Control of arbitrary waveforms for constant delivered energy

• US 20030125773A1
• Filed: 12/03/2002
• Published: 07/03/2003
• Est. Priority Date: 12/03/2001
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Havel, William J., Kemmetmueller, Gary, Degroot, Paul J., Kuehn, Kevin, Sinner, Thomas W., Wold, Warren W.
• Granted Patent: US 7,151,963 B2
• Time in Patent Office: Days
• US Class Current: 607/7
• 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 outlines structures and methods for delivering a controllable amount of energy to a patient by automatically compensating for the load impedance detected by an implantable-cardioverter defibrillator (ICD). The invention employs high speed, switching power converter technology for the efficient generation of high energy, arbitrary waveforms. Unlike a linear amplifier, switching power converters deliver high-energy waveforms with an efficiency that is independent of the size and amplitude of the desired waveform. An ICD that uses a switching power converter to deliver the desired energy to the patient stores the energy to be delivered in a storage capacitor. The converter then transforms this energy into an arbitrarily shaped output voltage-controlled or current-controlled waveform by switching the storage capacitor in and out of the output circuit at a high rate of speed. Preferably, the waveform comprises a ramp-type waveform.

Claims

1. A system for controlling waveform to deliver constant energy from a device to terminate a cardiac fibrillation condition, the system comprising:

means for measuring a load impedance of a subsystem between at least a pair of electrodes over a duration to deliver an initial portion of energy;

means for measuring a length of time it takes a storage capacitor voltage to decay by a certain percentage; and

means for calculating the load impedance that a voltage-controlled or current-controlled output waveform is delivered into based on the length of time; and

means for extending the voltage-controlled or current-controlled output waveform to deliver a pre-programmed level of energy irrespective of the load impedance.

2. A system according to claim 1, wherein said means for extending comprises a power converter circuit.

3. A system according to claim 1, wherein said separate electrode is a portion of an electrically conducting canister for an implantable medical device.

4. A system according to claim 1, wherein said pre-programmed level of energy is a set of discrete pre-programmed energy levels and each successive member of said set has a greater magnitude than the previous member of said set.

5. A system according to claim 1, wherein said voltage-controlled or current-controlled output waveform is at least a one of the following waveforms:

an ascending amplitude waveform, a bi-phasic waveform, a descending amplitude waveform, a truncated waveform, a multi-phase waveform, a multi-phasic waveform, a substantially square-shaped waveform.

6. A system according to claim 1, wherein said means for extending the voltage-controlled or current-controlled output waveform comprises a switching converter.

7. A system according to claim 6, wherein the switching converter comprises at least a one of the following:

a step-down (buck) converter, a step-up (boost) converter, a combined step-down/step-up (buck-boost) converter.

8. A system according to claim 1, wherein the pair of electrodes comprises at least one of the following:

a percutaneous electrode, a subcutaneous electrode, an epicardial electrode, an endocardial electrode, a transcutaneous electrode, a surface electrode, a canister electrode, a coil electrode, a ring electrode.

9. A system for delivering an arbitrary waveform to a subject while monitoring the voltage on an energy storage capacitor in a cardiac defibrillator, comprising:

means for determining a voltage stored on a storage capacitor and the size of the storage capacitor to derive a total amount of energy stored on the storage capacitor;

means for truncating an arbitrary waveform after the voltage on the storage capacitor decays to a threshold value; and

means for delivering a specific amount of the total amount of energy via the truncated arbitrary waveform irrespective of the load resistance of a subject.

10. A system according to claim 9, wherein the means for truncating comprises a means for monitoring an output voltage parameter and a duty cycle parameter.

11. A system of delivery constant energy to stabilize cardiac rhythm in a patient, the system comprising:

means for monitoring a portion of a delivered energy being delivered to a portion of cardiac tissue of a patient using an arbitrary waveform in an attempt to successfully terminate an arrhythmia;

means for calculating a load impedance value of said patient; and

means for adjusting a remaining portion of the delivered energy supplied by the arbitrary waveform based on scaling an amplitude characteristic of the remaining portion of the delivered energy so a desired constant amount of energy is delivered.

12. A system according to claim 11, wherein said means for monitoring includes means for monitoring the remaining portion of the delivered energy as a function of time.

13. A system according to claim 11, wherein said means for setting includes means for controlling a voltage parameter or current parameter of the arbitrary waveform to substantially match the load impedance to thereby deliver a consistent amount of energy.

14. A system according to claim 11, further comprising the steps of

monitoring the portion of cardiac tissue to determine if the arrhythmia has successfully terminated, and if not,

repeating the steps set forth in claim 11.

15. A system according to claim 14, wherein the step of repeating the steps set forth in claim 11 occurs with a second desired constant amount of energy is delivered that is greater in magnitude than the desired constant amount of energy.

16. A system according to claim 11, wherein the means for calculating a load impedance value comprises at least a pair of electrodes disposed about the portion of cardiac tissue.

17. A method of delivering a desired, predetermined and constant amount of energy to a portion of tissue, comprising the steps:

charging a storage capacitor;

measuring a load impedance of a portion of tissue using at least two electrodes disposed about said portion of tissue;

measuring the magnitude of an electrical potential present in the storage capacitor;

delivering an arbitrary waveform from the storage capacitor to the portion of tissue through a switching power converter circuit while simultaneously re-measuring the load impedance; and

in response to changes in the re-measured load impedance, adjusting the arbitrary waveform so that a predetermined, constant amount of energy is ultimately delivered to the portion of tissue.

18. A method according to claim 17, wherein the arbitrary waveform comprises at least a one of the following:

an ascending amplitude waveform, a bi-phasic waveform, a voltage-controlled waveform, a current-controlled waveform, a descending amplitude waveform, a truncated waveform, a multi-phase waveform, a multi-phasic waveform, a substantially square-shaped waveform.

19. A method according to claim 17, wherein the method is performed by a device selected from the following list:

an automatic external defibrillator, an implantable medical device, an implantable-cardioverter defibrillator, a pacemaker.

20. A method according to claim 17, wherein said method is applied following a positive detection of a potentially lethal arrhythmia and at least one low voltage therapy intended to terminate said potentially lethal arrhythmia.