Abstract:
A low profile, tailored stiffness intravascular balloon catheter is disclosed for use especially in treatment of intracranial aneurysm. Treatment utilizing the device can be performed without the need for a guide wire during delivery of embolic implants. A profiled metal hyptotube that is machine-cut or laser cut in a dual, off-set helical pattern, is the foundation for the device. A polymer jacket may be disposed upon the hypotube. A thin wall elastomeric balloon is bonded to the distal end of the system in fluid communication with the hypotube. The system may have one or more delivery ports for the release of embolic implants.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional application No. 61/319,926, filed on Apr. 1, 2010, the full disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to medical devices and specifically to intravascular balloon catheters for treatment of vascular disease such as aneurysm, including for delivery of embolic implants. 
         [0004]    Stroke is the third leading cause of death in the United States, and is the leading cause of disability. Types of stroke are divided into ischemic stroke and hemorrhagic stroke. Hemorrhagic stroke results from the rupture of an aneurysm in the wall of an intracranial vessel. Numerous intravascular procedures have been developed to treat both ischemic and hemorrhagic stroke. Most procedures employ the sequential introduction of a guide wire, a guide catheter, and subsequent therapy. In the treatment of hemorrhagic stroke, a balloon catheter is often used to accompany the delivery of embolic coils used to fill an aneurysm to prevent further blood flow into the aneurysm. 
         [0005]    Current balloon catheter systems employ the guide wire for delivery and deployment of the inflatable balloon catheter and as a safety measure. Firstly, a guide wire is used for tracking the catheter to the treatment site. The guide wire is introduced first, and is used to “find” the path through the tortuous anatomy to the treatment site. The catheter is then tracked over the guide wire, which may provide a “rail” for or otherwise guide the catheter. Following tracking to a treatment site, the guide wire is then typically used during deployment of the balloon catheter. After the balloon is inflated within the vessel, the guide wire is used to confirm a tolerance fit for the balloon. The tolerance fit confirms an almost fluid seal for injection of contrast die. Further, the wire provides a fail-safe to permit balloon deflation in the event aspiration through the system lumen cannot be achieved. And finally, the interference fit of the wire may confirm that any residual air has been eliminated from the system. Current conventional systems to perform the procedure are typically 2.5 French in size. 
         [0006]    In the aneurysm coil embolization procedure, a guide wire and catheter are introduced into the femoral artery and navigated through the vascular system to the site of the aneurysm under fluoroscopic visualization. In some instances, an inflatable balloon is used to secure the position of the catheter at the site of the aneurysm. Also, in some instances, a stent is deployed across the “neck” of the aneurysm, and coils are delivered from the catheter, through the interstices of the stent, and into the aneurysm. 
         [0007]    However, in smaller diameter vessels, it is often difficult to “bridge” the neck of the aneurysm with a stent. Under these circumstances, it may be desirable to bridge the neck of the aneurysm with the balloon positioned at the distal end of the catheter. The inflatable balloon may be used to “remodel” the neck of the aneurysm and to secure the delivery catheter at the treatment site during delivery and deployment of the coils. The inflated balloon may further prevent escape of embolic implants during release into the aneurysm. Multiple coils may be introduced into a single aneurysm cavity for optimal filling of the cavity. The deployed coils serve to block blood flow into the aneurysm and reinforce the aneurysm against rupture. 
         [0008]    2. Description of the Background Art 
         [0009]    Catheters having tubular bodies with helical or other cuts to control flexibility are described in U.S. Pat. Nos. 7,785,289; 7,815,600; 6,074,407; 6,527,790; 6,293,960; and U.S. Patent Publication Nos. 2006/0084939; 2009/0157048; and 2004/0019322. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    Catheters according to the invention herein may be used to remodel the neck of the aneurysm without requiring the use of a guide wire for deployment of a balloon or release of embolic implants. A catheter according to the invention will have a low profile allowing delivery using a guide catheter as small as 1.5 French. A catheter according to the invention will provide a balloon having a tailored stiffness that will permit it to serve some of the purposes of a guide wire. The interior volume of the balloon catheter disclosed herein is significantly smaller than currently marketed systems, rendering any residual air bubble negligible, and thereby further reducing the need for a guide wire for safety. Still further, a tailored balloon rupture pressure and/or a slow distal leak through the balloon distal tip will reduce the need for a guide wire for safety. 
         [0011]    The inflatable balloon catheter of the present invention may be delivered through any appropriately sized guide catheter or microcatheter. The distal end of the microcatheter is introduced into the femoral artery through a small incision near the groin. Deployment of the disclosed balloon catheter system will be achieved by filling the balloon and catheter lumen using the same technique as conventional filling or inflating of PTCA balloon catheters. A distal end of the catheter may be positioned at the target site via the microcatheter, and the distal balloon inflated at the target site. Contrast dye may be injected into the catheter for enhanced visualization of the artery. 
         [0012]    The novel balloon catheter design employs a profiled machine cut or laser cut metal hypotube which transitions to a softer profile towards the distal end by controlling the pitch of the tube. The cut pattern utilizes a dual helical or spiral cut where the second cut is offset from the first (typically being out-of-phase by an angle in the range from 90° to 180°) in order to provide an interference locking mechanism to provide stretch resistance in the tube while at the same time preserving lateral flexibility. A polymer jacket will be placed over at least a portion of the machine/laser cut hypotube to provide a fluid tight seal to allow delivery contrast to the balloon and to provide a bonding substrate to bond the proximal end of the balloon to the metal hypotube shaft. The polymer jacket will also provide a tie layer for the hydrophilic coating to adhere in order to enhance deliverability. The system may further be manufactured to have enhanced visibility. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a side view of an embodiment according to the invention in its deployed configuration. 
           [0014]      FIG. 2  is a “see-through” side view of a component of the embodiment of  FIG. 1 . 
           [0015]      FIG. 3  illustrates a balloon catheter system according to the invention within a vessel of a subject. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  illustrates a balloon catheter system according to the invention. Balloon catheter system  10  includes an elongate tubular member  12  extending from proximal end  14  to distal end  18 , in fluid communication with inflatable balloon  20 . Though not drawn to scale, a truncated version of system  10  is illustrated in  FIG. 1  with balloon  20  in its inflated configuration. A balloon catheter according to the invention may be characterized as having any length, outer diameter and other dimensions that are suitable for carrying out procedures within the intracranial vasculature. In the example of  FIG. 1 , balloon catheter system  10  has a length ranging from 70 cm to 110 cm. 
         [0017]    Proximal end  14  of tubular member  12  is attached to a standard hub or luer  16  or other comparable device for connection to a suitable means for delivery and withdrawal of inflation media. Tubular member  12  is provided with an inflation lumen (not shown) in fluid communication with balloon  20 . A delivery port, (not pictured), for release of embolic coils or other embolic material may be disposed near the distal end of tubular member  12  and balloon  22 . Alternatively, a delivery port may be disposed along the length of balloon  20 , which may be lobed (and include openings between adjacent lobes) to permit unobstructed release of embolic material. 
         [0018]    An exemplary balloon  20  is a sealed, compliant balloon constructed of a thin walled elastomer, typically a polyurethane thermoelastic elastomer such as ChronoThane™, available from AdvanSource Biomaterials of Wilmington, Mass., or other suitable material. The material can either be cast or extruded to a desired thickness in order to achieve a desired compliance and accommodate the expected inflation pressure. Typical balloon wall thicknesses will range from 0.00075 inch to 0.0015 inch, depending on the properties desired. Providing catheter system  10  with an atraumatic distal tip and tailored stiffness, balloon  20  provides some of the function of a guidewire in placement of the distal end  18  of balloon catheter system  10  in the distal vasculature and at the site of an aneurysm or other defect (not pictured in  FIG. 1 ). The rupture pressure of balloon  20  may be selected to provide a safety feature, lessening the need for a guide wire to confirm a tolerance fit in the vessel. Balloon  20  may also be fabricated to allow a slow distal leak of inflation medium as an added safety feature to ensure reliable deflation of balloon  20  without the use of a guide wire, and to ensure safe removal of system  10  following the conclusion of a procedure. 
         [0019]    The elastomer forming balloon  20  may be loaded with radiopaque material to enhance visibility under fluoroscopy. Alternatively, or in addition, one or more radiopaque marker bands may be disposed about balloon catheter system  10  to further ensure accurate placement of the system. Further, balloon catheter system  10  may be filled with contrast die for enhanced visualization prior to deployment of balloon  20 . Balloon  20  is affixed to a polymer jacket  22  (shown in broken line), which overlays a hypotube (such as the hypotube  40  illustrated in  FIG. 2  and described in greater detail below). 
         [0020]    Polymer jacket  22  may be, for example, a PEBAX (polyether block amide) having a hardness of 35-55D as measured with a durometer. Jacket  22  may be applied utilizing heat shrinking and distributed over the length of the hypotube. The jacket  22  may optionally stop just short of the distal end of the underlying hypotube. Polymer jacket  22  provides a fluid tight seal over the hypotube. Further, it provides a bonding substrate to which the balloon  20  is bonded at or near the distal end of the hypotube and system  10 . A hydrophilic coating may be applied over most or all of the polymer jacket  22 , balloon  20 , and the exterior of balloon catheter system  10 . Polymer jacket  22  provides a tie layer for the hydrophilic coating, which may enhance deliverability of the system  10 . 
         [0021]    Though balloon  20  is illustrated in its inflated configuration in  FIG. 1 , during tracking of balloon catheter system  10  to a treatment site, balloon  20  is not fully inflated. During tracking of balloon catheter system  10  to a treatment site, the device is in its delivery configuration, and balloon  20  will be fully or partially deflated and may be completely or partially folded or crimped. In such a delivery configuration (not pictured), prior to inflation of balloon  20 , the delivery profile of balloon catheter  10  is approximately equal to 0.018 inch. Accordingly, balloon catheter system  10  can be delivered to a treatment site using a guide catheter as small as 1.5 French. 
         [0022]    An example of a hypotube component suitable for use in construction of balloon catheter system  10  is illustrated in  FIG. 2 .  FIG. 2  illustrates a laser cut or profiled machine cut NiTi (Nitinol®) hypotube  40  which may alternatively be constructed from any number of compositions having suitable biocompatibility and strength characteristics. Alternative suitable metals include stainless steel such as, for example,  316 L SS, and cobalt chrome for enhanced visibility. 
         [0023]    An exemplary hypotube  40  has an approximate inner diameter of 0.009 inch, and an approximate outer diameter of 0.014 inch, but may be dimensioned in any number of suitable sizes and lengths depending upon the entry point into the vasculature, the location of the aneurysm, variances in patient anatomy, and any extenuating circumstances. Hypotube  40  may desirably be cut using an oxygen laser to remove oxide from either the inner or outer surface of hypotube  40 . The cut pattern of hypotube  40  includes a first helical cut  46  typically having a varied pitch from proximal end  50  to distal end  52 . Pitch will be understood to mean the proximity of successive cut lines, with increasing pitch referring to increasing proximity. The first helical cut  46  typically has a pitch increasing as it approaches distal end  52 , to confer increased flexibility at the distal end. (The pattern appears as dotted lines where it would appear on the opposite side of hypotube  40  as though “seen through” hypotube  40 .) The increasing pitch approaching the distal end  52  will be selected to confer the desired support profile on the tube. Hypotube  40  is cut with a second helical cut  48 , typically being 180° out of phase from the first helical cut  46 , thus avoiding cross-over of the cuts, and following the same variation in pitch from proximal end  50  to distal end  52 . The offset spiral cuts  46  and  48  provide an interference locking mechanism to confer stretch resistance in hypotube  40  while at the same time preserving lateral flexibility. The offset spiral cuts  46  and  48  decrease in pitch approaching proximal end  50 , until they terminate to finish on a solid tube (not pictured). Additional (third, fourth, etc.) helical cuts may be made to further enhance stretch resistance and lateral flexibility. For example, a third spiral cut out of phase by 120° may be made. After forming the desired spiral cuts, the cut hypotube  40  is ready for application of a polymer jacket, hydrophilic coating and balloon attachment. 
         [0024]    After sterilization, a system manufactured according to the invention may be utilized in any one of a number of intravascular procedures. In a typical procedure according to the invention, a guide catheter is introduced into the femoral artery and navigated through the vascular system under fluoroscopic visualization. The guide catheter may be as small as 1.5 French. The distal end of the guide catheter is positioned near the proposed treatment site within the vasculature or other luminal structure of a subject. (The treatment site may be, for example, an aneurysm, an arterio-venous malformation, an occlusion, or other defect.) The balloon catheter system according to the invention is then advanced to the treatment site through the guide catheter. The catheter is then placed proximate the defect, and the balloon inflated. 
         [0025]    In the example illustrated in  FIG. 3 , an inflatable balloon catheter system  10  has been tracked to the treatment site within vessel  60  via a guide catheter (not shown). Aneurysm  62  is disposed within vessel  60 . The balloon  20  disposed near the distal end of the balloon catheter system  10  may be suitably and safely positioned at the treatment site without the use of a guide wire. For example, as illustrated in  FIG. 3 , the balloon  20  can be positioned at the neck  64  of the aneurysm  62 . The inflatable balloon  20  can then be inflated to remodel the neck  64  of the aneurysm  62  and to secure balloon  20  of catheter system  10  across the neck of aneurysm  62 . 
         [0026]    Following inflation of balloon  20 , an embolic coil  70  or other suitable embolic material (not pictured) may be delivered to the aneurysm  62  through the lumen of the catheter tube  12 . Balloon  20  holds system  10  in place during delivery of embolic material, and further prevents escape of embolic coils or material from aneurysm  62  into vessel  60  during delivery. Upon completion of delivery of embolic coil  70  to aneurysm  62 , balloon  20  may be deflated and withdrawn from vessel  60  and from the subject. 
         [0027]    While the invention may be modified and alternative forms may be used, specific embodiments of the invention have been illustrated and described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed. The invention and following claims are intended to cover all modifications and equivalents falling within the spirit and scope of the invention.