Guidewire with a variable stiffness distal portion

Abstract

A guidewire having a core section formed of a NiTi alloy which is in an austenite phase when being manufactured but which is converted to the martensite phase at operating (body) temperature (37° C.) and can be transformed to an austenite phase by heating to a temperature above body temperature but below 50° C. When in the austenite phase, the core section is at a high strength level which ensures the tracking of a catheter over the guidewire within a patient's body lumen. In one preferred embodiment the core section is heated by electrical resistance or inductance

What is claimed is:  
     
         1 . An intravascular guidewire comprising: 
 a) an elongated proximal core section which has proximal and distal ends;    b) an intermediate core section which has proximal and distal ends, which is formed of a shape memory alloy with an A f  above 37° but not more than about 50° C. and which is secured by its proximal end to the distal end of the proximal core section;    c) means to heat the intermediate core section; and    d) a distal core section which has proximal and distal ends and which is secured by its proximal end to the distal end of the intermediate core section; and    e) a flexible body disposed about and secured to the distal core section.    
     
     
         2 . The intravascular guidewire of    claim 1    including a first electrical conductor in electrical contact with a proximal extremity of the intermediate core section and a second electrical conductor in electrical contact with a distal extremity of the intermediate core section to facilitate heating the intermediate core section by induction.  
     
     
         3 . The intravascular guidewire of    claim 2    wherein the guidewire has a first electrode on a proximal portion of the proximal core section which is electrically connected to the first electrical conductor and a second electrode on the proximal portion of the proximal core section spaced distal to the first electrode which is electrically connected to the second electrical conductor.  
     
     
         4 . The guidewire of    claim 3    wherein the first and second electrical conductors are layers of electrical conducting material.  
     
     
         5 . The guidewire of    claim 4    wherein a first layer of insulating material is disposed on the exterior of the proximal core section and the layer of conducting material of the first electrical conductor is disposed on the layer of insulating material.  
     
     
         6 . The guidewire of    claim 5    wherein a second layer of insulating material is disposed on the electrical conducting material of the first electrical conductor and the layer of conducting material of the second electrical conductor is disposed on the second layer of insulating material.  
     
     
         7 . The guidewire of    claim 6    wherein a third layer of insulating material is disposed on the electrical conducting material of the second electrical conductor.  
     
     
         8 . The guidewire of    claim 1    wherein the insulating and electrical conducting layers encircle a length of the proximal core section.  
     
     
         9 . The guidewire of    claim 2    including means to electrically connect the electrodes on the proximal extremity of the guidewire to a source of electrical energy to facilitate heating the intermediate core section by induction.  
     
     
         10 . The guidewire of    claim 2    wherein the means to electrically connect the proximal end of the guidewire to a source of electrical energy has electrical contact means biased against the electrodes on the proximal end of the proximal core section.  
     
     
         11 . The guidewire of    claim 10    wherein the means to electrically connect the proximal end of the guidewire to a source of electrical energy has means to secure the proximal extremity of the proximal core section to prevent the disengagement thereof.  
     
     
         12 . The guidewire of    claim 1    wherein the intermediate core section is formed from an alloy of nickel and titanium and which contains from about 10 to about 75% martensite phase at body temperature.  
     
     
         13 . The guidewire of    claim 1    wherein the intermediate core section is formed from an alloy of nickel and titanium and which contains from about 25 to about 50% martensite phase.  
     
     
         14 . The guidewire of    claim 1    wherein the distal core section is formed of a superelastic NiTi alloy with an A f  greater than body temperature.  
     
     
         15 . The guidewire of    claim 1    wherein a cylindrical connecting member interconnects the distal core section with the intermediate core section.  
     
     
         16 . The guidewire of    claim 15    wherein the cylindrical connecting member is formed of a superelastic NiTi alloy with an A f  greater than body temperature.  
     
     
         17 . The guidewire of    claim 1    wherein a cylindrical connecting member interconnects the proximal core section with the intermediate core section.  
     
     
         18 . The guidewire of    claim 17    wherein the cylindrical connecting member is formed of a superelastic NiTi alloy with an A f  greater than body temperature.  
     
     
         19 . The guidewire of    claim 1    wherein the proximal core section has a solid proximal portion and a hollow distal portion with an inner lumen extending therein.  
     
     
         20 . The guidewire of    claim 19    wherein the first electrical conductor is an individually insulated electrical wire which extends through the inner lumen of the hollow distal portion of the proximal core section and is electrically connected to a proximal extremity of the intermediate core section.  
     
     
         21 . The guidewire of    claim 19    wherein the second electrical conductor is an individually insulated electrical wire which extends through the inner lumen of the distal portion of the proximal core section and is electrically connected to a distal extremity of the intermediate core section.  
     
     
         22 . The guidewire of    claim 1    wherein the intermediate core section is formed from an alloy consisting essentially of about 30 to about 52 atomic % titanium and the balance nickel and up to 10 atomic % of one or more additional alloying elements selected from the group consisting of up to 3 atomic % each of iron, cobalt, platinum, palladium and chromium and up to about 10 atomic % copper and vanadium.  
     
     
         23 . A method of performing an intraluminal procedure within a patient's body lumen comprising: 
 a) providing a guidewire which has an intermediate core section formed of a NiTi alloy which has a substantial level of martensite phase at body temperature and which has a final austenite transformation temperature above body temperature but below 50° C.;    b) positioning the guidewire at a desirable location within the patient's body lumen;    c) heating the intermediate core section to a temperature above body temperature to convert at least part of the martensite phase of the intermediate core section to the austenite phase; and    d) advancing a catheter over the intermediate core section of the guidewire while the intermediate core section is predominantly in the austenite phase to a desired location within the patient's body lumen.    
     
     
         24 . The method of    claim 23    wherein at least 50% of the martensite phase in the intermediate core section is converted to the austenite phase when the intermediate core section is heated within the body lumen.  
     
     
         25 . A method of making an intraluminal guidewire comprising: 
 a) providing a cold worked, heat treated elongated member formed of a nickel-titanium alloy having a finish austenite temperature of less than body temperature;    b) further heat treating the elongated member at a temperature of about 375° to about 450° C. for at least 15 minutes.    c) mechanically working the elongated member into an intermediate core member of a final desired size and shape;    d) securing a proximal extremity of the intermediate core member to a distal extremity of a high strength proximal core member;    e) securing a distal extremity of the intermediate core member to a proximal extremity of a distal core member; and    f) securing a helical coil to at least the distal core member.    
     
     
         26 . The method of    claim 25    wherein the elongated member is heated at a temperature between about 375° to about 450° C. for a period of about 0.5 to about 12 hours.