Abstract:
A coaxial guide catheter to be passed through guide catheter having a first lumen, for use with interventional cardiology devices that are insertable into a branch artery that branches off from a main artery. The coaxial guide catheter is extended through the lumen of the guide catheter and beyond the distal end of the guide catheter and inserted into the branch artery. The device assists in resisting axial and shear forces exerted by an interventional cardiology device passed through the second lumen and beyond the flexible distal tip portion that would otherwise tend to dislodge the guide catheter from the branch artery.

Description:
RELATED APPLICATION 
     This application is a division of application Ser. No. 11/416,629 filed May 3, 2006, now U.S. Pat. No. 8,048,032 which is hereby fully incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to catheters used in interventional cardiology procedures. More particularly the present invention relates to methods and apparatus for increasing backup support for catheters inserted into the coronary arteries from the aorta. 
     BACKGROUND OF THE INVENTION 
     Interventional cardiology procedures often include inserting guidewires or other instruments through catheters into coronary arteries that branch off from the aorta. For the purposes of this application, the term “interventional cardiology devices” is to be understood to include but not be limited to guidewires, balloon catheters, stents and stent catheters. In coronary artery disease the coronary arteries may be narrowed or occluded by atherosclerotic plaques or other lesions. These lesions may totally obstruct the lumen of the artery or may dramatically narrow the lumen of the artery. Narrowing is referred to as stenosis. In order to diagnose and treat obstructive coronary artery disease it is commonly necessary to pass a guidewire or other instruments through and beyond the occlusion or stenosis of the coronary artery. 
     In treating a stenosis, a guide catheter is inserted through the aorta and into the ostium of the coronary artery. This is sometimes accomplished with the aid of a guidewire. A guide catheter is typically seated into the opening or ostium of the artery to be treated and a guidewire or other instrument is passed through the lumen of the guide catheter and inserted into the artery beyond the occlusion or stenosis. Crossing tough lesions can create enough backward force to dislodge the guide catheter from the ostium of the artery being treated. This can make it difficult or impossible for the interventional cardiologist to treat certain forms of coronary artery disease. 
     Prior attempts to provide support to the guiding catheter to prevent backward dislodgement from the coronary ostium (referred to as “backup support”) fall generally into four categories. 
     First are guiding catheters that, through a combination of shape and stiffness, are configured to draw backup support from engaging the wall of the aortic arch opposing the ostium of the coronary artery that is being accessed. Examples of this approach can be found in U.S. Pat. No. 6,475,195 issued to Voda and U.S. Pat. No. 5,658,263 issued to Dang et al. These guiding catheters all share the common limitation that a guide catheter stiff enough to provide adequate backup support is often too stiff to be safely inserted into the aorta without the possibility of causing damage to the aortic wall. In addition, attempts to deep seat the guide catheter have been made but the rigid nature of the guide catheter creates the risk that the guide catheter may damage the coronary artery wall or that the guide catheter may occlude the coronary artery and interfere with blood flow to the heart muscle. 
     Second are guiding catheters that include a retractable appendage. The appendage in these catheters can be extended to engage the opposing wall of the aortic arch to provide backup support or the appendage may be placed under tension to stiffen a bend in the catheter to provide backup support. Examples of this approach may be found in U.S. Pat. Nos. 4,813,930 issued to Elliot; 5,098,412 issued to Shiu; and 6,860,876 issued to Chen. These guiding catheters tend to be somewhat mechanically complex and have not been widely adopted by practitioners. 
     Third are guide catheters that have a portion that seeks to expand laterally to grip the interior wall of the ostium of the coronary artery to provide a force acting in opposition to the backward forces created when trying to maneuver a therapeutic device past a lesion or blockage in the coronary artery. These devices can include a balloon secured to a guidewire or a catheter or another device for expanding to grip the walls of the coronary artery from within. Examples of this approach may be found in U.S. Pat. Nos. 4,832,028 issued to Patel; 6,595,952 issued to Forsberg; and U.S. Published Application No. 2005/0182437 by Bonnette et al. Again, these devices tend to be mechanically complex and can completely occlude the coronary ostium thus stopping perfusion of the coronary artery. 
     A fourth technique includes the placement of a smaller guide catheter within a larger guide catheter in order to provide added support for the crossing of lesions or for the distal delivery of balloons and stents. This technique has been described in an article by Takahashi entitled “New Method to Increase a Backup Support of Six French Guiding Coronary Catheter,” published in Catheterization and Cardiovascular Interventions, 63:452-456 (2004). This technique is used in order to provide a method of deep seating the guide catheter within the ostium of the coronary artery. Deep seating refers to inserting the catheter more deeply into the ostium of the coronary artery than typically has been done before. Unfortunately, deep seating by this technique with a commonly available guide catheter creates the risk that the relatively stiff, fixed curve, guide catheter will damage the coronary artery. This damage may lead to dissection of the coronary artery when the catheter is advanced past the ostium. 
     Several other problems arise when using a standard guide catheter in this catheter-in-a-catheter fashion. First, the inner catheters must be substantially longer than the one hundred centimeter guide catheter. Second, a new hemostasis valve must be placed on the inner guide catheter which prevents the larger guide catheter from being used for contrast injections or pressure measurements. Third, the smaller guide catheter still must be inserted into the coronary vessel with great care since the smaller guide catheter has no tapered transition or dilator at its tip and does not run over a standard 0.014 inch guidewire. 
     Thus, the interventional cardiology art would benefit from the availability of a system that would be deliverable through standard guide catheters for providing backup support by providing the ability to effectively create deep seating in the ostium of the coronary artery. 
     SUMMARY OF THE INVENTION 
     The present invention is a coaxial guide catheter that is deliverable through standard guide catheters by utilizing a guidewire rail segment to permit delivery without blocking use of the guide catheter. The coaxial guide catheter preferably includes a tapered inner catheter that runs over a standard 0.014 inch coronary guidewire to allow atraumatic placement within the coronary artery. This feature also allows removal of the tapered inner catheter after the coaxial guide catheter is in place. The tapered inner catheter provides a gradual transition from the standard 0.014 inch diameter guidewire to the diameter of the coaxial guide catheter which is typically five to eight French. 
     The coaxial guide catheter preferably can be delivered through commonly existing hemostatic valves used with guide catheters while still allowing injections through the existing Y adapter. In addition, the coaxial guide catheter preferably has an inner diameter that is appropriate for delivering standard coronary treatment devices after it is placed in the coronary artery. 
     In one embodiment, the coaxial guide catheter is made in at least three sizes corresponding to the internal capacity of 8 French, 7 French, and 6 French guide catheters that are commonly used in interventional cardiology procedures. An 8 French catheter has an internal diameter greater than or equal to 0.088 inches. A 7 French catheter has an internal diameter greater than or equal to 0.078 inches. A 6 French guide catheter has an internal diameter greater than or equal to 0.070 inches. Thus, for three exemplary sizes the effective internal diameter of the coaxial guide catheter may be as follows. For a 7 French in 8 French coaxial guide catheter the internal diameter should be greater than or equal to 0.078 inches. For a 6 French in 7 French coaxial guide catheter the internal diameter should be greater than or equal to 0.070 inches. For a 5 French in 6 French coaxial guide catheter the internal diameter should be greater than or equal to 0.056 inches. 
     Interventional cardiology procedures are typically carried out under fluoroscopy or another x-ray or imaging technique. Therefore, one embodiment of the coaxial guide catheter of the present invention includes a radiopaque marker at its distal tip to facilitate positioning and manipulation of the coaxial guide catheter. 
     The present invention generally includes the coaxial guide catheter and a tapered inner catheter. The coaxial guide catheter includes a tip portion, a reinforced portion, and a substantially rigid portion. The coaxial guide catheter will generally have an overall length of preferably approximately 125 cm, though this should not be considered limiting. 
     In one embodiment, the tip portion may include a soft tip and a marker band. The soft tip is tapered and may be formed from a low durometer polymer or elastomer material such as polyether block amide polymer, (PEBA, Pebax®) the marker band may be formed from a platinum iridium alloy sandwiched between the Pebax® that extends from the bump tip and a PTFE liner. 
     In one embodiment, the reinforced portion may be reinforced, preferably with metallic fibers in a braided or coiled pattern. The braided or coiled portion is lined by a PTFE liner and may be covered on its exterior with Pebax®. The braided or coiled portion may extend approximately 20 to 110 cm in length. In one exemplary embodiment, the braided portion extends approximately 32 to 36 cm. 
     Preferably, the rigid portion may be advantageously formed from a stainless steel or Nitinol tube. The rigid portion may be joined to the braid or coil portion by welding. The rigid portion may include a cutout portion and a full circumference portion. For example, the cutout portion may include a section where about 45% of the circumference of the cylindrical tubular structure has been removed. The cutout portion may also include a section where 75-90% of the circumference of the tubular structure has been removed. In one exemplary embodiment, the portion having approximately 45% removed may extend for approximately 75 cm and the portion having 75-90% of the structure removed extends for about 15 cm. The full circumference portion of the rigid portion is typically located at the most proximal end of the coaxial guide catheter. 
     The rigid portion may include a plurality of radially oriented slits or other cuts in its distal portion to increase and control the flexibility of the rigid portion 
     In an exemplary embodiment, the tapered inner catheter generally includes a tapered inner catheter tip and a cutout portion. The tapered inner catheter tip includes a tapered portion and a straight portion. The tapered portion is typically at the most distal end of the tapered inner catheter. Both the straight portion and the tapered portion are pierced by a lumen through which a guidewire may be passed. 
     The cutout portion supports a track passing along the concave side thereof that continues from the lumen that passes through the straight portion and the tapered portion. The tapered inner catheter may also have a clip or snap attachment at its proximal end to releasably join the tapered inner catheter to the coaxial guide catheter. 
     In operation, the tapered inner catheter is inserted inside and through the coaxial guide catheter. The tapered inner catheter is positioned so that the tapered inner catheter tip extends beyond the tip portion of the coaxial guide catheter. The coaxial guide catheter-tapered inner catheter combination may then be inserted into a blood vessel that communicates with the aorta. The coaxial guide catheter-tapered inner catheter combination may be threaded over a preplaced 0.014 inch guidewire. The tapered inner catheter-coaxial guide catheter combination is advanced up the aorta until the tapered inner catheter is passed into the ostium of a coronary artery over the guidewire. Once the coaxial guide catheter-tapered inner catheter combination has been inserted sufficiently into the ostium of the coronary artery to achieve deep seating the tapered inner catheter may be removed. During this entire process at least part of the coaxial guide catheter-tapered inner catheter combination is located inside of the guide catheter. 
     Once the tapered inner catheter is removed a cardiac treatment device, such as a guidewire, balloon or stent, may be passed through the coaxial guide catheter within the guide catheter and into the coronary artery. As described below, the presence of the coaxial guide catheter provides additional backup support to make it less likely that the coaxial guide catheter guide catheter combination will be dislodged from the ostium of the coronary artery while directing the coronary therapeutic device past a tough lesion such as a stenosis or a chronic arterial occlusion. 
     A guide catheter inserted into the ostium of a branch artery where it branches off from a larger artery is subject to force vectors that tend to dislodge the distal end of the guide catheter from the ostium of the branch artery when a physician attempts to direct a guidewire or other interventional cardiology device past an occlusive or stenotic lesion in the branch artery. This discussion will refer to a guide wire but it is to be understood that similar principles apply to other interventional cardiology devices including balloon catheters and stent catheters. 
     One of the forces that acts on the guide catheter is an axial force substantially along the axis of the branch artery and the portion of the guide catheter that is seated in the ostium. This force vector is a reactive force created by the pushing back of the guide wire against the guide catheter as the physician tries to force the guidewire through or past the lesion. It tends to push the distal end of the catheter out of the ostium in a direction parallel to the axis of the branch artery and the axis of the distal end of the guide catheter. 
     Another of the force vectors that acts on the guide catheter is a shearing force that tends to dislodge the distal end of the guide catheter from the ostium of the branch artery in a direction perpendicular to the axis of the branch artery and the axis of the distal end of the guide catheter. This force vector arises from curvature of the guide catheter near its distal end and the guide wire pushing on the curved portion of the guide catheter as the physician applies force to the guidewire. The coaxial guide catheter of the present invention assists in resisting both the axial forces and the shearing forces that tend to dislodge a guide catheter from the ostium of a branch artery. 
     The system is deliverable using standard techniques utilizing currently available equipment. The present invention also allows atraumatic placement within the coronary artery. Further, the invention is deliverable through an existing hemostatic valve arrangement on a guide catheter without preventing injections through existing Y adapters. Finally, the invention has an inner diameter acceptable for delivering standard coronary devices after it is placed in the blood vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of the coaxial guide catheter and a tapered inner catheter in accordance with the present invention; 
         FIG. 2  is schematic depiction of the coaxial guide catheter and tapered inner catheter assembled in accordance with the present invention; 
         FIG. 3  is a plan view of a guide catheter, the coaxial guide catheter, and a treatment catheter in accordance with the present invention; 
         FIG. 4  is a sectional view of the coaxial guide catheter in accordance with the present invention; 
         FIG. 5  is a cross sectional view of the coaxial guide catheter and tapered inner catheter in accordance with the present invention; 
         FIG. 6  is another cross sectional view of the coaxial guide catheter and tapered inner catheter in accordance with the present invention; 
         FIG. 7  is a schematic view of a guide catheter and a guidewire located in an aortic arch and a coronary artery and the guide catheter and guidewire in a second position depicted in phantom; 
         FIG. 8  is a schematic view of a guide catheter, a guidewire, a coaxial guide catheter in accordance with the present invention and a tapered inner catheter located in the aortic arch and coronary artery; 
         FIG. 9  is a schematic view of a guide catheter, a guidewire and a coaxial guide catheter in accordance with the present invention located in the aortic arch and coronary artery; 
         FIG. 10  is a flat pattern for making relief cuts in a curved rigid portion of the coaxial guide catheter in accordance with the present invention; 
         FIG. 11  is a detailed view taken from  FIG. 10 ; 
         FIG. 12  is a plan view of the rigid portion in accordance with the present invention; 
         FIG. 13  is an elevational view of the rigid portion; 
         FIG. 14  is a sectional view of the rigid portion taken along section line  14 - 14  of  FIG. 13 ; and 
         FIG. 15  is a sectional view of the rigid portion taken along section line  15 - 15  of  FIG. 13 . 
         FIG. 16  is a sectional view of the rigid portion taken along section line  16 - 16  of  FIG. 13 . 
         FIG. 17  is a plan view of a coaxial guide catheter having a longer rail segment and a tapered inner catheter in accordance with the present invention. 
         FIG. 18  is a plan view of the tapered inner catheter as depicted in the  FIG. 17 . 
         FIG. 19  is a cross-sectional view of the tapered inner catheter taken along section lines  19 - 19  of  FIG. 18 . 
         FIG. 20  is a plan view of a coaxial guide catheter in accordance with the present invention. 
         FIG. 21  is an elevational view of a coaxial guide catheter in accordance with the present invention. 
         FIG. 22  is a cross-sectional view taken along section line  22 - 22  of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 and 2 , coaxial guide catheter assembly  10  of the present invention generally includes coaxial guide catheter  12  and tapered inner catheter  14 . 
     Coaxial guide catheter  12  generally includes tip portion  16 , reinforced portion  18 , and rigid portion  20 . The overall length of the coaxial guide catheter typically can be approximately 125 cm. This length should not be considered limiting. 
     Tip portion  16  generally includes bump tip  22  and marker band  24 . Bump tip  22  includes taper  26 . Bump tip  24  is relatively flexible and may be formed, for example, from 4033 Pebax®. Bump tip  22  may be yellow or another high visibility color for ease of handling. 
     Marker band  24  is formed of a radiopaque material such as platinum/iridium alloy usually at a 90/10 ratio. Marker band  24  may be sandwiched between an outer Pebax® material  28  and a PTFE liner  30 . Outer Pebax® material  28  in this location may be formed of 5533 Pebax, for example. 
     Reinforced portion  18  includes braid or coil reinforcement  32 . Braid or coil reinforcement  32  may be formed of metal, plastic, graphite, or composite structures known to the art. Reinforced portion  18  may be lined on the interior by PTFE liner  30  and covered on the exterior by Pebax® material  28 . Tip portion  16  and reinforced portion  18  together form a substantially cylindrical structure. Braid or coil reinforcement  32  may extend approximately 20 to 30 cm. In one exemplary embodiment, braid or coiled portion has a length of approximately 32 to 36 cm. 
     Rigid portion  20  may be secured to braid or coil reinforcement by, for example, welding or bonding. Rigid portion  20  may be formed from a hypotube or a section of stainless steel or Nitinol tubing. Other substantially rigid materials may be used as well. Rigid portion  20  includes first full circumference portion  34 , hemicylindrical portion  36 , arcuate portion  38 , and second full circumference portion  40 . 
     First full circumference portion  34  is joined to braid or coil reinforcement  32 . First full circumference portion  34  extends for a relatively short distance, for example, 0.25 cm. 
     Hemicylindrical portion  36  desirably includes 40% to 70% of the circumference of the tube. Hemicylindrical portion  36  may extend, for example, approximately 20 to 75 cm in length. 
     Hemicylindrical portion  36  tapers into arcuate portion  38 . 
     Arcuate portion  38  extends from 25% to 40% of the circumference of the tube. Arcuate portion  38  may extend linearly, for example, for about 15 cm. 
     Arcuate portion  38  connects to second full circumference portion  40 . Second full circumference portion  40  may extend for a short distance, for example, approximately 3 cm. 
     Tapered inner catheter  14  generally includes tapered inner catheter tip  42  and cutout portion  44 . Tapered inner catheter tip  42  tapers gradually from the diameter of a guide wire to the diameter of tip portion  16 . 
     Tapered inner catheter tip  42  includes tapered portion  46  at a distal end thereof, and straight portion  48 . Both tapered portion  46  and straight portion  48  are pierced by lumen  50 . 
     Cutout portion  44  defines a concave track  52  along its length. Concave track  52  is continuous with lumen  50 . 
     Tapered inner catheter  14  may also include clip  54  at a proximal end thereof to releasably join tapered inner catheter  14  to coaxial guide catheter  12 . Thus, tapered inner catheter  14  is keyed to coaxial guide catheter  12 . 
     Coaxial guide catheter  12  may include, starting at its distal end, a first portion having a flexural modulus of about 13,000 PSI plus or minus 5000 PSI, a second portion having a flexural modulus of about 29,000 PSI plus or minus 10,000 PSI, a third portion having a flexural modulus of about 49,000 PSI plus or minus 10,000 PSI and a fourth portion having a flexural modulus of about 107,000 PSI plus or minus 20,000 PSI. Coaxial guide catheter  12  may be formed, for example, of 4033 Pebax® at bump tip  22  for the first 0.1 cm. This portion may followed by a section about three cm long of 5533 Pebax® that covers marker band  24  and the distal portion of braid or coil reinforcement  32 . Next may come an approximately five cm portion of 6333 Pebax® which encloses part of braid or coil reinforcement  32  followed by an approximately twenty seven cm portion of 7233 Pebax® covering the most proximal portion of braid or coil reinforcement  32 . Braid or coil reinforcement  32  is bonded to rigid portion  20  which may be formed from stainless steel or a similar biocompatible material. Rigid portion  20  may extend for approximately ninety cm and include first full circumference portion  34  (approximately 0.25 cm), hemicylindrical portion  36  (approximately seventy five cm), arcuate portion (approximately fifteen cm) and second full circumference portion (approximately three cm.) Rigid portion  20  may be formed from a stainless steel or Nitinol hypo tube. 
       FIG. 7  depicts a typical guide catheter  56  passing through aortic arch  58  into ostium  60  of coronary artery  62 .  FIG. 7  also depicts guidewire  64  passing through the guide catheter  56  and into coronary artery  62 . Located in coronary artery  62  is stenotic lesion  66 . In a typical procedure, guidewire  64  is placed through the aortic arch  58  and into the ostium  60  of the coronary artery.  62 . The guide catheter  56  is passed over guidewire  64  until distal end  68  of guide catheter  56  is seated in ostium  60  of coronary artery  62 . Force is then applied to the guidewire  64  to push guidewire  64  past stenotic lesion  66  or an occlusive lesion (not shown). Once the guidewire  64  is pushed past stenotic lesion  66  or occlusive lesion (not shown), a treating catheter including a stent or balloon can be passed along the guidewire to stenotic lesion  66  or occlusive lesion (not shown). The lesion can then be treated. 
     As can be seen in phantom, in  FIG. 7 , the application of force to guidewire  64  can cause guide catheter  56  to dislodge from ostium  60  of coronary artery  62 . This can occur in the case of a tough stenotic lesion  66  or occlusive lesion (not shown) when it is difficult to pass the guidewire  64  beyond the stenotic lesion  66  or occlusive lesion (not shown). 
     Referring the  FIG. 8  coaxial guide catheter  12  is depicted as used with guide catheter  56 , guidewire  64 , and tapered inner catheter  14 . Here, coaxial guide catheter  12  with tapered inner catheter  14  is passed through guide catheter  56  and over guidewire  64  into coronary artery  62  after the guide catheter  56  has been placed in the ostium  60  of coronary artery  62 , as depicted in  FIG. 7 . Coaxial guide catheter  12 , with tapered inner catheter  14 , provide an inner support member for proper translation over guidewire  64 . Tapered inner catheter tip  42  provides a distal tapered transition from guidewire  64  to coaxial guide catheter  12 . Once coaxial guide catheter  12  is in place, tapered inner catheter  14  is removed from the inside of coaxial guide catheter  12 . 
     Coaxial guide catheter  12  is now ready to accept a treatment catheter such as a stent or balloon catheter. Referring to  FIG. 9 , the combination of guide catheter  56  with coaxial guide catheter  12  inserted into ostium  60  of coronary artery  62  provides improved distal anchoring of guide catheter  56  and coaxial guide catheter  12 . The presence of coaxial guide catheter  12  within guide catheter  56  also provides stiffer back up support than guide catheter  56  alone. The combination of improved distal anchoring and stiffening of the guide catheter  56 /coaxial guide catheter  12  combination provides additional back up support to resist dislodging of guide catheter  56  from ostium  60  when force is applied to guidewire  64  to pass through stenotic lesion  66  or another lesion. In addition, the improved back up support assists in the positioning of a treating catheter that may include a stent or balloon. 
     Referring to  FIGS. 10 and 11 , in some embodiments of coaxial guide catheter  12 , rigid portion  20  may be perforated by relief cuts  70 . Relief cuts  70  may be classed into first group  72  and second group  74 . 
     First group  72  may be located near to the juncture between rigid portion  20  and reinforced portion  18 . First group  72  of relief cuts  70  are relatively closely spaced. For example, first group  72  of relief cuts  70  may be spaced approximately 0.010 inches apart. First group  72  of relief cuts  70  extends for a relatively short distance, for example, approximately 2 inches. 
     Second group  74  of relief cuts  70  may extend for a relatively long distance, for example, approximately 30-35 inches. Second group  74  of relief cuts  70  are spaced farther apart than first group  72 . For example, relief cuts  70  of second group  74  may be spaced approximately 0.020 inches between cuts. Referring particularly to  FIG. 11 , relief cuts  70  may include single cuts  76  and double cuts  78 . Single cuts  76  may include an individual linear cut, as can be seen in  FIG. 11 . Double cuts  78  may include two linear cuts along a single line but separated by a short section of uncut structure. Typically, single cuts  76  and double cuts  78  are alternated along the length of rigid portion  20 . Generally, the overall length of single cut  76  may be less than the overall length of two double cuts  78 . 
     In an embodiment depicted in  FIGS. 12-15 , rigid portion includes full circumference portion  80 , greater than 180° portion  82 , and less than 180° portion  84 . Greater than 180° portion  82  may, for example, include structure forming approximately 300° of the circumference of the cylinder. Less than 180° portion may include, for example, structure forming approximately 90° of the circumference of a cylinder. Greater than 180° portion  82  may extend approximately 22-25 inches. Greater than 180° portion  82  holds tapered inner catheter  14  within rigid portion  20 . 
     When tapered inner catheter is inserted into coaxial guide catheter  12  greater than 180° portion  82  grips tapered inner catheter  14  which is exposed through the opening in greater than 180° portion  82 . Thus, the overall structure of tapered inner catheter  14  along with greater than 180° portion  82  is substantially cylindrical. Accordingly, when inserted through a guide catheter  56  having a Touhey-Borst style adapter, the Touhey-Borst style adapter can still seal around rigid portion  20  and enclosed inner tapered catheter  14 . 
     Referring to  FIG. 16 , another embodiment of coaxial guide catheter assembly  10  includes coaxial guide catheter  12  and tapered inner catheter  14 . Tapered inner catheter  14  is keyed to coaxial guide catheter  12  at hub  86 . 
     Referring to  FIGS. 17 and 18 , tapered inner catheter  14  generally includes connector hub  88  and catheter tube  90 . 
     Connector hub  88  generally includes connector portion  92 , grip portion  94  and joining portion  96 . Connector hub  88  defines funnel portion  98  therein. 
     Catheter tube  90  generally includes straight portion  100 , tapered portion  102  and marker band tip  104 . Catheter tube  90  is joined to connector hub  88  at joining portion  96 . Tapered inner catheter  14  may be formed in whole or in part from low-density polyethylene plastic, for example. Other suitable materials known to the catheter arts may be used as well. 
     Grip portion  94  desirably includes gripping ears  106 . Gripping ears  106  may extend outwardly from grip portion  94  substantially radially and be shaped for convenient gripping by a physician. 
     Referring to  FIGS. 19 through 21 , in this embodiment, coaxial guide catheter  12  includes interrupted hub  108 , hemi-tube portion  110 , braided portion  112  and tip portion  114 . 
     Interrupted hub  108  defines an opening  116 , along a side thereof. Interrupted hub  108  may be substantially C-shaped or U-shaped in cross section. Opening  116  is sized so that tapered inner catheter  14  may be passed readily therethrough in a direction perpendicular to the long axes of both interrupted hub  108  and tapered inner catheter  14 . Hemi-tube portion  110  is immediately distal to interrupted hub  108 . Hemi-tube portion  110  may be formed, for example, from a metal hypo tube forming approximately 50% of the circumference of a cylinder. Hemi-tube portion  110  is aligned so that opening  116  of interrupted hub  108  is coextensive with opening  118  of hemi-tube portion  110 . Hemi-tube portion  110  is joined to braided portion  112 , for example, by adhesive, bonding or welding. The location where hemi-tube portion  110  and braided portion  112  join defines the entire circumference of a cylinder. 
     Braided portion  112  may be reinforced by a coil or braid,  120 . Coil or braid  120  may be formed of metal or another suitable reinforcing material. 
     Tip portion  114  is generally not reinforced and is substantially soft. Tip portion  114  is similarly structured to tapered inner catheter tip  42 . Tip portion  114  may include a radiopaque marker band  24 . 
     Beginning at the distal end of coaxial guide catheter  12 , tip portion  114  may be formed substantially of, for example, 2533 Pebax® This may be followed by a section of 3533 Pebax®, then by a section of 5533 Pebax®, then by a further section of 7233 Pebax®. These Pebax® portions may all incorporate, for example, about 20% barium sulfate (BaSO 4 ). 
     In one embodiment, tip portion  114  and braided portion  112  may have an overall length together of approximately one hundred nine centimeters. Hemi-tube portion  110  and interrupted hub  108  may together have an overall length of approximately eighteen centimeters. 
     In this embodiment, coaxial guide catheter  12  may be lined with a PTFE liner  122 . 
     In operation, a guide catheter  56  is inserted into a major blood vessel in the body such as aortic arch  58  over guidewire  64  and the distal end  68  of guide catheter  56  is brought into proximity of ostium  60  of a smaller branch blood vessel, such as coronary artery  62 , that it is desired to enter. Coaxial guide catheter  12 , with tapered inner catheter  14 , is inserted through guide catheter  56  and over guidewire  64 . Guide catheter  56 , guidewire  64 , coaxial guide catheter  12 , and tapered inner catheter  14  are manipulated to insert tapered inner catheter tip  42  into the ostium  60  of the blood vessel that branches off from the major blood vessel. The bump tip  22  of coaxial guide catheter  12  is inserted with tapered inner catheter tip  42  well into ostium  60  of coronary artery  62  or other blood vessel until bump tip  22  of coaxial guide catheter  12  achieves a deep seated position. Tapered inner catheter  14  is then withdrawn from the lumen of coaxial guide catheter  12 . An interventional cardiology treatment device such as a catheter bearing a stent or a balloon (not shown) is then inserted through the lumen of coaxial guide catheter  12  which remains inside guide catheter  56 . 
     When the interventional cardiology device reaches a stenosis or blockage in coronary artery  62  or another branch blood vessel, force may be applied to the interventional cardiology device catheter while reinforced portion  18  and rigid portion  20  of coaxial guide catheter  12  provide back up support. The back force that would tend to dislodge bump tip  22  from a deep seated position in the ostium in the branch blood vessel is transferred through reinforced portion  18  to rigid portion  20  of coaxial guide catheter  12 . A physician may apply a force to the proximal end of the coaxial guide catheter  12  to resist dislodging of bump tip  22  from the ostium of the branch artery. 
     One advantage of the present invention over prior art approaches is that the present invention does not interfere the injection of fluids via the Y-adapter of guide catheter  56  as does the use of a smaller catheter within a larger catheter. 
     The present invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.