SYSTEM AND METHOD FOR MEASUREMENT OF AN IMPEDANCE USING A CATHETER SUCH AS AN ABLATION CATHETER

• US 20090171345A1
• Filed: 12/28/2007
• Published: 07/02/2009
• Est. Priority Date: 12/28/2007
• Status: Active Grant

• Current Assignee: St. Jude Medical, Atrial Fibrillation Division, Inc. (Abbott Laboratories)
• Original Assignee: St. Jude Medical, Atrial Fibrillation Division, Inc. (Abbott Laboratories)
• Inventors: Kastner, Glen H., Deno, D. Curtis, Miller, Stephan P.
• Granted Patent: US 10,660,690 B2
• Time in Patent Office: Days
• US Class Current: 606/35
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1492 having a flexible, catheter-like structure, e.g. for heart ablation A61B18/1477 takes precedence
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/165 Multiple indifferent electrodes

Abstract

A catheter and patch electrode system is provided for use with an apparatus, such as an ablation generator, having a 4-wire interface for improved impedance measurement. The 4-wire interface includes a pair of source connectors across which an excitation signal is produced and a pair of sense connector wires across which the impedance is measured. The RF ablation generator may also produce an ablation signal across a source wire and an indifferent return patch electrode. The system further includes a cable that connects the generator to a catheter. The catheter includes a shaft having a proximal end and a distal end, with an ablation tip electrode disposed at the distal end. A source lead is electrically coupled to the tip electrode and extends through the shaft to the proximal end where it is terminated. An optional sense lead is also electrically coupled to the tip electrode and extends through the shaft to the proximal end. The system further includes a source return (e.g., skin patch) and a sense return (e.g., skin patch), either or none of which may be combined with the indifferent return, and if used may be placed on opposite sides of the patient for improved performance. The impedance sensor circuit produces an excitation signal across the source connectors, which is then carried to the catheter by the cable, then to the tip electrode, travels through the complex load (tissue volume), and returns to the generator via a patch electrode. The impedance is measured by observing the voltage drop across the sense connectors caused by the excitation signal.

Claims

1. A catheter, comprising:

an elongated shaft having a proximal end and a distal end;

an electrode disposed at said distal end;

a source lead electrically connected to said electrode and extending through said shaft to said proximal end; and

a sense lead, different from said source lead, electrically connected to said electrode and extending through said shaft to said proximal end.

2. The catheter of claim 1 wherein said shaft includes a first lumen and a second lumen isolated from said first lumen, said source lead being disposed in said first lumen and said sense lead being disposed in said second lumen.

3. The catheter of claim 1 wherein said shaft includes a first lumen in which said source and sense leads are disposed.

4. The catheter of claim 1 wherein said source and sense leads are terminated separately at said proximal end and configured for connection to at least one of a cable, an ablation generator and a complex impedance sensor configured to determine a complex impedance.

5. The catheter of claim 1 wherein said electrode is an ablation electrode, said source lead being configured for connection to an RF ablation generator to supply RF power to said electrode and to supply an excitation signal for measuring complex impedance.

6. The catheter of claim 1 wherein said sense lead is configured for connection to a complex impedance sensor.

7. The catheter of claim 1 wherein said electrode is an ablation electrode, said source lead being configured for connection to an RF ablation generator to supply RF power to said electrode and for measuring complex impedance.

8. A catheter system for use with an apparatus having a four-wire interface including positive and negative source connectors across which is produced an excitation signal and positive and negative sense connectors, said system comprising:

a catheter comprising an elongated shaft having a proximal end and a distal end, a tip electrode disposed at said distal end, a source lead electrically connected to said tip electrode and extending through said shaft to said proximal end and configured for connection to said positive source connector to receive said excitation signal, said electrode being further configured for connection to said positive sense connector;

a source return configured for connection to said negative source connector;

a sense return configured for connection to said negative sense connector;

wherein said apparatus is configured to determine an impedance between said sense connectors.

9. The system of claim 8 wherein said catheter further includes a sense lead, different from said source lead, electrically connected to said electrode and extending through said shaft to said proximal end, said source and sense leads being terminated separately at said proximal end;

and said system further including a cable having a first end configured for connection to said apparatus and a second end configured for connection to said catheter, said cable having a source conductor and a sense conductor, said source and sense conductors being terminated separately at said first end for connection to said positive source and sense connectors, respectively;

said source and sense conductors being terminated separately at said second end for respective connection to said source and sense leads of said catheter.

10. The system of claim 9 further including a patch configured for affixation to a patient and including said source and sense returns.

11. The system of claim 9 further including a first patch configured for affixation to a patient and including said source return and a second patch separate from said first patch configured for affixation to the patient and including said sense return.

12. The system of claim 11 wherein said first and second patches are separated by a predetermined distance.

13. The system of claim 8 further including a cable having a first end configured for connection to said apparatus and a second end configured for connection to said catheter, said cable having a source conductor and a sense conductor, said source and sense conductors being terminated separately at said first end for connection to said positive source and sense connectors, respectively;

said source and sense conductors being electrically joined at said second end for connection to said source lead of said catheter.

14. The system of claim 13 further including a patch configured for affixation to a patient and including said source and sense returns.

15. The system of claim 13 further including a first patch configured for affixation to a patient and including said source return and a second patch separate from said first patch configured for affixation to the patient and including said sense return.

16. The system of claim 15 wherein said first and second patches are separated by a predetermined distance.

17. The system of claim 8 wherein said catheter includes a ring electrode disposed proximate to but offset from said tip electrode, and wherein at least one of said source and sense returns comprises said ring electrode.

18. The system of claim 8 further comprising an indifferent/dispersive return including electrically-conductive material configured for contact with and affixation to a patient, said indifferent return being further configured to be used in cooperation with said tip electrode and said apparatus in conducting one of a diagnostic and therapeutic function, wherein at least one of said sense and source returns comprising said indifferent/dispersive return.

19. The system of claim 18 wherein said indifferent return includes both of said sense and source returns.

20. The system of claim 8 wherein said apparatus comprises an ablation generator, said tip electrode comprising an ablation electrode, said ablation generator including an RF power source configured to produce an RF ablation signal across said source connectors for delivery by said ablation electrode.

21. The system of claim 20 wherein said excitation signal has a first frequency, said RF ablation signal has a second frequency, said first and second frequencies being distinguishable.

22. The system of claim 8 wherein said excitation signal has a first frequency between about 2 kHz and 200 kHz.

23. The system of claim 22 where said first frequency is about 20 kHz.

24. The system of claim 21 wherein said ablation signal has a second frequency of about 450 kHz or higher.

25. The system of claim 8 wherein said tip electrode defines a first terminal, said source return defines a second terminal and said sense return defines a third terminal, said system having a four-wire, three-terminal configuration for measuring impedance.

26. An RF ablation generator having a four-wire impedance measurement interface, comprising:

an RF power source configured to produce an RF ablation signal across positive and negative source connectors;

an excitation signal source configured to produce an excitation signal across said source connectors; and

a complex impedance sensor coupled said positive and negative source connectors and to positive and negative sense connectors different from said source connectors and configured to determine a complex impedance across said sense connectors when said excitation signal is generated.