Abstract:
A temporary inferior vena cava filter including a guidewire and a doublet cage filter distally located on the guidewire. The doublet cage filter has a proximal cage filter and a distal cage filter, both of resilient and biased toward their expanded or deployed state. The proximal and distal cage filters may be collapsed by actuation, preferably with a sheath. A method of protecting from pulmonary embolism during treatment of a deep vein thrombosis is disclosed. The doublet cage provides stability when deployed in the inferior vena cava, is readily retrieved and readily manufactured. A method of manufacturing the doublet cage filter assembly is also disclosed and involves a nitinol tube with plural cuts to form struts which are heat treated in an expanded state.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims benefit from the earlier filed U.S. Provisional Application No. 60/813,570 entitled “Catheter” filed Jun. 14, 2006, and is hereby incorporated into this application by reference as if fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is for a filter on a guidewire and, in particular, relates to a peripheral guidewire with a deployable doublet filter for temporarily protecting the inferior vena cava of a patient from passage of thrombus debris leading to pulmonary embolism during treatment for deep vein thrombosis. 
         [0004]    2. Description of the Prior Art 
         [0005]    Deep vein thrombosis (DVT) is a dangerous medical condition in which a blood clot forms in a large vein, typically a large vein in a leg. This condition is also more commonly known as “traveler&#39;s thrombosis” or “economy-class syndrome” and is believed to be particularly associated with sitting motionless for long periods of time. Consider, for example, a vein in the leg which becomes burdened with a large blood clot. The leg then becomes quite painful and swollen and may eventually even develop open sores. If all or a portion of the clot is liberated from the original site in the leg, such debris will travel through the vein toward the heart, traveling in particular through the inferior vena cava (IVC) and then into the heart for subsequent pumping to the lungs. Next, such liberated debris lodges in the vasculature of the lungs, generating far more serious medical consequences for the patient. This result is known as a pulmonary embolism (PE). Pulmonary embolism is a blockage of the vasculature of the lung, and can destroy the affected lung tissue, as well as its normal function. It has been estimated that if left untreated, roughly one-in-three pulmonary embolisms will prove fatal, and also that between one-in-twenty or one-in-ten pulmonary embolisms are fatal within the first hour of occurrence. Therefore, interventional medical strategies are often employed to eliminate the thrombosis or clot while still located in the vein of the leg. Such is the significance of the earlier mentioned deep vein thrombosis or DVT. 
         [0006]    The interventional strategies for addressing deep vein thrombosis are varied. Historically, heparin treatment has been employed, but heparin treatment tends to leave the deep vein thrombosis in place and serves more to prevent the formation of new sites of deep vein thrombosis while also reducing the occurrence of pulmonary embolism. The patient, however, continues to be plagued by swelling, pain, and possibly eventual open sores on the leg. More aggressive interventional strategies include application of fibrinolytic agents, more commonly called “clot buster drugs,” which begin to break down and/or dissolve the clot, and thrombectomy operations which aim to physically cut up and remove the clot. Significantly, these more aggressive interventional strategies may be accompanied by an increasing danger of inadvertently liberating chunks of debris, again leading to increased possibility of pulmonary embolism. Note that if a liberated chuck of debris or clot passing through the inferior vena cava is sufficiently large to inhibit pulmonary function, then the event is classified as a pulmonary embolism. 
         [0007]    To address this possible inadvertent liberation of chunks of debris during aggressive intervention while eliminating the deep vein thrombosis, a filter mechanism is at times employed between the site of the deep vein thrombosis being treated and the heart. In particular, the filter typically is located within the inferior vena cava so as to capture and thereby prevent passage of larger liberated chucks of debris into the heart and then on to the lungs. Such filter mechanisms are termed inferior vena cava filters or “IVC filters.” The currently available IVC filters may be permanent or temporary installations. Unfortunately, currently available IVC filter mechanisms are also plagued by shortcomings. In particular, currently employed IVC filter mechanisms may spontaneously generate a clot or thrombosis centered at the IVC filter. Further, because the IVC filters are generally temporarily placed by penetrating fine projecting hooks through an inside wall of the inferior vena cava, the hooks attachments to the inside wall may fail and allow inadvertent migration of the IVC filter toward the heart, or the hooks may fully puncture the wall of the inferior vena cava, or if a temporary IVC filter is left in a patient too long, it may unintentionally become a virtually permanent IVC filter. Additionally, removing a temporary IVC filter involves snaring the temporary IVC filter and pulling it free from the inferior vena cava interior wall. In other words, removal and retrieval of the temporarily implanted IVC filter can be an unexpectedly complex operation, fraught with additional undesirable complications. Given these many shortcomings and challenges, some physicians view the risk associated with temporarily implantable IVC filters as too extreme and proceed to aggressively intervene in treating a deep vein thrombosis without employing any protective IVC filter. 
         [0008]    Clearly there is a need for a new IVC filter which may be temporarily deployed during aggressive interventional treatment of a deep vein thrombosis. Such a new IVC filter would provide the advantages of filtration and avoid the many shortcomings of the current temporary implantable IVC filters. The present invention, as explained below, is a device which answers this need. It is easily deployed and easily retrieved. Further, it is readily manufactured. Most importantly, it provides protection from pulmonary embolism while performing aggressive interventional treatment of deep vein thrombosis. 
       SUMMARY OF THE INVENTION 
       [0009]    The general purpose of the present invention is to provide a filter for protection against pulmonary embolism during aggressive intervention treatments for deep vein thrombosis. 
         [0010]    According to one embodiment of the present invention, there is provided a temporary inferior vena cava filter. The temporary inferior vena cava filter includes a guidewire and a two-cage or doublet cage filter. The guidewire has a distal and a proximal end. The two-cage or doublet cage filter is distally situated on the guidewire and includes a first resilient filter cage and a second resilient filter cage. Both the first and second resilient filter cages are actuatable between a collapsed state and a deployed state. The second resilient filter cage is situated distal to the first resilient filter cage. Preferably, the first resilient filter cage and the second resilient filter cage of the two-cage filter are actuated between the collapsed state and the deployed state by a sheath. More preferably, the sheath is of a polyimide material. Most preferably, the sheath is braided polyimide with a size of about # 6 or # 7 French. The doublet cage assembly is preferably formed of nitinol. More preferably, nitinol tubing receives a first plurality of parallel cuts in the nitinol tubing at the desired location for one of the doublet cages and a second plurality of parallel cuts for the other of the doublet cages. The cuts define struts. The cuts of a particular plurality of cuts can be oriented linearly (i.e., longitudinally and parallel to the tube axis) or helical relative to the tube axis. The struts are then heat set in an expanded deployed state to provide the resilient expanded characteristic to the filter cage. Advancing a sheath over the filter cages forces the two-cage filter to a collapsed state and retracting the sheath allows the two-cage filter to resiliently expand to the expanded or deployed state. In the deployed state, each filter cage has a convex exterior. Preferably, there are from about eight to about 16 cuts and, therefore, about eight to 16 struts in the pluralities of cuts in the nitinol tube. If helical, the cuts are oriented at about a 25 degree angle. 
         [0011]    In another embodiment, the present invention is a method of providing temporary protective filtering to protect from pulmonary embolism for a patient being treated for deep vein thrombosis. In the method are included steps of providing a guidewire with a doublet cage filter, as described above; inserting the two-cage filters on the guidewire into a vein of the patient and advancing the two-cage filters to a protective location distally relative to the deep vein thrombosis, and then deploying the two-cage filters at the protective location; treating the deep vein thrombosis; retracting the two-cage filters to the collapsed state by advancing a sheath; and withdrawing the two-cage filters in the collapsed state with the attached guidewire and sheath. The method also may include debulking the two-cage filter prior to retraction within the sheath. 
         [0012]    In still another embodiment, the present invention is a method of forming or manufacturing a filter cage assembly for attachment to the distal end of a guidewire. The method includes the steps of providing a tube; and cutting a plurality of parallel cuts in the tube to define a plurality of struts. The tube is nitinol and the cuts are parallel and may be linear or helical. If the cuts are helical, then they are oriented at about 25 degrees to the tube axis. The struts are expanded, preferably by a heat resistant insert, and then heat treated. 
         [0013]    One significant aspect and feature of the present invention is the continuous attachment of the new IVC filter to a peripheral guidewire. 
         [0014]    Another significant aspect and feature of the present invention is the lack of hooks on the new IVC filter. 
         [0015]    Still another significant aspect and feature of the present invention is the ease of initial deployment of the new IVC filter in a patient. 
         [0016]    Yet another significant aspect and feature of the present invention is the ease of subsequent removal of the new IVC filter from a patient. 
         [0017]    Yet another significant aspect and feature of the present invention is the ease of manufacture of the new IVC filter. 
         [0018]    Yet another significant aspect and feature of the present invention is the improved wall apposition within the inferior vena cava of a patient. 
         [0019]    Yet another significant aspect and feature of the present invention is that thrombotic debris that is located internally in either of the cages will likely be macerated as the doublet is withdrawn into the sheath. 
         [0020]    Having thus described embodiments of the present invention and set forth significant aspects and features of the present invention, it is the principal object of the present invention to provide an IVC filter for protection from pulmonary embolism in a patient being aggressively treated for deep vein thrombosis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein: 
           [0022]      FIG. 1  is a temporary IVC filter, shown in an expanded or deployed state with an associated sheath retracted, the present invention; 
           [0023]      FIG. 2  is the temporary IVC filter of  FIG. 1 , shown in a contracted or undeployed state with the associated sheath extended or advanced to cover the doublet filter (portions of the sheath are removed to allow the underlying doublet filter to be viewed); 
           [0024]      FIG. 3  is the expanded doublet filter cage assembly (prior to joining to guidewire subsequent to heat treatment); 
           [0025]      FIG. 4  is the doublet filter cage assembly, collapsed, prior to expansion and subsequent to forming cuts therein; 
           [0026]      FIG. 5  is an alternative embodiment of the doublet filter cage assembly showing its expanded or deployed state, in an isometric view; 
           [0027]      FIG. 6  is the alternative embodiment of the doublet filter cage assembly of  FIG. 5  in a contracted state subsequent to cutting and prior to expanding and heat treating; and, 
           [0028]      FIG. 7  is an exemplary schematic view of a method of use of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]      FIG. 1  shows a temporary IVC filter  20 , the present invention. The temporary IVC filter  20  includes a guidewire  22 . The guidewire  22  has a proximal end (not shown) and a distal end  24 . The distal end  24  includes a shapeable tip  25 . A doublet filter cage assembly  26  overlies the guidewire  22  adjacent the distal end  24  and has a connection  28  to the guidewire  22 . The connection  28  is proximally located on the doublet filter cage assembly  26  and generally distally located on the guidewire  22 . A proximal cone  30  is present at or adjacent to the connection  28  and is directed proximally (i.e., proximal cone  30  has a smaller diameter oriented proximally and a greater diameter oriented distally). The doublet filter cage assembly  26  includes a proximal cage  32  and a distal cage  34 . The proximal cage  32  has a proximal end  36  adjacent the connection  28  and a distal end  38  located distal to the connection  28 . The distal cage  34  has a proximal end  40  and a distal end  42 . The distal end  38  of the proximal cage  32  and the proximal end  40  of the distal cage  34  are separated by an intervening portion or segment of tubing  44 . A second cone  46 , situated distal to the distal end  42  of distal cage  34 , is not connected to the doublet filter cage assembly  26  and is fixed to the guidewire  22 . The second cone  46  is also directed proximally (i.e., second cone  46  has a smaller diameter oriented proximally and a larger diameter oriented distally). A sheath  48  covers much of the guidewire  22  and has a distal end  50  which may be slid over, distally, or retracted from, proximally, the doublet filter cage assembly  26 . When advanced fully (i.e., slid fully distally), the distal end  50  of the sheath  48  accepts the second cone  46 . The proximal end of the sheath is not shown, but remains outside of a patient as does the proximal end of the guidewire  22 . As shown in  FIG. 1 , the sheath  48  is retracted and the doublet filter cage assembly  26  including proximal cage  32  and distal cage  34  are both in an expanded state. 
         [0030]    Preferably, the guidewire  22  is about 0.035 inch in diameter. Preferably, the sheath  48  has an outer diameter of about 0.092 inch and an inner diameter of about 0.082 inch. Such a sheath  48  corresponds to about # 6 or # 7 French scale. In an alternative, a # 6 French might be used in the sheath  48 . Preferably, the sheath  48  is of a polyimide material, and most preferably, a braided polyimide material. Preferably, the proximal cone  30  has a length of about 0.320 inch and transistions from a proximal smaller end of about 0.035 inch to a distal end of about 0.072 inch. The proximal cone  30 , if present, provides a smooth entrance of the doublet filter cage assembly  26  into the sheath  48  at distal end  50 . Preferably, the proximal cone  30  is plastic or metal. Most preferably, the proximal cone  30 , if plastic, is molded or bonded to the guidewire  22  and, if metal, is welded or crimped onto the guidewire  22 . Preferably, the distal or second cone  46  has a length of about 0.320 inch and transistions from a distal smaller end of about 0.035 inch to a proximal end of about 0.072 inch, such that it may rest in distal end  50  of the sheath  48  when the sheath is fully advanced. Preferably, the cone  46  is plastic or metal. Most preferably, the distal free-floating cone  46 , if plastic, is molded or bonded to the guidewire  22 , and, if metal, is welded or crimped onto the guidewire  22 . Such a cone  46  needs to be distally spaced to allow for distal expansion and contraction of the doublet filter cage assembly  26  and might alternatively be used to limit travel of the doublet filter cage assembly  26 . Preferably, the shapeable tip  25  has a length of about 2.75 inches and extends distally from the second cone  46 . 
         [0031]      FIG. 2  shows portions of the sheath  48  in ghost or dotted outline so as to show the relationship of the doublet filter cage assembly  26 , when collapsed, to the sheath  48 . As shown in  FIG. 2 , when the sheath  48  is slid distally, the distal end  50  passes over the cone  30  and then sequentially causes the proximal cage  32  and the distal cage  34  to collapse. As they collapse, the proximal cage  32  and the distal cage  34  each increase in length while simultaneously decreasing in diameter. Upon completion of the distal movement of the sheath  48 , both cages  32  and  34 , as well as intervening portion or segment of tubing  44 , are enclosed within the sheath  48 . The distal end  50  of the sheath  48  then accepts the second cone  46 . The shapeable tip  25  continues to project past the distal end  50  of the sheath  48  and is not enclosed by the sheath  48 . 
         [0032]      FIG. 3  shows the doublet filter cage assembly  26 , in expanded state, independent of the guidewire  22 . As previously pointed out, the doublet filter cage assembly  26  includes a proximal cage  32  with proximal end  36  and distal end  38 , and a distal cage  24  with proximal end  40  and distal end  42 . An intervening segment or portion of tube  44  separates the proximal cage  32  from the distal cage  34 . 
         [0033]      FIG. 4  shows the doublet filter cage assembly  26  independent of the guidewire  22  in a collapsed state. Proximal cage  32 , in a collapsed state, is separated from distal cage  34  by intervening segment or portion of tubing  44 . Also shown are helical cuts  52   a - 52   p  defining helical struts  53   a - 53   p  of proximal cage  32 . Moreover, shown are straight cuts  54   a - 55   h  defining straight struts  55   a - 55   h  of distal cage  34 . It should be recognized that the doublet cage filter assembly could be of a proximal helical filter cage and a distal longitudinal filter cage or, alternatively, a proximal longitudinal filter cage and a distal helical filter cage, or alternatively, two helical filter cages, or alternatively, two longitudinal filter cages. 
         [0034]    Preferably, the doublet filter cage assembly  26  is prepared from nitinol tubing, especially nitinol tubing with an outer diameter of about 0.062 inch and an inner diameter of about 0.054 inch. Most preferably, the helical cuts  52   a - 52   p  and the straight cuts  54   a - 54   h  are about 0.003 inch in width and are radially directed on the nitinol tubing. Preferably, the helical cuts  52   a - 52   p  extend in a helical fashion and are regularly spaced apart from each other along the nitinol tubing for about 1.47 inches. Preferably, the straight cuts  54   a - 54   h  extend in a longitudinal fashion along the nitinol tubing for about 1.77 inches and are regularly spaced apart from each other. Cuts of such dimensions will result in cage filters  32  and  34  each having deployed or expanded dimensions of about 28 mm in diameter. Helical cuts  52   a - 52   p  of such dimensions, when expanded or deployed, will result in a cage filter  32  with a length of from about 10 mm to about 30 mm. Preferably, the helical angle of cuts  52   a - 52   h  is about 25 degrees. Most preferably, the helical cuts  52   a - 52   p  total 16 cuts and result in 16 helical struts  53   a - 53   p . Most preferably, the longitudinal straight cuts  54   a - 54   h  total eight cuts and result in eight straight struts  55   a - 55   h . Preferably, subsequent to forming the helical struts  53   a - 53   p  and straight struts  55   a - 55   h  by making helical cuts or slits  52   a - 52   p  and straight cuts or slits  54   a - 54   h , respectively, the nitinol tubing is heat treated such that the expanded filter cages  32  and  34  (as shown in  FIG. 3 ) resiliently attempt to assume the expanded or deployed state. One method to accomplish the heat treatment is to insert a sphere-like heat resistant object within the filter cages  32  and  34  and then exposed to appropriate heat for a sufficient time. An appropriate temperature would be below the annealing temperature for nitinol. A preferred heat resistant sphere-like object is a marble of diameter about 28 mm. Preferably, the heat is provided by a fluidized bed of sufficient temperature. It will be recognized that a variety of alternative objects could be used, as well as a variety of heat sources. Subsequently, the resulting resilient doublet filter cage assembly  26  is attached to the guidewire  22 . In particular, the proximal end adjacent proximal end  36  of proximal filter cage  32  of doublet filter cage assembly  26  is attached to the guidewire by adhesive, solder, or welding. It should be understood that increasing the number of cuts, whether longitudinally or helically oriented, will increase the number of struts in a particular filter cage. A greater number of struts will increase filtration, but the struts tend to be less robust. A smaller number of struts will decrease filtration and allow larger particles to pass but will provide more robust struts and thereby a more robust filter cage. 
         [0035]    In an alternative embodiment, instead of a sheath  48 , actuation of the doublet filter cage assembly  26  may be generated by a mandrel design. For example, if the guidewire  22  were a tube, a mandrel may pass through the tube guidewire  22  to oppose and overcome the resilient nature of the doublet filter cage assembly  26 . If the doublet filter cage assembly  26  resiliently is biased to the expanded state, the mandrel would force contraction by forcing the doublet filter cage assembly  26  to lengthen, or alternatively, if the doublet filter cage assembly  26  were biased to the contracted state, then the mandrel would force the doublet filter cage assembly  26  to shorten and thereby expand. 
         [0036]      FIG. 5  shows an alternative embodiment doublet filter cage assembly  60 . The alternative embodiment doublet filter cage assembly  60  includes a proximal filter cage  62  and a distal filter cage  64 . The proximal filter cage  62  includes a proximal end  66  and a distal end  68  and the distal filter cage  64  includes a proximal end  70  and a distal end  72 . 
         [0037]      FIG. 6  shows the alternative embodiment doublet filter cage assembly  60  in an unexpanded or collapsed state, as would also be encountered during manufacture. A plurality of helical cuts  82   a - 82   p  define helical struts  83   a - 83   p  of proximal filter cage  62  and a second plurality of helical cuts  84   a - 84   p  define helical struts  85   a - 85   p . An intervening tube portion  74  is present to separate the filter cages  62  and  64 . The both pluralities of helical cuts  82   a - 82   p  and  84   a - 84   p  are radially oriented and radially distributed about the tubing and extend in helical fashion. Preferably, the tubing is nitinol, and preferably, the nitinol tubing is 0.062 outer diameter with 0.050 inner diameter tubing. Preferably, the helical cuts total 16 and are about 0.003 inch in width and arranged on about a 25 degree angle relative to the tubing axis. Preferably, both pluralities of cuts are identical. An alternative low profile cage filter may be made using a smaller nitinol tubing of 0.047 inch outer diameter and 0.038 inch inner diameter, along with the same pattern of two pluralities of 16 helical cuts. In both cases, the resulting expanded filter cages are about 28 mm in diameter and about 10 mm in longitudinal extent. 
       MODE OF OPERATION 
       [0038]    With reference to  FIG. 7 , two modes of operation of the present invention may be understood as follows. In both modes of operation, a physician initially evaluates and determines the location or site of the deep vein thrombosis  90 . For example, consider a patient with deep vein thrombosis  90  in the right iliac vein  92  (leg vein). The physician may choose, in a first mode, to place the present invention  20  while accessing the right iliac vein  92  (i.e., push the device  20  through the thrombosis  90 ) and position the inferior vena cava doublet filter cage assembly  26  on guidewire  22  distal to the thrombus and thereby between the thrombus  90  and the patient&#39;s heart. In that first mode, the guidewire  22  could be used for delivering other interventional tools such as AngioJet® or infusion catheters or other thrombectomy devices. Alternatively, in a second mode of operation, the physician may decide to avoid crossing the thrombotic segment  90  with the present invention  20 . In such second mode of operation, the physician may use a contralateral approach, accessing the deep vein thrombosis  90  through the left leg veins  92 . In that case, the doublet cage filter assembly  26  of the present invention  20  could be positioned in the inferior vena cava. A separate guidewire (not shown) would be positioned across the thrombotic segment  90  for purposes of delivering interventional tools. As may be understood from these two modes of use, the present invention  20  enables a host of treatment options for the physician. 
         [0039]    Once the selected interventional procedure is complete, the physician would use fluoroscopy to verify that the doublet filter cage assembly  26  of the device  20  was not occluded with thrombotic debris. If there was thrombotic debris occluding the doublet filter cage assembly  26 , then a separate guidewire with AngioJet® could be delivered to the doublet filter cage assembly  26  and the doublet cage filter assembly  26  could be debulked prior to retrieval from the vein  92  of the patient. Retrieval is as simple as withdrawing the doublet filter cage assembly  26  back into sheath  48  via distal end  50  of sheath  48  and then withdrawing the device  20  from the vein  92  of the patient. 
         [0040]    Alternatively, instead of debulking the doublet filter cage assembly  26  by using another separate guidewire and an AngioJet® or infusion catheter or other thrombectomy device, an AngioJet® or infusion catheter or other thrombectomy device might be directed to the doublet filter cage assembly  26  on the same guidewire  22  that is connected to the doublet filter cage assembly  26 . In another variation, another additional inferior vena cava filter might be placed in the patient distal to the doublet filter cage assembly  26  by employing jugular access. This variation enables debris to be trapped by the additional inferior vena cava filter during removal of the doublet filter cage assembly  26 . In yet another variation, it should be noted that collapsing the doublet filter cage assembly  26  tends to macerate any thrombus carried therein. The macerated thrombus would either be of such small particulate size as to be generally harmless or larger particulate sized macerated thrombus would be filtered out by the additional inferior vena cava filter, mentioned previously, or removed by an AngioJet® or infusion catheter or other thrombectomy device. 
         [0041]    Various modifications can be made to the present invention without departing from the apparent scope thereof.