Tissue characterization using intracardiac impedances with an implantable lead system
First Claim
1. A method, comprising:
- generating a first pulse to apply to a bodily tissue via an electrode, Wherein the first pulse has a first applied waveform that is charge-balanced and voltage-balanced and wherein the first applied waveform has a duration less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue;
applying the first pulse having the first applied waveform to the bodily tissue;
sensing a first waveform response to the first pulse;
measuring a morphology of the first waveform response;
generating a second pulse to apply to the bodily tissue via an electrode, wherein the second pulse has a second applied waveform that is charge-balanced and voltage-balanced and wherein the second applied waveform has a duration that is different from the duration of the first applied waveform and less than the charging time constant of the electrode-electrolyte interface between the electrode and the bodily tissue;
applying the second pulse having the second applied waveform to the bodily tissue;
sensing a second waveform response to the second pulse;
measuring a morphology of the second waveform response;
determining a difference between the morphology of the first waveform response and the morphology of the second waveform response; and
determining a tissue characteristic based on at least the difference between the morphology of the first waveform response and the morphology of the second waveform response.
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Abstract
An implantable system acquires intracardiac impedance with an implantable lead system. In one implementation, the system generates frequency-rich, low energy, multi-phasic waveforms that provide a net-zero charge and a net-zero voltage. When applied to bodily tissues, current pulses or voltage pulses having the multi-phasic waveform provide increased specificity and sensitivity in probing tissue. The effects of the applied pulses are sensed as a corresponding waveform. The waveforms of the applied and sensed pulses can be integrated to obtain corresponding area values that represent the current and voltage across a spectrum of frequencies. These areas can be compared to obtain a reliable impedance value for the tissue. Frequency response, phase delay, and response to modulated pulse width can also be measured to determine a relative capacitance of the tissue, indicative of infarcted tissue, blood to tissue ratio, degree of edema, and other physiological parameters.
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Citations
20 Claims
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1. A method, comprising:
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generating a first pulse to apply to a bodily tissue via an electrode, Wherein the first pulse has a first applied waveform that is charge-balanced and voltage-balanced and wherein the first applied waveform has a duration less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue; applying the first pulse having the first applied waveform to the bodily tissue; sensing a first waveform response to the first pulse; measuring a morphology of the first waveform response; generating a second pulse to apply to the bodily tissue via an electrode, wherein the second pulse has a second applied waveform that is charge-balanced and voltage-balanced and wherein the second applied waveform has a duration that is different from the duration of the first applied waveform and less than the charging time constant of the electrode-electrolyte interface between the electrode and the bodily tissue; applying the second pulse having the second applied waveform to the bodily tissue; sensing a second waveform response to the second pulse; measuring a morphology of the second waveform response; determining a difference between the morphology of the first waveform response and the morphology of the second waveform response; and determining a tissue characteristic based on at least the difference between the morphology of the first waveform response and the morphology of the second waveform response. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method, comprising:
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generating pulses having applied waveforms that alternate between a first duration and a second duration, wherein the applied waveforms are charge-balanced and voltage-balanced and wherein the first and second durations are less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue, and wherein the first duration is different from the second duration; applying the pulses to one or more vectors of a bodily tissue via one or more electrodes; sensing waveform responses to the generated pulses along the one or more vectors of the bodily tissue; measuring a morphology of the waveform responses; determining a difference between the morphology of the sensed waveform responses along the one or more vectors of the bodily tissue; determining a tissue characteristic based on at least the difference between the morphology responses along the one or more vectors; integrating the sensed waveform responses to obtain area values of the sensed waveform responses; determining area values of the applied waveforms; summing the area values for each one or more vectors; calculating an impedance value of each of the tissue paths along the one or more vectors by comparing the area values of the sensed waveform responses with the area of the applied waveforms along each of the tissue paths; and determining a tissue characteristic based on the impedance value of each of the tissue paths. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A method, comprising:
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generating pulses having applied waveforms that alternate between a first duration and a second duration, wherein the applied waveforms are charge-balanced and voltage-balanced and wherein the first and second durations are less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue, and wherein the first duration is different from the second duration; applying the pulses to one or more vectors of a bodily tissue via one or more electrodes; sensing waveform responses to the generated pulses along the one or more vectors of the bodily tissue; measuring a morphology of the waveform responses; determining a difference between the morphology of the sensed waveform responses along the one or more vectors of the bodily tissue, determining a tissue characteristic based on at least the difference between the morphology responses along the one or more vectors, wherein; measuring the morphology of the waveform responses comprises measuring initial sensed voltages V0 or currents I0 and peak voltages Vp or currents p, and determining the difference between the morphology of the waveform responses comprises comparing the ratio of Vp/V0 to the ratio of Vp/V0′
or the ratio of Ip/I0 to Ip/I0′
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20. A method, comprising:
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generating a plurality of pulses to apply to one or more vectors of a bodily tissue via one or more electrodes, wherein the pulses have applied waveforms that are charge-balanced and voltage-balanced and wherein the applied waveforms have durations that are each less than a charging time constant of an electrode-electrolyte interface between the electrode and the bodily tissue and wherein the duration of the applied waveforms is modulated continuously over a spectrum of durations; applying the pulses to the one or more vectors of the bodily tissue using the one or more electrodes; sensing a waveform response to each of the pulses along each of the one or more vectors; measuring a morphology of each of the waveform responses; determining a difference between the morphology of each of the waveform responses along each of the one or more vectors; determining a physiological parameter based on at least the difference between the morphologies of the waveform responses along each of the one or more vectors; integrating the sensed waveform responses to obtain area values of the sensed waveform responses; determining area values of the applied waveforms; summing the area values for each one or more vectors; calculating an impedance value of each of the tissue paths along the one or more vectors by comparing the area values of the sensed waveform responses with the area of the applied waveforms along each of the tissue paths; and determining a tissue characteristic based on the impedance value of each of the tissue paths.
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Specification