Retrievable blood clot filter

A compact retrievable blood clot filter has a filter section, a releasable lock and an alignment section connected to the filter section. Alignment ribs of the alignment section have releasable upstream ends that are locked to the filter by the releasable lock. The releasable upstream ends of the alignment ribs are capable of being released from the releasable lock so that during retrieval of the filter, the alignment ribs can slide through the endothelial tissue that may have grown around the alignment ribs.

FIELD OF THE INVENTION

The present invention relates to a medical device apparatus and method for the capturing of thrombus. More particularly, the present invention relates to a retrievable vena cava filter device and a method of retrieving the same from a vessel.

BACKGROUND OF THE INVENTION

Vena cava filters are used to capture potentially fatal blood clots at an anatomical location where they may pose less risk of pulmonary emboli for the patient. Since the vast majority of pulmonary emboli originate from the lower body, filters are mainly placed in the inferior vena cava.

The optimal filter device should capture blood clots while ensuring continued blood flow through a blood vessel of a patient. Studies have demonstrated that a conical filter configuration provides optimal filtering efficiency. Conical designs force clots toward the center of the filter, allowing blood flow passage around the clot. Continued blood flow through the filter when a clot load is present ensures that captured clots are exposed to the lysing action of the blood flow.

Although conical filter configurations currently available on the market provide optimal filtering capabilities, these designs are prone to tilting and misalignment. When not in proper alignment, filtering ability is compromised. The central conical portion of the filter may tilt to the extent that it becomes embedded in the vessel wall. In retrievable filter designs, a retrieval hook is typically located at the central apex of the filter cone. If the filter tilts, this may result in the retrieval hook coming in contact with the vessel wall, making retrieval efforts more difficult or even preventing removal of the filter device. Tilting may also cause disruption of laminar blood flow, decrease in lysing of captured clots, or thrombus build-up and occlusion of the filter.

To maintain alignment of conical filters, centering or alignment features have been incorporated into filter designs. Centering has been accomplished by the use of free arms that extend radially outward from the filter to contact the vessel wall at a plane spaced apart from the contact point of the filter legs. While free arm centering designs ensure that the conical filtering section generally remains centered within the vessel, these designs are disadvantageous in that the free arms are prone to vessel perforation, fracture and in some cases misalignment due asymmetrical spacing of the free arms. Moreover, occasionally, when attempting to snare the alignment arms, they will become bent upwards making the retrieval of the filter even more difficult.

To overcome problems with free arm designs, closed loop alignment structures have been utilized. A closed loop alignment structure is comprised of alignment ribs that are connected at each end to a hub or other filter element and thus have no free standing arms. The non-perforating curved portion of each alignment rib may rest against the vessel wall to provide a centering function. These closed loop centering structures are less prone to fracture and will not perforate a vessel wall.

Although overcoming problems associated with free arm centering structures, filters designed with closed loop structures are difficult to retrieve from the vessel, particularly if a portion of the alignment structure has become incorporated into the vessel wall by endothelial overgrowth. Endothelial overgrowth may occur at any point where the filter contacts the vessel wall. Over time, the endothelial overgrowth may partially or completely encapsulate any portion of the filter in contact with the wall. This process is called neointimal hyperplasia and occurs as early as two weeks after implantation. The vessel wall responds to a foreign presence such as a filter by increased smooth muscle cell growth and neointimal thickening at the contact points. A band of endothelial tissue over a filter segment makes retrieval of the filter from the vessel more difficult, especially those filters designed with a closed loop configuration.

Accordingly, it is desirable to provide a retrieval blood clot filter with a filtering configuration and a centering structure that can be easily retrieved from the vessel even in the presence of endothelial growth over portions of the centering structure. The filter should be designed to allow percutaneous removal without significant trauma or damage to the vena cava wall even after neointima overgrowth has embedded those portions of the filter that are in contact with the vessel wall.

BRIEF SUMMARY OF THE DISCLOSURE

A retrievable blood clot filter according to one embodiment includes a filter section having a plurality of filter legs, a releasable lock and an alignment section coupled to the filter section. The alignment section includes alignment ribs having releasable upstream ends that are locked by the releasable lock. The releasable lock is capable of releasing at least one releasable upstream end of the alignment ribs so that during retrieval of the filter, the alignment ribs with their released upstream ends can slide through the endothelial tissue that may have grown around the alignment ribs.

In another aspect of the invention, a retrievable blood clot filter includes a conical filter section, a releasable lock, an alignment section and a shaft. The conical filter section has a filter hub and filter legs having downstream ends coupled to the hub and upstream ends that extend radially outwardly. The alignment section has an alignment hub and a plurality of alignment ribs having downstream ends coupled to the alignment hub and releasable upstream ends locked by the releasable lock. The alignment ribs extend radially outwardly from the downstream ends and then further extends radially inwardly in a cage like closed configuration. The releasable lock is capable of releasing the releasable upstream ends of the alignment ribs in response to a force applied to the releasable upstream ends during retrieval of the retrievable blood clot filter. The shaft couples the alignment hub to the filter hub even when all of the releasable upstream ends of the alignment ribs are released.

In another aspect of the present invention, a retrievable blood clot filter having a longitudinal axis is provided. The filter has a filter section, an alignment section and a releasable coupler disposed between the two sections. The alignment section has a plurality of alignment ribs and is spaced from the filter section along the longitudinal axis. The releasable coupler releasably holds the upstream ends of the alignment ribs.

In another aspect of the present invention, a blood clot filter including a conical filter section and an alignment section is provided. The conical filter section has a filter hub and a plurality of filter legs having downstream ends coupled to the hub and upstream ends that extend radially outwardly. The alignment section is spaced from the filter section along a longitudinal axis in a non-overlapping manner. The alignment section has an alignment hub and a plurality of alignment ribs having downstream and upstream ends. The alignment ribs extend radially outwardly from the downstream ends and then further extends radially inwardly.

In yet another aspect of the present invention, a method of retrieving a blood clot filter is provided, the filter having a filter section and an alignment section with the alignment section including a plurality of alignment ribs with each alignment rib having a releasable upstream end. To retrieve the filter, the alignment section is captured with a retrieval device and the releasable upstream ends of the alignment ribs are released. The filter with its released upstream ends of the alignment ribs is withdrawn into a retrieval sheath for removal.

These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings. The invention will be explained in greater detail below with reference to the attached drawings of a number of examples of embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the present application, the terms upstream and downstream refer to the direction of blood flow within a blood vessel. Accordingly, blood flows from an upstream direction towards a downstream direction. Also, it is important to note that although the filters disclosed herein are capable of being retrieved, they can be used as permanent filters without being retrieved.

Referring toFIG. 1, there is shown an embodiment of the present invention in a plan view of an expanded vena cava filter device1. When deployed in the path of the bloodstream, typically in the vena cava vein, the filter device1captures blood clots of a predetermined size and prevents them from traveling further downstream.

The vena cava filter device1is comprised of a conical filtering section3, an alignment section5, a center shaft/rod4and a retrieval hook subassembly25. The conical filtering section3captures and lyses blood clots, anchors the filter device1, and prevents the filter device1from migrating downstream. The alignment section5has a closed loop geometry (i.e., both ends of the alignment ribs8are attached to the filter1) and provides central alignment of the conical filtering section3within the lumen of a vessel. The closed loop alignment section5also ensures that the conical filtering section3is maintained in proper longitudinal alignment relative to the alignment section5. The center shaft4provides a moveable connection between the alignment section5and the conical filtering section3for retrieval. The retrieval hook subassembly25allows retrieval of the filter device1from the vessel using a snare device or other retrieval device known in the art.

In one embodiment, the conical filtering section3is comprised of a plurality of primary filtering legs13and secondary filtering legs29. The primary filtering legs13having downstream ends7and upstream ends9. Downstream ends7of the primary filtering legs13are connected to the primary filtering hub11and extend axially and radially outward from the primary filtering hub11to the upstream ends9. Upstream ends9may be configured with vessel wall-engaging ends15such as barbs or other vessel anchoring mechanisms known in the art.

Each secondary filter leg29branches off into two branch legs27at a branch point39which is upstream of the filter hub11. Unlike the primary filter legs13, the upstream ends of the two branch legs of secondary filter legs29have a smooth profile without wall-engaging ends and are adapted to simply rest on a vessel wall.

The conical filtering section3captures clots and funnels the clots toward the conical primary filtering hub11which is located at the center of the vessel, where the clots are optimally exposed to the lysing action of the blood flow. The primary filtering hub11has an open configuration that includes a through lumen. This design is advantageous in that it minimizes blood flow turbulence while maintaining the structural integrity of the filter device1.

The alignment section5provides central alignment of the conical filtering section3within the vessel. The alignment section5is formed of a plurality of alignment ribs8in a closed loop configuration. The downstream ends21of the alignment ribs8are permanently connected to the alignment hub19, which is connected to the retrieval hook subassembly25. The alignment ribs8extend radially outward from the alignment hub19, form an arc, and then extend radially inward to the primary filtering hub11to form a closed loop. The alignment ribs8are securely positioned and interlocked within the primary filtering hub11until they are released during retrieval, as will be explained in more detail below.

As few as three alignment ribs8may be used to achieve centering of the filter device1. In the deployed position the alignment section5is fully expanded to a cross-sectional diameter of approximately 18 mm, corresponding to the internal cross-sectional diameter less than that of the vessel. Accordingly, some or all of the alignment ribs8may rest against the vessel wall depending on vessel diameter. For vena cava vessels larger than 18 millimeters, the alignment ribs8will only contact the vessel wall if the filter device1begins to tilt away from the center of the lumen of the vessel. A filter placed in a vena cava that is less than 18 mm in diameter will contact the vessel wall with all alignment ribs8. When the alignment ribs8contact the vessel wall, further tilting and misalignment of the filtering section3is prevented. Thus, alignment of the filtering section3within the vessel wall is achieved by alignment ribs8contacting the vessel wall, whether that contact is continual (as is the case for smaller diameter vessels) or occurs only when the filter device1begins to tilt (as is the case for larger diameter vessels).

The closed loop structure formed by the plurality of alignment ribs8avoids the problems associated with free-ended centering structures, which are prone to misalignment, tangling, and fracture. Misalignment may also cause the retrieval hook of prior art filters to become embedded in the vessel wall, making retrieval difficult or impossible. In contrast, the closed loop design of the present invention has no free ends when deployed and thus is not prone to misalignment or entanglement with other interventional devices.

The longitudinal moveable center shaft4and retrieval hook subassembly25, illustrated inFIG. 1, provide a mechanism for easy retrieval of the filter device1. The center shaft4extends from the alignment hub19through the primary filtering hub11terminating within the conical filter section3downstream of the filtering leg13ends9. The primary filtering hub11will longitudinally slide along the center shaft4when force is applied to the retrieval hook subassembly, as will be explained in more detail below. Located at the downstream end of the filter device1and connected to the alignment hub19, the retrieval hook subassembly25is configured to capture the end loop of a snare device during filter retrieval.

Referring now toFIG. 2, a downstream end view of the filter device1in an assembled and expanded state is illustrated. Extending radially outward from the retrieval hook subassembly25are primary filtering legs13and secondary filtering legs29. Anchoring ends15of the primary filtering legs13contact and engage the vessel wall, providing an attachment mechanism to prevent filter migration. Secondary filtering legs29also contact the vessel wall at a downstream location relative to the primary filtering legs13.

The alignment ribs8are in axial alignment with the primary filtering legs13in a circumferential direction. With this configuration, the alignment ribs8do not provide unnecessary supplemental clot capturing. Instead, clots passing through the filtering section3will also pass freely through the alignment ribs8. By allowing smaller, non-fatal clots to pass through the entire filter device1, occlusion of the filter device1at the alignment section5is less likely. Downstream clot buildup in a filter results in blood flow turbulence and potential thrombi on the periphery of the vessel. By eliminating unnecessary secondary filtering, stable laminar blood flow is maintained, and captured clots can be effectively lysed within the center of the filtering section3.

In the preferred embodiment, the filly expanded axial diameter of the filter device1at the upstream ends9is typically between 38-40 millimeters to accommodate larger cava diameters. The expanded filter1diameter will vary depending on the diameter of the patient's vena cava, which will partially constrain the expansion of filter1, but may range from 18 to 23 millimeters for a typical patient. Although the angle of legs13proximate to the vessel wall may be reduced when under constraint from the vessel wall, the angle of the legs13relative to each other near the center of the vessel remains unchanged, as shown inFIG. 2. Specifically, the cross-sectional area between each secondary filter leg29from the downstream end7to the branch point39remains constant even when the relative angle between leg portion27and adjacent primary leg13has been decreased due to the constraint of the small vessel diameter. Although the branch legs27may move closer to adjacent filter legs13when constrained, the secondary leg29downstream of the branch point39remains in an unchanged position, i.e., the angle between each secondary leg29downstream of the branch point39relative to the longitudinal axis of the filter1does not change regardless of the vessel diameter. Thus, even when constrained within smaller diameter vessels, the filter1of the current invention maintains constant area coverage at the center of the vessel. As a result, the filter1is less likely to occlude when placed in a small vessel.

Still referring toFIG. 2, leg branches27do not individually connect to the filter hub11. Rather, a set of two legs27merges into a single secondary leg29, which then connects to the filter hub. Thus the secondary filter section provides an increased number of legs extending to the vessel wall for additional filter coverage at the outer circumferential area of the vein while minimizing the amount of filter material at the center of the vessel. Prior art filters with increased mass at the center of the filter have been shown to have increased filter occlusion rates. The design of this invention overcomes this problem by reducing the number of legs29that merge into the hub11. As shown inFIG. 2, the reduced central area profile has only eight legs connecting to the filter at hub11, with twelve leg ends contacting the vessel wall at an upstream location for enhanced filtering. The reduced mass at the hub area is also beneficial in that it minimizes non-laminar blood flow and turbulence near the center of the vessel. As a result, filter-induced thrombus build-up and comprised lysing is minimized.

FIG. 3is a side view of the filter1in an assembled, unexpanded state. The filter1is comprised of the hook subassembly25, a first tubular body6which forms the alignment hub19and alignment ribs8, and a second tubular body17forming the primary hub11and filtering legs13. A third tubular body18(not visible inFIG. 3) is axially arranged within the second tubular body17and forms the secondary hub35and filtering legs29with their branch leg portions27.

Each tubular body6,17and18are preferably comprised of material with shape-memory characteristics, such as Nitinol, to allow expansion from a collapsed state illustrated inFIG. 3, to a deployed state at body temperature as illustrated inFIG. 1. Nitinol is an alloy well-suited for vena cava filters because of its shape-memory characteristics, which enables it to return to a pre-determined expanded shape upon release from a collapsed position. During manufacture of the filter device1, the tubular bodies6,17, and18are first cut into the desired configurations using laser-machining techniques commonly known in the art. Other cutting techniques such as photo or acid etching may be used to form the desired cut patterns for the filter device1.

Prior to final manufacturing assembly, the first tubular body6which forms the alignment section5, is approximately 1.1 inches in length. The second tubular body17, from which the primary filtering3is cut, is approximately 1.4 inches in length. When assembled as shown inFIG. 3, the combined length of tubular body6and17is approximately 2.5 inches, and the overall length of the device is 2.65 inches, including the assembled retrieval hook subassembly25, which has an exposed hook portion of approximately 0.15 inches in length. The total filter1length of 2.65 inches shortens to approximately 2.15 inches after the filter1is expanded into the deployed state shown inFIG. 1.

The outer diameter of the first tubular body6and second tubular body17at their respective hubs are preferably 0.072 inches to accommodate insertion of the filter device1through a small sheath. Both tubular bodies have an inner diameter of 0.052 inches and a wall thickness of approximately 0.010 inches. The third tubular body18, from which the secondary filtering section26is composed, has a length of approximately 1.3 inches, an outer diameter of approximately 0.051 inches, a wall thickness of approximately 0.009 to 0.010 inches, and an inner diameter of approximately 0.033 inches. These dimensions allow tubular body18to be inserted into the annular space of tubular body17during assembly.

After being laser cut, the first, second, and third tubular bodies6,17, and18are heat treated to form the final expanded filter device1configuration shown inFIG. 1. The filter device1may be polished before final assembly to provide a smooth outer surface finish using electro-polishing techniques or other methods commonly known in the art.

Thus, in one novel aspect of the invention, a filter device1is provided that has a separate alignment section5and a filtering section3that can be delivered through a small sheath. Although several prior art filters are sized to be delivered through a 6 F sheath, these filters do not provide both centering and symmetrical conical filtering features. Prior art filters that do provide both centering and conical filtering capabilities generally require larger delivery devices due to the overlap of wire elements when the filter device1is in the collapsed state. By longitudinally separating the alignment section5and the conical filtering section3in a non-overlapping manner, the filter device1can be constrained in a delivery device that is substantially equal to the outer diameters of the first and second tubular bodies6,17. As an example, a filter fabricated from a tube with a 0.072 inch outer diameter will be able to be delivered using a sheath with an internal diameter as small as 0.075 inches, or within a 6 French sheath.

The assembly steps of the filter device1are illustrated inFIG. 4. To assemble the filter device1, a center spacer20is first inserted into and welded to the secondary filtering hub35. The center spacer20is a hollow tubular structure made of Nitinol or other similar material. The center spacer20lumen is approximately 0.020″ with an outer diameter of 0.032″ to allow insertion of the spacer20into the through lumen of secondary filtering hub35, which is dimensioned at approximately 0.033″. Weld hole37facilitates welding of the center spacer20to the secondary filtering hub35.

The center spacer20performs the dual function of a spacer and a stopper mechanism. The center spacer20ensures that the center shaft4, when inserted through the spacer20lumen, is maintained in a centered position within the secondary filtering hub35lumen. The center shaft4has an outer diameter of approximately 0.015″ which fits freely within the 0.020″ inner diameter of the center spacer20, allowing the center shaft4to move freely in a longitudinal direction relative to the vessel without becoming misaligned and off-center. The center spacer20, in conjunction with stop member14, also provides a travel stop feature by preventing the upstream end of center shaft4from moving completely through the spacer20lumen during retrieval.

The combined secondary filtering hub35/center spacer20subassembly is then inserted into the lumen of primary filtering hub11as shown by the dotted line. The outer diameter of secondary filtering hub35is approximately 0.051″ to allow ease of insertion into the primary filtering hub11lumen which has a diameter of 0.052″. The secondary filtering hub35with spacer20is inserted into the lumen of the primary filtering hub11, and then welded together using weld hole43. With this method and configuration, the filtering section3maintains an outer diameter in an unexpanded state of 0.072″.

The center shaft4is then attached to the hook subassembly25. The hook subassembly25includes a hook insert section49formed of a solid cylindrical element extending in an upstream direction from the base section45. A longitudinally arranged channel48is formed in the hook insert section49. The center shaft4is inserted into channel48and welded in place.

The opposite end of center shaft4is passed through the alignment hub19lumen until the upstream edge of alignment hub19abuts against outer rim75of retrieval hook subassembly25. Pin hole57of the alignment hub19and pin hole47of the hook subassembly25are brought into alignment with each other. A pin41is inserted through the aligned holes to secure the retrieval hook subassembly25and the alignment hub19. The pin41is dimensioned so as to create an interference fit with the pin holes57and47. The pin41may be made of any suitable material. Preferably, the pin41is at least partially made of Titanium, as illustrated in the preferred embodiment of the present invention. Pin41is of a length greater than the outer diameter of the alignment hub19. For example, for a 0.072 inch alignment hub19diameter, the pin41may be 0.079 inches in length.

After the pin41is positioned within the aligned retrieval hook pin hole47and the alignment hub19pin hole57, the connected retrieval hook subassembly25and the alignment hub19are placed in a swaging die and cold swaged to cause the outer surface of the pin41to be flush with the outer surface alignment hub19. The swaging process also creates an interference fit between the pin41and the aligned pin holes47and57, resulting in a strong, reliable attachment that does not require additional heating of the metal or welding, both of which may compromise the material of which the retrieval hook subassembly25and alignment hub19are composed.

The assembled filtering section3is then assembled to the alignment section5by inserting the downstream end of center shaft4through the lumen of center spacer20which was previously attached to the secondary filtering hub35. Center shaft stop14is then welded to the downstream end of center shaft4. The center shaft stop14prevents the filtering section3from becoming separated from the rest of the filter device1and ensures alignment of the filtering section3during retrieval. The center shaft4is stopped from additional downstream travel when the center shaft stop14comes into contact with the downstream end of the center spacer20. The rod stop14, which has a diameter of approximately 0.032″, is too large to fit through the 0.020″ of the spacer20, and accordingly, is stopped from further downstream movement.

Although the shaft4disclosed herein with reference toFIG. 4is a rigid rod, alternative designs are possible. For example, the shaft4may be comprised of a non-rigid material formed as a cable, wire or polymer connecting element. With this design, the connecting element4does not need to extend upstream of the primary filter hub11.

The last assembly step is to insert the free upstream ends23of alignment ribs8into an interlocking relation with a releasable lock in the secondary filter hub35. This last step is illustrated more clearly inFIGS. 5A-5Band6A-6C.FIG. 5AandFIG. 5Bdepict partial further enlarged views of the interlocking relationship between the alignment ribs8and the secondary filtering hub35.FIG. 5Aillustrates the engaging tabs24at the upstream end of the alignment ribs8prior to insertion into the receiving pockets22of the secondary filtering hub35.FIG. 5Bdepicts the interlocking relationship after the engaging tabs24have been locked by the releasable lock.

In the embodiment shown inFIGS. 5 and 6, the releasable lock (releasable coupler) is comprised of a plurality of spaced apart recesses/pockets22disposed at the downstream end of the filter hub35, tapered forward segment (cover piece)16and center spacer20. Each recess includes alignment rib receiving portion98, two barb receiving sections (retaining surfaces)100and tapered portions102.

The upstream end23of each alignment rib8of alignment section5is laser cut in a pattern forming an engaging tab24. Each engaging tab24formed at the upstream end23of the alignment rib8includes a pocket engaging surface (projecting surface)88, barb extensions90, inwardly tapered sections92and a downstream face94. The engaging tab24profile includes the two pocket engaging surfaces88that extend outwardly from the upstream end23, and barb extensions90. Barb extensions90form an expanded width of approximately 0.022 inches relative to the width of upstream ends23, which are 0.016 inches. Engaging tab24also include two inwardly tapered sections92which terminate in downstream engaging face94. When inserted into receiving pocket22of hub35as shown inFIG. 5B, the projecting surfaces88of barb extension90with its expanded width is retained by the retaining surfaces100to prevent axial movement and disengagement of engaging tab24from receiving pocket22. In other words, the engaging tabs24at the upstream end of the alignment ribs8are locked by the releasable lock (22,98,100,102).

Receiving pocket22of hub35is dimensioned to receive engaging tab24in an interlocking relationship, as shown inFIG. 5B. Alignment rib receiving portion98is dimensioned at 0.018 inches to allow upstream end23of rib8, which is 0.016 inches, to be positioned within pocket22snugly, but without interference. Similarly, barb receiving section100is dimensioned at 0.026 inches in width to freely accommodate pocket engaging surfaces88and barb extensions90, While simultaneously preventing disengagement of tab24when the alignment rib8is under axial force. Taper portion102of the receiving pocket22is dimensioned to be approximately 0.001 inch larger than the corresponding tapered section92of engaging tab24to allow a small clearance between the components without allowing movement.

FIG. 6Aillustrates an enlarged partial plan view of the alignment ribs8positioned within and being restrained within the primary filtering hub11after final assembly and expansion of filter1.FIG. 6Bis a partial cross-sectional view ofFIG. 6Ataken along lines A-A. Each alignment rib8with corresponding engaging tab24is positioned within receiving pocket22. The engaging tab24is held securely in position between the center spacer20and the tapered forward segment (cover piece)16of the primary filtering hub11which circumferentially surrounds and covers the engaging tabs24. In the embodiment shown inFIG. 6A, the engaging tabs have an uncovered portion between the retaining surface100and the downstream end of the cover16in an axial direction to facilitate the release of the tabs during retrieval as will be discussed later herein in detail. Thus, the releasable alignment ribs8are restrained from movement in an inwardly radial direction by the center spacer20and restrained from movement in an outwardly radial direction by the inner wall of the segment16. As previously discussed, the alignment rib8is also prevented from movement in an axial direction by the profile of the receiving pocket24, which prevents movement of the barb extension90.

Accordingly, in one aspect of the invention, an implantable, retrievable filter1is provided that will not release from a closed loop to an open loop structure under normal body movements experienced during implantation due to the interlocking design. The device1provides for central alignment within the vessel using a closed loop configuration that will not perforate the vessel wall, become entangled or fracture.

The present invention also pertains to a method of retrieving the implanted filter device1of the present invention from a vessel of a patient body. This method utilizes the alignment ribs' releasing feature to facilitate removal under those conditions in which filter portions have been encapsulated in endothelial overgrowth. The method involves inserting a retrieval sheath into the vessel, capturing the filter retrieval hook subassembly with a snare, advancing the retrieval sheath over the alignment ribs, thereby applying a prying force to release the alignment ribs from the filtering hub, and sliding the free rib ends through the overgrowth and into the sheath. The method further involves the steps of further advancing the retrieval sheath over the filtering section thereby capturing the filter legs within the sheath and removing the retrieval sheath and filter1from the vessel.

The retrieval steps of this method are illustrated inFIGS. 8 through 13and also with reference toFIG. 7A-7D.FIGS. 7A-7Drepresent the circled area ofFIG. 6Band illustrate the sequence of steps by which the engaging tab24is released by retrieval forces during removal of the filter1through endothelial tissue.FIG. 8depicts a side view of the filter device1in an expanded state inside of a vessel61at the beginning of the filter device1retrieval process.

In the deployed state the filter device1is in an expanded position in the vessel61, as shown inFIG. 8. The alignment ribs8extend radially outward from alignment hub19to contact the vessel wall at alignment rib contact portions10, before extending inwardly to the filtering hub11in a closed loop configuration. The alignment rib contact portions10of the alignment ribs8are shown encapsulated in the endothelial overgrowth band73of the vessel wall65. The filter legs13extend radially outward from the primary filtering hub11to contact the vessel wall65at wall engaging ends15. The secondary filtering legs29also extend radially outward from the filtering hub11to contact the vessel wall65at a separate plane from wall engaging ends15. Alternatively, the secondary filtering legs29may extend to contact the vessel wall on the same plane as the primary filtering legs13. Center shaft4extends along the longitudinal axis of the vessel from the alignment hub19through the alignment ribs8and filtering hub11terminating in center shaft stop14.

During implantation and prior to retrieval of the filter1, the engaging tabs24of each alignment rib8are held within the receiving pockets22of the secondary hub35, as previously described. An enlarged partial cross-sectional view of the engaging tabs24in an engaged position is shown inFIG. 7A. In the absence of a retrieval force, the engaging tab24remains constrained in this position by the center spacer20, the receiving pocket22, and the primary filtering hub11.

To retrieve the filter device1, a sheath78coaxially surrounding a snare device63is inserted into the vessel61and advanced to the filter1. The snare device63is then advanced beyond the distal end79of the sheath78, as shown inFIG. 8. The hook51of the retrieval hook subassembly25is captured by looping the snare wire64of the snare device63around the hook51and applying tension to securely engage the hook51, as is well known in the art.

Referring now toFIGS. 9A and 9B, tension is applied to the proximal end of snare device63in a downstream direction to draw the retrieval hook subassembly25and alignment hub19of the filter1into the sheath78lumen. Alternatively, the retrieval hook subassembly25and alignment hub19may be captured by advancing sheath78in an upstream direction while holding the snare device63stationary. As the downstream end of the filter1is drawn into the sheath78using either method, pressure is exerted upon the alignment ribs8by the distal end79of the retrieval sheath78. This radially inward pressure forces the downstream ends23of the alignment ribs8begin to collapse and radially retract inward toward the center shaft4into a flattened position along the center shaft4.

As previously described, the filtering hub11including the spacer20is slidably and coaxially mounted onto the center shaft4. As the alignment ribs8collapse inwardly, they elongate and flatten out against the center shaft4as the shaft is pulled forward into sheath78. The center shaft4thus functions to maintain axial alignment of both the alignment section5and the filtering section3during retrieval. The center shaft4also provides a central travel rail over which the alignment ribs8can elongate longitudinally without causing the filtering hub11to move.

The band of endothelial overgrowth73at the wall contacting portion10of the ribs8is illustrated in the enlarged view ofFIG. 9B. As shown in this figure, the portion of the vessel61associated with the encapsulated alignment rib wall contacting portion10will be drawn inwardly toward the center of the vessel61as the alignment rib8begins to collapse. As the ribs8collapse inwardly, the band of endothelial overgrowth73is pulled inwardly and slides in an upstream direction along the alignment rib8toward the filtering hub11.

As the alignment section5begins to collapse, the engaging tabs24are pushed radially outward from the central axis of the filter1. This force, depicted by the arrow inFIG. 7B, is created by the band of endothelial overgrowth73which slides in an upstream direction along the alignment rib8. The endothelial overgrowth73causes the upstream end23of the alignment rib8to bow outwardly. Specifically, the upstream portion23of the alignment rib8that is located within the alignment rib receiving portion98is pried away by this radially outward force created by the advancement of the endothelial band73toward the filtering hub11. The barb extension90remains constrained within the barb receiving portion100of the receiving pocket as the upstream rib portion23begins to bow outwardly.

The tapered forward segment16of hub11may undergo a small amount of material deformation as pressure is applied by the engaging tab24against segment16, causing it to flex slightly as tab24disengages from receiving pocket22. The flexing of the hub forward segment16is illustrated inFIGS. 7B and 7C. If the filter1is constructed of Nitinol or other shape-memory material, segment16of primary filtering hub11will undergo deformation within the elastic limit, thus returning to its original shape after the alignment ribs8are released from the hub11. Alternatively, the hub11may be made of material that will exceed the elastic limit when force is applied by the engaging tab24, resulting in the segment16of hub11remaining in a slightly flexed position.

As illustrated inFIG. 10A, as the retrieval sheath78is further advanced toward the alignment rib contact portions10, the outwardly directed force against the exposed portion of the alignment rib8increases further and causes the upstream end23of the rib8to flex and bow outwardly as shown inFIG. 7C. The force generated by the collapse of the alignment ribs8combined with the advancing endothelial tissue73acts as a lever, prying the engaging tab24out of the receiving pocket22. As the alignment rib downstream end23bows outwardly, the barb extension90is moved both longitudinally upstream and radially outward, until the barb90is oriented such that it has sufficient clearance to disengage from the receiving pocket22. Specifically, when barb extension90has been pushed to a point downstream and radially outward of barb receiving portion100by the force of the sliding endothelial band73, the tapered portion of the engaging tab92, which is of a smaller width than the barb extension90, freely slides out of the receiving pocket22.

FIGS. 11A and 11Bdepict the filter device1after the alignment ribs8have been completely released from the filtering hub11, but prior to retraction of the rib8through the endothelial band73. The radially outward force created by the endothelial band73along with the force created by the retraction of the snare63within the sheath78(depicted by the horizontal arrow inFIG. 7D) cause the engaging tab24to completely disengage from the receiving pocket22. The vessel wall65remains partially collapsed by the alignment ribs upstream ends23, which are disengaged from the filter1, but remain encapsulated within the vessel wall65. Except for the upstream ends23, the alignment ribs8are completely collapsed, elongated against the center shaft4And constrained within the sheath78.

A substantial length of the center shaft4is drawn into sheath78, as shown by the position of the center shaft stop14, which is advanced to just upstream of the filtering hub11. The center shaft stop14prevents the center shaft4from moving completely through the primary filtering hub11and secondary filtering hub35. As the center shaft stop14contacts and is restrained from further longitudinal movement by the filtering hub11, any additional retrieval force placed on the filter1is carried by the center shaft4and stop14, which together advance the filter1further into the sheath78.

To disengage the alignment ribs8completely from the vessel wall65, the snare wire64is further retracted. This movement causes the upstream ends23of the alignment ribs8be pulled through the endothelial overgrowth73in a downstream direction exiting through exit point104. The upstream ends23of the ribs8are pulled through the overgrowth73at an angle that leaves only an opening104, thus minimizing vessel trauma, and avoiding longitudinal tearing through the endothelial tissue73. Thus, in one novel aspect of the invention, a method of filter retrieval is provided that is minimally traumatic to the vessel wall and does not cut through or otherwise damage the vessel61.

Once the alignment ribs8are released from the vessel wall65, the vessel wall65is no longer constrained by the filter1and the vessel61returns to its original shape, as shown inFIG. 12. As the retrieval sheath78is advanced, it completely encloses the alignment section5and the primary filtering hub11. The primary filtering legs13and the secondary filtering legs29remain deployed, but begin to disengage from the vessel wall65.

Finally, as illustrated inFIG. 13, the sheath78is then further advanced over and completely encloses the plurality of primary filtering legs13and the secondary filtering legs29. The filter device1becomes completely enclosed within the retrieval sheath78. The entire collapsed filter device1, along with the sheath78is then removed as a single unit from the blood vessel61.

The method may also be used to retrieve a filter that had not been incorporated into the vessel wall65. If there is no or minimal endothelial overgrowth73, the radially outward prying force created by the band of endothelial tissue73as it slides upstream along the alignment rib8is not created. In the absence of this force, the alignment ribs8will collapse inwardly against the center shaft4but will not release from the filtering hub11. Instead, the filter collapses in a linear fashion as previously described, with the alignment ribs8remaining captured within the filtering hub11.

The method may also be effectively used to retrieve a vena cava filter1that has one or more but not all alignment ribs8encapsulated within endothelial bands73of tissue. In this aspect of the invention, those alignment ribs8that are encapsulated will release during retrieval due to the radially outward force created by the bands73as they slide upstream toward the filtering hub11. Those alignment ribs8that have not been incorporated into the vessel wall65will flatten out against the center shaft4but will not undergo sufficient radially outward force to release from the filtering hub11. Thus, in another novel aspect of the present invention, a retrievable filter1is provided that can be successfully retrieved in the absence or presence of vessel overgrowth on one or more alignment ribs8.

FIG. 14is a plan view of an alternative embodiment of the present invention. Similar to the device ofFIG. 1, the retrievable filter device80includes a filter section3and an alignment section5, except that the upstream ends of the alignment ribs8are fixedly attached to the filter hub11. The alignment section5and filter section3are optimally comprised of a single tubular structure. Some of the filter legs13may include vessel wall-engaging ends15at their upstream ends while some may have a smooth profile without such wall-engaging ends at their upstream ends. Like previous embodiments, the filter section3and alignment section5are longitudinally spaced from one another in a non-overlapping relationship. This embodiment may be placed as a permanent implant or as short term retrieval device which is removed prior to significant overgrowth of vessel tissue, typically four to eight weeks. Optionally, the downstream end of the filter hub11may be sharpened to incise any tissue that may be present during retrieval. WhileFIG. 14shows the filter legs13without any branches, the filter80can be provided with the primary filter legs13and secondary filter legs29each with two branch legs27as shown inFIG. 1.

The closed loop configuration of device depicted inFIG. 14is advantageous over prior art filters with centering structures comprised of individual legs with free ends that are prone to entanglement and misalignment. In addition, the device is formed from a single Nitinol or other metallic tube with no welded joints. This construction is cost-effective and provides enhanced structural integrity and strength over welded devices. The single tube construction with the longitudinal separation of the alignment and conical filtering sections allows the device to be constrained within a smaller delivery system that is substantially equal to the outer diameter of the tube.

FIGS. 15A and 15Bshow alternative structures of a releasable lock and releasable upstream ends of the alignment ribs. As shown inFIG. 15A, the releasable lock may be designed to automatically release or weaken the coupling after a predetermined time has elapsed. As an example, the tapered forward segment (cover piece)16of the primary filtering hub11as shown inFIGS. 6A and 6Bwhich circumferentially surrounds and covers the engaging tabs24may be comprised of a biodegradable material such as polyglycolide, polylactide, or other synthetic polymer commonly known in the art. The material is designed to gradually degrade and be absorbed by the body over a period of time, typically two weeks to six months, depending on the material formulation. During this period of time, the vessel wall contact points10of the filter will become incorporated into the vessel wall, thus stabilizing the filter within the vessel. Once the biodegradable material has been absorbed by the body, the engaging tabs24are no longer restrained and will disengage from hub11with relatively little force. The endothelial overgrowth at the vessel wall contact points of the filter immobilizes the alignment ribs preventing misalignment and migration of the device as well as perforation of the vessel by the ribs.

Alternatively, the releasable upstream ends23of the alignment ribs8can be permanently attached to the hub11and be made of biodegradable material at point84as shown inFIG. 15B. After a predetermined time period, the releasable upstream ends23of the ribs8will be released into open ends or will be sufficiently weakened so that the upstream ends23of the alignment ribs8will break with relatively little force. In this case, the filter hub11acts as the releasable lock.

In yet another embodiment, the releasable lock may be designed with releasable upstream ends23that are structurally weakened relative to the remaining portions of the alignment ribs8to deform or break under a predetermined retrieval force. The alignment ribs8may include releasable upstream ends23that have a reduced profile section as shown at84inFIG. 15B(either in width, thickness or both), which will deform or break at a lower retrieval force than the other filter components, thereby causing the alignment rib upstream ends23to be released from hub11. Alternatively, the reduced profile of the upstream ends23can be a reduced thickness or width of the tabs24such that they will deform or break at a lower retrieval force than the other filter components. Another possibility is that the alignment ribs8may include releasable upstream ends23that have a reduced profile section at point84as inFIG. 15Band be made of biodegradable material at the same point84.

In yet another embodiment of the releasable locking mechanism, the engaging tab24and the recess22may be laser cut so as to create an interference friction fit as shown inFIG. 15A. The engaging tabs which have a slightly larger profile than the receiving recesses22, are forcibly inserted into the recesses. The material interference between each engaging tab24and recess22creates a friction fit which will release only under a retrieval force sufficient to overcome the retaining force. The advantage of this embodiment is that it does not rely on the endothelial overgrowth band to create a prying force. Instead the friction fit may be overcome by a direct longitudinal force.

Other configurations and methods of retrieving a vena cava filter1are also possible. Modifications of the details illustrated in this disclosure, including filter and component shapes, numbers, wall-engaging designs, dimensions, materials, methods of construction, and methods of use, are within the scope of this invention. For example, the number of filtering legs on both the primary and secondary filtering structures may be varied. The filter1may be assembled without utilizing a secondary filtering structure26. The assembly methods, component dimensions and materials may be varied. In addition, the interlocking profiles of the alignment ribs8and filtering hub11may also be modified and remains within the scope of the present invention. Any engaging tab24and receiving pocket22profile may be used if it is configured to provide a holding force in an axial direction and allow release when an outwardly radial force is present. Tab shapes including circular, semi-circular, rectangular, tear-drop or elliptical are within the scope of the invention. The center shaft4component may be of a variable length in a spring configuration or comprised of a non-metallic material such as a nylon wire. The center shaft4may be of any configuration that provides a travel path that exceeds the elongated length of the alignment section. Accordingly, the scope of the invention is not limited to the foregoing specification.