Sheath visualization method by means of impedance localization and magnetic information

Abstract

Catheterization is carried out by inserting a sheath into a human patient and moving a catheter having an electrode through the sheath lumen. A variation between a first threshold value and a second threshold value in electrical current through the electrode is identified. Responsively to the variation, it is reported that a portion of the catheter has transitioned between an in-sheath condition and an out-of-sheath condition. The sheath is defined and identified by the historical data of the readings of the magnetic sensor during its movements.

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         11 . An apparatus, comprising:
 a plurality of body surface electrodes, which are adapted to be fixed to a surface of a body at respective locations;   a controller having current-measuring circuitry, which is adapted to be coupled to a catheter having a distal portion and at least one catheter electrode disposed on the distal portion and to body surface electrodes, the controller being operative for passing electrical current through the body between the at least one catheter electrode and the body surface electrodes, and for determining position coordinates of the catheter by measuring respective characteristics of the electrical current passing through the body surface electrodes;   a memory;   a processor, having access to the memory and cooperative with the controller to perform the steps of:   
       while the catheter is being moved in a human patient through a sheath having a lumen and a distal end, measuring the electrical current through the at least one catheter electrode with the current-measuring circuitry; 
       identifying a variation in the electrical current between a first threshold value and a second threshold value; and 
       responsively to the variation, reporting that a portion of the catheter has transitioned between an in-sheath condition and an out-of-sheath condition. 
     
     
         12 . The apparatus according to  claim 11 , wherein the current-measuring circuitry is a component of an impedance measuring system and wherein measuring the electrical current comprises measuring an impedance of a heart of the human patient. 
     
     
         13 . The apparatus according to  claim 11 , wherein the sheath has an outer wall, the outer wall having a perforation formed therethrough, wherein identifying a variation is performed while the catheter electrode is passing by the perforation. 
     
     
         14 . The apparatus according to  claim 13 , wherein the at least one catheter electrode comprises a plurality of catheter electrodes:
 while the catheter is being moved, concurrently measuring the electrical current in the plurality of catheter electrodes, respectively, wherein identifying a variation comprises recognizing a transient decrease in current flow in one of the catheter electrodes that does not fall below a lower threshold; and   concluding that a position of the one catheter electrode opposes the perforation during the transient decrease.   
     
     
         15 . The apparatus according to  claim 14 , wherein the processor and the controller are operative responsively to identifying a variation determining a location of the distal end of the catheter relative to the perforation. 
     
     
         16 . The apparatus according to  claim 13 , wherein the portion of the catheter is the distal end of the catheter. 
     
     
         17 . The apparatus according to  claim 13 , wherein the portion of the catheter is another electrode. 
     
     
         18 . The apparatus according to  claim 11  wherein the memory contains a database of sheath-catheter combinations. 
     
     
         19 . The apparatus according to  claim 11 , further comprising a position processing system operative for reading signals from a magnetic sensor disposed in the catheter at a predetermined distance from the distal end of the catheter and reporting a location of the distal end of the catheter from the reading.