Apparatus and method for retrieving an implanted device from a body vessel

An apparatus for retrieving an implanted device from a body vessel includes a distal hub with an elongated, bendable distal tip and with a first marker visible through body tissue with at least one imaging method; a proximal hub with a central longitudinal channel therethrough, arranged proximal from the distal hub, and bearing a second marker. A stylet wire extends from the distal hub through the central longitudinal channel of the proximal hub to a proximal stylet wire end. A flexible, radially expandable interlocking arrangement extends from the distal hub to the proximal hub. An elongated positioning device extending proximally from the proximal hub to a proximal device end. The positioning device and the stylet wire may be configured to perform a longitudinal relative movement between proximal hub and the distal hub, and the interlocking arrangement expands radially when the proximal and distal hubs approach each other.

TECHNICAL FIELD

This invention relates to an apparatus for removing devices implanted in biological tissue. More particularly, the invention relates to an apparatus for removing a vena cava filter from a body vessel, especially a vena cava filter that may not be removable by grabbing a removal hook.

BACKGROUND

Filtering devices that are percutaneously placed in a vena cava have been available for many years. A need for filtering devices arises in trauma patients, orthopedic surgery patients, neurosurgery patients, or in patients having medical conditions requiring bed rest or non-movement. During such medical conditions, the need for filtering devices arises due to the likelihood of thrombosis in the peripheral vasculature of patients wherein thrombi break away from the vessel wall, risking downstream embolism or embolization. For example, depending on the size, such thrombi pose a serious risk of pulmonary embolism wherein blood dots migrate from the peripheral vasculature through the heart and into the lungs.

A filtering device can be deployed in the vena cava of a patient when, for example, anticoagulant therapy is contraindicated or has failed. Filters have been used or considered in preoperative patients and in patients predisposed to thrombosis which places the patient at risk for pulmonary embolism.

In certain situation, it is desirable to remove a vena cava filter from the patient body. After deployment of a filter in a patient, however, proliferating intimal cells begin to accumulate around the filter struts which contact the wall of the vessel. Additionally, filters may become off-centered or tilted with respect to the hub of the filter and the longitudinal axis of the vessel in which it has been inserted. As a result, the filter including the hub and the retrieval hook may engage the vessel wall along their lengths and potentially become endothelialized therein. Under such conditions, it is very difficult if not impossible to engage the retrieval hook in a known manner with a snare.

SUMMARY

It is an object of the present invention to provide an apparatus and a method that make it possible to retrieve a vena cava filter from a body vessel without engaging the retrieval hook of the vena cava filter.

According to a first aspect of the invention, a device for retrieving an implanted device from a body vessel is provided. The apparatus comprises a distal hub having an elongated, bendable distal tip and bearing a first marker visible through body tissue with at least one imaging method; a proximal hub with a central longitudinal channel therethrough, the proximal hub being arranged proximal from the distal hub and bearing a second marker visible through body tissue with the at least one imaging method; a stylet wire proximally extending from the distal hub through the central longitudinal channel of the proximal hub to a proximal stylet wire end; a flexible, radially expandable interlocking arrangement extending from the distal hub to the proximal hub; and an elongated positioning device extending proximally from the proximal hub to a proximal device end. The positioning device and the stylet wire may be configured to perform a longitudinal relative movement between proximal hub and the distal hub, and the interlocking arrangement may be configured to radially expand when the proximal and distal hubs approach each other.

According to another aspect of the invention, the interlocking arrangement may include a plurality of flexible elongated elements extending from the proximal hub to the distal hub. For example, the flexible elongated elements may be wires. According to a further aspect of the invention, the flexible elongated elements may be twisted around a portion of the stylet wire that extends between the proximal hub and the distal hub.

According to yet another aspect of the invention, the interlocking arrangement may include a plurality of bendable, generally flat strips extending from the proximal hub to the distal hub. The flat strips may be arranged circumferentially adjacent to each other and separated from each other by slits. Each of the flat strips may describe a helical curve around a portion of the stylet wire that extends between the proximal hub and the distal hub.

According to yet another aspect of the invention, the strips may be unitary with the distal hub.

According to another aspect of the invention the distal hub has a length of at least about 3 cm, preferably about 5 cm. Alternatively, the length of the distal hub may be about equal to a length of a vena cava filter.

According to a further aspect of the invention, the distal hub has a hub diameter and the interlocking arrangement has a passive state and an active state. In the passive state, the interlocking arrangement has a passive length and a passive diameter, and in the active state the interlocking arrangement has an active length and an active diameter. The passive diameter may be no greater than about the hub diameter, the active diameter may be greater than the hub diameter, and the passive length may be shorter than the active length. Further, the passive length of the interlocking arrangement may be smaller than the hub length of the distal hub. For example, the passive length may be between about 20 mm and about 40 mm, more particularly, between about 25 mm and about 35 mm.

According to yet another aspect of the invention, the passive length may be adjustable by inserting a subassembly into a tubular distal hub that radially restricts a distal first axial portion of the subassembly and allows an unrestricted radial expansion of a second axial portion proximal of the first axial portion, the second axial portion forming the radially expandable interlocking arrangement.

According to another aspect of the invention, the proximal hub may be formed by a coil of wires with axially gap-free windings.

According to yet another aspect of the invention, a method is provided for removing a generally cone-shaped, collapsible vena cava filter from a filter location inside a body vessel, wherein the vena cava filter has a filter hub at a hub side and a generally cone-shaped filter body extending from the filter hub toward a body side, the filter body having open spaces therethrough. The removal method comprises the steps of providing a catheter with a length about sufficient to extend from an operator to the filter location; providing a removal device with a distal hub having an elongated, bendable distal tip and bearing a first marker visible through body tissue with at least one imaging method; a proximal hub with a central longitudinal channel therethrough, the proximal hub being arranged proximal from the distal hub and bearing a second marker visible through body tissue with the at least one imaging method; and a flexible, radially expandable interlocking arrangement extending from the distal hub to the proximal hub; inserting the catheter into the body vessel from the hub side to a position, in which a distal end of the catheter resides proximally from the filter location; inserting the removal device through the catheter into the body vessel from the hub side; distally advancing the distal hub through one of the open spaces of the filter body to a position distal from the filter hub; further advancing the removal tool through the open space until the proximal hub is located distal from the filter hub inside the filter body; proximally moving the distal hub relative to the proximal hub so as to radially expand the interlocking arrangement; proximally retracting the removal tool while engaging at least one of the filter body and the filter hub; proximally displacing the vena cava filter into the distal end of the catheter; and removing the catheter.

Further details and advantages of the invention will become apparent from the following description of several embodiments of the invention shown in the accompanying drawings. The drawings are provided for purely illustrative purposes and are not intended to limit the scope of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawings are purely schematic illustrations of various aspects of the invention and are not necessarily to scale, unless expressly stated.

FIG. 1depicts a first embodiment of a filter removal apparatus10, that comprises a stylet12, a distal hub14covering a distal end16of the stylet12, a proximal hub18movably disposed around the stylet12, and a radially expandable interlocking arrangement20extending from the distal hub14and distally attached to the proximal hub18. An actuator portion22, such as an elongate cannula is slidably disposed over the stylet12proximal from the interlocking arrangement20.

The actuator portion22is shown at an axial distance from the proximal hub18, but is preferably placed adjacent to the proximal hub during use as will be explained in connection withFIGS. 4athrough4d. The interlocking arrangement20has a plurality of expandable members24configured to deform plastically or elastically as the interlocking arrangement20is longitudinally compressed, at least some of the expandable members24eventually bowing outward.

The expandable members24provide a positive fixation inside the body of a vena cava filter, for example between struts, by filling up a space axially distal from a filter hub, which allows the stylet12retract the filter from the body vessel into which it has been implanted. This positive fixation with respect to a movement in the proximal direction allows the filter to be pulled proximally and to allow the struts of the filter body to withdraw from the walls of the body vessel. The filter removal apparatus10has a pull strength sufficient to provide the traction needed to free the filter, absent complicating factors such as extensive formation of scar tissue along the length of the lead.FIGS. 4athrough4dwill illustrate further details of the filter removal process.

In the embodiment ofFIG. 1, the expandable members24of the interlocking arrangement20are formed by a multifilar wire bundle26that comprises a series of adjacent wires28helically wrapped around the stylet12. In the illustrative embodiment, the multifilar wire bundle26includes six individual expandable members24formed by the helically wound metal wires28; however any practical number of wires28can be used. It has been found that using a multifilar wire bundle26, rather than a single helically wound wire, allows for greater expansion. The shown arrangement results in a 0.015″ outer diameter locking stylet that can expand to a sufficient diameter to engage and remove the vena cava filter. The term ‘engage’ as used within the portion of the specification describing the embodiments shown inFIGS. 1-4, is defined as a situation in which the expandable members24displace, shift, or otherwise intersperse with a filter body in a manner that forms a locking interaction or biting engagement.

One method of forming the multifilar wire bundle26is to helically wind the six individual wires28together over a pin with a diameter about equal to or slightly larger than that of the stylet12in the configuration that will ultimately be distally attached to the stylet12. The individual wires28can be soldered together, if so desired, at their proximal end, which in that case, the stylet wire should be made of a material like titanium or nitinol or another material, to which the solder will not stick. Once helically wound, the multifilar wire bundle26is inserted over the stylet12as shown inFIG. 1.

The interlocking arrangement20comprising the multifilar wire bundle26of the illustrative embodiment is connected to both a relatively tightly wound distal portion29and the proximal hub18. In the shown embodiment, the distal hub14fixates the tightly wound distal portion29of the multifilar wire bundle26that is affixed to the stylet12near the distal end16of the locking stylet10with a distal fixation joint32such as a solder joint, a crimped band, or some other well-known attachment of fixation means. Alternatively, the distal end of the interlocking arrangement may be fixated on the distal hub14, which in turn may be fixed on the stylet12.

In the illustrative embodiment ofFIG. 1, the multifilar wire bundle26is wound with spaces between the windings of the expandable interlocking arrangement20to permit expansion during deployment by proximally pulling the distal hub14toward the proximal hub18with the stylet12. While a radial expansion of the wires28can be achieved with wires28extending straight in a longitudinal direction between the proximal hub18and the distal hub14, the twisted arrangement of the wires28further causes the wires28to intertwine with each other and to form a sturdy bunched structure34similar to a knot, as illustrated inFIG. 4c.

InFIG. 1, the proximal hub18is also formed by tightly wound proximal wire ends with a lumen of a diameter that allows a relative longitudinal movement between the proximal hub18and the stylet12. In the area of the proximal hub18, gaps between the individual wires28are generally minimal (e.g., about 0.0035″) to nonexistent.

The distal hub14is formed by a flexible, elongated tip36in the shape of a unilaterally closed tube. The closed end38forms the distal end of the distal hub14and may be rounded for easier insertion into the body vessel. Both the proximal hub18and the distal hub14bear markers40visible through customary imaging methods, for example radiopaque markers for x-ray monitoring or echogenic markers for ultrasound monitoring. The marker40on the proximal hub is preferably arranged near the proximal end of the proximal hub to ensure, as will be described later, that the proximal hub18has been advanced past a filter hub. The marker40on the distal hub is preferably adjacent to or near the expandable arrangement20for monitoring the position of the distal hub14relative to the proximal hub18. Because the distal hub14is longer than the proximal hub, the marker40disposed on the distal hub may be larger than the marker40on the proximal hub18. It is, however, well within the scope of the present invention that the two markers40have the same size or that the markers40occupy the entire surface of the respective hub14or18.

While in the shown example the individual wires28of the multifilar wire bundle26are aligned tightly together within the bundle26, gaps between the wires28are well within the scope of the present invention. In the distal portion29, gaps between the individual wires28are generally minimal (e.g., 0.0035″) to nonexistent. The pitch, i.e. the longitudinal distance over which a given wire makes a 360° turn around the stylet12, can vary for the interlocking arrangement20, depending on a number of parameters (number of wires, wire diameter, etc.) and the range of expansion desired. In the illustrative embodiment, the expandable interlocking arrangement has a length of about 1.2″ (3 cm) and includes a six-wire bundle26of about 0.004″ stainless steel wire so that the multifilar wire bundle26measures about 0.024″ in width. The length of the expandable interlocking arrangement20may vary depending on the desired application and may range between about 2 cm and about 4 cm, preferably between about 25 mm and about 35 mm.

Over the length of the interlocking arrangement20, the wire bundle surrounds the stylet12about one or two times so that the pitch of the wires28lies in the range of about 1.5 cm to about 3 cm. These dimensions are merely illustrative and can be varied according to various structural parameters selected and the desired performance characteristics of the filter removal apparatus10. At the proximal hub18, a proximal fixation joint30, such as a silver solder joint or other bonding means, may be included. At the proximal hub18, only the individual wires28may be soldered together in the proximal fixation joint30, leaving the interlocking arrangement20free to slide over the stylet12at that point. An optional ring, section of cannula, or other structure can be attached to the proximal hub18to provide a surface against which the actuator portion22may contact. Alternatively, the proximal hub18or the proximal end of the interlocking arrangement20may be attached to the actuator portion22.

In the illustrative embodiment ofFIG. 1, the stylet12comprises a 0.0075″ 304 stainless steel spring tempered wire with a tensile strength of 382/455 ksi. The actuator portion22comprises a thin wall cannula, such as a 28 gauge hypodermic needle cannula. The actuator portion22extends approximately 60 cm to a distal handle (not shown) to which it is affixed. The wires28are, for example, 0.0035-0.004″ annealed304stainless steel wires. The combination of a 0.0075″ stylet12and 0.004″ wires28yields a device having a 0.0155″ outer diameter, but the invention is not limited to any of these dimensions.

As previously mentioned, the interlocking arrangement20is about 3 cm long. The distal hub14may have a length of up to about 5 cm, and the proximal hub may measure about 0.5 cm. The dimensions of the interlocking arrangement20can be quite variable. The length of the interlocking arrangement20being about 3 cm, however, allows for a sufficient radial expansion for removing a vena cava filter. Depending on the specific situation, a distal hub14of a shorter length may be used so that the interlocking arrangement20is longer because fewer windings are covered by the distal hub14. For example, the distal hub may have a length within a range of about 3 cm to about 7 cm. The overall length of the locking stylet inFIG. 1is approximately 140 cm.

As depicted inFIG. 1, proximal from the proximal hub18, the actuator portion22provides support to axially compress and radially expand the expandable interlocking arrangement20by moving the distal hub14toward the proximal hub18. The actuator portion22may even be formed integral with the proximal hub18adjacent the interlocking arrangement20or separate from the proximal hub18. A braided tube of metal, plastic, or some other material may form the actuator portion22. In each of these embodiments, handles on the proximal ends of the stylet12and the actuator portion22which are used to expand the expandable interlocking arrangement20are not shown inFIG. 1and may be arranged in a known manner.

As previously noted, the configuration of the interlocking arrangement20is variable, largely depending on materials of its construction. It is preferred that the wires28be annealed; however, it is possible that only a selected portion of the interlocking arrangement20, e.g. the expandable interlocking arrangement20, be annealed, or it is possible to have different degrees of annealing across the length of the expandable portion. While the illustrative embodiment utilizes round wire, wires with alternate cross-sectional geometries (e.g., square, triangular, flattened, etc.) may be used to provide different properties for expanding and engaging the coils of the lead. Other features could be incorporated such as altering the surface properties of the wire by adding roughness or applying a polymeric coating that could possibly improving engagement with the coils. Yet another embodiment would be to include wires with different physical properties within a single multifilar wire bundle26.

FIGS. 2aand2bas well asFIG. 3depict alternative expandable interlocking arrangements suitable for use in a filter removal apparatus similar to the embodiment shown inFIG. 1. In the embodiment ofFIGS. 2aand2b, a filter removal apparatus110comprises a tubular flexible element150that unitarily forms a distal hub114, an expandable interlocking arrangement120, and a proximal hub118as depicted inFIG. 2a. Expandable members124are formed as strips between axial slits152that extend in a substantially parallel manner along the length of the expandable interlocking arrangement120. Markers140are applied to the distal hub and the proximal hub in analogy to the embodiment ofFIG. 1.

The number of expandable members124correspond to the number of slits and is variable depending on the desired stiffness of the expandable members124. The distal hub114, which is not shown in its entire length, may be closed off at its distal end and is fastened to the distal end of a stylet112extending from the proximal side into the distal hub114in analogy to the removal apparatus ofFIG. 1. The proximal hub118, which is longitudinally movable relative to the stylet112, may be separate from an actuator portion122as shown, or it may be connected to the actuator portion122, in a unitarily manner or by attachment.

As illustrated inFIG. 2b, the stylet112extends centrally through the tubular flexible element without interfering with the expandable members124. Due to the attachment of the stylet112to the distal hub14, a proximal movement of the stylet relative to the proximal hub118and the actuator portion112causes the expandable members124to decrease their axial length and to increase the radial dimension.

FIG. 3shows a variation ofFIG. 2a. Like the embodiment ofFIG. 2a, a filter removal apparatus210comprises a tubular flexible element250that unitarily forms a distal hub214, an expandable interlocking arrangement220, and a proximal hub218. Expandable members224are formed between slits252that extend in a substantially parallel manner along the length of the expandable interlocking arrangement220. In contrast toFIG. 2a, however, the slits252are slanted relative to the longitudinal direction so that they describe helical curves around a portion of the stylet. The slanted slits252have the effect that the individual expandable members224have a greater length than the expandable interlocking arrangement220. Thus, a greater radial expansion can be achieved with the filter removal apparatus210ofFIG. 3compared to the filter removal apparatus110ofFIG. 2awith an identical axial length of the expandable interlocking arrangements120and220. Markers240are applied to the distal hub and the proximal hub in analogy to the embodiment ofFIG. 1.

For obtaining the greatest possible radial expansion of the expandable members224, the distal hub214moves proximally relative to the proximal hub218and also performs a relative rotational movement relative to the proximal hub in a direction that places the distal ends of the expandable members224in the same angular positions as the proximal ends of the expandable members224. Both the proximal movement of the distal hub214and the rotation of the distal hub can be achieved by manipulating the stylet wire (not shown) for a proximal end of the filter removal device210.

The number of expandable members224correspond to the number of slits252and is variable depending on the desired stiffness of the expandable members224. The distal hub214is shown to be closed off at its distal end and is fastened to the distal end of the stylet (not shown) extending from the proximal side into the distal hub214in analogy to the removal apparatus ofFIG. 1. As previously described, the proximal hub218, which is longitudinally movable relative to the stylet, may be separate from an actuator portion, or it may be connected to the actuator portion, in a unitarily manner or by attachment.

FIGS. 4athrough4dillustrate a process of removing a vena cava filter from a body vessel. The steps ofFIGS. 4athrough4dare illustrated by way of the embodiment shown inFIG. 1. The process, however applies in analogy to alternative embodiments ofFIGS. 3aand3b, and ofFIG. 4.

InFIG. 4a, a vena cava filter300is schematically shown to be implanted in a body vessel302. The vena cava filter300has a quasi-conical shape with a proximal filter hub304forming the apex of the quasi-conical shape and a plurality of struts306extending from the filter hub304outward in a distal direction to form the body of the quasi-cone.

Now referring toFIG. 4a, in order to retrieve the filter300, an outer catheter42is placed proximally from the filter hub304in a generally known manner. The distal end44of the outer catheter42is placed close to the filter hub304, for example about 0.5 cm to 2 cm away.

In a next step, as shown inFIG. 4b, the filter removal apparatus10is introduced into the outer catheter42and distally advanced. During this step, the interlocking arrangement20has a passive state, wherein in the passive state the interlocking arrangement20is passive, i.e. fully longitudinally extended without any radial expansion. In the passive state, the diameter of the expandable interlocking arrangement20is no greater than about the diameter of the distal hub14or the proximal hub18. The interlocking arrangement20is advanced to a position relative to the filter300that places the proximal hub18distally from the filter hub304. The proper position of the proximal hub18is verifiable by monitoring the position of the marker40on the proximal hub18. In embodiments in which the actuator portion22is movable relative to the proximal hub18, the actuator portion22is placed adjacent to the proximal hub18to prevent a proximal movement of the proximal hub18past the filter hub304. The actuator portion22may optionally bear an additional marker for facilitating proper positioning. In all embodiments, the actuator portion22is then held in place for securing the position of the proximal hub18distal from the filter hub304.

Subsequently, as illustrated inFIG. 4c, the stylet12is proximally withdrawn so as to cause a relative movement between the distal hub14and the proximal hub18so that the distal hub14approaches the proximal hub18so that the expandable interlocking arrangement occupies an active state. If the expandable members24are wound about the stylet in the passive state, the movement between the distal hub14and the proximal hub18may also involve a rotation that unwinds the expandable members24. The expandable members24bulge outward and may additionally intertwine with each other, which may provide an increased stability of the active state. Expandable interlocking arrangements, such as the arrangements20and220, with slanted or twisted expandable members24and224exhibit a greater tendency of intertwining members than those embodiments with axially straight expandable members124, such as arrangement120.

FIG. 4cshows the active state of the expandable interlocking arrangement20, in which the wires28are bunched up into a radially expanded cluster46. For verifying the proper position of the distal hub14to insure a proper formation of the cluster46, the marker40on the distal hub14may be monitored, especially for its relative position with respect to marker40on the proximal hub18. The resulting cluster46has a diameter that is greater than the diameters of the hubs14,18, and304. Because the struts306extend distally from the filter hub304, the distance between the proximal ends of the struts306is smaller than the diameter of the cluster46. Accordingly, the cluster is confined between the struts distally from the filter hub304. While the cluster46has a greater diameter than the hubs14,18, and304, the cluster diameter is preferably small enough to be insertable into the distal end44of the catheter42. This means that the cluster need not be smaller than the inner diameter of the catheter42if the respective expandable members24forming the cluster46are soft enough to be deflected while the filter removal apparatus10is retracted into the outer catheter42.

FIG. 4dshows a partially retracted filter removal apparatus that, due to the expanded interlocking arrangement20forming the cluster46, takes along the vena cava filter. As the vena cava filter enters the outer catheter42with the filter hub entering the catheter before the struts, the struts are radially compressed so that the struts, like the filter hub, can be completely accommodated in the outer catheter (not shown).

After the entire filter removal apparatus10including the vena cava filter300has been accommodated inside the catheter42, the filter removal apparatus20may be proximally removed from the catheter42. Alternatively, the entire catheter may be withdrawn so that the filter removal apparatus10may be retrieved from the catheter42after the catheter has been withdrawn from the patient body.

Because the filter removal apparatus10and the described variations thereof do not need to engage with a filter retrieval hook, the filter removal apparatus10is suited even for vena cava filters that may reside in a tilted position, in which it is difficult to engage the retrieval hook, especially if the retrieval hook has been embedded in body tissue, for example due to overgrowth.