Universal shaft for magnetic manipulation of catheters

Abstract

A magnetically-guided catheter includes a tip positioning magnet in the distal end portion thereof configured to interact with externally applied magnetic fields for magnetically-guided movement. The magnet may be geometrically asymmetric, for example, a C-shape in radial cross-section, so as to allow side-loading of an irrigation fluid lumen and other wire(s) or lines during fabrication. The outer shaft includes a plurality of segments, including a generally soft segment at the distal end thereof for magnetically-guided navigation. The fluid lumen, which extends through the outer shaft, and further extends completely through the magnet for coupling to the ablation electrode irrigation fluid inlet, is constructed so that its mechanical properties (i.e., flexibility) substantially matches that of the outer shaft. The combination of the outer shaft, inner fluid lumen and positioning magnet has interoperability with a broad range of ablation tip assemblies.

1 - 15 . (canceled) 
     
     
         16 . A method for operating a magnetically-guided catheter system where the catheter includes a shaft having a distal-most shaft segment with a first flexibility, a proximally adjacent shaft segment with a second flexibility less than the first flexibility, a tip positioning magnet in the shaft at the shaft distal end, a tip ablation electrode, and a ring electrode, said method comprising the steps of:
 (A) determining a first position of the tip ablation electrode during magnetically guided operation;   (B) determining a second position of the ring electrode during magnetically guided operation;   (C) determining a curve based on the determined first and second positions; and   (D) detecting contact between the tip ablation electrode and tissue based on the determined curve and the first flexibility of the distal-most shaft segment.   
     
     
         17 . The method of  claim 16  wherein said step of detecting contact includes the sub-step of:
 determining contact when a distance between at least two points on the curve decreases. 
 
     
     
         18 . A method for operating a magnetically-guided catheter system where the catheter includes a distal-most shaft segment having a first flexibility, first and second tip positioning magnets in the shaft at the shaft distal end having respective, different polarizing axes, said method comprising the step of deflecting the distal end by subjecting the catheter to a consistent magnetic field. 
     
     
         19 . The method of  claim 18  wherein the distal end is pre-curved in the absence of a magnetic field, said deflecting step being operative to straighten the distal end. 
     
     
         20 - 21 . (canceled) 
     
     
         22 . The method of  claim 16  wherein the ring electrode is placed at the location of the positioning magnet, and wherein said step of detecting contact includes the substep of:
 determining contact when a distance between the ring electrode and the tip electrode decreases. 
 
     
     
         23 . The method of  claim 22  further comprising measuring the distance between the ring electrode and the tip electrode using an electro-anatomical mapping system. 
     
     
         24 . The method of  claim 23  further comprising:
 after the catheter has buckled such that the tip electrode moves from a perpendicular position relative to the tissue to being parallel relative to the tissue, delivering energy to the tissue through the tip electrode. 
 
     
     
         25 . The method of  claim 24  further comprising:
 moving the catheter tip electrode along the tissue surface in a sweeping motion so as to create a drag lesion. 
 
     
     
         26 . The method of  claim 24  further comprising:
 configuring the first flexibility of the distal-most shaft segment so that the distal-most shaft segment will buckle before a force corresponding to a potentially unsafe condition is exerted on the tissue by the catheter. 
 
     
     
         27 . The method of  claim 22  wherein the distance decreases relative to that of the catheter in a non-contact condition. 
     
     
         28 . The method of  claim 16  further comprising:
 providing feedback of at least one of (i) said detection of contact and (ii) said decrease in distance, to a navigation system that is guiding movement of the catheter to the tissue surface. 
 
     
     
         29 . The method of  claim 28  wherein the navigation system performs the magnetically guided operation. 
     
     
         30 . The method of  claim 16  wherein the tissue comprises heart tissue of a heart organ, further comprising:
 before determining contact, advancing the catheter towards the tissue to until contact with the tissue and then further advancing the catheter towards the tissue until the distal-most shaft segment buckles, upon which a catheter location is defined; and 
 maintaining the catheter location as the heart beats such that the distal-most shaft segment will flex and bend in response to a movement of a heart wall as the heart beats. 
 
     
     
         31 . The method of  claim 18  wherein the second tip positioning magnet is movable relative to the first tip positioning magnet, wherein said subjecting the catheter to the consistent magnetic field causes the first and second tip positioning magnets to move relative to each other so that the different polarizing axes align to thereby deflect the distal-most shaft segment. 
     
     
         32 . A method for operating a magnetically-guided catheter system where the catheter includes a shaft having a distal-most shaft segment with a first flexibility, a proximally adjacent shaft segment with a second flexibility less than the first flexibility, a tip positioning magnet in the shaft at the shaft distal end, a distal tip ablation electrode, and a ring electrode placed at the location of the positioning magnet, said method comprising the steps of:
 (A) determining a first position of the tip ablation electrode during magnetically guided operation;   (B) determining a second position of the ring electrode during magnetically guided operation;   (C) measuring a distance between the first and second positions; and   (D) detecting contact between the tip ablation electrode and the tissue when the measured distances decreases.