narveson, american residents, residing in Minneapolis, Minnesota.
Background
Various techniques and devices have been developed for removing or repairing tissue in arteries and similar body passageways. A common goal of such techniques and devices is to remove atherosclerotic plaque from a patient's artery. Atherosclerosis is characterized by the presence of fat deposits (atheroma) in the intimal layer (under the endothelium) of a patient's blood vessels. Over time, the initially deposited softer, cholesterol-rich atherosclerotic material will harden into calcified atherosclerotic plaques. Such atheroma will restrict blood flow and is therefore often referred to as stenotic lesions or stenoses (stenoses), and such obstructive material is also referred to as stenotic material. If left untreated, the stenosis can lead to angina, hypertension, myocardial infarction, stroke, etc.
Rotational atherectomy has become a conventional technique for removing such stenotic material. This step is frequently used to open the initial stages of calcified lesions in coronary arteries. Typically, the atherectomy procedure is not used alone, often followed by a balloon angioplasty procedure, often followed by a stent implantation to help maintain patency of the opened artery. For non-calcified lesions, balloon angioplasty alone is typically used to open the artery, and a stent is typically implanted to maintain patency of the opened artery. However, studies have shown that most patients who have undergone balloon angioplasty and have stents implanted in the artery have experienced stent restenosis (restenosis), which is often due to stent blockage caused by excessive growth of scar tissue within the stent over time. In this case, an excision procedure is the preferred procedure to remove excess scar tissue from the stent (which is not very effective internally using balloon angioplasty) and thereby restore patency to the artery.
Various atherectomy devices have been developed in an attempt to remove stenotic material. In one type of device, shown in U.S. patent No. 4,990,134 to Auth, a burr (burr) is provided on the distal end of a flexible drive shaft that is covered with an abrasive material, such as diamond particles. When the flash is introduced through the stenosis, the flash is rotated at high speeds (typically, for example, about 150,000 and 190,000 revolutions per minute). However, when the flash removes stenotic tissue, it will block blood flow. Once the burr has passed through into the stenosis, the artery is typically opened to a diameter equal to or slightly greater than the maximum outer diameter of the burr. The flash is therefore typically used to open the artery to a desired diameter and is not limited to one size.
U.S. patent No. 5,314,438 issued to Shturman discloses another resection device having a drive shaft with a portion of increased diameter, at least a portion of this increased surface being covered with an abrasive material to define an abrasive portion of the drive shaft. When rotated at high speed, the abrasive section can remove stenotic tissue in the artery. While this atherectomy device has some advantages over the Auth device due to its flexibility, it can only open the artery to a diameter approximately equal to the enlarged abrasive surface of the drive shaft since the device itself is not eccentric.
U.S. patent No. 6,494,890 to Shturman discloses a resection device having a drive shaft with an enlarged eccentric cross-section wherein at least a portion of the enlarged cross-section is covered with an abrasive material. At high speed rotation, the abrasive section removes stenotic tissue from the artery. Due in part to the orbital rotational motion at high speeds of operation, such devices are capable of opening an artery to a diameter greater than the remaining diameter of the enlarged eccentric section. Since the enlarged eccentric cross-section includes drive axes that are not connected to each other, the enlarged eccentric cross-section of the drive shaft will flex during high speed operation, but at the same time, reduce the amount of control over the predictability of the actual abraded artery diameter. In addition, some stenotic tissue will completely obstruct the passageway, causing the Shturman device to be unable to be placed therethrough. Since Shturman requires that the enlarged eccentric section of the drive shaft be placed within the stenotic tissue for abrading, its effect will not be apparent in the event that the enlarged eccentric section cannot be moved into the stenosis. The contents of U.S. Pat. No. 6,494,890 are incorporated herein by reference in their entirety.
U.S. patent No. 5,681,336 to Clement teaches an eccentric tissue deburr having a layer of abrasive grains held to a portion of its outer surface by a suitable bonding material. However, as described by Clement at column 3, lines 53-55, burrs due to asymmetry rotate at a "lower speed than the speed used by the high speed ablation apparatus" to compensate for heat or imbalance. I.e., where the size and weight of the solid burr is determined, it would not be feasible to rotate such burrs at high speeds, i.e., 20,000 and 200,000rpm, during resection practice, and thus, such a configuration is limited. Basically, a deviation from the center of gravity of the axis of rotation of the drive shaft will result in significant centrifugal forces, exerting excessive pressure on the artery wall and generating excessive heat and particles.
In general, existing tissue removal members are all of a unitary, rigid, inflexible design and are thus difficult to introduce/retrieve through tortuous vessels. Furthermore, known designs typically include a continuous, unbroken abrasive surface, such as an elliptical or spherical structure that is symmetrical or asymmetrical. It is known that in some cases a hydraulic wedge-shaped space (hydraulic wedge) will be created between the current tissue removal means device and the artery wall and plaque, reducing the contact of the abrasive surface with the plaque and thus reducing the efficiency of the overall procedure. Moreover, the smoother abrasive surface of current designs does not maximize the abrading action and/or cutting efficiency. Finally, when soft plaque and/or non-calcified lesions and/or diffuse lesions are targeted, the length of time that such smoother tissue removal member devices are known to operate cannot be predicted.
Accordingly, there is a need for an atherectomy device having a selectable and customizable number of individual eccentric abrading segments, and further including an additional cutting edge and sanding surface, and a mechanism to disrupt the hydraulic wedge-shaped spacing that occurs between the abrading surface and the arterial wall and plaque. Further, there is a need for a tissue removal member that is customizable for effective abrasive removal of hard and soft, non-calcified plaque when targeting such blockages involving hard and soft, non-calcified and/or diffuse stenotic tissue, thereby improving predictability of the outcome and length of time of the abrasion. Furthermore, all existing designs have a fixed weight and thus a fixed diameter of rotation. Thus, there is a need for a grinding bit that can be customized to existing eccentric masses. This, in turn, will allow for customization of the rotational diameter of the eccentric abrading head.
Detailed Description
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. 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.
Figure 1 illustrates one embodiment of an atherectomy device according to the present invention. The device includes a hand-held portion 10 and an elongated, flexible drive shaft 20 having an eccentric abrading head 100. As discussed herein, the abrading head 100 includes proximal and distal portions and a central portion, and further includes at least one eccentric cylindrical body portion therebetween. An elongated conduit 13 extends away from the hand-held portion 10. As is known in the art, the drive shaft 20 is comprised of helical coils to which the grinding bit 28 is fixedly attached. The catheter 13 has a lumen in which the majority of the length of the drive shaft 20 is located, except for the enlarged abrading head 28 and a short segment away from the enlarged abrading head 28. The drive shaft 20 also includes a lumen that allows the drive shaft 20 to be introduced and rotated via the guide wire 15. A fluid supply tube 17 is also provided to introduce a cooling and lubricating solution (typically saline or other biocompatible fluid) into the catheter 13.
The handpiece 10 preferably contains a turbine (or similar rotating device mechanism) to rotate the drive shaft 20 at high speed. The handpiece 10 is typically connected to a power source, such as compressed air fed through a tube 16. A two-fiber cable 25 is also provided and a single fiber cable may also be used to monitor the rotational speed of the turbine and drive shaft 20 (details regarding such hand-held parts and associated instrumentation are well known in the industry, such as described in detail in U.S. patent No. US5,314,407 by Auth). The handpiece 10 also preferably includes a control knob 11 to introduce and withdraw the turbine and drive shaft 20 relative to the catheter 13 and handpiece body.
Figures 2 and 3 show details of a prior art abrading head including an eccentric, enlarged diameter abrading segment 28A of drive shaft 20A. The drive shaft 20A includes one or more helically wound wires 18 defining a guide wire lumen 19A and a cavity 25A in an enlarged abrasive portion 28A. Except that guidewire 15 spans lumen 25A, lumen 25A is substantially empty. The eccentric enlarged diameter abrasive section 28A includes a proximal portion 30A, a central portion 35A and a distal portion 40A relative to the narrow location. The diameter of the turns 31 of the proximal portion 30A of the eccentric enlarged diameter portion 28A preferably increases with distance at a generally constant rate, thereby forming a generally conical shape. The diameter of the turns 41 of the distal portion 40A preferably decreases with distance at a substantially constant rate, thereby forming a substantially conical shape. The diameter of the turns 36 of the central portion 35A is gradually changing, resulting in a generally convex outer surface providing a smooth transition between the proximal and distal conical portions of the enlarged eccentric diameter portion 28A of the drive shaft 20A.
Continuing with the prior art apparatus, at least a portion of the eccentric enlarged diameter abrasive section of drive shaft 28A (preferably central portion 35A) includes an outer surface capable of removing tissue. The tissue-removing surface 37 has a layer of abrasive material 24A defining the tissue-removing portion of the drive shaft 20A, and is shown directly connected to the turns of the drive shaft 20A by a suitable connector 26.
Figure 4 shows another prior art rotational atherectomy device, in contrast to the substantially hollow device of figures 2 and 3, the device of figure 4 uses a rigid, asymmetric abrasive rim 28B that is attached to a flexible drive shaft 20B and rotated by means of a guide wire 15, as shown in U.S. patent No. 5,681,336 to Clement. Eccentric tissue removal burr 28B has a layer of abrasive particles 24B secured to a portion of its outer surface by a suitable bonding material 26B. However, as the Clement indicates at column 3, lines 53-55, the utility of this configuration is somewhat limited because the asymmetric burr 28B must be rotated at a "lower speed than that employed by the high speed ablation apparatus" to compensate for the heat or imbalance. I.e., in the case of sizing and weighting of the hard burr-like configuration, it would be impractical to rotate such burrs at high speeds, i.e., at 20,000 and 200,000rpm, during resection procedures. Furthermore, the abrasive portion of this prior device is smooth, i.e., has no grooves. Thus, such prior devices are less efficient when dealing with non-calcified and/or soft stenoses.
Turning now to fig. 5 and 6, one embodiment of the present invention is shown. The eccentric abrading head 100 includes three portions: a proximal portion 130, a cylindrical central portion 135 and a distal portion 140, the central portion 135 being located between the proximal and distal portions 130, 140 and spaced apart from the proximal and distal portions 130, 140.
The proximal portion 130 includes a proximal outer surface and may also include a proximal conical portion 132 and a proximal cylindrical portion 134, the proximal portion being mounted on the drive shaft 20. The central portion 135 includes at least one eccentric abrasive cylindrical portion 102 mounted on the drive shaft 20 adjacent to and distal from the proximal end portion 130, wherein the at least one eccentric abrasive cylindrical portion 102 is spaced apart from the cylindrical portion 134 of the proximal end portion 130. In the illustrated embodiment, there are 3 eccentric abrasive cylindrical portions 102. Each such eccentric abrading cylindrical portion 102 is spaced apart from adjacent cylindrical portions 102. The distal portion 140 includes a distal conical portion 142 and a distal cylindrical portion 140, and is mounted on the drive shaft 20 adjacent to and distal from the central portion 135. The proximal and distal portions 130, 140 are mounted such that they are spaced apart from the adjacent cylindrical portion 102.
The proximal portion 130 also includes a proximal inner surface 136, the proximal inner surface 136 facing the interior of the eccentric abrading head 100, and in particular the adjacent eccentric cylindrical portion 102. Similarly, the distal portion 140 further includes a distal inner surface 146, wherein the distal inner surface 146 faces the interior of the eccentric abrading head 100, and particularly the adjacent eccentric cylindrical portion 102, and is located in the opposite direction of the proximal inner surface 136. As shown, the proximal and distal inner surfaces 136, 146 are generally oriented in opposite directions relative to one another.
One skilled in the art will appreciate that, as described above, the proximal and/or distal portions 130, 140 may include a conical portion and a cylindrical portion, and/or the proximal and distal portions 130, 140 may be conically or cylindrically contoured.
Further, each such at least one eccentric abrasive cylindrical portion 102 includes an outer surface 104, a proximal inner surface 106p, a distal inner surface 106d, and inner surfaces 106p, 106d on opposing inner surfaces of each cylindrical portion. The outer surface 104 and/or the proximal and distal inner surfaces 106p, 106d may include abrasives thereon. As is known in the art, a polishing layer 26 may be provided as shown in fig. 8-10. It is contemplated that the particle size of the abrasives applied to the outer surface 104, the proximal and distal inner surfaces 106p, 106d may vary. The particle size of the abrasive of the outer surface 104 can be optimized to remove hard stenotic tissue, while the particle size of the abrasive of the proximal and distal inner surfaces 106p, 106d can be optimized to remove soft, non-calcified and/or diffuse stenotic tissue.
As a result of the spaced mounting of the at least one cylindrical portion 102 and the proximal and distal portions 130, 140, a resilient gap G is formed between the proximal inner surface 146 and the inner surface 106p opposite the adjacent cylindrical portion and between the distal outer surface 136 and the distal inner surface 106d opposite the adjacent cylindrical portion. Thus, in the simplest case comprising only a single cylindrical portion 102, a total of two elastic slits G will occur. In the case of a structure comprising two cylindrical portions 102 adjacent to but spaced apart from each other as described above, a total of 3 gaps G will occur: a first gap G between the proximal inner surface 136 and the proximal inner surface 106p opposite the adjacent cylindrical portion, a second gap G between the distal outer surface 146 and the distal inner surface 106d opposite the adjacent cylindrical portion, and a third gap G between the distal inner surface 106d opposite the proximal most cylindrical portion and the proximal inner surface 106p opposite the distal most cylindrical portion. Fig. 5 and 6 show the case of including 3 cylindrical portions 102, which would have 4 elastic slits G in accordance with the discussion above. The present invention includes an eccentric abrading head 100 having at least two elastic slits G. In any given embodiment of the eccentric abrading head of the present invention, the number of elastic slits G is of the general formula "N + 1", where N is the number of cylindrical portions 102.
Having at least two resilient slits G will provide the eccentric abrading head 100 and rotational atherectomy device with several highly desirable operational characteristics. First, the gap G allows the drive shaft to flex freely, thus making the drive shaft and abrading head 100 easier to insert into and pull out of a patient's tortuous vasculature. The ease of insertion will make it a more atraumatic step.
Second, as described above, different particle size abrasives may be used on the outer surface 104 and the proximal and distal inner surfaces 106p, 106d of the cylindrical portion(s). Thus, the abrasive of the outer surface 104 can be optimized to remove hard stenotic tissue while the abrasive of the proximal and distal inner surfaces 106p, 106d is optimized to remove soft, non-calcified and/or diffuse stenotic tissue. At this point, for example, when the abrading head 100 is moved under the manipulation of the manipulator to the proximal or distal end within the stenosis, the soft tissue will expand and extend a distance into the flexible gap G under the compression of the outer surface 104. Abrasives on the proximal and distal inner surfaces 106p, 106d of the gap G optimized to remove soft tissue may enhance the removal step described above.
Third, the elastic gap G provides a mechanism and method to collapse or disrupt the hydraulic wedge spacing that is known to occur when the smoother abrading head is rotated at high speeds relative to stenoses and/or arterial walls. Thus, the gap G may increase the contact between the polishing head 100, and particularly the outer surface 104, and the stenosis. Thus, the polishing head 100 of the present invention can improve polishing performance and effectiveness.
Fourth, the elastic gap G allows the polishing head 100 to partially flex during high speed rotation. This improves polishing performance and reduces damage during surgical procedures. In addition, the elastic gap G will allow the polishing head 100 to achieve a more natural, and thus more stable, frequency of oscillation.
In addition, the polishing head 100 of the present invention has a larger polishing surface area than prior art single body polishing heads. The abrasive surfaces 26 of the proximal and distal inner surfaces 106p, 106d increase the larger abrasive surface that is not available with known single body devices. The increased surface may improve the efficacy of the atherectomy procedure and reduce the time required to perform the procedure. Since the number of eccentric abrading cylindrical segments 100 can be varied, i.e., at least one cylindrical segment 100 can be used, the abrading surface area of the device 100 of the present invention can be customized and easily increased or decreased to a desired condition by increasing or decreasing the cylindrical segments 100 and/or selecting that the inner and/or outer surfaces 106p, 106d are not coated with an abrasive.
The abrasive material may be any suitable material, such as diamond powder, fused silica, titanium nitride, tungsten carbide, alumina, boron carbide, or other ceramic material, as will be well understood by those skilled in the art. Preferred abrasive materials include diamond chips (or diamond dust particles) that are attached directly to the tissue removal surface by a suitable connector. Such attachment means may be achieved using known methods such as conventional electroplating or fusion techniques (see, for example, U.S. Pat. No. 4,018,576). Alternatively, the outer tissue-removing surface may include a central portion 135, proximal and/or distal portions 130, 140 that are mechanically or chemically roughened on their outer surfaces to obtain a suitably abrasive tissue-removing surface. In another variation, the outer surface may be etched or cut (e.g., with a laser) to obtain a small but effective abrasive surface. Other similar techniques may also be used to obtain a suitable tissue-removing surface.
As best shown in fig. 5-7, an at least partially enclosed interior cavity or slot 23 is provided extending longitudinally through the eccentric abrading head 100 along the rotational axis 21 of the drive shaft 20 to secure the abrading head 100 to the drive shaft 20 in a manner well known to those skilled in the art. Thus, the proximal and distal portions 130, 140 are secured to the drive shaft 20 in this manner, as shown by the at least one cylindrical portion 100 in FIGS. 7 and 8A-8C. Fig. 7 shows a cylindrical portion 102 having a partially enclosed interior cavity 23 and attached to the drive shaft 20. Similarly, the proximal and distal portions 130, 140 include an at least partially enclosed lumen 23. Another aspect of the proximal and distal portions 130, 140 and/or the at least one cylindrical portion 100 may include a fully enclosed lumen 23, as shown in the cross-sectional views of fig. 8A-8C.
The embodiment of fig. 5 and 6 shows that the proximal and distal portions 130, 140 present in the conical portions 132, 142 in front of the central portion 135 have a symmetrical shape, length and the same slope. Another class of embodiments may increase the length of the proximal portion 130 or the distal portion 140 to achieve an asymmetric profile. In general, a symmetrical abrading head 100 of the present invention is preferred as shown in figures 5 and 6, although in other embodiments the proximal and/or distal portions 130, 140 may have a greater or lesser slope. Further, the length of the proximal and/or distal portions 130, 140 and/or the central portion 35 may be longer or shorter. Any combination falls within the scope of the invention.
As described above, in certain embodiments, the proximal and/or distal portions 130, 140 include the conical portions 132, 140 and/or the cylindrical portions 134, 144, while the central portion 135 is cylindrical. As shown in fig. 7 and 8A-8C, this geometry arises in part because of the ability to obtain the eccentric abrading head 100 of the present invention having a center of gravity 32, wherein the center of gravity 32 is geometrically offset radially from the longitudinal axis of rotation 21 of the drive shaft 20. As shown, each eccentric cylindrical portion 102 includes a center of gravity 32 that is offset from the axis of rotation 21 of the drive shaft 20. In addition, the proximal and distal portions 130, 140 also have a center of gravity that is offset from the drive shaft 21 of the drive shaft 20. Displacement of the center of gravity 32 away from the rotational axis 21 of the drive shaft will result in an eccentric abrading head 100 having an eccentricity that allows it to open the artery to a diameter much greater than the nominal diameter of the eccentric abrading head 100 during high speed rotation. The diameter that can be opened is preferably at least twice the nominal diameter of the eccentric abrading head 100. Further, the weight and center of gravity position of center portion 135 may be varied, for example, by employing two or more materials of different densities, to enhance, manipulate, and control such degree of offset of center of gravity 32.
It should be understood that the terms "eccentric" and "eccentricity" are used herein to refer to a positional distance between the eccentric abrading head 100 and the geometric center of the rotational axis 21 of the drive shaft, or a positional distance between the center of gravity 32 of the eccentric abrading head 100 and the rotational axis 21 of the drive shaft 20. Any such distance at an appropriate rotational speed will enable the eccentric abrading head 100 to open up to a diameter that is much larger than the nominal diameter of the eccentric abrading head 100. This is because the flexible slits G separate each cylindrical portion 102 and the proximal and distal portions 130, 140, allowing the abrading head 100 to flex slightly during high speed rotation. This ability to flex helps improve polishing performance. In addition, during high speed rotation, the eccentric abrading head 100 may achieve a more favorable natural frequency of oscillation than a rigid, single body abrading head.
The eccentric abrading head 100 of the rotational atherectomy device of the present invention may be made of stainless steel, tungsten, and/or the like.
Figures 8A-8C illustrate the position 32 of the center of gravity of three cross-sectional slices (shown in cross-section) of the eccentric abrading head 100 illustrated in figures 5 and 6, wherein the eccentric abrading head 100 is fixedly coupled to the drive shaft 20 via the lumen 32, and the drive shaft 20 is introduced via the guide wire 15. Notably, each of the proximal and/or distal end portions 130, 140 and the at least one cylindrical portion 100 includes a center of gravity position 32 relative to the rotational axis 21 of the drive shaft 20. Figure 8B is a view of the eccentric abrading head 100 in its position with its maximum cross-sectional diameter (where, in this embodiment, the diameter is the maximum diameter of the at least one cylindrical portion 102 of the eccentric abrading head 100 increasing in diameter), and figures 8A and 8C are cross-sections of the proximal and distal portions 130, 140, respectively, of the eccentric abrading head 10. In each of these cross-sectional slices the center of gravity 32 is displaced from the axis of rotation 21 of the drive shaft 20, while the axis of rotation of the drive shaft 20 coincides with the center of the guide line 15. The center of gravity 32 of each cross-sectional slice generally coincides with the geometric center of such cross-sectional slice, although those skilled in the art will appreciate that the use of materials having different densities will shift the center 32 away from the geometric center. Fig. 8B shows a cross-sectional slice of at least one cylindrical portion 102 that includes the largest cross-sectional diameter of the abrasive head 100, with the center of gravity 32 and geometric center thereof both furthest from the rotational axis 21 of the drive shaft 20 (i.e., spaced the greatest distance) as compared to the proximal and distal portions 130, 140.
Figure 9 illustrates a cross-section of at least one cylindrical portion 102 of the eccentric abrading head 100 of the present invention having a guidewire 20 and an attached abrading head 100 introduced via a guidewire 15, and in a resting position in an artery "a" after a stenosis has been substantially opened, thereby illustrating the ability of the device to open a stenosis to a diameter well beyond the nominal diameter of the device.
The extent to which a stenosis in an artery can be opened to a diameter greater than the nominal diameter of the eccentric abrading head 100 of the present invention depends on several factors, including but not limited to: the shape of the eccentric abrading head 100, the weight distribution, and the position of the center of gravity of the eccentric abrading head 100 relative to the rotational axis of the drive shaft, and the rotational speed. It will be apparent to those skilled in the art that the present invention can be employed to manipulate and control the weight and center of gravity position of the abrading head 100 by adding or removing the cylindrical portion 102 to achieve a desired weight and center of gravity position.
The rotational speed is an important factor in determining the centrifugal force to press the polishing surface 26 of the eccentric abrading head 100 against stenotic tissue, thereby allowing the operator to control the rate of tissue removal. Controlling the rotational speed may also control, to some extent, the maximum diameter to which the device will open the stenosis. Applicants have also found that the ability to reliably control the force with which the abrasive surface 26 is pressed against stenotic tissue not only allows the operator to better control the rate of tissue removal, but also better control the particle size being removed.
Figures 10-11 illustrate the substantially helical orbital path taken by various embodiments of the eccentric abrading head 100 of the present invention, showing the abrading head 100 in relation to the guide wire 15 through which the abrading head 100 is introduced. The pitch of the helical path is exaggerated for purposes of illustration, and in fact, each helical path of the eccentric abrading head 100 removes a very thin layer of tissue simply by virtue of the abrasive on the outer surface of the cylindrical portion 102, and the eccentric abrading head 100 creates many, if not many, of such helical paths as the device is repeatedly moved forward and backward, i.e., in the alternative, through a narrow to a fully open narrow. Figure 10 schematically illustrates three different rotational positions of the eccentric abrading head 100 of the rotational atherectomy device of the present invention. At each location, the abrasive surface of the eccentric abrading head 100 will contact the plaque "P" to be removed, identified by three different points of contact with the plaque "P," which are designated as points B1, B2, and B3. It is noted that at each point, the grinding surface of the eccentrically enlarged abrading head 100 contacts substantially the same portion of tissue, i.e., the portion of the grinding surface 26 on the outer surface 104 of the cylindrical portion 102 radially furthest from the rotational axis of the drive shaft.
While not wishing to be bound by any particular theory of operation, applicants believe that offsetting the center of gravity 32 from the rotational axis 21 of the drive shaft 20 allows for "orbital" movement of the eccentric abrading head 100, and that control of the diameter of the "orbit" can be achieved by varying, for example, the rotational speed of the drive shaft 20, the number and weight of the at least one cylindrical portion 102 employed, and the distribution of its center of gravity. Applicants have experienced that by varying the rotational speed of the drive shaft 20 and/or the number of cylindrical sections 102, the centrifugal force pressing the grinding surface 26 located on the outer surface 104 of the cylindrical section 102 of the eccentric abrading head 100 against a narrow surface can be controlled. The centrifugal force can be calculated according to the following formula:
Fc=mΔx(πn/30)2
where F0 is the centrifugal force, m is the weight of the eccentric abrading head 100, Δ x is the distance between the center of gravity 32 of the eccentric abrading head 100 and the rotational axis 21 of the drive shaft 20, and n is the rotational speed (revolutions per minute) (rpm). Controlling this force Fc controls the speed of tissue removal, controls the maximum diameter to which the device will open the stenosis, and improves control over the particle size of the tissue to be removed.
The abrading head 100 of the present invention may comprise a greater weight than conventional existing high-speed ablative abrading devices. Thus, a larger orbit, i.e., a larger diameter of rotation, may be achieved during high speed rotation, which in turn may allow for the use of smaller polishing heads than prior devices. In addition, the increased flexibility of the eccentric abrading head 100 allows for ease of insertion and a more atraumatic surgical procedure.
In an operational aspect, the eccentric abrading head 100 can be repeatedly moved distally and proximally while a stenosis is being navigated using the rotational atherectomy device of the present invention. By varying the rotational speed of the device, the operator can control the force with which the abrasive on the outer surface 104 of the cylindrical portion 102 is pressed against the stenotic tissue, thereby better controlling the speed of plaque removal and the particle size of the tissue to be removed. In addition, the steps of abrading and such tissue removal are optimized by moving the abrading head 100 distally and proximally, i.e., moving the head through stenotic, soft, non-calcified, and/or diffuse tissue, which can expand and fill the elastic gap G, thereby contacting the tissue with abrasive located on the proximal and/or distal surfaces 106p, 106 d. Since the stenosis is opened to a diameter greater than the nominal diameter of the eccentric abrading head 100, cooling solution and blood can continue to flow around the enlarged abrading head. In addition, the elastomeric slits G provide a path for fluid to flow around the polishing head 100.
The maximum cross-sectional diameter of the eccentric abrading head 100 is about 1.0mm to about 3.0 mm. Thus, the cross-sectional diameter of the eccentric enlarged abrading head may be, but is not limited to: 1.0mm, 1.25mm, 1.50mm, 1.75mm, 2.0mm, 2.25mm, 2.50mm, 2.75mm and 3.0 mm. Those skilled in the art will readily appreciate that the above-listed stepwise increments of 0.25mm in cross-sectional diameter are merely exemplary and the present invention is not limited to the exemplary enumeration and, thus, other stepwise increments of cross-sectional diameter are possible and within the scope of the present invention.
Since the eccentricity of the eccentric abrading head 100, as described above, depends on a variety of parameters, the applicant believes that it is necessary to consider the following design parameters in relation to the distance of the axis of rotation 21 of the drive shaft 20 from the geometric center of the cross-section, where the cross-section is chosen to be the maximum cross-sectional diameter of the eccentric abrading head 100, i.e. the position through the at least one cylindrical portion 102: for devices having eccentrically enlarged abrading heads with a maximum cross-sectional diameter of about 1.0mm to about 1.5mm, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.02mm, preferably at least 0.035 mm; for devices having an eccentrically enlarged abrading head with a maximum cross-sectional diameter of about 1.5mm to about 1.75mm, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.05mm, preferably at least about 0.07mm, and most preferably at least about 0.09 mm; for devices having eccentrically enlarged abrading heads with a maximum cross-sectional diameter of about 1.75mm to about 2.0mm, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.1mm, preferably at least about 0.15mm, and most preferably at least about 0.2 mm; and for devices having an eccentrically enlarged abrading head with a maximum cross-sectional diameter greater than 2.0mm, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.15mm, preferably at least about 0.25mm, and most preferably at least about 0.3 mm.
The design parameters may also be based on the location of the center of gravity. For a device having an eccentrically enlarged abrading head 100 with a maximum cross-sectional diameter of about 1.0mm to about 1.5mm, i.e., a maximum diameter of the at least one cylindrical portion 102, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.013mm, and preferably at least about 0.02 mm; for devices having an eccentrically enlarged abrading head 100 with a maximum cross-sectional diameter of about 1.5mm to about 1.75mm, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.03mm, and preferably at least about 0.05 mm; for devices having eccentrically enlarged abrading heads with a maximum cross-sectional diameter of about 1.75mm to about 2.0mm, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.06mm, and preferably at least about 0.1 mm; for devices having an eccentrically enlarged abrading head with a maximum cross-sectional diameter greater than 2.0mm, the desired distance of the geometric center from the rotational axis of the drive shaft is at least about 0.1mm, and preferably at least about 0.16 mm.
Preferably, the design parameters are selected such that the eccentric abrading head 100 is sufficiently eccentric so that, when rotated at a rotational speed greater than about 20,000rpm by means of the stationary guidewire 15 (held sufficiently taut to preclude any substantial movement of the guidewire), at least a portion of the outer surface 104 of the at least one cylindrical portion 102 can rotate along a path (whether the path is very regular or circular) having a diameter greater than the maximum nominal diameter of the eccentric abrading head 100, i.e., greater than the diameter of the at least one cylindrical portion 102. For example, and without limitation, for an eccentric abrading head 100 having a maximum cross-sectional diameter of about 1.5mm to about 1.75mm, at least a portion of the abrading head 100 rotates along a path having a diameter that is at least about 10% greater than the maximum nominal diameter of the eccentric increasing abrading head 100, preferably at least about 15% greater than the maximum nominal diameter of the eccentric abrading head 100, and most preferably at least about 20% greater than the maximum nominal diameter of the abrading head 100. For an abrading head 100 having a maximum cross-sectional diameter of about 1.75mm to about 2.0mm, at least a portion of the abrading head 100 rotates along a path having a diameter that is at least about 20% greater than the maximum nominal diameter of the abrading head 100, preferably at least about 25% greater than the maximum nominal diameter of the abrading head 100 and more preferably at least about 30% greater than the maximum nominal diameter of the abrading head 100. For an abrading head 100 having a maximum cross-sectional diameter of at least about 2.0mm, at least a portion of the abrading head 100 rotates along a path having a diameter at least about 30% greater than the maximum nominal diameter of the abrading head 100, and preferably at least about 40% greater than the maximum nominal diameter of the eccentrically enlarged abrading head 100.
Preferably, the design parameters are selected such that the enlarged abrading head 100 is sufficiently eccentric so that, when rotated at a rotational speed of about 20,000rpm to about 200,000rpm by means of the stationary guide wire 15, at least a portion of its abrading head 100 rotates along a path (whether the path is very regular or circular) having a maximum diameter that is much greater than the maximum nominal diameter of the stationary abrading head 102, i.e., much greater than the diameter of the stationary at least one cylindrical portion 102. In various embodiments, the present invention can define a general orbital path having a maximum diameter that increases between at least about 50% and about 400% greater than the maximum nominal diameter of the stationary grinding bit 102. Desirably, the maximum diameter of such orbital path is between at least about 200% to about 400% greater than the maximum nominal diameter of the stationary grinding bit 102, i.e., much greater than the diameter of the stationary at least one cylindrical portion 102.
The present invention is not to be considered as limited to the particular embodiments described above, but rather is to 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 instant specification.