Abstract:
A monorail tip catheter includes a low friction guide wire lumen to facilitate removal of the catheter over the guide wire without buckling or kinking the guide wire. The catheter guide wire lumen is provided with a low friction lining with anchoring means, together with additional guide means to facilitate threading the guide wire into the monorail guide wire lumen.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of intravascular catheters. Specifically, the invention is directed towards improvements in monorail catheter tip construction. 
     BACKGROUND OF THE INVENTION 
     Intravascular catheters and probes are used for a variety of diagnoses and treatments of vascular diseases and defects. Similar catheters are also used for examination and treatment of other body cavities and vessels. These catheters are inserted in the body until they reach the location of interest. In the case of intravascular catheters used for diagnoses of the coronary arteries, the catheter is inserted in the femoral artery and guided up through the descending aorta, arch of the aorta, down the ascending aorta, then into the left or right coronary arteries, continuing as far into the coronary arteries as the miniaturization of the catheter will allow. The small diameter of the vessels and the delicacy of the vessels necessitate great care in catheter deployment and removal, in order to avoid damage to the vessels. The delicacy and small size of the vessels, combined with the tortuous deployment path, impose severe restrictions on materials and structures used for such intravascular catheters. 
     One method of deploying intravascular catheters is called the monorail system. In the monorail system, a small diameter guide wire is first routed along the deployment path. When the guide wire is properly positioned, its distal tip lies in the coronary artery, just past the area of interest, and the proximal end extends out of the patient&#39;s thigh. Standard introducers and guide catheters may be used in the procedure. 
     When the guide wire is properly positioned, the proximal end of the guide wire is threaded through the monorail lumen of the diagnostic catheter. In a monorail tip catheter, the tip of the catheter is provided with a small lumen to receive the guide wire. The lumen starts at the extreme distal tip of the catheter, runs a short length from the distal tip before reaching the catheter circumference to provide an exit port very close to the distal tip. The guide wire is threaded through this lumen. Thus mounted, the diagnostic catheter is pushed into the femoral artery along the entire deployment path and further into the coronary artery, guided to the diagnostic site by the guide wire. In this manner, the guide wire facilitates placement of the diagnostic catheter. 
     The diagnostic catheter may identify sites for treatment such as atherectomy. The diagnostic catheter can be pulled out of the body while the guide wire remains in place so that a working catheter can be deployed along the same guide wire to the treatment site. The use of a stationary guide wire facilitates deployment of the working catheter to the treatment site previously identified by the diagnostic catheter. In some instances, the diagnostic and working mechanisms can be deployed on a single catheter, avoiding the need to use them sequentially. 
     A problem sometimes encountered with the monorail tip catheter is that, during withdrawal of the catheter over the guide wire, friction between the monorail lumen and the guide wire makes it difficult to withdraw the catheter without buckling the guide wire. Frictional and buckling forces are exacerbated by the tortuous bends which the catheter must negotiate during withdrawal, combined with the low rigidity of the guide wire. During withdrawal, the monorail tip is effectively axially pushing on the portion of the guide wire proximal to the monorail lumen. This may cause binding, applying excessive force on the guide wire, which force may cause damage to the arteries. Worse yet, the binding may cause the guide wire to become kinked so that withdrawal of the catheter over the guide wire is not possible, and withdrawal of the kinked guide wire is likely to damage the vessel&#39;s internal surface along the withdrawal path. 
     SUMMARY OF THE INVENTION 
     It is a principal object of the invention to eliminate or minimize friction between the guide wire lumen of a catheter and the guide wire. It is also an object of the invention to provide a low friction surface for the monorail lumen. 
     These and other useful objects are achieved by the present invention which is an improved catheter tip especially suited for low friction coupling to a guide wire. The present invention includes a catheter tip with a low friction resin lining for the monorail, along with suitable structures for securely mounting the lining in the monorail lumen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-section of the monorail lumen with a low friction lining. 
     FIG. 2 is a longitudinal cross-section of the monorail lumen with a low friction lining together with accessory parts used in its fabrication. 
     FIG. 3 is a longitudinal cross-sectional view of the monorail lumen with a low friction lining and tapered tip. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows an embodiment of the monorail catheter with a low friction insert. The catheter tip 1 is of a small internal diameter and is made of polyethylene, ethyl vinyl acetate or other suitable material. The low friction tube 2 is held within the catheter tip 1. The proximal end of thelow friction tube 2 is provided with one pair of opposing anchoring holes, one of which is shown as anchoring hole 3. Just distal of the anchoring holes, the low friction tube 2 is provided with another wedge anchoring hole 4. Inside the low friction tube 2 is a plug 5. The plug 5 has a wedgeshape at its distal end and the wedge is provided with a concave surface toassist in guiding the wire guide. Anchoring pins 6 fix the plug 5 to the catheter tip 1. An exit port 7 allows a guide wire inserted in the distal opening of the low friction lumen to pass out of the low friction lumen. The wedge of the plug 5 helps guide the guide wire out of the lumen and prevent snagging as the lumen is threaded. At the very tip of the assembly, the internal diameter of the catheter tip 1 is the same as the internal diameter of the low friction tube 2. This provides an additional anchoring structure, and also provides a smooth bore which facilitates threading the guide wire through the low friction lumen. 
     The assembly may be formed as shown in FIG. 2. A low friction tube 2 is provided with two pairs of holes at its proximal end, each pair offset by 90°. The proximal pair of holes will correspond to the anchoring holes 3 of FIG. 1 and the distal holes will correspond to the wedge anchoring hole 4 of FIG. 1, as will become apparent in later steps of the process. The low friction tube is placed on a straight mandrel 8 of matching diameter. The straight mandrel 8 is inserted along the entire length of the low friction tube 2. The low friction tube 2 is covered withthe catheter tip 1, and this assembly is covered with a plastic compressiontube 9 made of Silastic® plastic or other suitable material. The Silastic® plastic, when soaked with a solvent, expands to a large diameter so that it may be easily slipped over the catheter assembly. The Silastic® plastic compression tube 9 shrinks when the solvent evaporates, exerting considerable force on the catheter assembly. This assembly is heated so that the catheter tip 1 melts to fill the anchoring holes 3 and wedge anchoring holes 4 thereby forming anchoring pins which will secure the low friction tube 2. At the distal tip of the assembly, the catheter tip 1 melts to conform to the mandrel, forming a flange whichalso helps to secure the low friction tube 2. The low friction tube 2 can be etched to enhance adherence between the low friction tube 2 and the catheter tip 1. A gold ring can be secured at the distal tip of this assembly to provide a radiopaque marker. 
     FIG. 3 shows another embodiment in which the low friction tube 2 is disposed within a catheter tip 1 which is tapered. The angle of the axis of the guide wire lumen in relation to the axis of the tapered tip allows for the guide wire to pass through a relatively straight guide wire lumen.As shown in FIG. 3, the proximal end of the low friction tube 2 can be benttoward the axis of the catheter tip 1 so that plug 5 may be used to secure the low friction tube 2 in place without enlarging the diameter of the proximal portion of the catheter tip 1. 
     The inventors have found that Teflon® fluorinated resins or polytetrafluoroethylene are suitable for the low friction tube, ethyl vinyl acetate is suitable for the plug and tip, and polyethylene is suitable for the tip. 
     While the preferred embodiment of the invention has been described, it is merely illustrative of the principles of the invention. Other embodiments and configurations may be devised without departing from the spirit of theinvention and the scope of the appended claims. Specifically, it is expected that new materials will be developed which may prove suitable forthe uses described in the preferred embodiment.