Methods and implantable devices for inducing fibrillation by alternating constant current

• US 20060241698A1
• Filed: 04/26/2005
• Published: 10/26/2006
• Est. Priority Date: 04/26/2005
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Ostroff, Alan H.
• Granted Patent: US 7,555,338 B2
• Time in Patent Office: Days
• US Class Current: 607/2
• CPC Class Codes: A61N 1/385 Devices for inducing an abnormal cardiac function, e.g. fibrillation
• CPC Class Codes: A61N 1/3906 characterised by the form of the shockwave
• CPC Class Codes: A61N 1/3912 Output circuitry therefor, e.g. switches
• CPC Class Codes: A61N 1/3937 Monitoring output parameters

Abstract

The present invention is directed toward methods for inducing fibrillation in a patient using a controlled current AC signal applied via an implanted ICD. In some embodiments, the AC signal is applied as a series of alternating constant current pulses. Some embodiments make use of a specialized H-bridge circuit for applying the AC signal. A low-side current controlling portion of an ICD'"'"'s circuitry may make up part of the specialized H-bridge circuit. Further embodiments include devices embodying these methods.

Claims

1. A method of inducing fibrillation in a patient, the method comprising applying an alternating current to the patient from an ICD, wherein the alternating current comprises a series of pulses each having a substantially constant current.

2. The method of claim 1, wherein the alternating current has a period in the range of 8-100 milliseconds.

3. The method of claim 2, wherein the alternating current has a period in the range of 16-40 milliseconds.

4. The method of claim 1, wherein:

the ICD comprises circuitry including an H-Bridge having a high side and a low side, the high side having a first switch coupled to a first node and a second switch coupled to a second node, the first and second nodes being respectively coupled to first and second electrodes configured for delivering a shock to the patient, the low side comprising a third switch coupled to the first node and a fourth switch coupled to the second node, the third and fourth switches making up part of a current controlling portion of the ICD circuitry; and

the step of applying an alternating current comprises successively engaging the switches in an alternating sequence.

5. The method of claim 4, wherein the alternating sequence includes at least the following switch states:

first switch closed, second switch open, third switch open, and fourth switch engaged, wherein the fourth switch is engaged using the current controlling portion such that the fourth switch allows a substantially constant current to flow therethrough; and

first switch open, second switch closed, third switch engaged, and fourth switch open, wherein the third switch is engaged using the current controlling portion such that the third switch allows a substantially constant current to flow therethrough.

6. The method of claim 1, wherein

the ICD includes circuitry having a current controlling portion, the current controlling portion including a transistor having current inlet node, a current outlet node, and a control node, the control node being coupled to an output of an amplifier that is also part of the current controlling portion, wherein the amplifier has first and second inputs, the first input being used to receive a feedback signal coupled to the current outlet node, the second input being used to receive a control voltage;

and

the step of applying an alternating current includes controlling the current magnitude by providing the control voltage to the second input of the amplifier.

7. The method of claim 6, wherein the ICD includes a digital to analog converter (DAC) coupled to the second input of the amplifier, wherein the step of providing the control voltage includes providing a digital signal to the DAC.

8. The method of claim 1, wherein the ICD includes an energy storage system for use in providing defibrillation stimulus, the method further comprising at least partly charging the energy storage system, wherein the step of applying an alternating current includes at least partly discharging the energy storage system to the patient.

9. A method of creating fibrillation in a patient using an implanted ICD, the ICD including an energy storage system configured for collecting and discharging defibrillation stimuli, the method comprising:

charging the energy storage system to a predetermined level;

discharging the energy storage system such that an alternating current signal having a substantially constant current is formed.

10. The method of claim 9, wherein the ICD comprises an H-bridge configuration having a low side including first and second low side switches driven by first and second operational amplifiers each receiving a feedback signal from the H-bridge as one input and a control signal as another input.

11. An ICD comprising:

a housing;

a battery contained in the housing; and

circuitry contained within the housing and coupled to the battery, the circuitry configured for generating defibrillation signals and including an energy storage system;

wherein;

the circuitry includes an H-bridge having a high side and a low side, each side having a first branch and a second branch, wherein the first and second branches of the low side are coupled to a current regulating means for regulating current flowing therethrough; and

the circuitry includes a controller coupled to the current regulating means, the controller having a fibrillation inducing mode configured to cause the H-bridge to create an output of a controlled current alternating stimulus.

12. The ICD of claim 11, wherein the controlled current alternating current stimulus comprises a number of positive and negative pulses having substantially constant current magnitude.

13. The ICD of claim 12, wherein the positive and negative pulses are separated by periods lacking either a positive or a negative pulse.

14. The ICD of claim 11, wherein the current regulating means includes a selectable current control circuit coupled to a switch, the switch enabling the current regulating means to be switched into and out of operation to control current discharged by the ICD.

15. The ICD of claim 11, wherein each leg of the low side outputs current to a common resistor used as part of the current regulating means for each leg.

16. The ICD of claim 11, wherein the controller'"'"'s fibrillation inducing mode includes instructions for performing the following sequence:

at least partially charge the energy storage system; and

discharge the energy storage system to create the controlled current alternating current stimulus.

17. The ICD of claim 16, wherein the controller'"'"'s fibrillation inducing mode is adapted such that the instructions cause the energy storage system to be charged to a level more than sufficient to provide the controlled current alternating current stimulus.

18. An ICD comprising:

a housing;

a battery contained in the housing;

an energy storage system including at least one capacitive element;

an H-bridge having a high side and a low side, each side having a first branch and a second branch, wherein current flow through the H-bridge is selectively controllable; and

a controller coupled to the battery and the H-bridge, the controller having a fibrillation inducing mode configured to cause the H-bridge to create an output of a controlled current alternating stimulus.

19. The ICD of claim 18, wherein the controlled current alternating current stimulus comprises a number of positive and negative pulses having substantially constant current magnitude.

20. The ICD of claim 18, wherein the controller'"'"'s fibrillation inducing mode includes instructions for performing the following sequence:

at least partially charge the energy storage system; and

discharge the energy storage system to create the controlled current alternating current stimulus.

21. The ICD of claim 20, wherein the controller'"'"'s fibrillation inducing mode is adapted such that the instructions include charging the energy storage system to a level more than sufficient to provide the controlled current alternating current stimulus.