Patent Publication Number: US-6905490-B2

Title: Apparatus and methods for reducing embolization during treatment of carotid artery disease

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of the U.S. patent application Ser. No. 09/333,074, 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, filed Mar. 5, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to apparatus and methods for protecting against embolization during vascular inventions, such as carotid artery angioplasty and endarterectomy. More particularly, the apparatus and methods of the present invention induce substantially continous retrograde flow through the internal carotid artery during treatment during an interventional procedure, without significant blood loss. 
     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. 
     An important problem encountered in carotid artery surgery is that emboli may be formed during the course of the procedure, and these emboli can rapidly pass into the cerebral vasculature and cause ischemic stroke. 
     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 angioplasty and 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 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. 
     Solano et al. U.S. Pat. No. 4,921,478 describes cerebral angioplasty methods and devices wherein two concentric shafts are coupled at a distal end to a distally-facing funnel-shaped balloon. A lumen of the innermost shaft communicates with an opening in the funnel-shaped balloon at the distal end, and is open to atmospheric pressure at the proximal end. In use, the funnel-shaped balloon is deployed proximally (in the direction of flow) of a stenosis, occluding antegrade flow. An angioplasty balloon catheter is passed through the innermost lumen and into the stenosis, and then inflated to dilate the stenosis. The patent states that when the angioplasty balloon is deflated, a pressure differential between atmospheric pressure and the blood distal to the angioplasty balloon causes a reversal of flow in the vessel that flushes any emboli created by the angioplasty balloon through the lumen of the innermost catheter. 
     While a seemingly elegant solution to the problem of emboli removal, several drawbacks of the device and methods described in the Solano et al. patent seem to have lead to abandonment of that approach. Chief among these problems is the inability of that system to generate flow reversal during placement of the guide wire and the angioplasty balloon across the stenosis. Because flow reversal does not occur until after deflation of the angioplasty balloon, there is a substantial risk that any emboli created during placement of the angioplasty balloon will travel too far downstream to be captured by the subsequent flow reversal. It is expected that this problem is further compounded because only a relatively small volume of blood is removed by the pressure differential induced after deflation of the angioplasty balloon. 
     Applicant has determined another drawback of the method described in the Solano patent: deployment of the funnel-shaped balloon in the common carotid artery (“CCA”) causes reversal of flow from the external carotid artery (“ECA”) into the internal carotid artery (“ICA”), due to the lower flow impedance of the ICA. Consequently, when a guide wire or interventional instrument is passed across a lesion in either the ECA or ICA, emboli dislodged from the stenosis are introduced into the blood flow and carried into the cerebral vasculature via the ICA. 
     The insufficient flow drawback identified for the system of the Solano patent is believed to have prevented development of a commercial embodiment of the similar system described in EP Publication No. 0 427 429. EP Publication No. 0 427 429 describes use of a separate balloon to occlude the ECA prior to crossing the lesion in the ICA. However, like Solano, that publication discloses that flow reversal occurs only when the dilatation balloon in the ICA is deflated. 
     Chapter 46 of  Interventional Neuroradioloqy: strategies and practical techniques  (J. J. Connors &amp; J. Wojak, 1999), published by Saunders of Philadelphia, Pa., describes using a coaxial balloon angioplasty system for patients having with proximal ICA stenoses. In particular, a small, deflated occlusion balloon on a wire is introduced into the origin of the ECA, and a guide catheter with a deflated occlusion balloon is positioned in the 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. 
     Applicant has determined that cerebral damage still may result from the foregoing previously known procedure, which is similar to that described in EP Publication No. 0 427 429, except that the ICA is occluded prior to the ECA. Consequently, both of these previously known systems and methods suffer from the same drawback—the inability to generate flow reversal at sufficiently high volumes during placement of the guide wire and dilation catheter across the stenosis. Both methods entail a substantial risk that any emboli created during placement of the balloon will travel too far downstream to be captured by the flow reversal. 
     Applicants note, irrespective of the method of aspiration employed with the method described in the foregoing  Interventional Neuroradiology  article, substantial drawbacks are attendant. If, for example, natural aspiration is used (i.e., induced by the pressure gradient between the atmosphere and the artery), then only a relatively small volume of blood is expected to be removed by the pressure differential induced after deflation of the angioplasty balloon. If, on the other hand, an external pump is utilized, retrieval of these downstream emboli may require a flow rate that cannot be sustained for more than a few seconds, resulting insufficient removal of emboli. 
     Furthermore, with the dilation balloon in position, the occlusion balloons are not inflated until after inflation of the dilation balloon. Microemboli generated during advancement of the dilation catheter into the stenosed segment may therefore be carried by retrograde blood flow into the brain before dilation, occlusion, and aspiration are even attempted. 
     A still further drawback of both the device in EP Publication No. 0 427 429 and the  Interventional Neuroradiology  device is that, if they are used for placing a stent in the ICA instead of for ICA angioplasty, the stent often extends beyond the bifurcation between the ECA and the ICA. The occlusion balloon placed by guide wire in the ECA may snag the stent during retrieval. Emergency surgery may then be required to remove the balloon. 
     Imran U.S. Pat. No. 5,833,650 describes a system for treating stenoses that comprises three concentric shafts. The outermost shaft includes a proximal balloon at its distal end that is deployed proximal of a stenosis to occlude antegrade blood flow. A suction pump then draws suction through a lumen in the outermost shaft to cause a reversal of flow in the vessel while the innermost shaft is passed across the stenosis. Once located distal to the stenosis, a distal balloon on the innermost shaft is deployed to occlude flow distal to the stenosis. Autologous blood taken from a femoral artery using an extracorporeal blood pump is infused through a central lumen of the innermost catheter to provide continued antegrade blood flow distal to the distal balloon. The third concentric shaft, which includes an angioplasty balloon, is then advanced through the annulus between the innermost and outermost catheters to dilate the stenosis. 
     Like the device of the Solano patent, the device of the Imran patent appears to suffer the drawback of potentially dislodging emboli that are carried into the cerebral vasculature. In particular, once the distal balloon of Imran&#39;s innermost shaft is deployed, flow reversal in the vasculature distal to the distal balloon ceases, and the blood perfused through the central lumen of the innermost shaft establishes antegrade flow. Importantly, if emboli are generated during deployment of the distal balloon, those emboli will be carried by the perfused blood directly into the cerebral vasculature, and again pose a risk of ischemic stroke. Moreover, there is some evidence that reperfusion of blood under pressure through a small diameter catheter may contribute to hemolysis and possible dislodgment of emboli. 
     In applicant&#39;s co-pending U.S. patent application Ser. No. 09/333,074, filed Jun. 14, 1999, which is incorporated herein by reference, applicant described the use of external suction to induce regional reversal of flow. That application further described that intermittently induced regional flow reversal overcomes the drawbacks of naturally-aspirated systems such as described hereinabove. However, the use of external suction may in some instances result in flow rates that are too high to be sustained for more than a few seconds. In addition, continuous use of an external pump may result in excessive blood loss, requiring infusion of non-autologous blood and/or saline that causes hemodilution, reduced blood pressure, or raise related safety issues. 
     In view of these drawbacks of the previously known emboli removal systems, it would be desirable to provide methods and apparatus for removing emboli from within the carotid arteries during interventional procedures, such as angioplasty or carotid stenting, that reduce the risk that emboli are carried into the cerebral vasculature. 
     It also would be desirable to provide methods and apparatus for removing emboli from within the carotid arteries during interventional procedures, such as angioplasty or carotid stenting, that provide substantially continuous low retrograde blood flow from the treatment zone, thereby reducing the risk that emboli are carried into the cerebral vasculature. 
     It further would be desirable to provide emboli removal methods and apparatus that prevent the development of reverse flow from the ECA and antegrade into the ICA once the CCA has been occluded, thereby enhancing the likelihood that emboli generated by a surgical or interventional procedure are effectively removed from the vessel. 
     It still further would be desirable to provide an occlusion balloon on a guide wire for placement in the ECA during stenting of the ICA that mitigates the risk of snagging the stent during removal. 
     It also would be desirable to provide methods and apparatus for removing emboli during a carotid stenting procedure that enable filtering of emboli and reduced blood loss. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of this invention to provide methods and apparatus for removing emboli from within the carotid arteries during interventional procedures, such as angioplasty or carotid stenting, that reduce the risk that emboli are carried into the cerebral vasculature. 
     It also is an object of the present invention to provide methods and apparatus for removing emboli from within the carotid arteries during interventional procedures, such as angioplasty or carotid stenting, that provide substantially continuous low retrograde blood flow from the treatment zone, thereby reducing the risk that emboli are carried into the cerebral vasculature. 
     It is another object of the present invention to provide emboli removal methods and apparatus that prevent the development of reverse flow between the ECA and ICA once the common carotid artery has been occluded, thereby enhancing the likelihood that emboli generated by a surgical or interventional procedure are effectively removed from the vessel. 
     It is a further object of this invention to provide methods and apparatus for an occlusion balloon on a guide wire for placement in the ECA during stenting of the ICA that mitigates the risk of snagging the stent during removal. 
     It is yet another object of the present invention to provide methods and apparatus for removing emboli during a carotid stenting procedure that enable filtering of emboli and reduced blood loss. 
     The foregoing objects of the present invention are accomplished by providing interventional apparatus comprising an arterial catheter, an occlusion balloon disposed on a guide wire, a venous return catheter, and optionally a blood filter. 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., an angioplasty catheter or 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. 
     In accordance with the principles of the present invention, the arterial catheter 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 substantially continuous flow reversal in the ICA during the procedure (other than when a dilatation balloon is inflated), thereby flushing blood containing emboli from the vessel. The blood is filtered and reperfused into the body through the venous return catheter. 
     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 and 1B  are schematic views of previously known emboli protection systems; 
         FIG. 2  is a schematic view of the emboli protection system of the present invention; 
         FIGS. 3A-3D  are, respectively, a schematic view, and detailed side and sectional views of the distal end of an interventional device of the present invention; 
         FIGS. 4A and 4B  are views of the distal end of an alternative interventional device suitable for use in the system of the present invention; and 
         FIGS. 5A-5D  illustrate a method of using the system of  FIG. 3  in accordance with the principles of the present invention; 
         FIGS. 6A-6B  are, respectively, a schematic view and a cross-sectional view of an alternative embodiment of the device of  FIG. 3 ; 
         FIGS. 7A-7B  are, respectively, a schematic view of an alternative embodiment of the guide wire balloon elements of the device of  FIG. 3 , and a method of using the alternative embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1A and 1B , drawbacks of previously known emboli removal catheters are described with reference to performing percutaneous angioplasty of stenosis S in common carotid artery CCA. 
     With respect to  FIG. 1A , drawbacks associated with naturally-aspirated emboli removal systems, such as described in the above-mentioned patent to Solano and European Patent Publication, are described. No flow reversal is induced by those systems until after balloon  10  of angioplasty catheter  11  first is passed across the stenosis, inflated, and then deflated. However, applicant has determined that once member  15  of emboli removal catheter  16  is inflated, flow within the ECA reverses and provides antegrade flow into the ICA, due to the lower hemodynamic resistance of the ICA. Consequently, emboli E generated while passing guide wire  20  or catheter  11  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  16  by opening the proximal end of the aspiration lumen to atmospheric pressure. Furthermore, natural-aspiration may not remove an adequate volume of blood to retrieve even those emboli that have not yet been carried all the way into the cerebral vasculature. 
     In  FIG. 1B , system  17  described in the above-mentioned patent to Imran is shown. As described hereinabove, deployment of distal balloon  18 , and ejection of blood out of the distal end of the inner catheter, may dislodge emboli from the vessel wall distal to balloon  18 . The introduction of antegrade flow through inner catheter  19  is expected only to exacerbate the problem by pushing the emboli further into the cerebral vasculature. Thus, while the use of positive suction in the Imran system may remove emboli located in the confined treatment field defined by the proximal and distal balloons, such suction is not expected to provide any benefit for emboli dislodged distal of distal balloon  18 . 
     Referring now to  FIG. 2 , apparatus and methods of the present invention are described. Apparatus  30  comprises catheter  31  having an aspiration lumen and occlusion element  32 , and guide wire  35  having inflatable balloon  36  disposed on its distal end. In accordance with the principles of the present invention, antegrade blood flow is stopped when both occlusion element  32  in the CCA and inflatable balloon  36  are deployed. Furthermore, the aspiration lumen of catheter  31  is connected to a venous return catheter (described hereinbelow), disposed, for example, in the patient&#39;s femoral vein. In this manner a substantially continuous flow of blood is induced between the treatment site and the patient&#39;s venous vasculature. Because flow through the artery is towards catheter  31 , any emboli dislodged by advancing a guide wire or angioplasty catheter  33  across stenosis S causes the emboli to be aspirated by catheter  31 . 
     Unlike the previously known naturally-aspirated systems, the present invention provides substantially continuous retrograde blood flow through eh ICA while preventing blood from flowing retrograde in the ECA and antegrade into the ICA, thereby preventing emboli from being carried into the cerebral vasculature. Because the apparatus and methods of the present invention “recycle” emboli-laden blood from the arterial catheter through the blood filter and to the venous return catheter, the patient experiences significantly less blood loss. 
     Referring now to  FIG. 3A , embolic protection apparatus  40  constructed in accordance with the principles of the present invention is described. Apparatus  40  comprises arterial catheter  41 , guide wire  45 , venous return line  52 , tubing  49  and optional blood filter  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 . Guide wire  45  includes balloon  46  that is inflated via inflation port  47 . Tubing  49  couples blood outlet port  48  to filter  50  and blood inlet port  51  of venous return line  52 . 
     Guide wire  45  and balloon  46  are configured to pass through hemostatic port  43  and the aspiration lumen of catheter  41  (see FIGS.  3 C and  3 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. 
     Guide wire  45  preferably 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 . 
     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. 
     With respect to  FIGS. 3B and 3C , distal occlusion element  42  comprises expandable bell or pear-shaped balloon  55 . In accordance with manufacturing techniques which are known in the art, balloon  55  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  55  is affixed to distal end  56  of catheter  41 , for example, by gluing or a melt-bond, so that opening  57  in balloon  55  leads into aspiration lumen  58  of catheter  41 . Balloon  55  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. 3D , 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  55 . 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. 
     Referring now to  FIGS. 4A and 4B , an alternative embodiment of occlusion element  42  of the system of  FIG. 3A  is described. In  FIGS. 4A and 4B , occlusion element  42  of emboli removal catheter  41  comprises self-expanding wire basket  65  covered with elastomeric polymer  66 , such as latex, polyurethane or polyisoprene. Alternatively, a tightly knit self-expanding wire mesh may be used, with or without an elastomeric covering. 
     Catheter  41  is surrounded by movable sheath  67 . Catheter  41  is inserted transluminally with sheath  67  in a distalmost position, and after basket  65  has been determined to be in a desired position proximal to a stenosis, sheath  67  is retracted proximally to cause basket  65  to deploy. Upon completion of the procedure, basket  65  is again collapsed within sheath  67  by moving the sheath to its distalmost position. Operation of the system of  FIG. 3A  using the emboli removal catheter of  FIGS. 4A and 4B  is similar to that described hereinbelow for  FIGS. 5A-5D , except that the occlusion element self-expands when sheath  67  is retracted, rather than by infusing an inflation medium to balloon  55 . 
     Referring now to  FIGS. 5A-5D , use of the apparatus of  FIGS. 3  in accordance with the methods of the present invention is described. In  FIGS. 5 , stenosis S is located in internal carotid artery ICA above the bifurcation between the internal carotid artery ICA and the external carotid artery ECA. In a first step, 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  55  of distal occlusion element  42  is then inflated, preferably with a radiopaque contrast solution, via inflation port  44 . As seen in  FIG. 5A , 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 then 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 will establish a low rate continuous flow of blood through aspiration lumen  58  of catheter  41 , as seen in  FIG. 5B , to the patient&#39;s vein via venous return line  52 . 
     This low rate continuous flow due to the difference between venous pressure and arterial pressure will continue 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. 
     Continuous blood flow (except during inflation of any dilatation instruments) with reperfusion in accordance with the present invention provides efficient emboli removal with significantly reduced blood loss. Alternatively, filter  50  may be omitted, in which case emboli removed from the arterial side will be introduced into the venous side, and eventually captured in the lungs. Because of a low incidence of septal defects, which could permit such emboli to cross-over to the left ventricle, the use of filter  50  is preferred. 
     Referring to  FIG. 5C , with balloon  55  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 conventional angioplasty balloon catheter  71  having balloon  72 , is loaded through hemostatic port  43  and aspiration lumen  58  and positioned within the stenosis. Hemostatic port  43  is closed and instrument  71  is actuated to disrupt the plaque forming stenosis S. 
     As seen in  FIG. 5D , upon completion of the angioplasty portion of the procedure using catheter  71 , balloon  72  is deflated. 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 ICA to flow in a retrograde direction in the ICA 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. 
     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 device  40  at any point during the interventional procedure. Instrument  71 , guide wire  45 , emboli removal catheter  41 , and venous return line  52  are then removed from the patient, completing the procedure. 
     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 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  FIG. 6 , apparatus  140  constructed in accordance with the present invention is described. Apparatus  140  is an alternative embodiment of apparatus  40  described hereinabove and comprises arterial catheter  141  having distal occlusion element  142 , proximal hemostatic port  143 , inflation port  144  and blood outlet port  148 . Guide wire  145  includes balloon  146  that is inflated via inflation port  147 . Biocompatible tubing  149  couples blood outlet port  148  to filter  150  and to blood inlet port  151  of venous return line  152 . Arterial catheter  141 , guide wire  145 , venous return line  152  and tubing  149  are constructed as described hereinabove, except as noted below. 
     Guide wire  145  and balloon  146  are configured to pass through guide wire lumen  164  of catheter  141  (see FIG.  6 B), so that the balloon may be advanced into and occlude the ECA. Additionally, catheter  141  comprises aspiration lumen  158  which is sized to permit interventional devices, such as angioplasty balloon catheters, atherectomy devices and stent delivery systems to be advanced through port  143  and the aspiration lumen. As shown in  FIG. 6B , the key difference between catheters  41  and  141  lies in the method of advancing the guide wire through the catheter: guide wire  45  is advanced through the aspiration lumen of catheter  41 , whereas guide wire  145  is advanced through separate guide wire lumen  164  of catheter  141 . 
     Catheter  141  preferably is constructed from inner layer  160  of low-friction material, such as polytetrafluoroethylene (“PTFE”), covered with a layer of flat stainless steel wire braid  161 , and polymer cover  162  (e.g., polyurethane, polyethylene, or PEBAX). Inflation lumen  163  is disposed within polymer cover  162  and couples inflation port  144  to occlusion element  142 . Guide wire lumen  164  also is disposed within polymer cover  142 , and is sized to permit guide wire  145  and balloon  146  to pass therethrough. In a preferred embodiment of catheter  141 , the diameter of inflation lumen  163  is 0.014″, the diameter of guide wire lumen  164  is 0.020″, and the diameter of lumen  158  is 7 Fr. To retain an outer catheter diameter in the preferred embodiment of approximately 9 Fr., the thickness of the catheter wall varies around the circumference from a maximum of 0.026″ at the location of guide wire lumen  164  to a minimum of 0.005″ 180 degrees away. 
     Referring now to  FIG. 7 , an alternative embodiment of the guide wire occlusion apparatus of the present invention is described. Occlusion apparatus  200  comprises guide wire  201 , occlusion balloon  202 , inflation lumen  203 , and wedge  204 . Wedge  204  may comprise a resilient material, such as a polymer or resilient wire, and reduces the risk that balloon  202  will snag on a stent that extends beyond the bifurcation of the ICA and ECA. 
     For the reasons described hereinabove, it is desirable when performing a stenting procedure in the ICA to occlude the ECA, to prevent flow reversal from the ECA and into the ICA. Accordingly, an occlusion balloon on a guide wire is placed in the ECA and inflated to block that artery. A stent then may be placed in the ICA to ensure proper blood flow to the ICA. It is often desirable, however, for such stents 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 the stent. In such cases, emergency surgery is often required to remove the balloon. 
     Referring now to  FIG. 7B , occlusion apparatus  200  is illustratively shown in conjunction with catheter  41 . Stent S extends beyond the bifurcation between the ECA and the ICA and into the CCA. Balloon  202  is deflated and positioned for retrieval. Because balloon  202  is disposed on guide wire  201  instead of a traditional, larger diameter balloon catheter, its cross-sectional diameter is significantly reduced, and thus the risk that the balloon will snag on stent S is reduced. Resilient wedge  204  further reduces this risk by urging the balloon outward away from the stent during retrieval of guide wire  201  and balloon  202 . Alternatively, a separate sheath may be advanced over guide wire  201  and occlusion balloon  202  to surround those components, and therefore reduce the risk that the occlusion balloon or guide wire will snag the stent. 
     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.