Intracardiac impedance and its applications

• US 20070043394A1
• Filed: 08/22/2005
• Published: 02/22/2007
• Est. Priority Date: 08/22/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Zhang, Yongxing, Zhang, Yunlong, Moon, Boyce, Gilkerson, James
• Granted Patent: US 8,494,618 B2
• Time in Patent Office: Days
• US Class Current: 607/8
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/39622 Pacing therapy

Abstract

A system to measure intracardiac impedance includes implantable electrodes and a medical device. The electrodes sense electrical signals of a heart of a subject. The medical device includes a cardiac signal sensing circuit coupled to the implantable electrodes, an impedance measurement circuit coupled to the same or different implantable electrodes, and a controller circuit coupled to the cardiac signal sensing circuit and the impedance measurement circuit. The cardiac signal sensing circuit provides a sensed cardiac signal. The impedance measurement circuit senses intracardiac impedance between the electrodes to obtain an intracardiac impedance signal. The controller circuit determines cardiac cycles of the subject using the sensed cardiac signal, and detects tachyarrhythmia using cardiac-cycle to cardiac-cycle changes in a plurality of intracardiac impedance parameters obtained from the intracardiac impedance signal.

Claims

1. A system comprising:

implantable electrodes to sense electrical signals of a heart of a subject; and

a medical device including;

a cardiac signal sensing circuit coupled to the implantable electrodes, the sensing circuit to provide a sensed cardiac signal;

an impedance measurement circuit, coupled to the same or different implantable electrodes, the impedance measurement circuit to sense intracardiac impedance between the electrodes to obtain an intracardiac impedance signal; and

a controller circuit coupled to the cardiac signal sensing circuit and the impedance measurement circuit, the controller circuit operable to determine cardiac cycles of the subject using the sensed cardiac signal and to detect tachyarrhythmia using cardiac-cycle to cardiac-cycle changes in a plurality of intracardiac impedance parameters obtained from the intracardiac impedance signal.

2. The system of claim 1, wherein the plurality of intracardiac impedance parameters is selected from the group consisting essentially of:

a baseline intracardiac impedance value;

a maximum intracardiac impedance value;

an area between the intracardiac impedance signal waveform and the baseline impedance value;

a time interval of maximum intracardiac impedance change; and

a slope of the intracardiac impedance waveform signal measured at one-half (½

) the time interval of maximum impedance change.

3. The medical device of claim 1, further including a memory circuit to store intracardiac impedance parameters measured in accordance with at least one cardiac cycle, and wherein the controller circuit is further operable to detect tachyarrhythmia using a change from stored parameters and measured parameters.

4. The medical device of claim 3, wherein the medical device is operable to store at least one trend for at least one intracardiac impedance parameter.

5. The system of claim 1, wherein the medical device is implantable and further includes a communication circuit to communicate at least one trend for at least one intracardiac impedance parameter to an external device, and wherein the external device is in communication with a communication network.

6. The system of claim 5, wherein the external device includes a display, and wherein the external device is further operable to display intracardiac impedance information.

7. The medical device of claim 1, further including a therapy circuit coupled to the controller circuit, wherein the controller circuit is operable to initiate a therapy upon detection of tachyarrhythmia.

8. The system of claim 7, further including at least one electrical lead, and wherein the implantable electrodes includes at least one coil shock electrode located distally to other electrodes on the lead, the coil shock electrode adaptable for placement in a right ventricle of a heart.

9. The system of claim 7, further including at least one electrical lead, and wherein the implantable electrodes includes at least one coil shock electrode located proximally to other electrodes on the lead, the coil shock electrode adaptable for placement in a superior vena cava.

10. The system of claim 1, wherein the implantable electrodes includes at least one electrode adaptable for placement in a left atrium of the heart.

11. The system of claim 1, wherein the implantable electrodes includes at least one electrode adaptable for placement in a left ventricle of the heart.

12. A method comprising:

sensing cardiac cycles of a patient;

sensing intracardiac impedance to obtain an intracardiac impedance waveform;

measuring a plurality of intracardiac impedance parameters from the waveform in correspondence with the cardiac cycles; and

detecting tachyarrhythmia using at least one change in the plurality of intracardiac impedance parameters, wherein the change is measured between multiple cardiac cycles.

13. The method of claim 12, wherein measuring a plurality of intracardiac impedance parameters includes measuring a baseline intracardiac impedance value.

14. The method of claim 13, wherein measuring a plurality of intracardiac impedance parameters includes measuring an area between a sensed intracardiac impedance signal waveform and the measured intracardiac impedance baseline value.

15. The method of claim 12, wherein measuring a plurality of intracardiac impedance parameters includes measuring a maximum intracardiac impedance value.

16. The method of claim 15, wherein measuring a plurality of intracardiac impedance parameters includes measuring a time interval from when a sensed intracardiac impedance signal waveform exceeds the measured baseline intracardiac impedance value to the time it reaches the maximum intracardiac impedance value.

17. The method of claim 12, wherein measuring a plurality of intracardiac impedance parameters includes measuring a slope of the intracardiac impedance waveform.

18. The method of claim 12, wherein sensing cardiac cycles and sensing intracardiac impedance includes sensing cardiac cycles and intracardiac impedance using an implantable medical device (IMD).

19. A method comprising:

sensing electrical cardiac signals of a subject;

detecting tachyarrhythmia and determining whether the tachyarrhythmia is ventricular tachycardia or ventricular fibrillation, or supraventricular tachycardia using the electrical cardiac signals;

sensing an intracardiac impedance signal during the tachyarrhythmia;

determining whether the tachyarrhythmia is stable using a plurality of intracardiac impedance parameters derived from the intracardiac impedance signal; and

providing a shock therapy to the subject if the tachyarrhythmia is ventricular tachycardia or fibrillation and is unstable, and providing anti-tachycardia pacing (ATP) therapy to the subject if the tachyarrhythmia is ventricular tachycardia or fibrillation and is stable.

21. The method of claim 19, further including providing a therapy to the subject if the tachyarrhythmia is supraventricular tachycardia and unstable and withholding a therapy if tachyarrhythmia is supraventricular tachycardia and stable.

20. The method of 19, wherein providing ATP therapy to the subject if the tachyarrhythmia is ventricular tachycardia or fibrillation and stable includes providing ATP therapy before resorting to shock therapy if ATP does not mitigate the tachyarrhythmia.

22. The method of 19, wherein determining whether the tachyarrhythmia is stable using the intracardiac impedance signal includes measuring a plurality of intracardiac impedance parameters from a sensed intracardiac impedance signal waveform in association with cardiac cycles.

23. The method of 19, wherein sensing the electrical cardiac signals and sensing the intracardiac impedance signal includes sensing using an IMD, and wherein providing a shock therapy includes providing shock therapy using an IMD.

24. A method comprising:

sensing cardiac cycles of a patient;

sensing intracardiac impedance using an IMD to obtain an intracardiac impedance waveform;

measuring a plurality of intracardiac impedance parameters from the waveform in correspondence with the cardiac cycles; and

deeming that a cardiac decompensation event occurred using at least one change in the plurality of intracardiac impedance parameters, wherein the change is measured between multiple cardiac cycles.

25. The method of claim 24, wherein the method further includes monitoring heart rate of the patient to detect tachycardia, and wherein deeming that a cardiac decompensation event occurred includes detecting a decrease in cardiac performance in the absence of tachycardia using the change in the intracardiac impedance parameters measured between multiple cardiac cycles.

26. The method of claim 25, wherein measuring a plurality of intracardiac impedance parameters includes measuring an area between the intracardiac impedance waveform and a baseline impedance value, and wherein detecting a decrease in cardiac performance includes detecting a decrease in the measured area.

27. The method of claim 25, wherein measuring a plurality of intracardiac impedance parameters includes measuring a slope of the intracardiac impedance waveform at one-half the time interval from when the waveform exceeds a baseline impedance value to when it reaches a maximum impedance value, and wherein detecting a decrease in cardiac performance includes detecting a decrease in the measured slope.

28. The method of claim 24, further including adjusting a therapy provided to the patient by the IMD based at least in part on an occurrence of cardiac decompensation.

29. A method comprising:

sensing cardiac cycles of a patient using an implantable medical device (IMD);

sensing intracardiac impedance using the IMD to obtain an intracardiac impedance waveform;

measuring a plurality of intracardiac impedance parameters from the waveform in correspondence with the cardiac cycles; and

trending changes in the plurality of intracardiac impedance parameters, wherein the changes are measured between multiple cardiac cycles.

30. The method of claim 29, wherein the method further includes changing at least one therapy parameter of the IMD according to the trending.

31. The method of claim 29, wherein the method further includes deeming that cardiac remodeling has occurred according to the trending.