Abstract:
Methods and apparatus are provided for removing emboli during an angioplasty, stenting, or surgical procedure comprising apparatus for occluding the external carotid artery to prevent reversal of flow into the internal carotid artery during carotid stenting, the apparatus further comprising a wedge or capsule configured to reduce the risk of potentially dangerous interaction with the stent during retrieval.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 09/333,074, now U.S. Pat. No. 6,206,868, filed Jun. 14, 1999, which is a continuation-in-part of International Application PCT/US99/05469, filed Mar. 12, 1999, which is a continuation-in-part of U.S. patent application Ser. No. 09/078,263, now U.S. Pat. No. 6,413,235, filed Mar. 5, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to apparatus and methods for occluding a body lumen. More particularly, the present invention provides a puncture resistant balloon for occlusion of the external carotid artery during stenting of the internal carotid artery. 
     BACKGROUND OF THE INVENTION 
     Carotid artery stenoses typically manifest in the common carotid artery, internal carotid artery or external carotid artery as a pathologic narrowing of the vascular wall, for example, caused by the deposition of plaque, that inhibits normal blood flow. Endarterectomy, an open surgical procedure, traditionally has been used to treat such stenosis of the carotid artery. 
     In view of the trauma and long recuperation times generally associated with open surgical procedures, considerable interest has arisen in the endovascular treatment of carotid artery stenosis. In particular, widespread interest has arisen in transforming interventional techniques developed for treating coronary artery disease, such as stenting, for use in the carotid arteries. Such endovascular treatments, however, are especially prone to the formation of emboli. 
     Such emboli may be created, for example, when an interventional instrument, such as a guide wire or angioplasty balloon, is forcefully passed into or through the stenosis, as well as after dilatation and deflation of the angioplasty balloon or stent deployment. Because such instruments are advanced into the carotid artery in the same direction as blood flow, emboli generated by operation of the instruments are carried directly into the brain by antegrade blood flow. 
     Stroke rates after carotid artery stenting have widely varied in different clinical series, from as low as 4.4% to as high as 30%. One review of carotid artery stenting including data from twenty-four major interventional centers in Europe, North America, South America, and Asia had a combined initial failure and combined mortality/stroke rate of more than 7%. Cognitive studies and reports of intellectual changes after carotid artery stenting indicate that embolization is a common event causing subclinical cerebral damage. 
     Several previously known apparatus and methods attempt to remove emboli formed during endovascular procedures by occluding blood flow and trapping or suctioning the emboli out of the vessel of interest. These previously known systems, however, provide less than optimal solutions to the problems of effectively removing emboli generated during stenting. The elements used to occlude blood flow may, for example, dangerously interact with a stent. 
     Chapter 46 of  Interventional Neuroradiology: Strategies and Practical Techniques  (J. J. Connors &amp; J. Wojak, 1999), published by Saunders of Philadelphia, Pa., describes use of a coaxial balloon angioplasty system for patients having proximal internal carotid artery (“ICA”) stenoses. In particular, a small, deflated occlusion balloon on a wire is introduced into the origin of the external carotid artery (“ECA”), and a guide catheter with a deflated occlusion balloon is positioned in the common carotid artery (“CCA”) just proximal to the origin of the ECA. A dilation catheter is advanced through a lumen of the guide catheter and dilated to disrupt the stenosis. Before deflation of the dilation catheter, the occlusion balloons on the guide catheter and in the ECA are inflated to block antegrade blood flow to the brain. The dilation balloon then is deflated, the dilation catheter is removed, and blood is aspirated from the ICA to remove emboli. 
     EP Publication No. 0 427 429 describes a similar device with a first balloon for occluding a patient&#39;s CCA, and a second balloon for occluding the patient&#39;s ECA prior to crossing a lesion in the ICA. 
     A drawback of both the device in EP Publication No. 0 427 429 and the  Interventional Neuroradiology  device is that, if either is used to place a stent in the ICA, the stent may extend beyond the bifurcation between the ECA and the ICA. The occlusion balloon placed by guide wire in the ECA may then snag the stent during retrieval, causing the balloon to puncture or get caught within the artery, and requiring emergency surgery to remove the balloon. 
     In view of drawbacks associated with previously known systems, it would be desirable to provide methods and apparatus for removing emboli from within the carotid arteries during carotid stenting that simultaneously reduce the risk of emboli being carried into the cerebral vasculature while preventing dangerous interaction between the apparatus and the stent. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide methods and apparatus for removing emboli from within the carotid arteries during carotid stenting that simultaneously reduce the risk of emboli being carried into the cerebral vasculature while preventing dangerous interaction between the apparatus and the stent. 
     The foregoing objects of the present invention are accomplished by providing interventional apparatus for occluding flow in a branch artery, the apparatus being resistant to puncture. The apparatus preferably is employed with an arterial catheter, a venous return catheter, and, optionally, a blood filter or flow control valve disposed between the arterial and venous return catheters. The arterial catheter has proximal and distal ends, an aspiration lumen extending therebetween, an occlusion element disposed on the distal end, and a hemostatic port and blood outlet port disposed on the proximal end that communicate with the aspiration lumen. The aspiration lumen is sized so that an interventional instrument, e.g., a stent delivery system, may be readily advanced therethrough to the site of a stenosis in either the ECA (proximal to the balloon) or the ICA. 
     The arterial catheter illustratively is disposed in the CCA proximal of the ICA/ECA bifurcation, the occlusion balloon on the guide wire is disposed in the ECA to occlude flow reversal from the ECA to the ICA, and the blood outlet port of the arterial catheter is coupled to the venous return catheter, with or without the blood filter disposed therebetween. Higher arterial than venous pressure, especially during diastole, permits low-rate flow reversal in the ICA during an interventional procedure (other than when a dilatation balloon is inflated) to flush blood containing emboli from the vessel. The blood is filtered and reperfused into the body through the venous return catheter. 
     In accordance with the principles of the present invention, the occlusion balloon on the guide wire is puncture resistant, so as to prevent dangerous interaction between the balloon and a stent during retrieval. In a first embodiment, the apparatus comprises a wedge configured to deflect the balloon away from contacting a portion of the stent extending past the ECA/ICA bifurcation during retrieval of the balloon. In a second embodiment, the apparatus comprises a balloon that retracts into a capsule prior to retrieval of the balloon from the ECA. 
     Methods of using the apparatus of the present invention are also provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which: 
     FIGS. 1A-1C are schematic views depicting a prior art method of emboli protection during carotid stenting; 
     FIGS. 2A-2D are, respectively, a schematic view, and detailed side and sectional views of the distal end of apparatus constructed in accordance with the present invention; 
     FIGS. 3A-3D illustrate a method of using the apparatus of FIG. 2 in accordance with the principles of the present invention; 
     FIGS. 4A and 4B are schematic views of an alternative embodiment of the guide wire balloon element of the apparatus of FIG. 2, shown, respectively, in a deployed configuration and in a retrieval configuration; and 
     FIGS. 5A-5B illustrate a method of using the apparatus of FIG. 4 in accordance with the principles of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1A-1C, drawbacks of previously known emboli removal catheters are described with reference to performing carotid stenting in internal carotid artery ICA. Naturally-aspirated or vacuum suction emboli removal system  10 , such as described in the above-mentioned  Interventional Neuroradiology  article and in the European Patent Publication, is disposed in common carotid artery CCA. As seen in FIG. 1A, inflation member  12 , disposed on the distal end of emboli removal catheter  14 , is inflated to occlude flow in the CCA. 
     Applicant has determined that once member  12  is inflated, flow within the external carotid artery ECA reverses and provides antegrade flow into the ICA, due to the lower hemodynamic resistance of the ICA. Consequently, emboli generated while passing stent  16  across stenosis S may be carried irretrievably into the cerebral vasculature—before flow in the vessel is reversed and directed into the aspiration lumen of emboli removal catheter  14  by opening the proximal end of the aspiration lumen to atmospheric pressure or suction. 
     To solve this problem, previously known methods teach the use of an occlusion balloon to stop the development of retrograde flow from the ICA to the ECA. Thus, as depicted in FIG. 1B, balloon  18  on wire  20  is advanced into and occludes the ECA prior to placement of stent  16  in the ICA. Once stent  16  is in place, balloon  18  is deflated, and wire  20  is retracted, as depicted in FIG.  1 C. System  10  then may be removed from the patient. However, when stent  16  extends beyond the ECA/ICA bifurcation, a common problem experienced in clinical practice is snagging of balloon  18  on stent  16  during retrieval of balloon  18 . Balloon  18  may puncture or may occlude the ECA, requiring emergency open surgery to remove the balloon and reopen the vessel. 
     The present invention is directed to an improvement in the balloon-on-a-guide wire device used to occlude the ECA. Specifically, in accordance with the principles of the present invention, the balloon is puncture resistant and is designed to reduce snagging or puncture of the balloon during retrieval. 
     Referring now to FIG. 2A, embolic protection apparatus  40 , suitable for use with the occlusion balloon  45  of the present invention, is described. Apparatus  40  comprises arterial catheter  41 , venous return line  52 , tubing  49 , and optional blood filter or flow control valve  50 . Catheter  41  includes distal occlusion element  42 , proximal hemostatic port  43 , e.g., a Touhy-Borst connector, inflation port  44 , and blood outlet port  48 . Tubing  49  couples blood outlet port  48  to filter  50  and blood inlet port  51  of venous return line  52 . 
     More specifically, with respect to FIGS. 2B and 2C, distal occlusion element  42  comprises expandable bell or pear-shaped balloon  42   a . In accordance with manufacturing techniques which are known in the art, balloon  42   a  comprises a compliant material, such as polyurethane, latex, or polyisoprene, which has variable thickness along its length to provide a bell-shape when inflated. Balloon  42   a  is affixed to distal end  56  of catheter  41 , for example, by gluing or a melt-bond, so that opening  57  in balloon  42   a  leads into aspiration lumen  58  of catheter  41 . Balloon  42   a  preferably is wrapped and heat treated during manufacture so that distal portion  59  of the balloon extends beyond the distal end of catheter  41  and provides an atraumatic tip or bumper for the catheter. 
     As shown in FIG. 2D, catheter  41  preferably comprises inner layer  60  of low-friction material, such as polytetrafluoroethylene (“PTFE”), covered with a layer of flat stainless steel wire braid  61  and polymer cover  62  (e.g., polyurethane, polyethylene, or PEBAX). Inflation lumen  63  is disposed within polymer cover  62  and couples inflation port  44  to balloon  42   a . In a preferred embodiment of catheter  41 , the diameter of lumen  58  is 7 Fr, and the outer diameter of the catheter is approximately 9 Fr. 
     Venous return line  52  includes hemostatic port  53 , blood inlet port  51  and a lumen that communicates with ports  53  and  51  and tip  54 . Venous return line  52  may be constructed in a manner per se known for venous introducer catheters. Tubing  49  may comprise a suitable length of a biocompatible material, such as silicone. Alternatively, tubing  49  may be omitted, and blood outlet port  48  of catheter  41  and blood inlet port  51  of venous return line  52  may be lengthened to engage either end of filter  50  or each other. 
     Still referring to FIG. 2A, the branch artery occlusion device of the present invention comprises guide wire  45  having balloon  46  that is inflated via inflation port  47 . Guide wire  45  and balloon  46  are configured to pass through hemostatic port  43  and the aspiration lumen of catheter  41  (see FIGS.  2 C and  2 D), so that the balloon may be advanced into and occlude the ECA. Port  43  and the aspiration lumen of catheter  41  are sized to permit additional interventional devices, such as angioplasty balloon catheters, atherectomy devices and stent delivery systems to be advanced through the aspiration lumen when guide wire  45  is deployed. 
     In accordance with a first embodiment of the present invention, guide wire  45  comprises means for reducing puncture of balloon  46 , illustratively wedge  55 . Wedge  55  preferably comprises a resilient material, such as a polymer or resilient wire, and reduces the risk that balloon  46  will puncture or snag on a stent that extends beyond the bifurcation of the ICA and ECA. Preferably, guide wire  45  further comprises a small diameter flexible shaft having an inflation lumen that couples inflatable balloon  46  to inflation port  47 . Inflatable balloon  46  preferably comprises a compliant material, such as described hereinabove with respect to occlusion element  42  of emboli removal catheter  41 . 
     Referring now to FIGS. 3A-3D, use of the apparatus of FIG. 2 in accordance with the methods of the present invention during carotid stenting is described. First, a flow of blood is induced between the treatment site and the patient&#39;s venous vasculature. Because flow through the artery is towards catheter  41 , any emboli dislodged by advancing a stent across stenosis S causes the emboli to be aspirated by catheter  31 . 
     In FIG. 3A, stenosis S is located in internal carotid artery ICA above the bifurcation between the internal carotid artery ICA and the external carotid artery ECA. Catheter  41  is inserted, either percutaneously and transluminally or via a surgical cut-down, to a position proximal of stenosis S, without causing guide wire  45  to cross the stenosis. Balloon  42   a  of distal occlusion element  42  is then inflated, preferably with a radiopaque contrast solution, via inflation port  44 . This creates reversal of flow from the external carotid artery ECA into the internal carotid artery ICA. 
     Venous return line  52  then is introduced into the patient&#39;s femoral vein, either percutaneously or via a surgical cut-down. Filter  50  is coupled between blood outlet port  48  of catheter  41  and blood inlet port  51  of venous return line  52  using tubing  49 , and any air is removed from the line. Once this circuit is closed, negative pressure in the venous catheter during diastole establishes a low rate flow of blood through aspiration lumen  58  of catheter  41 , as seen in FIG. 3B, to the patient&#39;s vein via venous return line  52 . 
     This low rate flow, due to the difference between venous pressure and arterial pressure, preferably continues throughout the interventional procedure. Specifically, blood passes through aspiration lumen  58  and blood outlet port  48  of catheter  41 , through biocompatible tubing  49  to filter  50 , and into blood inlet port  51  of venous return line  52 , where it is reperfused into the remote vein. Filtered emboli collect in filter  50  and may be studied and characterized upon completion of the procedure. 
     Referring to FIG. 3C, with balloon  42   a  of occlusion element  42  inflated and a retrograde flow established in the ICA, guide wire  45  and balloon  46  are advanced through aspiration lumen  58 . When balloon  46  is disposed within the ECA, as determined, e.g., using a fluoroscope and a radiopaque inflation medium injected into balloon  46 , balloon  46  is inflated. Occlusion of the ECA prevents the development of reverse flow in the ECA from causing antegrade flow in the ICA. Another interventional instrument, such as stent  70 , is loaded through hemostatic port  43  and aspiration lumen  58  and positioned across stenosis S to ensure proper blood flow to the ICA. 
     It is often desirable for stent  70  to extend beyond the bifurcation between the ECA and the ICA. Consequently, when the occlusion balloon on the guide wire is deflated and withdrawn from the ECA, there is a risk that the balloon may snag on the stent. In such cases, emergency surgery may be required to remove the balloon. 
     As shown in FIG. 3D, upon completion of the stenting portion of the procedure, balloon  46  is deflated, and guide wire  45  is prepared for retraction. Because balloon  46  is disposed on guide wire  45  instead of a traditional, larger diameter balloon catheter, its cross-sectional diameter is significantly reduced, and thus the risk that the balloon will snag or puncture on stent  70  is reduced. Resilient wedge  55  further reduces risk by urging the balloon outward away from the stent during retrieval of guide wire  45  and balloon  46 . Alternatively, a separate sheath may be advanced over guide wire  45  and occlusion balloon  46  to surround those components, and thereby reduce the risk that the occlusion balloon or guide wire will snag the stent. Guide wire  45 , emboli removal catheter  41 , and venous return line  52  are then removed from the patient, completing the procedure. 
     Optionally, increased volumetric blood flow through the extracorporeal circuit may by achieved by attaching an external pump, such as a roller pump, to tubing  49 . If deemed beneficial, the external pump may be used in conjunction with apparatus  40  at any point during the interventional procedure. 
     Throughout the procedure, except when the dilatation balloon is fully inflated, the pressure differential between the blood in the ICA and the venous pressure causes blood in the ICA to flow in a retrograde direction into aspiration lumen  58  of emboli removal catheter  41 , thereby flushing any emboli from the vessel. The blood is filtered and reperfused into the patient&#39;s vein. 
     As set forth above, the method of the present invention protects against embolization, first, by preventing the reversal of blood flow from the ECA to the ICA when distal occlusion element  42  is inflated and hemostatic port  43  is open, and second, by providing continuous, low volume blood flow from the carotid artery to the remote vein in order to filter and flush any emboli from the vessel and blood stream. Advantageously, the method of the present invention permits emboli to be removed with little blood loss, because the blood is filtered and reperfused into the patient. Furthermore, continuous removal of blood containing emboli prevents emboli from migrating too far downstream for aspiration. 
     Referring now to FIGS. 4A and 4B, an alternative embodiment of the guide wire occlusion apparatus of the present invention is described. Occlusion apparatus  80  comprises guide wire  81  having inflation lumen  82  and proximally terminating in inflation port  83 , occlusion balloon  84 , core wire  85  attached to balloon  84 , capsule  86 , radiopaque capsule features  87 , and radiopaque balloon feature  88 . Core wire  85  is preferably approximately 0.010″ in diameter and is configured to be received within inflation lumen  82  of guide wire  81 . Guide wire  81  is preferably approximately 0.018″ in diameter. 
     Balloon  84  may be inflated via inflation lumen  82  with a standard or radiopaque inflation medium. Balloon  84  then extends distally of, but remains attached to, capsule  86 . Upon completion of an interventional procedure, such as carotid stenting, balloon  84  is deflated. Proximal retraction of core wire  85  draws balloon  84  into capsule  86 , thereby preventing snagging during retrieval. 
     Referring now to FIGS. 5A and 5B, use of occlusion apparatus  80  in conjunction with arterial catheter  41  and venous return catheter  52  of FIG. 2 during carotid stenting is described. With balloon  42   a  of occlusion element  42  inflated and a retrograde flow established in the ICA as described hereinabove, occlusion apparatus  80  is advanced through aspiration lumen  58  of catheter  41 . Capsule  86  is disposed just within the ECA, as determined, e.g., using a fluoroscope and radiopaque capsule features  87 , as seen in FIG.  5 A. Occlusion balloon  84  is then inflated and its position verified by, for example, a fluoroscope and radiopaque balloon feature  88  or a radiopaque inflation medium injected into balloon  84 . Occlusion of the ECA prevents the development of reverse flow in the ECA from causing antegrade flow in the ICA. Another interventional instrument, such as stent  70 , is then loaded through hemostatic port  43  and aspiration lumen  58  and positioned across stenosis S to ensure proper blood flow to the ICA. 
     As discussed hereinabove, it is often desirable for stent  70  to extend beyond the bifurcation between the ECA and the ICA. Consequently, when the occlusion balloon on the guide wire is deflated and withdrawn from the ECA, there is a risk that the balloon may snag on the stent, with potentially dire consequences. 
     As shown in FIG. 5B, upon completion of the stenting portion of the procedure, balloon  84  is deflated, and core wire  85  is proximally retracted to draw deflated balloon  84  within capsule  86 . Because balloon  84  is disposed on guide wire  81  instead of a traditional, larger diameter balloon catheter, its cross-sectional diameter is significantly reduced, and thus the risk that the balloon will snag or puncture on stent  70  is reduced. Capsule  86  further reduces this risk by protecting the balloon during retrieval of occlusion apparatus  80 . Apparatus  80 , emboli removal catheter  41 , and venous return line  52  then are removed from the patient, completing the procedure. 
     As will of course be understood, the apparatus of the present invention may be used in locations other than the carotid arteries. They may, for example, be used in the coronary arteries, or in any other location deemed useful. 
     While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.