Implantable cardiac stimulus devices and methods with input recharge circuitry

• US 7,623,916 B2
• Filed: 12/20/2006
• Issued: 11/24/2009
• Est. Priority Date: 12/20/2006
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Julian, Marcus
• Primary Examiner(s): Manuel; George
• Assistant Examiner(s): Wieland; Robert N
• Application Number:
  US11/613,850
• Publication Number:
  US 20080154350A1
• Time in Patent Office: 1,070 Days
• Field of Search: 607 4- 28, 600508-519, 324/678
• US Class Current: 607/11
• CPC Class Codes: A61B 5/304 Switching circuits
• CPC Class Codes: A61B 5/308 for electrocardiography [ECG]
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: A61N 1/3918 characterised by shock pathway, e.g. by electrode configuration
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

An illustrative embodiment includes an implantable cardiac stimulus device comprising input circuitry configured to reduce the time required to return to small signal operation after a disturbance of small signal operation. In another illustrative embodiment, the present invention includes methods for operating an implantable cardiac stimulus device to reduce the time required to return to small signal operation after a disturbance of small signal operation. In yet additional embodiments, the initiation of small signal operation after a change in sensing vector and/or after delivery of a stimulus to the patient is improved by the inclusion of input circuitry and/or the use of methods adapted to reduce the time needed to reach small signal operation.

Claims

1. An implantable cardiac stimulus device comprising:

input circuitry for receiving a signal;

electrodes coupled to the input circuitry to provide a cardiac signal for analysis; and

a recharge circuit coupled to the input circuitry;

wherein an input offset voltage occurs at the input circuitry; and

wherein the implantable cardiac stimulus device is configured to;

identify whether a change in the input offset voltage is likely; and

if so, operate the recharge circuit to accommodate changes to the input offset voltage;

wherein the input circuitry comprises coupling capacitors, wherein the recharge circuit is coupled to the coupling capacitors;

the input circuitry further comprises an ECG Amplifier for amplifying signal from the electrodes;

a first of the coupling capacitors is disposed in series with a first input of the ECG Amplifier and a second of the coupling capacitors is disposed in series with a second input of the ECG Amplifier, both relative to inputs from the electrodes;

the recharge circuit is selectively coupled to a first node defined between the first coupling capacitor and the first ECG Amplifier input;

the recharge circuit is selectively coupled to a second node defined between the second coupling capacitor and the second ECG Amplifier input; and

when the recharge circuit is operated, the recharge circuit is coupled to the first and second nodes via a relatively low impedance or no impedance.

2. The implantable cardiac stimulus device of claim 1, wherein the implantable cardiac stimulus device is configured to identify whether a change in the input offset voltage is likely by determining whether a stimulus has been provided to a patient.

3. The implantable cardiac stimulus device of claim 1, wherein:

the electrodes define multiple sensing vectors for sensing cardiac activity of a patient;

the input circuitry is configured with one or more switches for selecting a sensing vector; and

the implantable cardiac stimulus device is configured to identify whether a change in the input offset voltage is likely by determining whether a change in the selected sensing vector has occurred.

4. The implantable cardiac stimulus device of claim 1, wherein the input circuitry comprises a frequency selective filter having an impedance and the recharge circuit comprises a reference voltage source output having relatively low impedance when compared to the impedance of the frequency selective filter.

5. The implantable cardiac stimulus device of claim 1 wherein, when the recharge circuit is selectively coupled to the first node and the second node, the inputs to the ECG Amplifier are shorted together via the recharge circuit.

6. An implantable cardiac stimulus device comprising:

input circuitry for receiving a signal;

electrodes coupled to the input circuitry to provide a cardiac signal for analysis; and

a recharge circuit coupled to the input circuitry for accommodating post-shock after potential;

wherein the implantable cardiac stimulus device is configured to;

observe cardiac function of a patient,

determine whether stimulus is appropriate,

deliver stimulus when appropriate, and

after delivering stimulus, operate the recharge circuit;

the input circuitry comprises coupling capacitors and the recharge circuit is coupled to the coupling capacitors;

the input circuitry further comprises an ECG Amplifier for amplifying signal from the electrodes;

a first of the coupling capacitors is disposed in series with a first input of the ECG Amplifier and a second of the coupling capacitors is disposed in series with a second input of the ECG Amplifier;

the recharge circuit is selectively coupled to a first node defined between the first coupling capacitor and the first ECG Amplifier input;

the recharge circuit is selectively coupled to a second node defined between the second coupling capacitor and the second ECG Amplifier input; and

the implantable cardiac stimulus device is further configured such that, when the recharge circuit is operated, the recharge circuit is coupled to the first and second nodes via a relatively low impedance or no impedance.

7. The implantable cardiac stimulus device of claim 6, wherein the input circuitry comprises a frequency selective filter having an impedance and the recharge circuit comprises a reference voltage source having relatively low impedance when compared to the impedance of the frequency selective filter.

8. The implantable cardiac stimulus device of claim 6 wherein, when the recharge circuit is selectively coupled to the first node and the second node, the inputs to the ECG Amplifier are shorted together via the recharge circuit.

9. A method of operating a cardiac stimulus device implanted in a patient:

the device comprising at least first and second electrodes configured to electrically sense cardiac activity by the patient, the first and second electrodes being selectively coupled to an ECG Amplifier for amplifying signal from the first and second electrodes via input circuitry including coupling capacitors;

the method comprising;

providing a recharge circuit coupled to the coupling capacitors;

delivering a stimulus to the patient;

during the stimulus delivery, isolating the ECG Amplifier from the first and second electrodes; and

following stimulus delivery, operating the recharge circuit to accommodate changes in DC status of the system following stimulus delivery,

wherein;

the ECG Amplifier includes first and second inputs and the coupling capacitors include a first coupling capacitor coupled to the first ECG Amplifier input and a second capacitor coupled to the second ECG Amplifier input;

the first and second coupling capacitors have an electrode side and an ECG Amplifier side, the ECG Amplifier side of each of the coupling capacitors being coupled to the ECG Amplifier, and

the recharge circuit comprises a voltage source selectively coupled to the ECG Amplifier sides of the first and second coupling capacitors such that, when the recharge circuit is operated to accommodate changes in DC status of the system, the first and second inputs to the ECG Amplifier are shorted together.

10. The method of claim 9, further comprising analyzing cardiac signals and providing a blanking period comprising:

a first time period corresponding to the stimulus delivery;

a second time period immediately after stimulus delivery; and

a third time period following the second time period, the third time period corresponding to operation of the recharge circuit.

11. A method of operating an implanted cardiac stimulus device, the implanted cardiac stimulus device including input circuitry for receiving a signal and electrodes coupled to the input circuitry to provide a cardiac signal for analysis wherein an input offset voltage occurs at the input circuitry, the method comprising:

identifying whether a change in the input offset voltage is likely, and if so,

operating a recharge circuit to accommodate a change in the input offset voltage;

wherein the input circuitry includes an ECG Amplifier having first and second inputs and first and second coupling capacitors coupled to the first and second inputs, Respectively, of the ECG amplifier; and

wherein the step of the operating the recharge circuit includes selectively coupling the recharge circuit to the first and second inputs of the ECG Amplifier, shorting the first and second inputs together and charging/discharging the first and second coupling capacitors.

12. The method of claim 11, wherein the step of identifying whether a change in the input offset voltage is likely includes determining whether a stimulus has been provided to a patient.

13. The method of claim 11, wherein:

the electrodes define multiple sensing vectors for sensing cardiac activity of a patient;

the input circuitry is configured with one or more switches for selecting a sensing vector; and

the step of identifying whether a change in the input offset voltage is likely includes determining whether a change in the selected sensing vector has occurred.