Patent Application
20070112371
The invention relates generally to intraluminal distal protection devices for capturing particulate in the vessels of a patient. More particularly, the invention relates to a filter for capturing emboli in a blood vessel during an interventional vascular procedure.
Catheters have long been used for the treatment of diseases of the cardiovascular system, such as treatment or removal of stenosis. For example, in a percutaneous transluminal coronary angioplasty (PTCA) procedure, a catheter is used to insert a balloon into a patient's cardiovascular system, position the balloon at a desired treatment location, inflate the balloon, and remove the balloon from the patient. Another example is the placement of a prosthetic stent in the body on a permanent or semi-permanent basis to support weakened or diseased vascular walls to avoid closure or rupture thereof.
These non-surgical interventional procedures often avoid the necessity of major surgical operations. However, one common problem associated with these procedures is the potential release of atherosclerotic or thrombotic debris into the bloodstream that can embolize distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible for the metal struts of the stent to cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient's vascular system. Further, particles of clot or plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system during vessel treatment. One technique includes the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. A filter placed in the patient's vasculature before or during treatment of the vascular lesion can collect embolic debris in the bloodstream.
It is known to attach an expandable filter to a distal end of a guidewire or guidewire-like member that allows the filtering device to be placed in the patient's vasculature. The guidewire allows the physician to steer the filter to a location downstream from the area of treatment. Once the guidewire is in proper position in the vasculature, the embolic filter can be deployed to capture embolic debris. Some embolic filtering devices utilize a restraining sheath to maintain a self-expanding filter in a collapsed configuration. Once the restraining sheath is retracted by the physician withdrawing the proximal end of the sheath extending outside the patient's body, the expandable filter will attempt to transform itself into its fully expanded configuration. The restraining sheath can then be removed from the guidewire allowing the guidewire to be used by the physician to deliver interventional devices, such as a balloon angioplasty catheter or a stent delivery catheter, into the area of treatment. After the interventional procedure is completed, a recovery sheath can be delivered over the guidewire using over-the-wire techniques to collapse the expanded filter (with the trapped embolic debris) for removal from the patient's vasculature. Both the delivery sheath and recovery sheath should be relatively flexible to track over the guide wire and to avoid straightening the body vessel once in place.
Another distal protection device known in the art includes a filter mounted on a distal portion of a hollow guidewire or tube. A moveable core wire is used to open and close the filter. The filter is coupled at a proximal end to the tube and at a distal end to the core wire. With the physician manipulating a proximal portion of the device outside the patient's body, pulling on the core wire while pushing on the tube draws the ends of the filter toward each other, causing the filter framework between the ends to expand outward into contact with the vessel wall. Filter mesh material is mounted to the filter framework. To collapse the filter, the procedure is reversed, i.e., pulling the tube proximally while pushing the core wire distally to force the filter ends apart. A sheath catheter may be additionally used as a retrieval catheter at the end of the interventional procedure to reduce the profile of the “push-pull” filter, as due to the embolic particles collected, the filter may still be in a somewhat expanded state. The retrieval catheter may be used to further collapse the filter and/or smooth the profile thereof, so that the filter guidewire may pass through the treatment area without disturbing any stents or otherwise interfering with the treated vessel.
However, regardless of how a distal protection filter is expanded during a procedure, i.e., sheath delivered or by use of a push-pull mechanism, a crossing profile of the collapsed filter is to be at a minimum to reduce interference between the filter and other interventional devices or in-placed stents. As well, a compact filter profile is beneficial in crossing severely narrowed areas of vascular stenosis. Furthermore, it is advantageous for a filter to have a short or compact collapsed length, which allows the filter to be utilized in vessels that have minimal space distal to a stenosis. Thus, what is needed is a filter that achieves a reduced profile and/or a compact collapsed length without sacrificing the strength and stability needed for effective embolic capture and retention.
The present invention is a filter for collecting debris in a body lumen. The filter is constructed of an outer tubular member having a first spiral cut along a length thereof and an inner tubular member having a second spiral cut along a length thereof. The first spiral cut and the second spiral cut have opposite chirality, such that the first spiral cut is a right-handed helix and the second spiral cut is a left-handed helix. In an alternate embodiment, the first spiral cut may be a left-handed helix and the second spiral cut a right-handed helix without departing from the scope of the invention. The inner tubular member is coaxially positioned within the outer tubular member to situate the second spiral cut within the first spiral cut, such that when the filter is in an expanded configuration filter openings are defined by intersections between the first and second spiral cuts. The pitch of the first and second spiral cuts may be varied as the cuts extend distally. The pitch may also be decreased as the cuts extend distally to obtain filter openings in a proximal portion of the filter that are larger than filter openings in a distal portion of the filter. In another embodiment, the pitch of the first and second spiral cuts may be held constant over the proximal portions of the inner and outer tubular members and decreased over the distal portions of the inner and outer tubular members to obtain filter openings in a proximal portion of the filter that are larger than filter openings in a distal portion of the filter.
At least one of the inner or outer tubular members is preferably made from a metallic material, such as stainless steel, nitinol, or a cobalt-chromium super alloy. Accordingly, the filter may be heat treated in an expanded or a collapsed configuration to retain its shape. In another embodiment, the outer tubular member may be made from a polymeric material, such as polyethylene block amide copolymer, polyvinyl chloride, polyethylene, polyethylene terephthalate, polyamide, or polyimide. In another embodiment, each of the inner and outer tubular members is a metallic hypotube.
A method of making an embolic filter is also disclosed. The method includes cutting a left-handed helix in a section of outer tubing, cutting a right-handed helix in a section of inner tubing, and slidably inserting the inner tubing into the outer tubing, such that the right-handed helical cut is disposed within the left-handed helical cut. The steps of helically cutting the inner and outer tubing may include varying the pitch of the cuts, such as to gradually decrease the pitch of the cuts as they extend distally. In one embodiment, the method includes securing the distal end of the outer tubing to the distal end of the inner tubing and rotating the proximal end of the inner tube in one direction while rotating the proximal end of the outer tube in an opposite direction to expand the first and second helical cuts into the form of an expanded filter subassembly. The expanded filter subassembly is then heat treated in the expanded configuration to set the size and shape of the filter and the filter openings. In another embodiment, the inner and outer tube subassembly is longitudinally stretched to create elastically deformable open coils. A filter-shaped mandrel is then inserted between the coils to be positioned within the inner and outer tube subassembly. The coils are then arranged around the mandrel and heat treated to set the size and shape of the filter and the filter openings in the expanded filter configuration.
A method according to the present invention may also include selecting metallic hypodermic tubing for at least one of the inner and outer tubes, or for each of the inner and outer tubes. In another embodiment, polymeric tubing may be selected for the outer tube, and a shape memory alloy may be selected for the inner tube.
The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale.
Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” or “distally” are a position distant from or in a direction away from the clinician. “Proximal” and “proximally” are a position near or in a direction toward the clinician.
The present invention is a temporary distal protection device for use on a filter guidewire in minimally invasive procedures, such as vascular interventions or other procedures, where the practitioner desires to capture embolic material that may be dislodged during the procedure. With reference to
Catheter 125 is typically guided to treatment site 115 by a guidewire. In cases where the target stenosis is located in tortuous vessels that are remote from the vascular access point, such as with the coronary arteries 117 as shown in
The present invention is directed to a distal protection device, viz., temporary embolic filter 100, which has a reduced profile in its collapsed configuration or state. In the embodiment shown in
Core wire 318 may be made from a metal, such as nitinol, or a stainless steel wire. In an embodiment of the present invention (not shown), core wire 318 may be tapered at its distal end and/or be comprised of one or more core wire sections. Core wire 318 may be ground down and have several diameters in its profile in order to provide a stiffness transition. Core wire 318 has a proximal end (not shown) that extends outside of the patient from a proximal end (not shown) of proximal shaft 320. Core wire 318 also has coiled portion 308 with windings that extend from distal end 304 of filter 100. Coiled portion 308 may be a separate component from core wire 318, such as a flexible coil spring 608 shown in
In another embodiment of the present invention, proximal shaft 320 may be constructed of multiple shaft components of varying flexibility to provide a gradual transition in flexibility as the shaft extends distally. Such a shaft arrangement is disclosed in U.S. Pat. No. 6,706,055, which is incorporated by reference herein in its entirety. In addition, a liner or axial bearings (not shown) as disclosed in the '055 patent may be utilized between core wire 318 and proximal shaft 320 in order to facilitate sliding movement there between during expansion and collapse of filter 100. In another embodiment, proximal shaft 320 may be a hollow tube enabling filtering device 120 to also function as a medical guidewire.
As illustrated in
In
Second tube 426 is then slidably inserted within first tube 424, such that spiral cut 427 is situated within spiral cut 425 creating tubular subassembly 438, as shown in longitudinal cross-section in
In an embodiment of the present invention, both first and second tubes 424, 426 are comprised of a thin-walled, tubular structure of a metallic material, such as stainless steel, nitinol, or a cobalt-chromium super alloy. Such metallic tubing is commonly referred to as hypodermic tubing or a hypotube. Metallic tubing formed from other alloys, as disclosed in U.S. Pat. No. 6,168,571, which is incorporated by reference herein in its entirety, may also be used in the tubing of the present invention. When either of first or second tubes 424, 426 is made from a heat-treatable alloy, the filter subassembly is shaped into the configuration shown in
In a second embodiment, second inner tube 426 is made from a metal alloy and first outer tube 424 is comprised of tubing made from a thermoplastic material such as polyethylene block amide copolymer, polyvinyl chloride, polyethylene, polyethylene terephthalate, polyamide, or a thermoset polymer such as polyimide. In this embodiment, inner tube 426 is arranged by itself around mandrel 440 in the configuration shown in
Optionally, if outer tube 424 in the second embodiment comprises a thermoplastic material, then subassembly 438 can be heat treated at a temperature suitable to set the filter shape in outer tube 424. The temperature for such a second heat treating step would be lower than the temperature of the first heat treating step due to the differences in thermal properties between themoplastics and metals. The second heat treating step can be performed with or without mandrel 440 supporting the assembly of tubes 424 and 426, depending on the radial strength provided by pre-shaped inner tube 426. If used, mandrel 440 is removed by enlarging an opening 310 or 312 sufficiently to accommodate removing the mandrel without plastically deforming the filter, as described in the previous example. The second embodiment can have a lower collapsed profile than the all-metal embodiment described above because plastic outer tube 424, i.e. polyimide, can be thinner than metal inner tube 426.
In accordance with the present invention, the pitch of spiral cuts 425, 427 may be varied at a constant or variable rate, depending on the desired final size of proximal and distal openings 310, 312. In one embodiment, the pitch may be held constant over the proximal portions of the length of first and second tubes 424, 426, and varied over the distal portions to achieve the desired opening sizes for a particular filter. Alternatively, the pitch may be held constant at a first pitch over the proximal portions of the length of first and second tubes 424, 426, and held constant at a second, smaller pitch over the distal portions.
In
Alternatively, a filter in accordance with the present invention may be deployed and/or retrieved via a sheath catheter, such as by the method and apparatus disclosed in U.S. Pat. Nos. 6,059,814 and 6,346,116, which are incorporated by reference herein in their entireties. Further, the transformation of the filter may be impelled by external mechanical means alone or by self-shaping memory (either self-expanding or self-collapsing) within the filter materials. Preferably, filter 100 is self-expanding, meaning it has a mechanical memory to return to the expanded, or deployed configuration. As previously discussed, such mechanical memory can be imparted to the metallic tubing comprising filter 100 by thermal treatment to achieve a spring temper in stainless steel, for example, or to set a shape memory in a susceptible metal alloy, such as nitinol. Yet another method of transforming a filter in accordance with the invention between deployed and collapsed configurations is described infra with respect to
Inner tube 526 is then inserted within outer tube 524, such that spiral cut 527 is situated within spiral cut 525, creating tubular subassembly 538, as represented in
Optionally, a heat treatment may be performed on expanded tubular subassembly 538 to set a self-expanded size and shape of filter 500 and filter openings 510, 512. In the self-expanding embodiment, the proximal ends 530, 534 are rotated in opposite directions that are reversed relative to arrows A and B in
In an embodiment where outer and inner slotted tubes 524, 526 have unequal torsional stiffnesses, core wire 318 may be incorporated in the filter guidewire to provide rotational control of slotted tubes 524, 526. With core wire 318 affixed within filter distal end 504, outer tube proximal end 530 can be rotated with respect to core wire 318 to expand or collapse spiral cut 525. Similarly, inner tube proximal end can be rotated with respect to core wire 318 to expand or collapse spiral cut 527. Thus, by rotationally manipulating the proximal ends of core wire 318 and slotted tubes 524, 526 extending outside the patient, slotted tubes 524, 526 can be expanded or collapsed independently or simultaneously. For example, outer tube 524 can be rotationally expanded into the expanded configuration simultaneously or before inner tube 526 is expanded. Inner tube 526 can be rotationally collapsed simultaneously or before outer tube 524 is collapsed. For convenience, an accessory or tool (not shown) may be removably mounted to the proximal ends of core wire 318 and slotted tubes 524, 526 to aid in manually controlling and temporarily locking the relative rotational positions of the elements.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.
