Abstract:
A vena cava blood clot filter is described that is attached to the walls of the vena cava by barbed anchors. In its filtering state, the filter is cone shaped which causes the blood to be filtered. The cone shape is formed by an appropriate restraining mechanism. When it is desired to stop filtering, the restraining mechanism is released and the filter takes a cylindrical shape. The cylindrical shaped filter will then line the vena cava wall and cease filtration of the blood.

Description:
This is a divisional application under 37 CFR 1.53(b) of parent application 09/693,412 filed Oct. 20, 2000 Pat. No. 6,582,447 priority to which is claimed herein and, the entire disclosure of which is hereby incorporated herein by reference. 

   BACKGROUND 
   1. Field of Invention 
   The following invention relates to a clot filter and more specifically to a convertible vena cava blood clot filter. 
   2. Description of the Related Art 
   Vena cava blood clot filters are generally placed in the inferior vena cava, introduced either through the femoral or jugular vein. These filters trap blood clots that have arisen from the peripheral veins and that travel through the vena cava. By trapping the blood clots, the filter prevents the clots from lodging in the pulmonary bed, which can lead to a condition known as pulmonary embolus. 
   Pulmonary embolus (PE) has long been recognized as a major health care concern. Untreated PE is associated with a high mortality rate, widely held to be approximately 30%, although the exact rate is unknown. Symptomatic PE, however, represents only one manifestation of a more protean disorder, venous thromboembolic disease (VTD), which includes both deep venous thrombosis (DVT) and PE. Understanding of the interrelationship of these disorders has increased in recent years, as has the extent to which VTD contributes to patient mortality. 
   The current standard of care of VTD is anticoagulation for a minimum period of six months. If patients are properly treated with anticoagulation, the impact of VTD upon patient health is minimized. However, anticoagulant therapy carries the risk of bleeding complications. In patients with VTD or PE that 1) are at high risk of developing a bleeding complication, 2) have a contraindication to anticoagulant therapy, 3) had a failure of response to anticoagulant therapy (i.e. further episodes of PE), or 4) developed a bleeding complication because of anticoagulant therapy, vena cava blood clot filters play an important role in the management of VTD. 
   Vena cava clot filters can be categorized into two device families: permanently implanted devices and temporary devices. Permanently implanted devices are implanted for patients that require a filter for more than fourteen days. Fourteen days roughly approximates the time before which the points where the filter contact with the caval wall becomes covered by endothelial cells which thicken to eventually attach the filter permanently to the cava wall. If an attempt is made to remove the filter after this time point, severe damage may occur resulting in laceration or rupture of the vena cava, or at the very least, a focal disruption of the endothelial lining which may predispose to caval stenosis, thrombosis (clot formation) or occlusion. 
   Since the permanent blood clot filters are left in the body for the lifetime of the patient, the patient undergoes several risks that continue throughout the person&#39;s lifetime. The reported long-term sequela of some of the permanent devices include thrombotic occlusion of the vena cava, filter migration, filter fragmentation and filter embolization. 
   These problems can occur because the blood clot filter is directly in the blood stream and continually filtering the blood clots throughout the lifetime of the patient. Thrombotic occlusion and filter embolization can occur when a gradual buildup of blood clots forms in or around the filter due to the continuous filtering. Filter migration and filter fragmentation can occur because of the constant impact between the blood filter and the flowing blood can move the filter or break the structure of the filter. 
   Temporary blood clot filters do not share those long-term risks because they are removed from the patient&#39;s body. However, the situations in which temporary blood clot filters are used are limited. The patient must recover to the point that the risk from PE is reduced to an acceptable level prior to the 14-day limit or to a time point at which the patient may be safely anticoagulated. Otherwise, a permanently implanted blood clot filter must be used to avoid damage to the caval wall that may result if attempt is made in removal after 14-days. 
   Temporary blood clot filters fall into two categories. One group utilizes a permanently attached tethering catheter for retrieval, whereas the other requires the use of a retrieval device for removal. In addition to the limited amount of time that it can remain in the vena cava, the catheter-based design has the draw back of infectious complications at the entry site. Other temporary designs allow a filter to be placed and later retrieved using a device. 
   When a patient&#39;s need for a blood clot filter is known to be temporary, but longer than the 14-day period, the patient&#39;s only recourse is to receive a permanent blood clot filter. An example of a temporary need resulting in placement of a permanent vena cava blood clot filter is a patient who need needs protection from PE in the perioperative period or a woman with DVT during pregnancy. These patients will receive a permanent filter and be unnecessarily subjected to the lifelong risks associated with permanent blood clot filters. 
   Accordingly, it is the object of the present invention to disclose an implanted device that provides effective caval filtration for any length of time. However, if and when it is determined that the risk from the implanted device disrupting laminar blood flow exceeds the risk of further PE, the filter can be removed from the blood stream to eliminate the associated risks of having a permanent filter within the bloodstream. This can be done at any time without regard to the amount of time that the filter has been implanted and without causing damage to the caval wall. Another object of the present invention is to provide such a filter that allows trapping (capturing) of blood clots of sizes that result in a clinically significant PE that poses an unacceptably high risk of patient morbidity and mortality. The trapped clots in the filter are then dissolved by the bodies own intrinsic fibrinolytic system, without causing pulmonary function compromise. Still a further object of the present invention is to provide such a filter that is relatively simple in design and is relatively inexpensive to manufacture. 
   SUMMARY OF THE INVENTION 
   The present invention provides a blood clot filter and a method for its use. The blood clot filter comprises an expandable filter shaped in the form of a cylinder. The filter is composed of high memory wire and the wire is formed into a band of zigzag bends. 
   In its pre-deployment form, both ends of the filter are collapsed to form a slender wire construct. After deployment, one end of the cylinder is held together by a suitable restraining means such as a Teflon ring with a diameter of approximately 3 mm. The other end of the cylinder is expanded and has a sufficiently large diameter to contact the walls of the inferior vena cava with sufficient force to hold the filter in place against the inferior vena cava. Additional means are used to attach that end of the filter to the walls of the vena cava. 
   When it is desirable to stop filtering, the Teflon ring holding the narrower end of the filter is broken thereby releasing the end of the filter. Once released, the narrow end of the filter will expand until the entire filter lines the walls of the vena cava. The filter will no longer filter the blood nor will it be directly in the blood stream. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide an understanding of the invention and constitute a part of the specification. 
       FIG. 1  depicts a side view of a deployment device for the blood clot filter in accordance with the present invention. 
       FIG. 2  depicts a side view of the first embodiment of a blood clot filter deployed in accordance with the present invention. 
       FIG. 3  depicts a magnified side view of the narrow end of a blood clot filter of the first embodiment. 
       FIG. 4  depicts a magnified view of a portion of the blood clot filter showing the barbed anchor in accordance with the present invention. 
       FIG. 5  depicts a front view of the first embodiment of the blood clot filter deployed in accordance with the present. 
       FIG. 6  depicts a side view of the engagement of a balloon angioplasty catheter with the first embodiment of the blood clot filter. 
       FIG. 7  depicts a side view of the blood clot filter after the filter has been changed to its non-filtering state in accordance with the present invention. 
       FIG. 8  depicts a front view of the blood clot filter after the filter has been changed to its non-filtering state in accordance with the present invention. 
       FIG. 9A  depicts a side view of a second embodiment of a blood clot filter using a tied suture in accordance with the present invention. 
       FIG. 9B  depicts a front view of the second embodiment of a blood clot filter using a tied suture in accordance with the present invention. 
       FIG. 10A  depicts a side view of the second embodiment of a blood clot filter using a unitary ring in accordance with the present invention. 
       FIG. 10B  depicts a front view of the second embodiment of a blood clot filter using a unitary ring in accordance with the present invention. 
       FIG. 11A  depicts a side view an endovascular device used to change the filter to its non-filtering state in accordance with the present invention. 
       FIG. 11B  depicts a top view of an endovascular device used to change the filter to its non-filtering state in accordance with the present invention. 
       FIG. 11C  depicts a magnified side view an endovascular device used to change the filter to its non-filtering state in accordance with the present invention. 
       FIG. 11D  depicts a magnified top view of an endovascular device used to change the filter to its non-filtering state in accordance with the present invention. 
       FIG. 12  depicts a side view of a third embodiment of a blood clot filter deployed in accordance with the present invention. 
       FIG. 13  depicts the disengagement of a portion of the blood clot filter in accordance with the present invention. 
       FIG. 14  depicts a side view of a fourth embodiment of a blood clot filter deployed in accordance with the present invention. 
       FIG. 15  depicts the disengagement of a portion of the blood clot filter in accordance with the present invention. 
       FIG. 16  depicts a side view of a fifth embodiment of a blood clot filter in accordance with the present invention. 
       FIG. 17  depicts a front view of a fifth embodiment of a blood clot filter in accordance with the present invention. 
       FIG. 18  depicts a side view of a sixth embodiment of a blood clot filter in accordance with the present invention. 
       FIG. 19  depicts a front view of a sixth embodiment of a blood clot filter in accordance with he present invention. 
   

   DESCRIPTION OF THE INVENTION 
   Referring now to the detailed drawings, wherein like numerals are used to denote like elements, a description of the embodiments will be discussed.  FIG. 1  depicts a filter delivery catheter that can be used in implanting the blood clot filter  101  within the vena cava. The filter  101  is collapsed into a small slender profile container within an outer tube  103 . The outer tube  103  of the delivery catheter retains the blood clot filter  101  in this collapsed state and provides a substantial amount of the column strength of the delivery catheter. 
   An inner tube  105  is used to push the filter  101  out of the outer tube  103 . A retention hook wire  107  is attached to the filter  101  and allows the user to pull the filter back into the delivery system if the position, while deploying the filter  101 , is not satisfactory. Once the filter  101  is completely out of the outer tube  105 , the hook is advanced, turned and retracted. A hub system (not shown) at the proximal end of the delivery catheter will allow the user to easily operate the system. 
   To implant the filter, the delivery catheter is placed percutaneously into the jugular vein. The delivery catheter is advanced through the Superior Vena Cava, through the right heart, and into the Inferior Vena Cava. The filter  101  can be seen by fluoroscopy. To deploy, the filter will be held in place by maintaining position of the inner tube  103 . The outer tube  103  is retracted, thus uncovering the filter and allowing it to open. If the operator does not like the position of the filter  101 , the retention wire can be used to pull the filter back into the sheath for repositioning. 
     FIG. 2  shows the blood clot filter  101  properly implanted within the vena cava  207 . The filter  101  is an expandable structure that is normally in the shape of a cylinder. The body of the filter  101  is composed of a high memory wire predisposed to the fully expanded position. The wire of the filter  101  is formed in a zigzag pattern.  FIG. 2  depicts the filter  101  in its deployment phase in which it is held to the shape of a cone. 
   A ring  201  holds one end of the filter together. The ring  201  can be composed of Teflon or other suitable material that is resilient enough to withstand constant abrasion from the blood flow, but still capable of being broken with minimal force when desired. The ring  201  restricts the end of the filter  101  to a 3 mm diameter. In this position, the filter will be able to capture blood clots greater than 3 mm. The diameter of the ring  201  can be any diameter to adjust the size of the blood clots captured. The expandable nature of the filter  101  will accommodate different diameters established by the ring  201 . 
   The other end of the filter  101  is fully expanded to the diameter of the vena cava  207 . Shaped as such, the wire forms a plurality of legs  203  that contact the vena cava wall at the apices of the legs. Barbed anchors  205  are placed at each apex of each leg  203  to keep the filter in the intended location. The filter  101  is placed so that the conical end of the filter  101  is just below the renal veins. The barbed anchors  205  are angled so that the blood flow will impact the filter  101  and push the barbed anchors into the caval wall. 
   Using a conical shape allows for the efficient filtering of the blood. The highest velocity of flow is in the center of the blood stream and most blood clots will flow through the center to be caught by the ring. The legs  203  can be adjusted to vary the spacing between and leg to facilitate filtering. In addition, the legs  203  of the filter in this position will streamline the blood clots into the center of the filter  101 . 
     FIG. 3  depicts a magnified view of the narrower end of the filter  101 . A tie  301  attaches the ring  201  to the filter  101 . The tie  301  will hold on to the ring  201  when the ring is broken and the filter  101  expands to its cylindrical form. Consequently, the tie  301  is wrapped around the filter wire such that the tie  301  cannot be dislodged from the filter without breaking the tie  301 . The tie  301  is also securely connected to the ring by creating a hole in the middle of the ring band and looping the tie  301  through that hole. Tie  301  can be composed of Teflon or any other material that can withstand the abrasion of the blood flow and not break from it.  FIG. 4  depicts the barbed anchor that is used to attach the filter  101  to the vena cava wall. 
     FIG. 5  shows the filter  101  from the front view. Ring  201  has a notch  501  that weakens the ring such that the ring  201  will break at the point of notch  501  when stretched beyond its limits. The location of the notch  501  can be anywhere on the ring  201 . It can be diametrically opposed to the tie  301  to ensure that the ring  201 , when broken, will have equal portions to either side of the tie  301 . The broken ring will then be less obtrusive to the blood flow in the vena cava. The notch  501  should be large enough to ensure that the break will occur at the notch and not at the point at which the tie  301  is connected to the ring  201 . 
   When it is determined that the disadvantages of filtering blood clots outweighs the benefits, then the ring  201  will be broken to release the filter from its conical shape to its cylindrical shape.  FIG. 6  depicts one process by which the filter  101  is released from the ring  201 . A balloon angioplasty catheter  601  that has a large enough diameter is placed into the vena cava and inserted into the ring  201 . The balloon catheter  601  is then inflated until the ring  201  breaks at the position of notch  501 . The balloon catheter will then be extracted from the patient&#39;s body. 
   Upon breaking the ring, the filter  101  expands into its normal cylindrical shape. The expanded filter is shown in  FIGS. 7–8 . In this position, the filter will hug the walls of the vena cava and not be directly in the blood stream to filter the blood for blood clots. The filter is essentially converted into a stent device. The thickened endothelial cells around the apices of the legs of the filter will remain around the apices since the device will not be removed. 
   In keeping the filter within the patient and causing it to line up against the vena cava wall, endothelial cells will also develop around the entire filter and the filter will eventually grow into the caval wall. This will eliminate the risks that are usually present when keeping the filter directly in the blood stream and constantly filtering for blood clots. Any potential risk from potential thrombus formation due to laminar blood flow disruption and risk from device fracture or fragment embolization during the patients&#39; life will not be present. 
     FIGS. 9A–9B  depict a second embodiment of the present invention. Filter  101  is presented in its deployed form. Ring  201  retains the narrow end of the filter  101  in its conical shape and is intertwined with the wire of the filter such that the ring will not be dislodged from the filter body. Ring  201  is shown as a tied suture. Tie  301 , however, is not connected to the filter  101 . Not connecting the ring  201  to the filter  101  via tie  301  allows the ring  201  to be completely removed after the ring  201  has been broken. 
     FIGS. 10A and 10B  depict a modification of the second embodiment that uses a unitary ring  201 , rather than a tied suture, to contain the conical end of the filter  101 . The unitary ring  201  is slid over the barbed end by weaving it over and under alternating leg sets. The ring is slid fully to the opposite end where it remains in position holding the conical end of the filter in the constrained position. The advantage of this simple unitary ring is there is no knot that can be prone to premature failure. The ring is also the lowest profile design providing minimal turbulent formation in the blood stream. The ring in this design also does not have a predetermined break zone that may be prone to premature failure. 
   The ring removal device depicted in  FIGS. 11A–11D  will cut the ring  201  to release the filter  101  and remove it from the patient. Ring removal device has a hook  1103  that will act to grab the ring  201 . The size of the opening to the hook  1103  is smaller than the diameter of the wire, but is larger than the ring material. After grabbing the ring  201 , hook  1103  will be retracted into the outer tube of the device. The outer tube has a sharp portion  1105  that will cut the ring  201  when the hook is being retracted. Upon cutting the ring  201 , ring removal device  1101  will extract the ring  201  from the filter to be removed from the patient. In removing the ring  201 , it minimizes the amount of foreign material present within the body to be absorbed and eliminates any potential obstruction of the blood flow. 
     FIGS. 12 and 13  depict a third embodiment of the present invention. Filter  101  is composed of two pieces, the base section  1201  and the filter section  1203 . The base section  1201  is cylindrical in shape and completely lines the walls of the cava vena. Barbed anchors hold the base section in place against the caval wall. 
   The filter section  1203  is shaped into a cone and has a hooked portion  1205  at the end of each leg  1203 . This hooked portion  1205  will engage with corresponding bends in the wire of the base section  1201 . The blood flow will push the hooked portions  1205  against the bent wire to hold the filter section  1203  connected to the base section  1201 . At the apex of the cone, a disengaging hook  1207  is placed. 
   To disengage the filter section  1203  from the base section  1201 , a removal device  1301  is inserted. The removal device  1301  can have a hook  1303  contained within an outer tube  1305 . 
   The removal device is maneuvered over the disengaging hook  1207  of the conical filter section  1203 . When inserted into the removal device, the disengaging hook  1207  will engage with the hook  1303 . Outer tube  1305  will contact the legs of the filter portion and exert an inwardly radial force on the legs  1203  thereby forcing the hooked portions  1205  of the legs  1203  to disengage from the base section  1201 . Once disengaged from the base section, the filter section can be completely drawn into the removal device  1301  and safely removed from the patient&#39;s body. The base section  1201  will remain within the patient&#39;s body and be incorporated into the vena cava. 
     FIGS. 14 and 15  depict a fourth embodiment of the present invention. Similar to the third embodiment, the filter  101  is composed of two pieces, the base section  1401  and the filter section  1403 . Legs  1405 , however, contain weakened sections that are predisposed to be broken when desired. The weakened sections can be designed to be broken by the application of a low voltage electrical current or be a physically weaker substance.  FIG. 15  depicts the removal device to be used for the fourth embodiment in which hook  1503  engages disengaging hook  1407  and filter section  1403  breaks off at predetermined weakened sections  1409 . Once completely broken off, the filter section  1403  can be retracted into the removal device and extracted from the patient. 
     FIGS. 16 and 17  depict yet another embodiment of the present invention. Filter  101  is composed of a single wire structure and shaped in the form of a cone to filter the blood stream. At the narrow end of the filter, the apex of each return bend is shaped in a loop of approximately 1 mm inside diameter. Stacking all of the loops on top of each other forms the conical end. A hitch pin  1601  is inserted through all the loops and holds the loops and the filter legs in the filtering conical shape. The hitch pin  1601  is retains its position in the loops by an interference fit. 
   The hitch pin  1601  is also designed so that the pin can be grasped or hooked by a tool, pulled from its position, and removed from the body when the physician determines that clot filtering is not needed any longer. 
   Once the hitch pin  1601  is pulled form the loops, the filter springs open to its cylindrical non-filtering position. The hitch pin  1601  is formed of a high memory wire in an “infinity symbol” shape with the dimension across the shape of 1.1 mm, or greater than the 1 mm inside dimension of the loops at the filter strut apexes. The hitch pin  1601  also incorporates a densely radiopaque marker to aid the physician while attempting to grasp the pin under fluoroscopic guidance. This “infinity” design allows the hitch pin  1601  to be pulled from either direction. The physician can choose the best direction at the time of conversion based on patient factors. 
   Other pin designs can be produced essentially performing the same function. A modification of this design is the use of biodegradable materials to form the pin. The hitch pin  1601  can be formed from a material that will give a known service life and will open automatically. The hitch pin  1601  can also be formed from a biodegradable material, which requires activation. The hitch pin  1601  can be removed by infusion of an enzyme to dissolve the pin material and open the filter. 
     FIGS. 18 and 19  depict another embodiment of the present invention. This design does not depend on a second component such as a Teflon ring or removable pin to retain it in its conical deployed position. In this filter design, the apices at the conical end of the filter form an integral latch. At the conical end of the filter, the apexes of five of the six return bends are shaped in loops of approximately 1 mm inside diameter. The sixth apex forms a pin  1801 . The conical shape is formed by stacking the five loops on top of each, with the sixth apex inserted through the five loops. The filter is opened to its non-filtering state by grasping the legs of the sixth apex and pulling the pin back and away from the loops. The loops will slide off of the pin  1801  and the filter will open. 
   The sixth apex has an added densely radiopaque element that can be easily seen by fluoroscopy and can be grasped by biopsy forceps, or other catheter based means. This design has the advantage of having no polymer components that may weaken prematurely, and no components that need to be removed from the body. A latch may be formed by many other configurations of the wire filter body. 
   The present invention is not to be considered limited in scope by the preferred embodiments described in the specification. Additional advantages and modifications, which readily occur to those skilled in the art from consideration and specification and practice of this invention are intended to be within the scope and spirit of the following claims.