Patent Application
20150089785
1. Field of the Invention
The invention relates to devices and methods for removing tissue from body passageways, such as removal of atherosclerotic plaque from arteries, utilizing a high-speed rotational atherectomy device. More particularly, the present invention relates to attachment of heads that may be used with an atherectomy device.
2. Description of the Related Art
A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very often over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Rotational atherectomy procedures have become a common technique for removing such stenotic material. Such procedures are used most frequently to initiate the opening of calcified lesions in coronary arteries. Most often the rotational atherectomy procedure is not used alone, but is followed by a balloon angioplasty procedure, which, in turn, is very frequently followed by placement of a stent to assist in maintaining patency of the opened artery. For non-calcified lesions, balloon angioplasty most often is used alone to open the artery, and stents often are placed to maintain patency of the opened artery. Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience stent restenosis—i.e., blockage of the stent which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. In such situations an atherectomy procedure is the preferred procedure to remove the excessive scar tissue from the stent (balloon angioplasty being not very effective within the stent), thereby restoring the patency of the artery.
Several kinds of rotational atherectomy devices have been developed for attempting to remove stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (Auth), a burr covered with an abrasive abrading material such as diamond particles is carried at the distal end of a flexible drive shaft. The burr is rotated at high speeds (typically, e.g., in the range of about 150,000-190,000 rpm) while it is advanced across the stenosis. As the burr is removing stenotic tissue, however, it blocks blood flow. Once the burr has been advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr. Frequently more than one size burr must be utilized to open an artery to the desired diameter.
U.S. Pat. No. 5,314,438 (Shturman) discloses another atherectomy device having a drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged surface being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery. The disclosure of U.S. Pat. No. 5,314,438 is hereby incorporated by reference in its entirety.
U.S. Pat. No. 5,681,336 (Clement) provides an eccentric tissue removing burr with a coating of abrasive particles secured to a portion of its outer surface by a suitable binding material. This construction is limited, however because, as Clement explains at Col. 3, lines 53-55, that the asymmetrical burr is rotated at “lower speeds than are used with high speed ablation devices, to compensate for heat or imbalance.” That is, given both the size and mass of the solid burr, it is infeasible to rotate the burr at the high speeds used during atherectomy procedures, i.e., 20,000-200,000 rpm. Essentially, in this prior art device, the center of mass offset from the rotational axis of the drive shaft would result in development of significant centrifugal force, exerting too much pressure on the wall of the artery and creating too much heat and excessively large particles.
U.S. Pat. No. 5,584,843 (Wulfman) discloses one or more ellipsoidal burrs or cuffs attached to a flexible drive shaft. The drive shaft is placed over a preformed shaped guidewire so that the drive shaft and burrs conform to the shape and profile of the guide wire, i.e., a gentle “S” or “cork-screw” shape. Wulfman, however, requires the preformed guidewire to achieve the non-linear shaping of the drive shaft, a deformed shaping state that is, therefore, present when the device is not rotated. Thus, Wulfman's burrs comprise a sweeping diameter that is limited to, and by, the guidewire shaping. In addition, each of Wulfman's burrs are elliptical and symmetric about the rotational axis of the drive shaft with each center of mass for the burrs being on the drive shaft's rotational axis. Thus, the sweeping diameter of Wulfman is not induced by rotational speed and, therefore, cannot be controlled other than by the guidewire's shaping. Difficulties in positioning the shaped, undeformed, guidewire without damaging the patient's vasculature are also present.
In many of the above-described devices, the mentioned burrs may be secured to the drive shaft with a slip fit that engages the drive shaft relatively loosely if at all. The burrs may then be otherwise secured to the drive shaft with brazing or soldering, for example, which can be inconsistent. The present invention helps to overcome these inconsistencies.
In one embodiment, a method for attaching a head to a drive shaft may include winding a wire to create a drive shaft with an outside diameter and selecting a head having a length and having a bore with an inside diameter smaller than the outside diameter of the drive shaft. The method may also include forming a tapered tip on a distal end of the drive shaft, the tapered tip having a length greater than the length of the head, and placing the head on the tapered tip such that a distal end of the tapered tip extends from a distal end of the head. The method may also include engaging the distal end of the tapered tip and turning down the drive shaft to create a turned down portion having a length equal to or greater than the length of the head and having a reduced outside diameter that is less than or equal to the inside diameter of the bore. The method may also include advancing the head proximally over the turned down portion. The method may also include disengaging the distal end of the tapered tip, wherein, at or before disengaging, the turned down portion tends toward returning the reduced outside diameter to the outside diameter and is confined from doing so by the bore of the head thereby creating a friction fit between the drive shaft and the head.
In another embodiment, a method for attaching a head to a drive shaft may include selecting a head having a length and having a drive shaft engagement feature with a cross-sectional dimension smaller than an outside diameter of the drive shaft. The method may also include placing the head on an extension feature of the drive shaft such that a distal end of the extension feature extends from a distal end of the head. The method may also include engaging the extension feature and turning down the drive shaft to create a turned down portion having a reduced outside diameter that is less than or equal to the inside diameter of the engagement feature. The method may also include advancing the head proximally over the turned down portion and disengaging the distal end of the extension feature.
In yet another embodiment, a method for attaching a head to a drive shaft may include selecting a head having a length and having a drive shaft engagement feature with a cross-sectional dimension smaller than an outside diameter of the drive shaft. The method may also include reducing the outside diameter of the drive shaft for a portion of the drive shaft less than the full length of the drive shaft. The method may also include placing the head on the portion with the reduced outside diameter.
The figures and the detailed description which follow more particularly exemplify these and other embodiments of the invention.
The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, which are as follows.
While the invention is amenable to various modifications and alternative forms, specifics thereof are shown by way of example in the drawings and described in detail herein. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
The handle 10 may include a turbine (or similar rotational drive mechanism) for rotating the drive shaft 20 at high speeds. The handle 10 typically may be connected to a power source, such as compressed air delivered through a tube 16 or electrical power delivered with an electrical connection. A pair of fiber optic cables 25, or a single fiber optic cable, for example, may also be provided for monitoring the speed of rotation of the turbine and drive shaft 20. Details regarding such handles and associated instrumentation are well known in the industry. The handle 10 also may include a control knob 11 for advancing and retracting the turbine and drive shaft 20 with respect to the catheter 13 and the body of the handle.
As will be appreciated, there are several different types of heads 27 that may be provided for use in an atherectomy process. In some embodiments, a relatively symmetrical head may be used and in other embodiments an asymmetric head 27 may be provided such that a rotational eccentricity may be provided to increase the diameter of the path that the head 27 travels when rotated. In some embodiments, the head 27 may include a peripheral abrading surface for purposes of increasing the head's ability to clear away stenotic material. In any case, the head 27 may include a drive shaft 20 engagement feature such as a longitudinal bore or other receiving area for attaching the head 27 to the drive shaft 20.
In some cases, the head 27 may include a bore 30 having a diameter that is the same as or just slightly smaller than the outer diameter of the drive shaft 20 and the head 27 may be slip-fit onto the drive shaft. However, it is advantageous to have a fit that is more snug than the slip fit described. A more snug fit, or friction fit, may be provided by providing a head 27 with a bore diameter smaller than the outer diameter of the drive shaft 20. As shown by comparing
Referring to
The geometry of the tapered tip 34 may therefore be selected to allow the distal tip to project from the distal end of the head 27 when the head 27 is placed on the tapered tip 34. This geometry may allow the distal tip of the taper 34 to be engaged by a turning tool, such that the drive shaft 20 may be turned down and the head 27 may be moved proximally as shown in
Once a sufficient length of the drive shaft 20 has had its diameter reduced, the head 27 may be moved proximally over the turned down portion. Once the head 27 has been placed as desired, the distal tip of the drive shaft 20 may be released, or alternatively unwound, thereby causing the portion of the drive shaft within the head 27 to attempt to return to its original size. As will be appreciated, the inner diameter, or other internal cross-sectional dimension, of the head 27 will confine the drive shaft 20 to a smaller diameter than its at rest diameter causing the drive shaft 20 to press outwardly on the inner surface of the head 27 creating a friction fit. Once the head 27 is in place, the tapered tip 34 may be clipped off, or otherwise removed allowing the inner lumen of the drive shaft 20 to be available for passing through of a guidewire, for example.
In addition to the friction fit provided, the head 27 may also be secured to the drive shaft 20 with a secondary treatment. For example, in some embodiments, the head 27 may also be brazed to the drive shaft. In other embodiments, the head 27 may be welded, soldered, adhered, or otherwise affixed to the drive shaft 20. Still other secondary treatments may be provided for securing the head 27 to the drive shaft 20.
The tapered tip 34 may be pre-treated to allow the handling of the tip as described. That is, in some embodiments the tapered tip 34 may be heat-treated to harden the tip 34 and resist deformations when the tip 34 is gripped or otherwise engaged for the turning down process. In other embodiments, the tapered tip 34 may be brazed, welded, filled, or otherwise treated to resist collapse or deformation under the gripping or other engaging forces used during the turning down process. However, it is to be appreciated that where brazing, welding, filling, or other techniques are used, such techniques may be limited to portions of the tapered tip 34 that have diameters less than the inner diameter of the head 27 so as to avoid a situation where a portion of the tapered tip 34 is both larger than the inner diameter of the head 27 and also resists reduction in size wherein the head 27 may be more difficult or even prevented from being properly positioned.
It is to be appreciated that the turning down of the drive shaft 20 may be performed elastically. That is, the amount of reduction in the diameter may be such that the bending caused in the windings of the drive shaft 20 are limited to elastic bending forces such that, when released, the drive shaft 20 will tend toward returning to its previous size and shape. It is also to be appreciated that, due to the friction between the windings of the drive shaft 20, the effect of the turning down of the distal tip on the diameter of the drive shaft 20 may be reduced as you move proximally along the drive shaft 20. (i.e., away from point where the turning is imparted) This effect may be adjusted or modified depending on how much of, and at what location, the proximal portion of the drive shaft 20 is held stationary.
It is also to be appreciated that while the head 27 is shown to be positioned immediately proximal to the distal end of the drive shaft 20, the drive shaft 20 may be turned down for a longer length in
Turning now to
As with the embodiment of
Turning now to
It is to be appreciated that while the tightly wound extension 42 is shown to be arranged along the longitudinal axis 32 of the drive shaft 20, the extension 42 may also extend parallel to the longitudinal axis 32, but in line with an outer periphery of the drive shaft 20. This may avoid encountering bending forces that may be too high for the arm 44 shown in
Like the tapered tip 34, the tightly wound extension 42 may have a length at least slightly longer than the head 27 such that the distal end of the tightly wound extension 42 may be engaged by a gripping tool or other engaging too while the head 27 is in place thereon. In other embodiments, as also mentioned with respect to the tapered tip 34, the length of the tightly wound extension 42 may be selected to allow one or more heads 27 to be placed thereon such that one step of turning down the drive shaft 20 may allow placement of the one or more heads 27. In addition, and again like the tapered tip 34, all or a portion of the tightly wound extension 42 may be heat treated, brazed, soldered, or welded to provide a stronger member capable of withstanding the gripping or other engaging pressures encountered from the gripping or engaging tool.
It is to be appreciated that the methods shown in
In addition to particular drive shaft adaptations and particular tools that may be used to “reach” through the head 27, another approach shown in
In still other embodiments, a more conventional drive shaft 20 may be provided and more conventional tools may be used to grip and/or engage the drive shaft 20 such that it may be turned down. In this embodiment, as shown in
The present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present specification.
