Electrode displacement determination

1. A method comprising:

generating a baseline signal measurement between multiple intracardiac current injecting electrodes placed in stable internal locations relative to a patient's body and one or more measuring electrodes positioned at one or more stable external locations relative to the patient's body by:

causing current to flow among the multiple intracardiac current injecting electrodes placed in the stable internal locations relative to the patient's body to generate a field in an organ;

in response to the current flow, measuring a signal at the one or more measuring electrodes positioned at the one or more stable external locations relative to the patient's body; and

subsequent to generating the baseline signal measurement, determining whether a location of the multiple intracardiac current injecting electrodes relative to the patient's body has changed by:

causing current to flow among the multiple intracardiac current injecting electrodes;

in response to the current flow, measuring a signal at the one or more measuring electrodes positioned in stable external locations;

comparing the measured signal to the baseline signal to generate a comparison result; and

determining whether the location of the multiple intracardiac current injecting electrodes has changed based on the comparison result; and

subsequent to generating the baseline signal measurement, in response to the current flow generated by the multiple intracardiac current injecting electrodes, measuring a signal at each of multiple measuring electrodes being different from the one or more measuring electrodes positioned in the stable external locations on a catheter inside the patient's body; and

determining a relative location of the catheter based on the signals measured by the multiple measuring electrodes on the catheter.

2. The method of claim 1 , further comprising providing an audio or visual indicator indicative of unintentional displacement of the intracardiac current injecting electrodes upon determining that the location of the multiple intracardiac current injecting electrodes has changed relative to the one or more measuring electrodes and relative to the patient's body.

3. The method of claim 1 , wherein the one or more measuring electrodes positioned in the stable external locations comprises one or more ECG leads.

4. The method of claim 1 , wherein the one or more measuring electrodes positioned in the stable external locations comprises one or more body surface electrodes.

5. The method of claim 1 , further comprising, subsequent to generating the baseline signal measurement, in response to the current flow, measuring a signal at each of the multiple measuring electrodes on a catheter for each of multiple locations of the catheter; and

determining expected signals for the measuring electrodes on the catheter at additional locations within the organ based on the measured signals.

6. The method of claim 1 , wherein the one or more measuring electrodes includes one or more stable intracardiac electrodes.

7. The method of claim 1 , wherein the organ is a patient's heart.

8. The method of claim 1 , wherein generating the baseline signal measurement comprises compensating for respiration and heartbeat of the patient.

9. The method of claim 1 , wherein comparing the measured field to the baseline signal comprises calculating a residual norm between the baseline signal measurement and the measured signal.

10. The method of claim 9 , wherein comparing the measured field to the baseline signal measurement further comprises comparing the residual norm to a threshold value.

11. The method of claim 1 , further comprising providing information to enable a clinician to guide the current injecting electrodes to a location where the baseline signal measurement was generated.

12. The method of claim 1 , wherein comparing the measured field to the baseline signal measurement comprises calculating a displacement trajectory.

13. The method of claim 12 , wherein the displacement trajectory provides a three-dimensional model providing an indication of a current location of the intracardiac current injecting electrodes and an indication of the location where the baseline signal measurement was generated.

14. A method comprising:

positioning multiple current injecting electrodes in stable internal locations relative to the patient's body;

positioning one or more measuring electrodes in stable external locations relative to the patient's body;

positioning a catheter that includes one or more measuring electrodes inside the patient's body, the one or more measuring electrodes on the catheter being different from the one or more measuring electrodes positioned in the stable external locations;

generating a baseline signal measurement between the multiple current injecting electrodes placed in the stable internal locations relative to the patient's body and the one or more measuring electrodes positioned at the one or more stable external locations relative to the patient's body by:

causing current to flow among the multiple current injecting electrodes placed in the stable internal locations relative to the patient's body to generate a field in an organ;

in response to the current flow, measuring a signal at the one or more measuring electrodes positioned at the one or more stable external locations relative to the patient's body; and

subsequent to generating the baseline signal measurement, determining whether a location of the multiple current injecting electrodes relative to the patient's body has changed by: causing current to flow among the multiple current injecting electrodes;

in response to the current flow, measuring a signal at the one or more measuring electrodes positioned in stable external locations;

comparing the measured signal to the baseline signal to generate a comparison result; and

determining whether the location of the multiple current injecting electrodes has changed based on the comparison result;

and subsequent to generating the baseline signal measurement, in response to the current flow generated by the multiple current injecting electrodes, measuring a signal at each of multiple measuring electrodes on the catheter; and

determining a relative location of the catheter based on the signals measured by the multiple measuring electrodes on the catheter.

15. A method comprising:

positioning multiple intracardiac current injecting electrodes inside a patient's body and in stable internal locations relative to the patient's body;

positioning one or more measuring electrodes in stable external locations relative to the patient's body;

positioning a catheter that includes one or more measuring electrodes inside the patient's body, the one or more measuring electrodes on the catheter being different from the one or more measuring electrodes positioned in the stable external locations;

generating a baseline signal measurement between the multiple intracardiac current injecting electrodes placed in the stable internal locations relative to the patient's body and the one or more measuring electrodes positioned at the stable external locations relative to the patient's body by:

causing current to flow among the multiple intracardiac current injecting electrodes placed in the stable internal locations relative to the patient's body to generate a field in an organ;

in response to the current flow, measuring a signal at the one or more measuring electrodes positioned at the stable external locations relative to the patient's body; and

subsequent to generating the baseline signal measurement, determining whether a location of the multiple intracardiac current injecting electrodes relative to the patient's body has changed by:

causing current to flow among the multiple intracardiac current injecting electrodes;

in response to the current flow, measuring a signal at the one or more measuring electrodes;

comparing the measured signal to the baseline signal to generate a comparison result; and

determining whether the location of the multiple intracardiac current injecting electrodes has changed based on the comparison result; and

subsequent to generating the baseline signal measurement, in response to the current flow generated by the multiple intracardiac current injecting electrodes, measuring a signal at each of multiple measuring electrodes on the catheter; and

determining a relative location of the catheter based on the signals measured by the multiple measuring electrodes on the catheter.