Defibrillation pacing circuitry

• US 20050288714A1
• Filed: 06/07/2005
• Published: 12/29/2005
• Est. Priority Date: 11/05/2001
• Status: Active Grant

• Current Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Original Assignee: Cameron Health Inc (Boston Scientific Corporation)
• Inventors: Ostroff, Alan H.
• Granted Patent: US 7,522,957 B2
• Time in Patent Office: Days
• US Class Current: 607/4
• CPC Class Codes: A61N 1/362 Heart stimulators heart defibrillators A61N1/39
• CPC Class Codes: A61N 1/3912 Output circuitry therefor, e.g. switches
• CPC Class Codes: A61N 1/39622 Pacing therapy

Abstract

Electrical circuit componentry is switchable into a defibrillator circuit to deliver a constant pacing current to a patient. The circuitry may include a constant current source inserted in a leg of the defibrillator circuit or a resistor of selected value inserted between a high voltage source and the high side of a defibrillator circuit.

Claims

1. A circuit configured for placement inside an implantable cardiac stimulus device and operating from battery power, the circuit comprising:

an H-bridge circuit including first and second high side switches and first and second low side switches, each of the switches including an input, an output, and a control terminal, the output of the first high side switch electrically coupled to the input of the first low side switch at a node coupled to a first output for the device, the output of the second high side switch electrically coupled to the input of the second low side switch at a node coupled to a second output for the device;

a resistor coupled in parallel to an opt-out switch placed in series with the output of the first low side switch; and

control circuitry coupled to the control terminal of the first low side switch and taking a feedback signal from the output of the first low side switch, the control circuitry configured such that;

when a pulse is applied with the opt-out switch closed to short out the resistor, the first low side switch operates as an “

ON”

switch; and

when a pulse is applied with the opt-out switch open, the first low side switch causes a constant current to run through the patient.

2. The circuit of claim 1, wherein the control circuitry comprises an operational amplifier including:

a noninverting input for receiving a control signal;

an inverting input for receiving the feedback signal; and

an output coupled to the control terminal of the first low side switch.

3. The circuit of claim 2, wherein the control circuitry further comprises a digital-to-analog converter coupled to the noninverting input and generating the control signal.

4. The circuit of claim 1, further comprising:

a power capacitor storing energy for application of cardiac stimulus and having a generally decaying output when current is drained therefrom.

5. An implantable cardiac stimulus device comprising a canister and the circuit of claim 4, the circuit being housed in the canister.

6. An implantable cardiac stimulus device comprising a canister and the circuit of claim 1, the circuit being housed in the canister.

7. A method of providing stimulus to a patient using an H-bridge circuit via implanted electrodes from an implantable medical device having a battery power source, the method comprising:

providing, on a low side of the H-bridge, a resistor in series with a portion of the H-bridge circuit and in parallel with an opt-out switch;

selecting a first mode or a second mode; and

;

if in the first mode, capturing a feedback signal from a high side of the resistor and using the feedback signal to generate a control signal controlling current flow through the resistor;

or

if in the second mode, closing the opt-out switch to short the resistor.

8. The method of claim 7, wherein the resistor and parallel opt-out switch are placed in series with a first low side switch of the H-bridge circuit.

9. The method of claim 8, wherein the first low side switch has an input, an output, and a control terminal, wherein the control signal is applied to the control terminal of the first low side switch.

10. The method of claim 9, wherein the H-bridge further includes a second low side switch and first and second high side switches, each of the switches including an input, an output, and a control terminal, the output of the first high side switch electrically coupled to the input of the first low side switch at a node coupled to a first electrode for the device, the output of the second high side switch electrically coupled to the input of the second low side switch at a node coupled to a second electrode for the device.

11. The method of claim 10, wherein the high side switches are SCR devices, and the low side switches are insulated gate bipolar transistors.

12. The method of claim 7, wherein the H-bridge includes first and second low side switches, wherein the control signal is applied to one of the first or second low side switch.

13. The method of claim 7, wherein the device includes a power capacitor for providing signal to apply cardiac stimulus, wherein the method further includes charging the power capacitor to a predetermined level assured to maintain constant current when operating in a current controlled mode for a predetermined duration of time.

14. An apparatus for delivering electrical cardiac therapy to a patient, the apparatus comprising:

power circuitry for creating a cardiac therapy signal, the power circuitry including a capacitive circuit chargeable to create the cardiac therapy signal;

an H-bridge circuit for delivering the cardiac therapy signal from the power circuitry to a patient; and

current controlling circuitry coupled to a leg of the H-bridge circuit for selectively controlling current passing through said leg;

wherein the apparatus is adapted to have at least a first configuration wherein the current controlling circuitry modifies the cardiac therapy signal to provide a generally constant current signal to a patient, and a second configuration wherein the current controlling circuitry does not substantially modify the cardiac therapy signal to provide a ramped signal to a patient.

15. The apparatus of claim 14, wherein the first configuration is a pacing configuration, and the second configuration is a defibrillation configuration.

16. The apparatus of claim 14, wherein the current controlling circuitry includes:

a transistor element;

a voltage source coupled to the transistor element to provide a control signal controlling a current output of the transistor element;

an impedance element coupled to the transistor element to receive the current output of the transistor element; and

a switch placed in parallel with the impedance element.

17. The apparatus of claim 16, wherein:

the current controlling circuitry further includes an amplifier having a first input, a second input, and an output;

the voltage source is coupled to the transistor element via the amplifier;

the first input of the amplifier is coupled to the voltage source;

the second input of the amplifier is coupled to the current controlling circuitry to provide a feedback signal to compensate for the transistor; and

the output of the amplifier is coupled to the transistor.

18. The apparatus of claim 14, wherein the current controlling circuitry includes:

variable impedance circuitry having an input, an output, and a control node; and

a device for providing a control signal to the control node of the variable impedance device.

19. The apparatus of claim 18, wherein the variable impedance circuitry includes:

a resistor; and

a switch in parallel with the resistor;

wherein the control node is an input to the switch controlling whether the switch is opened or closed.