Removable Vascular Filter, Catheter System and Methods of Use

The present invention relates to apparatus and methods for filtering fluid flow within a vascular system, such as the bloodstream. More particularly, the present invention provides a removable filter for intraluminal use, and catheter apparatus and methods for percutaneous placement and removal of the filter.

Commonly used minimally-invasive procedures for relieving stenoses, such as angioplasty or atherectomy, may dislodge plaque or blood clots. Once dislodged, such atheroma may be carried downstream by the blood and occlude smaller vessels, potentially cutting off the flow of blood to tissue. Such a blockage may present a serious risk to a patient's health, especially if the blockage occurs in a critical vessel leading to the heart or brain.

Moreover, procedures in which foreign objects are introduced into the bloodstream may cause the formation of clots. These clots, if released into the bloodstream, may also block the flow of blood, with potentially life-threatening consequences.

To reduce the risk of embolism, numerous previously known methods have been, and are being, developed. One previously known method, under development by Percusurge, Inc., Sunnyvale, Calif., involves temporarily blocking blood flow in an area in which a procedure is to be performed using a balloontipped occlusion catheter. Materials proximal of the blockage are evacuated from the vessel upon completion of the procedure, the occlusion catheter is removed, and the flow of blood is restored.

The foregoing method has serious drawbacks, however. For example, depending upon the vessel being occluded, the blood flow may only be blocked for a limited time before there is a risk of damage to tissue fed by the blocked vessel. Additionally, use of a balloon-tipped occlusion catheter to block flow may disrupt or loosen plaque within a vessel, much like an angioplasty balloon. This plaque may be released into the bloodstream after the balloon-tipped catheter is removed, possibly causing an embolism.

Another previously known method of reducing the risk of embolization uses a filter to catch loose plaque and clots, while permitting blood to pass through the filter. Numerous implantable filter devices have been developed to prevent clots from reaching critical areas, such as the heart or brain. These filter devices generally are removable only by surgery, especially if a filter device has remained in a vessel for an extended period, e.g., several weeks. Due to the difficulty with removing such devices, previously known filter devices generally are not appropriate for use with procedures such as angioplasty or atherectomy. Also, because these filter devices typically are constructed of a loose wire mesh, they filter out only large clots or plaque fragments.

For example, patients afflicted with chronic thrombophlebitis of the lower extremities often have recurrent pulmonary thromboembolism, which is treated by interruption of the vena cava with implantable filters. Because permanent obstruction of the vena cava can itself have detrimental effect on the patient's health, it would be desirable to provide implantable vascular filters that could be removed after a desired period of implantation.

Apart from implantable filter devices, a number of removable filter devices have been developed for short term use. These devices typically comprise a filter attached to a distal end of a device used during an angioplasty procedure. For example, U.S. Pat. No. 4,723,549, to Wholey et al. shows an angioplasty catheter having a filter disposed near its distal end; U.S. Pat. No. 5,160,342, to Reger et al. describes a guide wire having a filter disposed at its distal end. Such filter devices typically are kept in place only for the duration of a procedure, and are not appropriate for use over an extended period.

In view of the above, it would be desirable to provide a vascular filter device and catheter system that enable the vascular filter to be readily implanted and removed.

It would also be desirable to provide a vascular filter device that may be readily implanted within a vessel, remain in place for an extended period, and may be readily removed at the end of the period.

It is an object of the present invention to provide a vascular filter device and catheter system that enable the vascular filter to be readily implanted and removed.

It is a further object of the present invention to provide vascular filter device that may be readily implanted within a vessel, remain in place for an extended period, and may be readily removed at the end of the period.

These and other objects are achieved by providing a filter device comprising a filter portion attached to a removable vascular stent portion. In a preferred embodiment, the filter portion is a nylon mesh bag or sack, and the removable vascular stent portion comprises a coiled-sheet stent. When the coiled-sheet stent portion is released within a vessel, it uncoils to engage a wall of the vessel and deploys the filter element across the flow path. The nylon mesh sack filters blood passing through the device, catching clots and plaque fragments that might otherwise cause harm.

In accordance with the principles of the present invention, the coiled-sheet stent portion includes a magnetic band disposed along its interior edge that is used to engage and remove the filter device from the vessel. A catheter system comprising an outer sleeve enclosing a shaft having an electromagnetic plate is positioned within the interior of the coiled-sheet stent portion. When the catheter system is disposed adjacent to the magnetic band on the coiled-sheet stent portion, the electromagnetic plate is activated, and the magnetic band is drawn through a slot in the outer sleeve and engages the electromagnetic plate. The shaft holding the electromagnetic plate is then rotated, coiling the stent around the shaft, and capturing the stent within the outer sleeve. As the stent is coiled, the diameter of the nylon mesh sack decreases, thereby enabling the sack and its contents to be readily removed from the vessel.

Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiment, in which like reference characters refer to like parts throughout, and in which:

FIGS. 1A and 1B are, respectively, a perspective view of an illustrative filter device constructed in accordance with the present invention in an expanded, deployed state, and in a contracted state for transluminal delivery;

FIGS. 2A-2C illustrate steps of a method of deploying the filter device of FIGS. 1 in a vessel;

FIG. 3 is an exploded perspective view of an illustrative catheter system constructed in accordance with the present invention;

FIGS. 4A and 4B are respectively, a perspective view and cross-sectional view, taken along view line 4B--4B, of the vascular filter device of FIGS. 1 engaged with the catheter system of FIG. 3;

FIGS. 5A and 5B are respectively, a perspective view and cross-sectional view, taken along view line 5B--5B, of the vascular filter device of FIGS. 1 wound within the catheter system of FIG. 3; and

FIGS. 6A-6C are cross-sectional views showing reduction of the circumference of the filter sack portion of the filter device of FIGS. 1 during the coiling process of FIGS. 5.

Referring to FIGS. 1A and 1B, illustrative removable vascular filter device 10 constructed in accordance with the present invention is described. Filter device 10 comprises filter sack 12 connected to end 13 of coiled-sheet stent portion 14. Filter sack 12 may be attached to coiled-sheet stent portion 14 by suitable means, such as sutures or a biocompatible adhesive.

Filter sack 12 preferably comprises a monofilament nylon mesh having openings 15 large enough to permit blood to pass freely through the mesh, but sufficiently small to filter out blood clots or plaque fragments that may cause an embolism. For example, for filter applications in vessels such as the superior vena cava or inferior vena cava, openings 15 in sack 12 preferably are between 4 and 9 square millimeters in area. Filter sack 12 also includes fold 16. Fold 16 enhances the ability of the filter sack to fold over itself when coiled-sheet portion 14 is coiled to its delivery state, and during removal of the filter device.

Coiled-sheet stent portion 14 has a contracted delivery state, wherein the stent may be wound down to a small diameter for transluminal delivery, and an expanded, deployed state, wherein the stent engages a wall of a vessel and deploys the filter sack to span the flow area of the vessel. In the deployed state, coiled-sheet stent portion 14 retains filter device 10 at a desired location within a vessel. An example of a coiled-sheet stent suitable for use in vascular filter device 10 of the present invention is described in U.S. Pat. No. 5,433,500 to Sigwart, which is incorporated herein by reference.

Coiled-sheet stent portion 14 preferably comprises a flexible biocompatible metallic material, such as stainless steel or a nickel-titanium alloy. If a nickel-titanium alloy is employed, coiled-sheet stent portion 14 may exhibit either thermally-activated shape memory or pseudoelastic behavior. Coiled-sheet stent portion 14 preferably includes a plurality of apertures in its lateral surface, to enable blood to nourish the vessel endothelium when the stent is implanted in a vessel.

In accordance with one aspect of the present invention, coiled-sheet stent portion 14 includes magnetic band 18 comprising a biocompatible ferrous material disposed along interior edge 19 of coiled-sheet stent portion 14. Magnetic band 18 is used to wind coiled-sheet stent portion 14 within a catheter to retrieve the filter device 10 after implantation in a vessel, as described in detail hereinafter.

With respect to FIG. 1B, filter device 10 is shown in its contracted delivery state, wherein coiled-sheet stent portion 14 is wound to form a series of overlapping turns and has a diameter sufficiently small to enable transluminal delivery. When coiled-sheet stent portion 14 is wound to its contracted delivery state, filter sack 12 also assumes a coiled shape having a reduced diameter. This reduced diameter enables filter device 10 to be readily moved through the vascular system for deployment or removal.

Referring now to FIGS. 2A to 2C, illustrative steps of percutaneously implanting vascular filter device 10 of FIGS. 1 are described. As will of course be apparent to one of skill in the art of stent delivery systems, other ways of deploying the stent portion of a filter device constructed in accordance with the present invention may be employed.

In FIG. 2A, catheter 20 includes filter device 10, wound to its contracted delivery state, disposed within distal end 21. Catheter 20 may be percutaneously and transluminally positioned within vessel V, in which the vascular filter device is to be deployed. Alternatively, filter device 10 may be advanced through catheter 20 once catheter 20 is in position.

With respect to FIG. 2B, after catheter 20 is determined to be in a desired position, e.g., using fluoroscopy, pushrod 24 is used to push filter device 10 out of distal end 21 of catheter 20. Alternatively, pushrod 24 may be held stationary while catheter 20 is retracted proximally. In either case, once filter 10 exits distal end 21, coiled-sheet stent portion 14 uncoils (either mechanically or by undergoing a thermal phase transition), and expands into engagement with the circumference of vessel V.

As shown in FIG. 2C, transition of coiled-sheet stent portion 14 to its expanded, deployed diameter also causes filter sack 12 to uncoil and expand across the flow path. Catheter 20 then is withdrawn, leaving filter device 10 in place within vessel V. Filter device 10 may remain in place while procedures such as angioplasty or atherectomy are performed, to capture plaque and blood clots released into the bloodstream by such procedures. Filter device 10 then may be removed using the apparatus of FIG. 3, as described hereinbelow, or left in place for an extended period of time, e.g., several weeks, to filter out any material which may enter the bloodstream later.

Referring now to FIG. 3, catheter system 30 constructed in accordance with the present invention is described. Catheter system 30, shown in an exploded view in FIG. 3, comprises shaft 32 disposed within outer sleeve 34. Shaft 32 includes electromagnetic plate 36 disposed in distal region 38. Electromagnetic plate 36 is preferably about the same length, or slightly larger than, magnetic band 18 of coiled-sheet stent portion 14 of vascular filter device 10, and may be selectively energized by a power source (not shown), to create a magnetic field surrounding plate 36.

Outer sleeve 34 includes slot 40 extending proximally from distal endface 42 for a distance about equal to the length of electromagnetic plate 36. When assembled, shaft 32 is disposed for rotation within outer sleeve 34 so that distal endface 44 of shaft 32 is approximately flush with distal end 42 of outer sleeve 34, and electromagnetic plate 36 may be aligned with slot 40 of outer sleeve 34. During removal of filter device 10, electromagnetic plate 36 is first activated to engage magnetic band 18, and then shaft 32 is rotated to coil filter device 10 around shaft 32.

Referring to FIGS. 4A and 4B, catheter system 30 is shown disposed within coiled-sheet stent portion 14 of implanted vascular filter device 10 in preparation for removal of device 10. Electromagnetic plate 36 first is aligned through slot 40 with magnetic band 18 of coiled-sheet stent portion 14, for example, as determined by fluoroscopy. Electromagnetic plate 36 then is activated to create a magnetic field that draws magnetic band 18 through slot 40 and into magnetic engagement with electromagnetic plate 36 (see FIG. 4B). Annular space 46, between outer sleeve 34 and shaft 32, is sized to accommodate coiled-sheet stent portion 14 of filter device 10 when wound around shaft 32.

Once magnetic band 18 is engaged with electromagnetic plate 36, shaft 32 is rotated within outer sleeve 34 in a direction that causes coiled-sheet stent portion 14 of device 10 to become wound around shaft 32, as shown in FIGS. 5A and 5B. As coiled-sheet stent portion 14 is wound onto shaft 32, filter sack 12 also is wound to a reduced diameter, as illustrated in FIG. 6A to 6C.

Fold 16 enables filter sack 12 to readily fold over itself, so that it may be wound to a smaller diameter without inhibiting the process of winding coiled-sheet stent portion 14 within outer sleeve 34. Once coiled-sheet portion 14 is coiled to a reduced diameter removal state within outer sleeve 34, catheter system 30, vascular filter device 10, and the contents of filter sack 12 may be transluminally withdrawn.

While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention, and the appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.