Abstract:
Methods and apparatus are provided for removing emboli during an angioplasty, stenting or surgical procedure using a catheter having an occlusion element disposed on its distal end, a suction device, and an aspiration lumen communicating therebetween. The occlusion element is configured to be placed proximal of a stenosis and deployed to occlude antegrade flow, so that flow is reversed in the vessel when the suction device is selectively activated. The aspiration lumen is sized so that an interventional device, such as an angioplasty catheter, may be readily advanced therethrough to the site of a stenosis. The suction device may be activated intermittently at key stages of the procedure to provide reverse flow through the vessel, and the catheter may include bypass holes for limiting suction levels and/or providing intermittent antegrade flow.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application 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 May 13, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to apparatus and method to protect against embolization during vascular interventions, such as carotid artery angioplasty and endarterectomy. More particularly, the apparatus and methods of the present invention induce retrograde flow in the vessel of interest by providing intermittent suctioning of blood from the vessel of interest at key stages of the procedure. 
     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. 
     A 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. Consequently, surgical procedures such as endarterectomy typically have high mortality rates. 
     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 formed, 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 from a direction “upstream” of the direction of blood flow, emboli generated by operation of the instruments are carried “downstream” by normal antegrade blood flow—directly into the brain. 
     Several previously known apparatus and methods attempt to removing 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 solution. Chief among these problems is the inability of that system to generate flow reversal during insertion 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 have traveled too far downstream to be captured by the 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. These same drawbacks appear to have prevented commercialization of a similar system described in EP Publication No. 0 427 429. 
     Kletschka U.S. Pat. No. 4,794,928 describes an angioplasty device and methods for removing emboli generated during angioplasty, comprising a catheter bundle having an expandable funnel-shaped trap/barrier disposed on its distal end. A removal lumen is situated within the trap/barrier so that a pressure differential generated between the proximal and distal ends causes the emboli to be removed from the trap/barrier. While the patent states that the funnel-shaped trap/barrier may be placed either proximal or distal to the stenosis, the patent illustrates the trap/barrier as being disposed in the direction of antegrade flow, and does not suggest causing flow reversal within a vessel. 
     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 is 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 view of these drawbacks of the previously known emboli removal systems, it would be desirable to provide methods and apparatus that establish retrograde flow in a vessel at key stages throughout a surgical or interventional procedure, thereby reducing the risk that emboli are carried downstream. 
     It also would be desirable to provide emboli removal methods and apparatus that ensure that an adequate volume of blood is removed from the system to enhance the likelihood that emboli generated by a surgical or interventional procedure are effectively removed from the vessel of interest. 
     It still further would be desirable to provide emboli removal methods and apparatus that intermittently provide regional reversal of flow in a vessel, and thus avoid deployment of balloons or other devices distal to the stenosis to delimit a confined treatment field. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of this invention to provide emboli removal methods and apparatus that establish retrograde flow in a vessel at key stages throughout a surgical or interventional procedure, thereby reducing the risk that emboli are carried downstream. 
     It is another object of the present invention to provide emboli removal methods and apparatus that ensure that an adequate volume of blood is removed from the system to enhance the likelihood that emboli generated by a surgical or interventional procedure are effectively removed from the vessel of interest. 
     It is also an object of this invention to provide emboli removal methods and apparatus that intermittently provide regional reversal of flow in a vessel, and thus avoid deployment of balloons or other devices distal to the stenosis to delimit a confined treatment field. 
     The foregoing objects of the present invention are accomplished by providing a catheter, an occlusion element disposed on a distal end of the catheter, a suction device, and an aspiration lumen communicating therebetween. The occlusion element is configured to be placed proximal of a stenosis and expanded to occlude antegrade flow, so that flow is reversed in the vessel when the suction device is activated. The aspiration lumen is sized so that an interventional device, such as an angioplasty catheter, may be readily advanced therethrough to the site of a stenosis. The suction device may be activated intermittently to provide reverse flow through the vessel at several stages of the procedure. 
     In a first preferred embodiment of the present invention, a controller is provided that monitors balloon inflation pressure and restores suction through the aspiration lumen when the pressure falls below a threshold value. In an alternative embodiment, circuitry is provided that monitors the rate of flow through the aspiration lumen, terminates or reduces suction when the flow rate falls below a threshold value, and restores suction through the aspiration lumen when the flow rate of blood through the aspiration lumen exceeds the threshold value. In still other embodiments, the controller may comprise a manually actuated footpedal or handpiece. 
     In yet another embodiment of the present invention, the emboli removal catheter includes bypass holes that draw blood from a location proximal of the occlusion element when the angioplasty balloon is fully inflated, thus permitting a longer periods of suction and providing some antegrade flow during the non-suction periods. In still other embodiments, the catheter on which the angioplasty balloon is disposed may include bypass lumens that permit reverse flow in the lumen to be established distal to the angioplasty balloon during suction intervals, and antegrade flow at other times. 
     Methods of using the apparatus of the present invention also are described, in which the catheter is surgically or percutaneously inserted so that the occlusion element is disposed proximal to a stenosis. Suction is drawn at least intermittently through an aspiration lumen of the catheter to induce reverse flow in the vessel at critical stages throughout the procedure, such as during initial placement of a guide wire or angioplasty catheter across a stenosis, and when an angioplasty balloon is cyclically inflated and deflated. 
    
    
     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 emboli removal catheter of the present invention; 
     FIGS. 4A and 4B are views of the distal end of an alternative emboli removal catheter suitable for use in the system of FIGS. 3; 
     FIGS. 5A-5C illustrate a method of using the system of FIGS. 3; 
     FIG. 6 is a schematic view of an alternative embodiment of the invention of FIGS. 3; 
     FIGS. 7A-7C are, respectively, a schematic view, and detailed views of the distal end of another alternative embodiment an emboli removal catheter of the present invention; 
     FIGS. 8A-8C illustrate a method of using the system of FIGS. 7 in accordance with the principles of the present invention; 
     FIGS. 9A and 9B are, respectively, a schematic view and detailed view of the distal end of a further alternative embodiment of the present invention; 
     FIGS. 10A and 10B illustrate a method of using the system of FIGS. 9; and 
     FIGS. 11A-11C illustrate a method of using the emboli removal catheter or the present invention in performing endarterectomy. 
    
    
     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. Thus, 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 member  15  of emboli removal catheter  16 . Moreover, such naturally-aspirated systems are not expected to cause aspiration of blood at high flow rates sufficiently high to cause regional short-term flow reversal and removal of emboli. 
     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 cause dislodgement of 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, applicants expect that 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 expected to provide no benefit for emboli dislodged distal of distal balloon  19 . 
     Moreover, the Imran system is incapable of providing “regional” reversal of flow in the vessel once the distal balloon is deployed. In the context of the present invention “regional” reversal of flow means flow in regions distal to the stenosis, as opposed to flow within a confined field, such as delimited by the proximal and distal balloons of the Imran system. 
     Referring now to FIG. 2, apparatus and methods of the present invention are described. Apparatus  30  comprises catheter  31  having occlusion element  32  and an aspiration lumen that is coupled to a suction device (see FIG.  3 A). In accordance with the principles of the present invention, the aspiration lumen of catheter  31  is coupled to a suction device just before or soon after deploying occlusion element  32 , thus inducing reversed flow in the vessel. Illustratively, angioplasty balloon catheter  33  then is inserted through a lumen of catheter  31  and disposed across the lesion. Because flow through the vessel 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 intermittently induces and maintains flow reversal at key stages throughout the procedure, such as prior to deployment of the occlusion element and when the stenosis is initially traversed. In addition, the methods and apparatus of the present invention rely in part on redistribution of flow through the Circle of Willis to perfuse regions distal to the stenosis, rather by providing antegrade flow distal to an occluding balloon. In this manner the risk of flushing any emboli generated by the use of a distal balloon, as in the above-mentioned Imran system, is significantly reduced. 
     Referring now to FIGS. 3A to  3 C, embolic protective system  40  constructed in accordance with the present invention is described. System  40  comprises emboli removal catheter  41  having distal occlusion element  42 , proximal hemostatic port  43 , aspiration port  44  and inflation port  45 , suction device  46  coupled to aspiration port  44  via hose  47 , and controller  48  coupled to pressure sensor  49  and suction device  46 . Pressure sensor  49  is located in a T-fitting that configured to be coupled between inflation port  50  of conventional angioplasty catheter  51  and the inflation mechanism, e.g., syringe, (not shown) used to inflate balloon  52  of angioplasty catheter  51 . Suction device  46 , which also may be manually operated by foot pedal  53  or a handpiece (not shown), and angioplasty catheter  51 , may comprise a previously-known, commercially available components. Alternatively, suction device  46  may comprise any other suitable mechanism for drawing a suction through catheter  41 , such as a vacuum canister or syringe. 
     In 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 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. 3C, 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  45  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. 
     Controller  48  preferably includes circuitry or programming that interprets the signal generated by pressure sensor  49  and controls actuation of suction device  46  responsive to the measured pressure. More specifically, the T-fitting housing pressure sensor  49  is configured to be coupled between angioplasty catheter  51  and an inflation mechanism, such as a syringe or piston. Pressure sensor  49  outputs a signal corresponding to the inflation pressure applied to balloon  55 . 
     Controller  48  may be designed or programmed to detect when the pressure signal output by sensor  49  exceeds a predetermined value corresponding to dilation of the angioplasty balloon  52 , and terminate or reduce suction through catheter  41 , e.g., either by shutting off suction device  46  or opening the inlet to the suction device to atmospheric pressure. When controller  48  subsequently detects a pressure signal from sensor  49  indicating that the inflation pressure has fallen below the predetermined value, corresponding to deflation of balloon  55 , controller briefly restores suction to lumen  58  of catheter  41 , thus causing any emboli generated by actuation of balloon  55  to be aspirated through lumen  58 . 
     Alternatively, suction device  46  may be selectively actuated by the physician at desired stages of the procedure by manually depressing footpedal  53 . As a yet further alternative, footpedal  53  may be coupled to controller  48 , and the controller may include timer circuitry or programming that actuates suction device  46  for a user-selectable interval once the footpedal is depressed. 
     Referring now to FIGS. 5A to  5 C, use of the apparatus of FIG. 2 in accordance with the methods of the present invention is described. In FIGS. 5, stenosis S is located in the common carotid artery below the bifurcation between internal carotid artery ICA and 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  20  to cross the stenosis. Balloon  55  is inflated, preferably with a radioopaque contrast solution, via inflation port  45 . Suction device  46  preferably is actuated to establish retrograde flow in the artery just prior to deployment of balloon  55 , so that any emboli generated by deployment of the balloon will be removed through lumen  58  of catheter  41 . Alternatively, suction device  46  may be actuated just after balloon  55  is deployed. 
     Suction then is maintained for the duration of the following step, a period of about 10 seconds. As depicted in FIG. 5B, guide wire  20  is advanced across the stenosis, as determined, for example, by fluoroscopy. Throughout this step of placing the guide wire, retrograde flow, for example, as may be determined using a Doppler ultrasound monitor, is maintained through the arteries ICA and ECA and into lumen  58  of catheter  41 . 
     Angioplasty catheter  51  illustratively is advanced along guide wire  20  through hemostatic port  43  and aspiration lumen  58  of catheter  41  until it is disposed across the stenosis. Throughout this step of placing the angioplasty catheter across the stenosis, generally about 15 to 20 seconds, suction device  46  is activated to drain blood and any emboli generated from the artery through aspiration lumen  58 . Once again, a Doppler monitor may be used to confirm that flow distal to the stenosis has been reversed. 
     Pressure sensor  49  then is coupled in the inflation circuit of the angioplasty catheter, and a desired inflation pressure is preset or input into controller  48  via an appropriate input device, i.e., keypad. Balloon  52  is inflated to or beyond the desired inflation pressure to disrupt the plaque constituting the stenosis. When angioplasty balloon  52  is subsequently deflated, pressure sensor  49  detects that reduction in inflation pressure, and controller  48  restores suction through lumen  58  for about 10 to 30 seconds to aspirate the blood distal to the balloon. Controller  48  thus triggers suction device  46  to induce retrograde flow of blood through the artery to remove any emboli generated during operation of the angioplasty catheter, as depicted in FIG.  5 C. 
     Alternatively, the physician may use footpedal  53  to reestablish suction for a selected interval. As is typical of angioplasty procedures, the steps of inflating and deflating the angioplasty balloon, and inducing reverse flow in the artery after each inflation cycle, may be repeated. Similar steps may be employed during subsequent deployment of a stent, if desired. 
     Preferably, regional reversal of blood flow is established only intermittently and for brief periods during the procedure. Although it is possible to sustain continuous reverse flow throughout the procedure, such sustained reverse flow may be less preferred as potentially depriving the brain of oxygen. Thus, in the preferred embodiment, during each stage of a procedure that could dislodge emboli, reverse flow is initiated only so long as needed to ensure that potential emboli have been removed. The suction periods described hereinabove are representative of periods believed useful in practice, but shorter or longer periods may be necessary or useful in a particular procedure or type of procedure or for a particular patient. 
     It is expected that the method of the present invention typically will result in the drainage of approximately 300 cc of blood, but the amount of blood drained may vary. If desired, the aspirated blood may be cleansed and intravenously reperfused to the patient using a previously known extracorporeal blood filter and pump. 
     As set forth above, the method of the present invention protects against embolization by reversing the blood of flow in the brain distal to the stenosis at key stages during a carotid angioplasty procedure. The total period of reversal of blood flow in the brain distal to the stenosis preferably should have a duration of about one minute. In a typical patient, blood flow may be reversed for up to approximately three minutes before there is likely to be any danger from ischemia. Less than five percent of patients are likely to have an anomalous insufficiency of segments of the Circle of Willis that reduces collateral flow, but even these patients are expected to tolerate flow reversals lasting a minute or less. 
     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 mesh 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 for FIGS. 5A-5C, except that the occlusion element self-expands when sheath  67  is retracted, rather than by infusing an inflation medium to balloon  55 . 
     Referring to FIG. 6, another alternative embodiment of the present invention is described. Emboli removal system  70  comprises emboli removal catheter  41  and suction device  46  identical to that described hereinabove with respect to FIG.  3 A. Controller  72  is coupled to flow rate sensor  73 , which is housed in a coupling configured to be disposed between aspiration port  44  and hose  47 . Flow rate sensor monitors the flow of blood through aspiration lumen  58 . Controller  72  includes circuitry or programming to terminate suction through catheter  41  when the rate falls below a user selected value, corresponding to the condition where the angioplasty balloon is fully inflated. 
     Controller  72  also includes circuitry or programming to restore suction to through the aspiration lumen of catheter  41  when the flow rate of blood increases beyond the threshold value, such as when there is a naturally-aspirated surge of blood caused by deflation of the angioplasty balloon. Thus, this embodiment of the present invention takes advantage of the surge of naturally-aspirated blood observed in the foregoing Solano et al. patent as a trigger for actuating the suction device for a user selected period, such as 15 to 30 seconds. Operation of system  70  is otherwise the same as described hereinabove with respect to FIGS.  5 . 
     In FIGS. 7A-7C, yet another alternative embodiment of the present invention is described. Emboli removal system  80  includes catheter  81  having occlusion element  82 , proximal hemostatic port  83 , aspiration port  84 , inflation port  85 , and one or more bypass holes  86  located just proximal of occlusion element  82 . Suction device  87  is coupled to aspiration port  83  via hose  88 , and may be actuated by a foot pedal (not shown). Catheter  81  preferably is used in conjunction with an angioplasty balloon catheter such as shown in FIG. 3A or a suitable stent deployment system. 
     The distal end of catheter  81  differs in construction from that described above with respect to FIGS. 3B and 3C only in that catheter  81  includes one or more through-wall bypass holes  86 . Bypass holes  86  permit blood to pass from a location proximal to occlusion element  82  (illustratively balloon  89 ) and into aspiration lumen  90  to limit the maximum suction level applied to the vessel wall section disposed between the occlusion element and the angioplasty balloon. Catheter  81  is otherwise constructed as described above for catheter  41  of FIGS.  3 . 
     Referring to FIGS. 8A-8C, methods of using the apparatus of FIGS. 7 are described. In FIG. 8A, catheter  81  is first inserted either surgically or percutaneously and transluminally to a position proximal of stenosis S. Occlusion element  82  is deployed while suction device  87  is actuated for 10-15 seconds to induce retrograde flow through the stenosis. Because aspiration lumen  90  is unblocked, only a small fraction of blood will be drawn through bypass holes  86 . 
     In FIG. 8B, balloon  52  of angioplasty catheter  51  is shown fully inflated, so that it occludes the vessel distal to the stenosis. In this case, once the supply of blood captured between occlusion element  82  and angioplasty balloon  52  is reduced, proportionately more blood will be drawn through bypass holes. This is expected to advantageously reduce the stress applied to the section of vessel wall between occlusion element  82  and the stenosis, thus reducing the risk of narrowing or collapsing the vessel. 
     With respect to FIG. 8C, once balloon  52  of the angioplasty catheter is deflated, the blood drained through aspiration lumen  90  again will consist mostly of blood drawn in a retrograde manner through the vessel, with a small proportion coming through bypass holes  86 . Accordingly, it is contemplated that the bypass holes employed in catheter  81  will enable suction to be used for longer periods of time while posing a smaller risk of injury to the vessel wall. 
     It is expected that the longer duration and larger volume of retrograde blood flow in and around the region of stenosis enabled by providing bypass holes  86  may allow for the removal of plaque and debris that lower blood volumes may not be able to remove. Bypass holes  86  also may reduce thrombus formation proximal to occlusion element  82  by providing for continuous suction of emboli from the vessel. In addition, bypass holes  86  may be beneficial patients with reduced collateral blood flow by allowing antegrade blood flow during those periods when suction is not applied to the aspiration lumen (and the angioplasty balloon is not fully inflated). Alternatively, or in addition, catheter  81  may be advantageously used with any of the occlusion elements or controllers described in the preceding embodiments. 
     Referring to FIGS. 9A and 9B, another alternative embodiment of the present invention is described. System  100  comprises emboli removal catheter  41  coupled to suction device  46  via hose  47 , wherein all of the components are identical to those described hereinabove with respect to FIGS. 3, and angioplasty catheter  101 . Angioplasty catheter  101  includes luer  102  having a hemostatic seal, balloon  103 , guide wire lumen  104 , and bypass holes  105 . Bypass holes  105  communicate with guide wire lumen  104 , which in turn terminates in an opening (not visible) in distal face  106  of catheter  101 . 
     Operation of system  100  is described with respect to FIGS. 10A and 10B. In FIG. 10A, catheter  41  is either surgically or percutaneously and transluminally deployed as described above with respect to FIG.  5 A. Angioplasty catheter  101  then is advanced across stenosis S while suction is drawn through catheter  41 . 
     Balloon  103  is inflated to disrupt the stenosis. As balloon  103  is initially inflated, suction device  46  is activated to cause blood to flow through the opening in the distal end of angioplasty catheter  101  and through bypass holes  105 , thereby inducing retrograde flow in the vessel distal to the inflated angioplasty balloon. This flow advantageously is expected to remove any emboli generated distal to the distal face of balloon  103  by first drawing such emboli into through the bypass holes into the space defined by the balloon  103  and occlusion element  42 . The emboli will then be removed from that space through aspiration lumen  58  of catheter  41 . 
     Alternatively, if angioplasty catheter  101  is used in conjunction with emboli removal catheter  81  of FIGS. 7, the combination of bypass holes  103  and  86  will provide some antegrade flow distal to the stenosis when suction device  46  is not active, even when the angioplasty balloon is fully inflated. This feature may be particularly beneficial in those situations where it is desired to leave the angioplasty balloon inflated for several minutes at a time. Importantly, such a combination provides the capability not only to provide antegrade flow, but also the ability to remove emboli generated distal to the distal surface of the angioplasty balloon. 
     In FIGS. 11A to  11 C, methods of using the emboli removal catheter of FIGS. 3A,  6  and  7  during endarterectomy is described. In FIG. 11A, catheter  41  is either surgically or percutaneously and transluminally inserted into common carotid artery CCA proximal to stenosis S. Suction is then drawn with suction device  46  while occlusion element  42  is deployed. 
     In FIG. 11B, cross clamp  110  is applied to common carotid artery CCA proximal of the bifurcation between internal carotid artery ICA and external carotid artery ECA, and lengthwise incision I is formed through which the stenosis is removed by means which are per se known. In FIG. 11C, after incision I is closed, illustratively using sutures  112 , suction device  46  is again actuated while cross-clamp  110  is removed. In this manner, any emboli dislodged from the wall of the vessel or by removal of cross-clamp  110  will be removed by the regional reversal of flow to catheter  41 . After suction device has been operated for about 10-30 seconds, suction is discontinued and the emboli removal device is removed. 
     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 therein without departing from the invention, and the appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.