Fast recovery sensor amplifier circuit for implantable medical device
First Claim
1. An implantable medical device, adapted to selectively generate therapeutic shocks to tissue of a heart through electrodes implanted in the heart, the therapeutic shocks causing a residual electrical charge on the electrodes and polarization of the tissue, comprising:
- a pulse generator that generates a short duration pulse;
an output circuit coupled to the pulse generator and arranged to apply the short duration pulse to the electrodes subsequent to a therapeutic shock to cause the charge to dissipate rapidly, the short duration pulse having a low amplitude to avoid stimulating the tissue of the heart; and
a switching circuit arranged to selectively short the electrodes together.
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Accused Products
Abstract
Therapeutic shocks generated by implantable cardiac stimulators, such as implantable cardioverter-defibrillator devices, may result in residual charges being deposited on the defibrillation electrodes and/or polarization of the tissues surrounding the defibrillation electrodes. These parasitic charges and polarization may mask a possible ventricular fibrillation of the heart following the application of the therapeutic shocks because such a ventricular fibrillation is characterized by intrinsic signals of very small amplitudes. A small duration pulse is applied to the electrodes right after a therapeutic shock. In addition, or alternatively, the electrodes can also be shorted together to dissipate the parasitic charges and the polarization of the tissue. As a result, a ventricular fibrillation can be detected earlier than in previous cardiac stimulators.
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Citations
8 Claims
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1. An implantable medical device, adapted to selectively generate therapeutic shocks to tissue of a heart through electrodes implanted in the heart, the therapeutic shocks causing a residual electrical charge on the electrodes and polarization of the tissue, comprising:
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a pulse generator that generates a short duration pulse;
an output circuit coupled to the pulse generator and arranged to apply the short duration pulse to the electrodes subsequent to a therapeutic shock to cause the charge to dissipate rapidly, the short duration pulse having a low amplitude to avoid stimulating the tissue of the heart; and
a switching circuit arranged to selectively short the electrodes together. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
the electrodes comprise an RV coil electrode, a tip electrode, and a case electrode; and
the switching circuit comprises a timing circuit that defines a shorting cycle following the second cycle, at least one of the RV coil electrode or the tip electrode being selective shorted to the case electrode during the shorting cycle.
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6. The implantable medical device of claim 1, wherein:
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the pulse generator generates a multiphasic therapeutic shock having a first polarity pulse followed by a second polarity pulse; and
the pulse generator further generates the short duration pulse with a polarity opposite the second polarity pulse.
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7. The implantable medical device of claim 1, wherein the electrodes comprise an RV coil electrode, a tip electrode, and a case electrode, further comprising:
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an amplifier that senses a voltage generated between the RV coil electrode and the tip electrode; and
a control circuit that produces a neutral reference for the amplifier based on the RV coil electrode and the case electrode.
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8. The implantable medical device of claim 7, wherein:
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the amplifier comprises a first resistor coupled to the RV coil and a second resistor coupled to the case electrode, the first and second resistors being variable; and
the control circuit further configured to vary the first and second resistors so as to neutralize the offset voltage produced by the RV coil electrode and the case electrode.
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Specification