLOGIES INC
Application year: 1992
Main classification: A61B17
IPC codes: A61B17, A61M25