Patent ID: 8694074

Claim:
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.