Removable vascular filter, catheter system and methods of use

A removable vascular filter and apparatus and methods for removing the removable vascular filter are provided. The removable vascular filter is held in place by a coiled-sheet stent portion having a magnetic band disposed on its interior edge. A catheter system is also provided having an electromagnet configured to engage the magnetic band and enable the coiled-sheet stent portion and filter sack to be wound to a reduced diameter to facilitate transluminal removal of the vascular filter and its contents.

FIELD OF THE INVENTION 
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. 
BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
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.

DETAILED DESCRIPTION OF THE INVENTION 
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.