Abstract:
An interventional catheter assembly comprises an operating head for removing obstructive material from a target site in a body lumen or cavity and at least one aspiration port located proximal to the operating head and penetrating the catheter assembly, the aspiration port being in communication with a sealed lumen that communicates with a vacuum system for withdrawing aspirate fluid and obstructive material from the target site. A rotatable member is positioned inside the catheter assembly at the site of the aspiration port and rotates during operation of the vacuum system. The rotatable member is provided with at least one upstanding bar that is sized to cooperate with the walls of the aspiration port and the inner surface of the catheter assembly to macerate debris that is drawn into the aspiration port.

Description:
REFERENCE TO PRIORITY APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Patent Applications No. 60/894,173 filed Mar. 9, 2007, and 60/828,209 filed Oct. 4, 2006. The disclosures of these priority applications are incorporated by reference herein in their entireties. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to systems and methods for removing material, such as obstructions and partial obstructions, from an internal lumen or cavity of a mammalian subject, such as a blood vessel. More particularly, the present invention relates to interventional catheters having an operating head incorporating a device for removing obstructions and partial obstructions from a lumen or cavity, and an active aspiration system for removal of fluids and debris cleared from the target site.  
       BACKGROUND OF THE INVENTION  
       [0003]     Removal of disease such as atherosclerotic plaque, thrombus and other types of obstructions and partial obstructions from internal body lumens or cavities using advanceable, rotating operating heads is a well-established interventional technique. Numerous interventional catheters have been conceived and developed. Most of these systems require placement of a guiding catheter and guide wire prior to introduction of the interventional catheter and placement of the interventional catheter at the target operating site. Many of these prior art systems incorporate mechanical aspiration systems to remove the ablated material from the site and some systems incorporate, or are used in conjunction with, other mechanisms such as distal filters for preventing removed material from circulating in the blood stream.  
         [0004]     In interventional catheters that employ a “cutting head,” cutter structures must be benign during navigation of the operating head to and from the interventional target site, yet effectively remove material during the operation. In addition, cutter structures must effectively remove diseased, or undesired, material without damaging delicate neighboring tissue, such as blood vessel walls or other healthy tissue, which often surrounds and may be attached to the undesired material. Thus, it is important for cutter structures of interventional catheters to accurately and reliably differentiate between the diseased material and healthy tissue.  
         [0005]     Differential cutting blades exert high shear forces against relatively hard substrates to cut or ablate relatively hard, inelastic, material. Softer, elastic structures, such as healthy tissue, blood vessel walls and the like, are deformed rather than cut by differential cutting blades, thereby reducing the shear forces and protecting elastic structures from damage. Less elastic material does not deform when contacted by a differential cutting blade, and shear stresses are consequently exerted on less elastic material to cut or scrape and ablate the material without damaging elastic tissue in proximity. In this manner, fragments of diseased, undesirable material are removed by differential cutting blades, while the more elastic, healthy tissue remains undamaged.  
         [0006]     U.S. Pat. No. 4,445,509 describes differential cutting in the context of an atherectomy device. This patent describes a cutter assembly having a plurality of cutting flutes, each cutting flute having a blade surface operating according to the principle of differential cutting. Aspiration ports are provided in the body of the cutter assembly for collection and removal of particulates and liquids from the site of the intervention. U.S. Pat. Nos. 6,565,588 and 6,818,001, together with U.S. Patent Publication 2004/0006358 A1, also disclose the use of cutter assemblies to separate undesired material from underlying tissue at a site of intervention, with an aspiration system incorporating aspiration ports provided between the cutting surfaces for withdrawal of liquids and particulate debris from the site.  
         [0007]     Some interventional catheters use diamond grit on a cutting surface in an effort to provide highly divided, small particle size debris. Relatively coarse diamond grit is more likely to damage elastic, healthy tissue such as blood vessel walls. Relatively fine diamond grit has slow material removal rates, requiring the use of higher rotational speeds. The use of grit or abrasive particles or surfaces can, however, be beneficial and generate small particulate debris, providing effective material removal.  
         [0008]     Alternative material removal systems may incorporate an Archimedes screw-type mechanism at a distal end of an interventional catheter, in which material is caught between the threads of the screw and withdrawn from the site using mechanical rotational motion. Material removal systems may also incorporate a plaque excision device having a blade that traverses and exits a window at a distal end of an interventional catheter to scrape plaque from a vessel wall and collect it in an internal collection space provided in the distal end of the interventional catheter.  
         [0009]     In any of these material removal systems, removal of debris generated at the site of intervention is critical to prevent distal embolization of the debris. Several prior art interventional catheters provide for aspiration of liquids and/or debris from the material removal site. Aspirating thrombectomy catheters employ a catheter having a vacuum system to draw thrombus into the catheter and remove it from the site. Many interventional catheters incorporate, or are used with, a distal filter mechanism that traps debris before it can be carried away in the bloodstream. Numerous interventional catheters also provide infusion of a liquid to the site of the intervention. Infused liquids may assist in the material removal process, or may be provided as diagnostic or therapeutic materials prior to, during or following an intervention.  
         [0010]     Despite the many and varied approaches to material removal from lumens such as blood vessels and the availability of many and varied material removal systems, challenges remain in providing systems for removing material from a lumen, such as a blood vessel, safely, reliably and effectively, without causing complications. The safety and reliability of the system is manifestly critical. Recovery of debris generated during a material removal operation, or breaking down the debris to a particle size that will not produce blood vessel damage or embolic events, is essential.  
       SUMMARY OF INVENTION  
       [0011]     The present invention provides interventional catheters that may be employed to rapidly and effectively remove unwanted material from body lumens or cavities. Interventional catheters and control systems disclosed herein may be adapted for use within a variety of body lumens or cavities such as blood vessels and vascular cavities, gastrointestinal cavities, lumens or cavities in the urinary system and in male and female reproductive organs, and other fluid cavities such as pulmonary lumens and gas exchange cavities, nasal and sinus cavities and the like. The lumen or cavity may form a generally tubular structure, such as a blood vessel, a ureter, a fallopian tube, a nasal passageway, and other tubular passageways. For example, systems of the present invention may be used for removing undesired material from native blood vessels such as native coronary, renal, cranial, peripheral and other blood vessels, artificial or grafted vessels such as saphenous vein grafts, and the like. The lumen may have implanted devices, such as stents, in place. The lumen or cavity may be within, or in proximity to, an organ such as a kidney, gall bladder, lung or the like, or the body cavity may form part of another system, such as a lymph node, spinal canal or the like. Interventional catheters are generally used to remove unwanted material from a target site in body lumens or cavities of mammalian subjects, particularly human patients.  
         [0012]     The undesired material that is removed using interventional catheter assemblies and control systems disclosed herein may be disease material such as atherosclerotic plaque, calcified plaque, thrombus, or other types of deposits, gallstones, a valve or portion thereof, and the like. In certain embodiments, the interventional catheter assemblies disclosed herein are employed in the treatment of cardiovascular or peripheral artery disease (PAD) to remove disease material from blood vessels, including peripheral blood vessels.  
         [0013]     The present interventional catheter assembly includes a catheter system that is at least partially inserted and navigated within a patient&#39;s body while an operator controls the system externally of the catheter system. The interventional catheters disclosed herein incorporate a material removal component, referred to herein as an “operating head,” which is generally positioned at or near the distal end of the interventional catheter system. As used herein, “proximal” refers to a direction toward the system controls and the operator along the path of the drive shaft and catheter system, and “distal” refers to the direction away from the system controls and the operator along the path of the drive shaft and catheter system toward or beyond a terminal end of the operating head.  
         [0014]     Fluidic communication between the operating head and externally positioned components of the interventional catheter system is generally provided by one or more sealed passageways of the catheter system. Other types of communication systems or pathways may also be provided for delivery of power, for rotationally driving and translating the operating head, for implementing various control features, and the like. The operating head may be driven, or controlled, using electrical systems, radio frequency and other remote control systems, mechanical systems, magnetic systems and other systems or modalities suitable for remote operation of an operating head. The operating head may also incorporate features providing additional functionalities such as ultrasound guidance and imaging systems and the like. The system components described below are described as exemplary components and are not intended to limit the scope of the invention.  
         [0015]     The interventional catheter system may be provided with a guidewire bore and be used in conjunction with a flexible guidewire that is navigated through internal pathways, such as blood vessels, to a target material removal site. For partial obstructions, the guidewire is generally placed across the lesion and the operating head of the interventional catheter is advanced on the guidewire to the target site and then into and through the lesion. When a lumen is totally obstructed and a guidewire cannot penetrate the obstruction without causing harm to nearby tissue or risking embolization, the operating head may be advanced beyond the distal tip of the guidewire and into and through the obstruction, or the operating head and guidewire may be advanced in tandem. Other methods that may be employed for guiding and steering the operating head include, but are not limited to, radio frequency systems, stereotactic systems, magnetic systems, remote control systems, and the like. The interventional catheters disclosed herein may be adapted for use with any of these steering systems.  
         [0016]     The operating head may take any of a variety of forms. In one embodiment, the operating head is rotatable, incorporates cutter elements, and is operably connected to a rotatable and axially translatable drive shaft and catheter system, a drive system and control systems, and comprises at least one distally located cutter assembly, wherein the cutter assembly includes at least one cutting, scraping or abrading surface, or blade. Although the “cutting” surfaces or blades of an interventional catheter of the present invention may be sharp and may actually “cut” material at the target site, the term “cut” or “cutting” or “cutter” or “blade(s),” as used herein, refers to cutting, scraping, abrading, ablating, macerating and otherwise breaking down undesired material into particles or smaller, removable, units of material.  
         [0017]     In some embodiments, interventional catheters incorporate cutter assemblies comprising a plurality of cutting blades. Such cutter assemblies may incorporate fixed and/or adjustable blades. Suitable cutter assemblies are disclosed, for example, in U.S. Pat. Nos. 6,565,588 and 6,818,001, which are incorporated herein by reference in their entireties. Suitable differential cutting blades are also disclosed, for example, in U.S. Patent Publication 2004/0006358 A1, which is incorporated herein by reference in its entirety. In some embodiments, the operating head may comprise an abrasive surface or an abrasive material provided on a surface of a rotational element. Interventional catheter operating heads comprising abrasive materials are well known in the art. In another embodiment, the operating head comprises at least one blade or cutter element positioned and oriented to exit a window, separate material from an inner lumen wall, and collect the material in an internal space. In an alternative embodiment, the operating head may comprise another type of ablating device, such as a plaque excision device, a laser ablation or high frequency ultrasound ablation device, or a radio frequency, heat-producing or electrical device that operates to remove unwanted material from body lumens or cavities.  
         [0018]     The drive shaft that conveys rotation and torque from a drive system to the operating head must be small enough and flexible enough to be navigated through small and tortuous passageways during navigation of the operating head to the target removal site, and must have sufficient mechanical integrity to transfer high rotational and torque loads, and operate in a high vacuum, or aspirate withdrawal, environment. Multi-filar helical coils are used as drive shafts in many types of interventional catheters having a rotatable operating head. Suitable drive shafts are well known in the art and are described in the patent publications incorporated herein by reference.  
         [0019]     Interventional catheters disclosed herein preferably incorporate an aspiration system for removal of debris from the intervention site via aspiration through one or more aspiration ports. Aspiration systems suitable for use in interventional catheters of the present invention are described, for example, in the patents incorporated herein by reference and in U.S. Patent Publication 2004/0220519 A1, which is also incorporated herein by reference in its entirety. Debris generated during a material removal operation is entrained in fluids (e.g. blood), and the aspirate fluid containing debris is removed by aspiration through the material removal port(s) and withdrawn through a sealed lumen of the interventional catheter. The sealed lumen is connectable to a vacuum source and aspirate collection system.  
         [0020]     In one embodiment of interventional catheters of the present invention, at least one aspiration port having a generally large opening is provided in proximity to the operating head (e.g., the cutter or plaque excision assembly). The aspiration port may be provided directly in a catheter structure, or it may be provided in a rigid shell structure mounted directly or indirectly to a distal portion of the catheter. Debris generated during a material removal operation is entrained in fluids (e.g. blood and infusate), and the aspirate fluid containing debris is removed by aspiration through the material removal port(s) and withdrawn through a sealed lumen of the interventional catheter. The sealed lumen is connectable to an aspirate conduit and aspirate collection system. In some embodiments, at least one large aspiration port is positioned proximal to the operating head. Generally smaller material aspiration ports may additionally be disposed on one or more surfaces of the cutter assembly itself.  
         [0021]     The interventional catheter may additionally incorporate a masticator assembly positioned for rotation inside the aspiration port to facilitate removal and breaking down of debris withdrawn from the site of intervention through the port. The rotatable masticator assembly may comprise a central core structure having one or more projecting bars, extending generally along the length of the central core. The central core structure is rotated during operation of the operating head. When the operating head comprises a rotating structure, the masticator assembly may be directly or indirectly connected to the same drive system that rotates the operating head.  
         [0022]     The outer surfaces of the projecting bars provided on the masticator central core structure are generally curved and, in some embodiments, generally match the inner surface of a shell structure in which the aspiration port is provided. The projecting bars may have a tapered structure, with a narrower profile toward a proximal end of the masticator assembly and a wider profile toward a distal end of the masticator assembly. The bars may also be configured so that their side walls have different dimensions and different undercut angles along the length of the bars. In general, the side walls are higher and have a smaller undercut angle toward a proximal end of the masticator assembly and are lower and have a larger undercut angle toward a distal end of the masticator assembly. As particulate material is drawn into the aspiration port by aspiration forces, the rotating macerator assembly facilitates further breakdown of the material and assists in moving the particulate material proximally and through the aspiration conduit for downstream collection and disposal.  
         [0023]     Liquid infusion may be provided in, or in proximity to, the operating head. Infusion of liquids may be used to provide additional liquid volume for removal of debris, or to deliver lubricating fluids, diagnostic or treatment agents, contrast agents and the like. Infusion of fluids such as saline in proximity to the target material removal area may be desirable because it tends to reduce the viscosity of the materials being removed, thus facilitating removal through relatively small diameter lumens. Infusion of liquids also desirably tends to reduce the volume of blood removed during a material removal operation, thereby reducing blood loss and allowing longer procedures if necessary. In addition, infusion of liquids reduces vessel collapse and keeps the vessel wall in tension, thereby improving the effectiveness of cutting and reducing damage to the vessel wall. Liquid infusion may also reduce guidewire friction in embodiments where guidewires are employed. Many different types of infusion systems are known and may be used in interventional catheters of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a schematic diagram of an interventional catheter assembly comprising an operating head mounted at or near a distal end of a catheter system, a controller and a console unit.  
         [0025]      FIG. 2  illustrates an enlarged perspective view of an interventional catheter of the present invention having a distal operating head with ports for aspiration or infusion and a proximal tubular structure having a relatively large port for aspiration.  
         [0026]      FIG. 3  illustrates an enlarged perspective view of an interventional catheter of the present invention having a distal operating head, a proximal aspiration port and liquid infusion ports located proximally to the aspiration port.  
         [0027]      FIG. 4  illustrates an enlarged cross-sectional view of an interventional catheter of the present invention having a distal operating head and a proximal aspiration port with an internal rotating member.  
         [0028]      FIG. 5  illustrates an enlarged view of an aspiration window and internal rotating macerator element of the present invention.  
         [0029]      FIG. 6  illustrates an enlarged perspective view of the internal rotating macerator element.  
         [0030]      FIG. 7  illustrates an enlarged cross-sectional view of the aspiration assembly of  FIG. 5  taken through line  7 - 7 .  
         [0031]      FIG. 8  illustrates an enlarged cross-sectional view of the aspiration assembly of  FIG. 5  taken through line  8 - 8 .  
         [0032]      FIG. 9  illustrates an enlarged cross-sectional view of the aspiration assembly of  FIG. 5  taken through line  9 - 9 . 
     
    
     DETAILED DESCRIPTION  
       [0033]     Certain preferred embodiments are described herein with reference to a material removal device having a rotational cutting head. It will be appreciated that this device embodiment is being described as illustrative and that the inventions and features disclosed herein are applicable to interventional catheters having different types of operating heads.  
         [0034]      FIG. 1  illustrates an exemplary embodiment of an interventional catheter assembly, including a console unit incorporating aspiration and infusion systems as disclosed herein. Interventional catheter assembly  10  comprises console unit  12 , controller  30 , and catheter system  32  having an operating head  40  located at or in proximity to the distal end of the catheter system. Controller  30  may be used to manipulate (e.g. advance and/or rotate) the catheter system  32  and operating head  40 , or alternative controls may be provided.  
         [0035]     Console unit  12  incorporates an infusion pump  14  and an aspiration pump  16 . During operation of the interventional catheter, an infusate conduit  18  draws fluid from an infusate reservoir  20  and operably contacts the infusion pump  14  to provide fluid flow through an infusion lumen in catheter system  32  to one or more infusion ports provided in proximity to the operating head  40 . Similarly but in reverse, fluids with entrained particulates are withdrawn from the site of intervention through an aspiration lumen in catheter system  32  and conveyed to aspiration conduit  22 , which is in operable contact with the aspiration pump  16 , and communicates with the aspirate collection vessel  24 . Console unit  12  may also provide a power source for operating the operating head and system components, or it may be in communication with an external power source. In the illustrated embodiment, console unit  12  provides power to the interventional catheter assembly and controller  30  by means of a device power port  25  and power cord  26 .  
         [0036]     Various microprocessor, electronic components, software and firmware components may be provided within or in communication with the console unit for controlling operation of the interventional catheter as described herein. Software may be provided in a machine-readable medium storing executable code and/or other data to provide one or a combination of mechanisms to process user-specific data. Alternatively, various systems and components may be controlled using hardware or firmware implementations. Data storage and processing systems may also be provided in console unit  12 .  
         [0037]     One function of console unit  12  is to provide feedback of system and/or environmental conditions or operating parameters. The console unit may output operational information concerning operating conditions and feedback from the material removal site to the operator. According to one embodiment, console unit  12  provides continuously updated output to an operator of operating parameters such as operating head rotation rate, which may include the actual run speed as well as the desired speed; operating head advance rate; aspiration rate and/or volume; infusion rate and/or volume; elapsed run time; and the like.  
         [0038]     Certain automated and selectable control features may be implemented in console unit  12 . Preset routines or programs involving various operating parameters may be preselected, stored and selectable by an operator, for example. Thus, according to one embodiment, the disclosed material removal system implements control features based on an operator&#39;s input of specified parameters. Specified parameters may include, for example: lesion length, lesion type and character, such as calcified, fibrotic, lipid/fatty and the like; historical factors, such as restenosis; rate of blood flow; volume of blood flow; percentage of restriction; lumen type and/or location; lumen diameter; desired rotation rate and/or rotation profile for the cutter assembly; desired advance rate and/or advance profile for the cutter assembly; desired aspiration rate and/or profile; desired infusion rate and/or profile; and the like. Based on the specified parameters input by the operator, the control unit may calculate and implement automated operating conditions, such as cutter assembly rotation rate and profile; cutter assembly advance rate and profile; aspiration rate and profile; infusion rate and profile; cutter assembly size; and the like. Various system operating parameters, operating conditions, patient conditions, and the like may also be recorded and stored during interventions to preserve a record of the patient and intervention operational parameters.  
         [0039]     High efficiency aspiration is important in the interventional catheter systems disclosed herein. In certain embodiments, fluid and associated particulates are aspirated from the intervention site at rates of at least 15 ml/min of operating head run time and in many embodiments, fluid and associated particulates are aspirated at rates of at least 25 ml/min of operating head run-time. In exemplary interventional catheter systems, the aspiration site may be more than a meter away from the controller  30  through an aspirate removal passageway located within the catheter system  32  and having a diameter of less than 0.10 inch, for example between about 0.050 to 0.070 inch. The distance that the aspirate travels between controller  30  and console unit  12  may be from about 0.5 meter to several meters, through an aspirate conduit that is between about 0.125 inch to about 1.0 inch in diameter. The blood and debris being aspirated are relatively viscous fluids, and achieving a relatively constant and high level of aspiration under these conditions is essential.  
         [0040]     In one embodiment, aspiration pump  16  comprises a multi-lobed roller pump. The rotation rates of multiple rollers, or of a multi-lobed rotating structure, may be variable or selectable to control the aspiration rate and volume. Roller pumps permit fluid to flow in a conduit through the rollers of the pump at atmospheric pressure, and thus reduce or prevent the formation of bubbles and foam in the liquid being evacuated. Because the aspirate is at atmospheric pressure when it exits the roller pump, a simplified, atmospheric pressure collection vessel may be used rather than an evacuated collection vessel. A simple bag or another collection vessel, such as those used for collection of blood, may be used. For example, a collection bag  24  and a sealed aspiration conduit may be provided as part of a sterile disposable interventional catheter kit. A distal end of the aspiration conduit may be pre-mounted on and sealed to the controller  30 . A proximal portion of the aspiration conduit is mounted on the aspiration pump  16  prior to operation of the interventional catheter and the aspirate collection bag is mounted to or in proximity to the control module  12 .  
         [0041]     Infusion pump  14  may also comprise a multi-lobed roller pump employing variable or selectable rotation rates to control the infusion rate and volume. A simple bag or another infusate reservoir, such as those used for intravenous infusions, may be used to supply the infusate. For example, an infusate reservoir  20  having a sealed conduit that is mounted in the infusion pump  16  during operation of the interventional catheter may be provided. In this embodiment, the sealed infusate conduit may be provided as part of the sterile disposable interventional catheter system and a distal end of the aspiration conduit may be pre-mounted on and sealed to the controller  30 . A proximal portion of the infusate conduit may be connected to an infusate reservoir  20 , such as a saline bag, and mounted in proximity to the infusion pump  14  prior to operation.  
         [0042]     In one embodiment, console unit  12 , together with aspiration pump  16  and infusion pump  14  and the associated control and display features, is provided as a separate, re-usable unit, that may be used as standard equipment in operating rooms, for example. In the system illustrated, console unit  12  is not contaminated by contact with blood or aspirate during operation, and the power and control systems are durable and long-lasting and may be reused for many interventions. Console unit  12  may be provided in a housing designed to sit on a platform during operation, or the housing may be designed for mounting on a portable structure, such as an i.v. pole or another structure. The interventional catheter system, comprising the catheter system  32  with operating head  40 , the controller  30 , aspirate conduit  22 , aspirate collection vessel  24 , and infusion conduit  18  may be provided as a sterile, single use system kit.  
         [0043]     The catheter system and operating head are described below with reference to a rotatable operating head employing a cutting material removal mechanism. In this application, aspiration and infusion conduits terminate at or within controller  30 , where they communicate with aspiration and infusion lumens within the catheter system  32 . A rotatable drive shaft for driving the operating head is provided in catheter system  32 . A guidewire may also transit controller  30  and catheter system  32 . In general, controller  30  or an associated control mechanism provides user-operated mechanisms for rotating and/or translating the operating head. Controller  30 , which is constructed from a durable, sterilizable material, such as hard plastic, may be provided in any convenient ergonomic design and constructed for placement in proximity to and/or in contact with the external body. In one embodiment, the controller may include an integrated handle for operator convenience in holding and supporting the controller during operation. Catheter system  32 , exiting controller  30 , is axially translatable with respect to controller  30  as the operating head and catheter system are guided to a target material removal site. It will be appreciated that some of the control and operational features described herein with reference to controller  30  may be provided in console unit  12  and, likewise, some of the control and operational features described with reference to console unit  12  may be provided in controller  30 .  
         [0044]     The operating head  40  of the interventional catheter disclosed herein may comprise any of a variety of rotational cutting devices or assemblies having one or more cutting surface(s) for cutting, fragmentizing, pulverizing, ablating, scraping, grinding or otherwise reducing the size of undesired material and/or separating undesired material from healthy tissue, such as the walls of a blood vessel, in proximity to the target removal site. Differential cutter assemblies may be provided, as described in the U.S. patent publications incorporated herein by reference. Operating heads comprising abrasive rotational surfaces may also be used. The operating head, or sub-components thereof, such as the cutting surfaces, may be coated with a radio-opaque material such as gold, platinum, inks and the like, to render the operating head radioscopically visible and to assist a medical professional in guiding and positioning the cutter assembly relative to an occlusion. In certain embodiments of interventional catheters of the present invention, non-rotational operating heads may also be used that incorporate alternative material removal modalities, such as laser or ultrasound ablation techniques, or other types of ablation techniques.  
         [0045]      FIG. 2  illustrates the distal end of one embodiment of an interventional catheter of the present invention. In this embodiment, the operating head comprises a multi-bladed cutter assembly  50  having a plurality of raised blades  52  arranged in a radially symmetrical configuration. Blades  52  are preferably differential cutting blades, and cutting assembly  50  may incorporate a plurality of ports  54  arranged in a radially symmetrical configuration in the spaces between blades  52 . Ports  54  are shown provided between each set of neighboring blade structures in  FIG. 2 , but it will be appreciated that fewer ports may be provided. Ports  54  are preferably provided in a generally proximal portion of cutter assembly  50  and may have a generally oblong configuration, as illustrated, or may take a variety of other configurations.  
         [0046]     The distal end of the interventional catheter illustrated in  FIG. 2  additionally comprises a large port  56  located in a distal portion of the catheter, or a proximal portion of the cutter assembly, proximal to blades  52 . Port  56  is generally provided as a window or cut-out in a cylindrical structure and preferably spans at least 10% of the circumference of the structure; more preferably at least 20% of the circumference of the structure; and yet more preferably at least 30% of the circumference of the structure. The cylindrical structure supporting port  56  may be a distal catheter portion, or port  56  may be provided in a generally cylindrical tubular shell structure mounted, directly or indirectly, to a distal catheter portion  60 . In one embodiment, illustrated in  FIG. 2 , a rigid cylindrical shell  58  is mounted to distal catheter portion  60  at its proximal end and is mounted to, or forms a stationary element of, bearing  62  at its distal end. Bearing  62  allows distal catheter portion  60  and cylindrical shell  58  to remain stationary during rotation of cutting assembly  50 . Bearing  62  may also provide limited articulation of cutting assembly  50  about its longitudinal axis.  
         [0047]     In the embodiment illustrated in  FIG. 2 , ports  54  may be operated as aspiration or infusion ports and enlarged proximal port  56  operates as an aspiration port and incorporates a rotating macerator assembly  64 , which is described in greater detail below. In one embodiment, proximal port  56  is provided as an aspiration port and communicates with an aspiration lumen within catheter  60  that communicates with aspiration conduit  22 , while ports  54  operate as infusion ports and communicate with an infusion lumen within catheter  60  that communicates with infusion conduit  26 .  
         [0048]     In another embodiment of an interventional catheter of the present invention illustrated in  FIG. 3 , operating head  70  comprises a distal cutter assembly  72  mounted to a bearing system  76  that allows rotation of the operating head while the catheter components proximal to the operating head remain stationary during rotation. The interventional catheter illustrated in  FIG. 3  additionally comprises a proximal aspiration port  78  provided as an opening in a cylindrical shell structure  80  located proximal to the cutter assembly  72 . Aspiration port  78  communicates with an aspiration lumen within catheter  82  that communicates proximally with aspiration conduit  22 .  
         [0049]     Proximal aspiration port  78  may be provided as an opening or window in a distal catheter portion, or it may be provided as an opening in a substantially rigid cylindrical shell  80 , as illustrated. Cylindrical shell  80  is constructed from a generally rigid, durable material, such as surgical steel or stainless steel, and has a length that is approximately the same as that of the cutter assembly. Shell  80  is generally mounted to, or forms a stationary component of, bearing  76  at its distal end. Bearing  76  allows catheter  82  and cylindrical casing  80  to remain stationary during rotation of operating head  50 . Bearing  76  may also provide limited articulation of operating head  70  about its longitudinal axis.  
         [0050]     Aspiration port  78  may be provided as a window spanning at least 15% of the circumference of the shell structure; more preferably at least 25% of the circumference of the shell structure; and yet more preferably at least 35% of the circumference of the shell structure. The proximal aspiration port may be provided, for example, in a generally ovoid, rectangular, or square profile. The surface area, or size of the opening of port  78  depends on the relative sizes of the operating head, the catheter and the size of debris that is anticipated will be generated during operation of the operating head. In one embodiment, port  78  has a length in the direction of the longitudinal axis of the interventional catheter that is from about 0.5 to about 2.5 times the transverse width of the port as measured on the arc of the cylindrical surface, preferably from about 0.7 to about 2.0 times the transverse width of the port. In certain embodiments, aspiration port  78  has an opening, or surface area that is between about 0.5 to about 20 mm 2 , preferably between about 0.5 and 10 mm 2  in surface area.  
         [0051]     The interventional catheter of  FIG. 3  incorporates a macerator assembly  90  mounted for rotation inside cylindrical shell  80 . Macerator assembly  90  rotates within the inner cavity of cylindrical shell  80  and has projecting bars, described in detail below, that interact with walls of the aspiration port  78  and the inner surface of cylindrical shell  80  to grind or macerate debris that is aspirated through port  78 .  
         [0052]     The interventional catheter illustrated in  FIG. 3  additionally incorporates a plurality of infusion ports  85  located proximally with respect to aspiration port  78 , but in proximity to the aspiration port and operating head  70 . Infusion ports  85 , which may be provided in an outer sheath  84 , as shown in  FIG. 3 , communicate with an infusion lumen in the catheter assembly, which communicates with infusion conduit  26 . In certain embodiments, between two and twenty, for example twelve, infusion ports  85  are provided in an infusion sheath  84  mounted to distal catheter  82 . The infusion ports may have a generally uniform size, or infusion ports of different sizes may be provided. The infusion ports may be generally cylindrical, as shown in  FIG. 3 , or they may have alternative configurations. Each infusion port  85  may have a diameter of approximately 0.005 in. to 0.20 in., more preferably from about 0.006 in. to about 0.015 in. Infusion ports having diameters of about 0.010 in. are especially preferred for certain applications. In one embodiment, the infusion ports are spaced in a generally circumferential pattern to provide a substantially uniform flow of infusate around the circumference of the infusion sheath.  
         [0053]      FIG. 4  shows a cross-sectional view of the distal end of the interventional catheter illustrated in  FIG. 3 . Distal cutter assembly  72  has an internal guidewire lumen terminating in guidewire bore  74 . This view illustrates a helical rotational drive  75 , which is mounted inside a central cavity in the core structure of macerator assembly  90  and fixed to the macerator, providing rotation of macerator assembly  90 . In embodiments employing a rotating operating head, drive  75  additionally drives the operating head, directly or indirectly. A bearing  76  member comprising a plurality of ball bearings  77  may be provided between the rotating cutter assembly  72  and/or the rotational macerator assembly  90  and the static cylindrical casing  80  and catheter  82 .  
         [0054]     The rotating macerator  90 , as illustrated in  FIGS. 5 and 6 , comprises a central core structure  92  and at least one projecting bar  94  aligned generally with the longitudinal axis of the interventional catheter. The central core structure  92  preferably has a generally cylindrical internal bore  91 . Multiple projecting bars  94  may be provided and are preferably arranged in a radially symmetrical arrangement with respect to the longitudinal axis of the catheter assembly. In one embodiment, illustrated in  FIGS. 6-9 , two projecting bars are provided.  
         [0055]     Projecting bars  94  preferably have a curved exterior surface that generally matches and rotates freely in the interior surface of cylindrical casing  80 . The width W of the arced exterior surface of the upstanding bars  94  tapers from a distal end (W d ) to a proximal end (W p ) of the rotating macerator. The proximal portion of projecting bar  94  has a narrower profile W p  that may be from about 5% to about 75% the width of the distal end profile W d . In one embodiment, the external diameter of central core structure  92  tapers from a larger diameter at the distal end to a smaller diameter at the proximal end. Consequently, upstanding bars  94 , as illustrated, may have a higher profile with respect to the surface of the central core structure  92  at the proximal end than at the distal end. In some embodiments, the radial height H of projecting bars  94  at a proximal portion measured from the surface of central core structure  92  is preferably at least about 50% greater than the radial height h of projecting bars  94  at a distal portion of the macerator assembly measured from the surface of central core structure  92 . In some embodiments, the radial height H of projecting bars  94  at a proximal portion measured from the surface of central core structure  92  is preferably at least about 100% greater than the radial height h of projecting bars  94  at a distal portion of the macerator assembly.  
         [0056]      FIGS. 7-9  illustrate the geometries of the macerator element and upstanding bars at various points along the macerator assembly  90 , with  FIG. 7  illustrating a cross-sectional view at a generally distal end of the macerator assembly,  FIG. 8  illustrating a cross-sectional view at a generally central portion of the macerator element, and  FIG. 9  illustrating a cross-sectional view at a generally proximal end of the macerator element. A multi-filar drive  75  and a central guidewire lumen  85  are visible. Window  78  is shown as a cut-out section of cylindrical casing  80  having a generally blunt perimeter wall  79 . The outer walls  93  of projecting bars  94  are illustrated having an arced surface that generally matches the internal surface of cylindrical casing  80  so that macerator assembly  90  is freely rotatable within cylindrical casing  80  about the longitudinal axis of the interventional catheter. The change in width of upstanding bars  94  from a wider distal end illustrated in  FIG. 7  to a narrower proximal end illustrated in  FIG. 9  is also evident.  
         [0057]     Angled walls  95  are provided between the outer walls  93  of projecting bars  94  and the exterior surface of central core structure  92 . Angled walls  95  are generally configured to present an undercut angle of from about 10° to about 60° with respect to a line bisecting the upstanding bar and intersecting the central longitudinal axis of the macerator assembly. The undercut angles of angled walls  95  may be from about 20° to about 45° in certain embodiments. The undercut angle of walls  95  is preferably greater at the distal end of the macerator assembly, as illustrated in  FIG. 7 , and less at the proximal end of the macerator assembly. In the embodiment illustrated, the undercut angle is 39° at a distal portion of the macerator device ( FIG. 7 ); 32° at a central portion of the macerator device ( FIG. 8 ) and 24° at a proximal portion of the macerator device. The difference in undercut angle between a distal end and a proximal end of the macerator assembly is preferably at least about 10°, more preferably at least about 15° and, in some embodiments, up to about 20° or 30°.  
         [0058]     The angle formed between the undercut angle of walls  95  of the projecting bar(s) and the face  79  of window  78  may also be adjusted to facilitate breaking down of particulates. In some embodiments, as illustrated in  FIG. 8 , the angle formed by the undercut angle of the projecting bar wall and the face of the aspiration window is about 32°. This angle also changes with changes in the undercut angles of the projecting bars and may range from about 15° to about 60° from the distal to the proximal end of the macerator assembly, more preferably from about 20° to about 50°.  
         [0059]     During operation of the cutter assembly or operating head, the central core and upstanding bars of macerator assembly  90  rotate, while the aspiration port and cylindrical shell structure in which the aspiration port is provided remain static. As the upstanding bars rotate and debris is aspirated through the aspiration window, the upstanding bars interact with the wall of the aspiration port and the interior surface of the cylindrical structure to shear, grind, macerate and/or break-up debris as it enters the aspiration port and is aspirated through the aspiration lumen. The tapered structure and undercut walls of the upstanding bars also facilitate movement of fluid and debris proximally in the macerator assembly to the aspiration lumen. The rotating element of the macerator assembly does not extend radially beyond the inner wall of the cylindrical structure and aspiration port, and is generally constructed from a rigid material such as, but not limited to, hardened stainless steel, titanium or titanium nitrate-coated stainless steel.  
         [0060]     The present invention has been described with reference to specific embodiments and figures. These specific embodiments should not be construed as limitations on the scope of the invention, but merely as illustrations of exemplary embodiments. It is further understood that many modifications, additions and substitutions may be made to the described interventional catheter and control system without departing from the scope of the present invention.