Abstract:
A device ( 10 ) for navigation within a patient&#39;s body, said apparatus comprising a tubular structure having an inner lumen and relatively rigid proximal ( 15 ) and distal portions ( 14 ) separated by at least one very flexible joint ( 12 ) with constant inner diameter and small bending radius. At least one magnetic element ( 13 ) is embedded in the distal portion of the device and responsive to externally applied magnetic fields, such that the orientation of distal portion aligns approximately with an externally applied magnetic field (B). The inner lumen of the device allows a flexible medical instrument ( 17 ) (e.g. catheter, endoscope, etc.) to be inserted and retracted, such that the flexible medical device is effectively steered in the direction of the lumen&#39;s distal section.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to medical devices in the field of minimally invasive surgery, wherein an elongate flexible device, such as a catheter or endoscope, is inserted into the vasculature of the human body for surgical or diagnostic purposes. In particular, the invention relates to magnetically steerable devices for interventional cardiac procedures. 
       BACKGROUND OF INVENTION 
       [0002]    The field of magnetically-assisted minimally invasive surgery, wherein a magnetically responsive element disposed on a catheter, endoscope or other such device is steered inside a patient by generating external magnetic fields, is a well-known and increasingly popular area of medical development especially in the field of interventional cardiology. 
         [0003]    One of the most common ailments of the heart is know as cardiac arrhythmia, a condition in which a portion of heart tissue contracts in a rapid and uncoordinated manner, out of sync with the rest of the heart. Many arrhythmias are now treated with transcatheter ablation, a minimally invasive procedure wherein a catheter is inserted through a small incision in the femoral artery and guided into the heart. Electrodes on the catheter tip identify the precise locations of anomalous electrical activity and RF energy is delivered through the electrodes to neutralize these areas, restoring the heart&#39;s natural rhythm. 
       SUMMARY OF THE INVENTION 
       [0004]    In light of the aforementioned prior art and the limitations thereof, it is the object of this invention to provide an improved device and method for performing minimally invasive interventions, especially cardiac ablations. 
         [0005]    Around the middle of the 20th century, an inventor named Joseph Friedman was granted a patent (U.S. Pat. No. 2,094,268) for a drinking straw having an intermediate corrugated section that allowed the top portion of the straw to easily bend in any direction and stay put, an innovation that would forever revolutionize the beverage industry. Milkshakes could now be shared without bumping heads. Spitballs could be fired around corners. The world was a different place. Friedman and others followed his original patent with several more (U.S. Pat. No. 2,550,797, U.S. Pat. No. 3,025,004, U.S. Pat. No. 3,409,224), progressively improving the design of the joint and describing simple methods for its mass-production. 
         [0006]    Considered as a mechanical joint, the concertina-like corrugated section of a plastic straw has several subtle but interesting properties. It essentially acts as a spring with no restoring force. In order to deform the joint, whether bending or expanding/contracting, some force is required (analogous to a spring constant), but this force does not depend on the joint&#39;s initial state or orientation. Furthermore, when force is removed, the joint does not return to its initial state as a normal spring would—it simply maintains its current shape. 
         [0007]    The properties of the corrugated bellows joint (as it will be called hereafter) relevant to the scope of this patent are briefly summarized here: 
         [0008]    Uniform flexibility—the joint&#39;s flexibility is the same in any direction, regardless of its current orientation. 
         [0009]    Expandability—The joint may be collapsed or expanded, changing its length and effective stiffness. 
         [0010]    Tight bending radius—The collapsible nature of the corrugated bellows allows the joint to make very sharp turns. 
         [0011]    Constant inner diameter—Because of the manner in which the corrugations either expand or fold into themselves, the joint maintains a constant inner diameter even at the limit of its bending radius. 
         [0012]    Stability/Stay-put action—The joint does not naturally return to any initial state. That is, once it is bent to an arbitrary angle or expanded to an arbitrary length, it will stay there until another force is applied. 
         [0013]    The proposed device comprises an inner ablation catheter and an outer lumen that guides the ablation catheter to the target site. The inner ablation catheter comprises a very flexible distal section (100-150 mm) and a relatively rigid proximal section and includes a standard ablation electrode array at its distal tip and all necessary electrical connections at its proximal end. The outer lumen or sheath comprises a short (10-20 mm) rigid distal section with embedded magnetically responsive element(s), and a long, relatively rigid proximal section, connected by a specially designed joint. This joint must act as a very flexible tube having a very small bending radius and a constant inner diameter, i.e. the cross-sectional diameter of the joint must not change based on the joint&#39;s curvature. In a preferred embodiment, the joint is a bellows joint fundamentally similar to the corrugated plastic section forming the flexible part of a drinking straw, but other potential joint embodiments include a spring bonded to a flexible medical tube, or a flexible tube with a number of periodically spaced rigid rings. 
         [0014]    The orientation of the magnetically responsive distal section of the outer lumen is controlled using externally generated magnetic fields, and when a desired orientation is obtained, the flexible inner ablation catheter can be easily inserted through the outer lumen and pushed against the tissue of the target site. The flexibility and tight turning radius of the outer lumen&#39;s distal joint allow the ablation catheter to reach sites near the sheath&#39;s entry point inside the heart which would otherwise be impossible or very difficult to access, and the joint&#39;s constant inner diameter does not inhibit the insertion of the ablation catheter, even at large angles. 
         [0015]    The expandable nature of the corrugated bellows joint can also be exploited to increase the sheath&#39;s capabilities. Actuating the joint&#39;s length—by hydraulic, pneumatic or mechanical means—adds an important extra degree of freedom to the sheath. 
         [0016]    By magnetically steering the sheath, instead of the catheter, the path of the catheter is constrained such that the catheter always approaches the target tissue site head-on, even if the target site is 180 degrees from the point of sheath insertion. With this navigation method, the tissue contact force no longer depends significantly on the location of the target site and the force resulting from a head-on approach is relatively easy to predict and control by selecting an appropriate catheter stiffness. 
         [0017]    By selecting appropriately low-stiffness materials for the flexible joint and distal catheter section, it is possible to ensure that any forces on the interior of the heart wall are below an arbitrary value deemed acceptably low to mitigate the risk of perforation but also sufficient to be effective for ablation. 
         [0018]    It is should also be noted that any tool of sufficient flexibility, not just ablation catheters, could be inserted into and controlled by the magnetically responsive outer lumen or sheath. 
         [0019]    In all embodiments the elongate tube has a proximal end and a distal end and a lumen extending therebetween, the expandable, flexible joint provides a small bending radius and constant inner diameter connecting the proximal and distal sections of the tube and the at least one magnetically responsive element on the distal end of the tube provides the navigational properties of the device. 
         [0020]    In a preferred embodiment the flexible joint comprises a corrugated bellows section whose corrugations permit the joint to expand and contract, bend freely in any direction and retain its cross-sectional shape in all orientations. 
         [0021]    In another embodiment the flexible joint comprises a light spring bonded to the inside of a soft elastomeric tube. The spring can be provided with a flexible tubing or encased in two layers of polymer. 
         [0022]    In another embodiment the flexible joint portion comprises a soft plastic tube with a plurality of embedded concentric rigid rings. The rings can also be completely encased in the elastomer tube material. 
         [0023]    In another embodiment, the proximal portion of the tube comprises an inner lumen wall creating an annular lumen surrounding the inner lumen, wherein the annular lumen is closed at the proximal side as well as at the distal side beyond the flexible joint portion. Furthermore, the annular lumen comprises a connector at its proximal side usually connected to a pump unit provided to fill or evacuate the annular lumen with a fluid to lengthen or shorten the flexible joint portion. Then the material of the inner lumen wall is stretchable over its length to the maximum length of the device, when the flexible joint portion is lengthened to its maximum extent, in the same way as the flexible joint portion can be lengthened over its initial length to its maximum extent. 
         [0024]    The one or more magnetically responsive element(s) are responsive to external magnetic fields to orient and stabilize the distal tip of the device. The joint connecting the proximal and distal ends of the tube has flexibility sufficient to permit the magnetically responsive distal element to align with any external magnetic field direction. Usually such external magnetic fields are on the order of 100 mT. 
         [0025]    The structure of the joint connecting the proximal and distal ends of the tube intrinsically resists any substantial change to its inner diameter as it bends so as not to impede the ability of a flexible medical device, such as an ablation catheter, to freely pass through the joint. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings, 
           [0027]      FIG. 1  is a perspective view of a preferred embodiment of the device, depicting the magnetically responsive distal tip aligning with an external magnetic field, thereby orienting the flexible instrument inside the sheath, 
           [0028]      FIG. 2 a    is a schematic view of the embodiment of the device of  FIG. 1  without a flexible medical instrument. 
           [0029]      FIG. 2 b    is a schematic cross-sectional view of the device of  FIG. 2   a,    
           [0030]      FIG. 2 c    is a schematic cross-sectional view of the device of  FIG. 1 , depicting the magnetically responsive distal tip aligning with an external magnetic field, 
           [0031]      FIG. 3  is a schematic cross-sectional view of a second embodiment of the device, wherein the flexible distal joint comprises a spring embedded in or surrounded by a flexible elastomeric material, 
           [0032]      FIG. 4  is a schematic cross-sectional view of a third embodiment of the device, wherein the flexible distal joint comprises a plurality of concentric rigid rings embedded in or surrounded by a flexible elastomeric material, 
           [0033]      FIG. 5 a    is a schematic cross-sectional view of a fourth embodiment of the device having a second interior lumen, 
           [0034]      FIG. 5 b    is an illustration of the changing length of the distal joint of the device of  FIG. 5 a    as fluid is pumped into the space between the inner and outer lumens, 
           [0035]      FIG. 5 c    is a schematic cross-sectional view of the device of  FIG. 5 a   , depicting the magnetically responsive distal tip aligning with an external magnetic field, 
           [0036]      FIG. 6  is a schematic view of a fifth embodiment of the device having two or more flexible distal joints and magnetically responsive elements, 
           [0037]      FIG. 7 a    is a schematic cross-sectional view of a sixth embodiment of the device having a rigid telescoping distal section controlled proximally by means of a control wire, 
           [0038]      FIG. 7 b    depicts the telescoping section of the device according to  FIG. 7 a    in the fully extended position, 
           [0039]      FIG. 7 c    depicts the telescoping section of the device according to  FIG. 7 a    in the fully retracted position. 
           [0040]      FIG. 7 d    is a schematic view of the device according to  FIG. 7 a   , depicting the magnetically responsive distal tip aligning with an external magnetic field and the rigid telescoping section fully extended, 
           [0041]      FIG. 8  is a schematic cross-sectional view of a seventh embodiment of the device wherein the corrugated bellows joint of the device of  FIG. 1  is enclosed in a flexible sleeve bonded to the each end of the joint, 
           [0042]      FIGS. 9 a  to 9 d    are illustrations of the device&#39;s ability to navigate into the right ventricle to treat arrhythmias in the RVOT in four different stages. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0043]      FIG. 1  shows a perspective view of a preferred sheath embodiment  10 , comprising a proximal tubular sheath  11  connected to a corrugated bellows joint  12  and a short distal section containing one or more magnetically responsive elements  13 . A soft a traumatic tip  14  is disposed at the distal tip of the device and is preferably radiopaque for fluoroscopy localization. A standard Luer fitting  15  is disposed at the proximal end of the sheath  11  to facilitate easy attachment to hemostatic valves. A flexible instrument having a proximal section  16  and a functional distal tip  17  is inserted through the sheath  10  and the distal tip  17  is thus steered by the magnetically responsive element(s)  13 . 
         [0044]    The magnetically responsive distal tip  13  is aligning with an external magnetic field of direction according to arrow B, thereby orienting the flexible instrument inside the sheath. Tip  14  comprises a tapered section made from a soft elastomeric material to minimize potential trauma as the device is inserted into the patient&#39;s vasculature and is preferably radiopaque for fluoroscopy localization. Such radiopaque a traumatic tips are common in traditional introducer sheaths and well known to those familiar with the art. The magnetically responsive element  13  comprises a hollow permanent magnet. 
         [0045]    The three or more sections of the device described in the first embodiment, and all further embodiments, are composed of diverse materials and must be permanently bonded together without obstructing the inner lumen of the device. Bonding of these elements may be achieved by thermal bonding, cyanoacrylate adhesives or UV-curing adhesives, among other methods, all of which will be well known to those familiar with the art. 
         [0046]      FIG. 2 a    is a schematic view of sheath  10  of  FIG. 1  without the flexible instrument of  FIG. 1 .  FIG. 2 b    is a cross-sectional view of sheath  10  of  FIG. 2 a    wherein the nature of the corrugated joint  12  and the inner lumen  18  are clearly depicted. 
         [0047]    The proximal section  11  of the sheath is a stiff plastic tube much like traditional introducer sheaths, providing the sheath shell. A small distal section  13 ,  14  of the sheath is separated from the proximal section  11  with the highly flexible joint  12  with a predetermined minimum inner diameter and small bending radius. The magnetically responsive element  13  is embedded in the distal sheath section. The inner diameter of the proximal section  11  as well as of the distal section  13 ,  14  is preferably of the same size as the minimum inner diameter of the flexible joint  12 . The magnetic element  13  is shown as a hollow permanent magnet attached between the corrugated bellows joint  12  and the a traumatic distal tip  14 . 
         [0048]      FIG. 2 c    is a cross-sectional view of sheath  10  being steered by an external magnetic field with the direction of arrow B, wherein the magnetic element  13  is oriented in the direction determined by the magnetic field. In this view it is clear how the corrugations in joint  12  allow it to make sharp turns greater than 180 degrees while maintaining its minimum inner diameter so that the flexible instrument  16  can be freely inserted and retracted. 
         [0049]      FIG. 3  is a cross-sectional view of the distal portion of a second embodiment of the device  20 , identical in every way to  10  except that the corrugated bellows joint  12  is replaced with a spring  22  bonded to or enclosed in an extremely flexible elastomer  21 . The spring  22  is flexible enough to allow the magnetically responsive element  13  to align with an externally generated magnetic field of direction according to arrow B, and the coils of the spring  22  prevent the elastomer  21  from kinking, allowing a flexible medical instrument  16  to be freely inserted through the device  20 . 
         [0050]    According to  FIG. 3  the material of the proximal sheath is formed integrally with the flexible elastomer part  21 , which is in turn directly attached to the hollow sleeve-like magnetic element  13 . 
         [0051]    In the embodiment shown in  FIG. 3 , the spring  22  is simply bonded to the inside of the elastomer  21 , thus defining a minimum free lumen. It is also possible that the spring is embedded in a flexible plastic tube or that a further layer of the flexible elastomer is attached at the inside of the spring and attached to the proximal and distal sheath parts. For instance, if the spring is dip-coated with a flexible elastomer, a process well known to those familiar with the art, the resulting elastomer  21  will fully enclose the spring, forming a smooth surface on both the outside of the flexible joint and the inside lumen. 
         [0052]      FIG. 4  is a cross-sectional view of the distal portion of a third embodiment of the device  30 , identical in every way to  20  except that the spring is replaced with a series of concentric rigid rings  32  bonded to or enclosed in an extremely flexible elastomer  31 . The rigidity of the concentric rings prevents the elastomer  31  from kinking and obstructing the passage a flexible medical instrument  16 , and the flexibility of the elastomer is sufficient to allow the magnetically responsive element  13  to align with an externally generated magnetic field B. 
         [0053]    The concentric rigid rings of  FIG. 4  can be made of metal, preferably non-ferromagnetic metal, or hard plastic and partly or fully embedded in or surrounded by the flexible elastomeric material  31 . Within the embodiment shown, the cross-section of each of the rings  32  is a circle and these rings  32  have about  2 / 3  of their cross-section embedded in the elastomer  31 . As in the embodiment of  FIG. 3 , the elastomer  31  is directly attached to the proximal sheath and the distal magnetic sleeve  13 . 
         [0054]      FIG. 5 a    is a cross-sectional view of a fourth embodiment of the device  40  having an additional inner tube  42  disposed from the proximal to distal end of the device. Inner tube  42  is attached and sealed to outer tube  11  at or near the luer fitting  15  at the proximal end  44  and at or near the magnetic sleeve  13  at the distal end  45 , thus forming an intermediate, sealed lumen  46  surrounding the inner tube for introduction of the instrument/catheter. Gas or liquid is pumped in through valve  41  and the length of joint  12  varies with the pressure in intermediate lumen  46 . A flexible medical device can be freely inserted through inner lumen  43 . Joint  12  is the corrugated bellows joint of the device of  FIG. 1  with the proviso that the bellows joint is attached to the outer sheath sleeve and the outer portion of the magnetic element  13 . 
         [0055]    In the embodiment of  FIG. 5 a   , the inner wall, separating the intermediate fluid extension lumen  46  from the instrument lumen is extended beyond the joint  12  towards the tip  14 . Then the hollow magnetic element  13  is attached via the distal seal  45  on one side and via the ring of the a traumatic tip  14  on the other side at said inner wall. In other words, the magnetic element  13  does not directly form the wall with the instrument lumen as in the other embodiments. Instead, a flexible inner liner runs throughout the length of the device and forms a smooth and continuous inner surface. Such an inner liner is of course also possible within the embodiments of  FIGS. 1 to 4 . 
         [0056]      FIG. 5 b    illustrates three states of joint  12 : fully collapsed—corresponding to a negative relative pressure in intermediate lumen  46 , partially extended—corresponding to ambient pressure in  46 , and fully extended—corresponding to positive relative pressure in  46  and maximum length of joint  12 . Of course, the length of joint  12  can transition continuously between fully collapsed and fully extended states. 
         [0057]      FIG. 5 c    is a cross-sectional view of the distal portion of the fourth sheath embodiment  40  of  FIG. 5 a    aligning with an externally generated magnetic field of a direction according to arrow B and making a sharp turn greater than 180 degrees. 
         [0058]      FIG. 6  is a schematic view of a further embodiment  50  of the device wherein two or more magnetically responsive elements  13  and/or two or more flexible distal joints  12  are disposed at the distal end of the device. The joints  12  are shown as corrugated bellows joints according to  FIG. 1 , but it is also possible to replace them by any of the other joint embodiments. It is also possible to provide the lumen extension embodiment for e.g. the first proximal joint  12  and an embedded spring or ring-based joint for the more distal joint of the embodiment of  FIG. 6 . 
         [0059]      FIG. 7 a    is a cross-sectional view of a sixth embodiment of the device  60  having a rigid tubular telescoping section  62  located in the lumen  18  near the distal tip of the device. The telescoping section can be extended or retracted by means of a control wire  61  which runs through the length of the device and out the luer fitting  15  to allow proximal control of the telescoping section  62 . The telescoping section  62  has an a traumatic tip  63  similar to tip  14 . 
         [0060]      FIG. 7 b    depicts the telescoping section  62  in the fully extended position. This increases the useful range of the device by supporting the catheter at distances from the distal tip  14  which would otherwise be too great for the flexible medical instrument to apply significant forces to tissue walls. 
         [0061]      FIG. 7 c    depicts the telescoping section  62  in the fully retracted position. In this position the rigid section  62  extends throughout the length of the flexible joint  12 , making this section effectively rigid. This configuration is especially useful when the device is first being inserted into the patient&#39;s vasculature and it is desirable to have a uniform rigidity throughout the device. 
         [0062]    The embodiment of  FIGS. 7 a  to 7 c    shows a length of the rigid telescopic section which is essentially equal to the length of the magnetic element  13  or distal portion (including distal tip  14 ) and which is also essentially equal to the length of the flexible joint, to be able to stiffen the entire flexible joint. Of course, the rigid telescopic section can then also be longer than the flexible joint portion. The wire  61  is preferably guided in the wall of instrument lumen proximal to flexible joint  12 . 
         [0063]      FIG. 7 d    is a schematic view of embodiment  60  illustrating the distal magnet  13  aligning with an external magnetic field and the rigid telescoping section  62  fully extended to support the catheter and substantially increase the effective range of the device. 
         [0064]      FIG. 8  is a schematic cross-sectional view of the distal portion of a seventh embodiment of the device  70  wherein the corrugated bellows joint  12  is enclosed in a smooth flexible sleeve  71 . The sleeve  71  is bonded to each end of the joint but the intermediate joint section is not bonded to the sleeve, allowing the joint to flex without being compromised by the sleeve. The sleeve  71  thus forms a smooth and continuous outer surface when the joint  12  is straight, which is desirable to minimize trauma when the device is being inserted into or withdrawn from a patient&#39;s vasculature. The camber of sleeve  71  in  FIG. 8  is exaggerated to emphasize the fact that the sleeve is only bonded to the ends of joint  12  and is not intended to illustrate the preferred embodiment. It is preferred that the diameter of the bellows joint part  12  has essentially the same outer diameter as the magnetic element  13  and the proximal sheath tube  11 . The sleeve  71  can be stretched over the corrugated part leaving almost no space between sleeve  71  and the corrugated bellows joint  12  material. 
         [0065]    Sleeve  71  is preferably formed from a microporous or fibrous material, such as ePTFE, which has mechanical properties more similar to cloth than to a traditional plastic tube, and as such will not significantly increase the stiffness of the joint. Materials such as ePTFE are also well suited for this purpose due to their low friction and biocompatibility. In addition, the use of an ePTFE material for sleeve  71  would allow a gas exchange with the surrounding space when the bellows joint  12  bends, and the sleeve is bent as well. Of course such an outer sleeve could also be implemented in any of the other embodiments, wherein the flexible joint comprises a spring or a plurality of rings instead of a corrugated bellows. The sleeve  71  may also be extended beyond the magnetic element(s)  13  all the way to the a traumatic tip  14 , in order to cover the magnet(s) and prevent direct contact with the patient&#39;s vasculature. 
         [0066]      FIGS. 9 a - d    illustrate the ability of embodiment  5  to navigate multiple turns inside the heart by utilizing a combination of magnetic steering and expansion of the distal joint. The right ventricular outflow tract (RVOT) is an area of the heart that is currently difficult to reach using magnetically guided catheters. In  FIG. 9 a   , the distal tip of the device is aimed at the valve leading to the right ventricle. In  FIG. 9 b   , the bellows joint is expanded, pushing the distal tip into the right ventricle. In  FIG. 9 c   , the whole device is inserted further into the vasculature until the flexible joint is entirely in the right ventricle. At this point the distal tip may be aimed at the RVOT and the catheter may be inserted to perform an ablation, as illustrated in  FIG. 9   d.