Patent ID: 8868185

Claim:
A medical device for delivering a cardiac therapy, comprising: a plurality of electrodes to sense a first impedance signal along a thoracic electrode vector extending within a portion of a thoracic cavity and a second impedance signal along an extra-thoracic electrode vector extending outside the thoracic cavity; a therapy delivery module to deliver the therapy via electrodes of the plurality of electrodes: and a processor configured to compare first amplitude measurements corresponding to the first impedance signals and second amplitude measurements corresponding to the second impedance signals, compare first slope measurements corresponding to the first impedance signals and second slope measurements corresponding to the second impedance signals, and control the therapy delivery module to deliver the cardiac therapy in response to the comparing, wherein the processor is further configured to determine amplitude differences between the first amplitude measurements and the second amplitude measurements at a predetermined amplitude difference interval, determine whether the amplitude differences correspond to decreasing impedance along the thoracic electrode vector relative to the extra-thoracic electrode vector, and deliver a first therapy in response to decreasing impedance along the thoracic electrode vector relative to the extra-thoracic electrode vector, and wherein the processor is further configured to determine whether the amplitude differences correspond to decreasing impedance along the extra-thoracic electrode vector relative to the thoracic electrode vector, and deliver a second therapy different from the first therapy in response to decreasing impedance along the extra-thoracic electrode vector relative to the thoracic electrode vector.