METHOD AND APPARATUS FOR DETECTING FIBRILLATION USING CARDIAC LOCAL IMPEDANCE

• US 20080097539A1
• Filed: 10/19/2006
• Published: 04/24/2008
• Est. Priority Date: 10/19/2006
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Belalcazar, Andres
• Granted Patent: US 7,890,163 B2
• Time in Patent Office: Days
• US Class Current: 607/17
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

A cardiac rhythm management (CRM) system detects tachyarrhythmia using cardiac local impedance indicative of cardiac local wall motion. A cardiac local impedance signal indicative of an impedance of a cardiac region is sensed by using a pair of bipolar electrodes placed in that cardiac region. Tachyarrhythmia such as VF is detected by analyzing one or more cardiac local impedance signals sensed in one or more cardiac regions.

Claims

1. A cardiac rhythm management system coupled to a heart, the system comprising:

a first implantable lead including a proximal end, a distal end, and an elongate lead body coupled between the proximal end and the distal end, the distal end configured to be placed in the heart and including a first pair of impedance sensing electrodes configured to sense a cardiac local impedance signal indicative of a cardiac local wall motion; and

an implantable medical device configured to be coupled to the proximal end of the first implantable lead, the implantable medical device including;

an impedance sensing circuit adapted to sense the cardiac local impedance signal using the first pair of impedance sensing electrodes; and

an impedance-based tachyarrhythmia detector adapted to detect a predetermined-type tachyarrhythmia using the cardiac local impedance signal.

2. The system of claim 1, wherein a distance between two impedance sensing electrodes of the first pair of impedance sensing electrodes is in a range of approximately 2 millimeters to 40 millimeters.

3. The system of claim 2, wherein the distance between the two impedance sensing electrodes is within approximately 20 millimeters.

4. The system of claim 1, wherein the implantable medical device further comprises:

a cardiac sensing circuit to sense one or more electrograms; and

an electrogram-based tachyarrhythmia detector adapted to detect the predetermined-type tachyarrhythmia using the one or more electrograms.

5. The system of claim 1, wherein the impedance sensing circuit comprises:

a current source circuit adapted to deliver a first current through the first pair of impedance sensing electrodes;

a voltage sensing circuit adapted to sense a first voltage across the first pair of impedance sensing electrodes; and

an impedance detector adapted to produce the cardiac local impedance signal using the sensed voltage.

6. The system of claim 5, wherein the impedance detector is adapted to produce the cardiac local impedance signal as a ratio of the sensed first voltage to the delivered first current.

7. The system of claim 1, wherein the impedance-based tachyarrhythmia detector comprises an impedance-based ventricular fibrillation (VF) detector including:

a detection zone generator adapted to produce a VF detection zone specified by one or more threshold amplitudes; and

a comparator including a signal input to receive the cardiac local impedance signal, one or more threshold inputs to receive the one or more threshold amplitudes, and an output to indicate a VF detection when the amplitude of the cardiac local impedance signal falls into the VF detection zone.

8. The system of claim 7, wherein the detection zone generator is adapted to adjust the VF detection zone based on a trend of the cardiac local impedance signal.

9. The system of claim 1, wherein the impedance sensing circuit comprises a differentiator adapted to produce a cardiac local impedance derivative signal using the cardiac local impedance signal, the cardiac local impedance derivative signal indicative of a rate of change in the cardiac local impedance, wherein the impedance-based tachyarrhythmia detector is adapted to detect the predetermined-type tachyarrhythmia using the cardiac local impedance derivative signal.

10. The system of claim 9, wherein the impedance-based tachyarrhythmia detector comprises an impedance-based ventricular fibrillation (VF) detector including:

a detection zone generator adapted to produce a VF detection zone specified by one or more threshold amplitudes; and

a comparator having a signal input to receive the cardiac local impedance derivative signal, one or more threshold inputs to receive the one or more threshold amplitudes, and an output to indicate a VF detection when the amplitude of the cardiac local impedance derivative signal falls into the VF detection zone.

11. The system of claim 9, wherein the impedance-based tachyarrhythmia detector comprises an impedance-based ventricular fibrillation (VF) detector including a motion event detector adapted to detect an impedance event in the cardiac local impedance derivative signal, the impedance event representative of a cardiac local wall motion during a systolic phase of each cardiac cycle, the motion event detector adapted to indicate a detection of the impedance event when the cardiac local impedance derivative signal exceeds an event threshold.

12. The system of claim 11, wherein the impedance-based VF detector comprises an event threshold generator adapted to adjust the event threshold based on a trend of the cardiac local impedance derivative signal.

13. The system of claim 1, wherein the first implantable lead comprises an implantable left ventricular (LV) lead including a pair of LV impedance sensing electrodes configured to sense an LV local impedance signal (LVZ) indicative of an LV local impedance, and wherein the impedance sensing circuit comprises an LV impedance sensing circuit adapted sense the LVZ using the LV impedance sensing electrodes.

14. The system of claim 13, further comprising an implantable right ventricular (RV) lead including a pair of RV impedance sensing electrodes configured to sense an RV local impedance signal (RVZ) indicative of an RV local impedance, and wherein the impedance sensing circuit further comprises an RV impedance sensing circuit adapted sense the RVZ using the RV impedance sensing electrodes.

15. The system of claim 14, wherein the impedance-based tachyarrhythmia detector is adapted to detect the predetermined-type tachyarrhythmia using the LVZ and the RVZ.

16. The system of claim 14, wherein the impedance sensing circuit further comprises an LV differentiator adapted to produce of an LV local impedance derivative signal (LV dZ/dT) indicative of a rate of change in the LV local impedance and an RV differentiator adapted to produce of an RV local impedance derivative signal (RV dZ/dT) indicative of a rate of change in the RV local impedance, and wherein the impedance-based tachyarrhythmia detector is adapted to detect the predetermined-type tachyarrhythmia using the LV dZ/dT and the RV dZ/dT.

17. The system of claim 16, wherein the impedance-based VF detector comprises a ventricular motion event detector adapted to detect LV impedance events by comparing the LV dZ/dT to an LV event threshold and to detect RV impedance events by comparing the RV dZ/dT to an RV event threshold, the LV impedance events each representative of an LV local wall motion during a systolic phase of a cardiac cycle, the RV impedance events each representative of an RV local wall motion during the systolic phase of the cardiac cycle.

18. The system of claim 17, wherein the impedance-based VF detector comprises an event threshold generator adapted to adjust the LV event threshold based on a trend of the LV dZ/dT and to adjust the RV event threshold based on a trend of the RV dZ/dT.

19. The system of claim 17, wherein the impedance-based VF detector is adapted to detect VF using a pattern of the LV impedance events and the RV impedance events.

20. The system of claim 19, wherein the impedance-based VF detector comprises an interventricular synchrony analyzer adapted to detect VF by determining whether the pattern of the LV impedance events and the RV impedance events indicates a degree of dyssynchrony between the LV and RV local wall motions that exceeds a predetermined threshold degree.

21. A method for detecting tachyarrhythmia, the method comprising:

sensing a cardiac local impedance signal indicative of a cardiac local wall motion using a first pair of impedance sensing electrodes at a distal end of a first implantable lead; and

detecting a predetermined-type tachyarrhythmia using the cardiac local impedance signal.

22. The method of claim 21, further comprising sensing one or more electrograms, and wherein detecting the predetermined-type tachyarrhythmia comprises detecting the predetermined-type tachyarrhythmia using the cardiac local impedance signal and the one or more electrograms.

23. The method of claim 21, wherein sensing the cardiac local impedance signal comprises:

delivering current pulses through the first pair of impedance sensing electrodes at a frequency between approximately 3 and 500 Hz, the current pulses each have an amplitude between approximately 20 microamperes and 400 microamperes and a pulse width between approximately 10 microseconds and 100 microseconds;

sensing a voltage across the first pair of impedance sensing electrodes; and

producing the cardiac local impedance signal using the sensed voltage.

24. The method of claim 23, wherein producing the cardiac local impedance signal comprises producing the cardiac local impedance signal as a ratio of the sensed voltage to the amplitude of the delivered current pulses.

25. The method of claim 21, wherein detecting the predetermined-type tachyarrhythmia comprises:

producing a ventricular fibrillation (VF) detection zone specified by one or more threshold amplitudes; and

indicating a VF detection when the cardiac local impedance signal falls into the VF detection zone.

26. The method of claim 25, wherein detecting the predetermined-type tachyarrhythmia further comprises adjusting the VF detection zone based on a trend of the cardiac local impedance signal.

27. The method of claim 21, further comprising producing a cardiac local impedance derivative signal indicative of a rate of change in the cardiac local impedance, and wherein detecting the predetermined-type tachyarrhythmia comprises detecting the predetermined-type tachyarrhythmia using the cardiac local impedance derivative signal.

28. The method of claim 27, wherein producing the cardiac local impedance derivative signal comprises using a high-pass filter having a cutoff frequency between approximately 0.1 Hz and 1 Hz.

29. The method of claim 27, wherein detecting the predetermined-type tachyarrhythmia comprises:

detecting an impedance event by comparing the cardiac local impedance derivative signal to an event threshold, the impedance event representative of a cardiac local wall motion during a systolic phase of each cardiac cycle; and

adjusting the event threshold based on a trend of the cardiac local impedance derivative signal.

30. The method of claim 21, wherein sensing the cardiac local impedance signal using the first pair of impedance sensing electrodes at the distal end of the first implantable lead comprises sensing a left ventricular (LV) local impedance signal (LVZ) indicative of an LV local impedance using a pair of LV impedance sensing electrodes at a distal end of an implantable LV lead.

31. The method of claim 30, further comprising sensing a right ventricular (RV) local impedance signal (RVZ) indicative of an RV local impedance using a pair of RV impedance sensing electrodes at a distal end of an implantable RV lead.

32. The method of claim 31, further comprising:

producing an LV local impedance derivative signal (LV dZ/dT) using the LVZ, the LV dZ/dT indicative of a rate of change in the LVZ; and

producing an RV local impedance derivative signal (RV dZ/dT) using the RVZ, the RV dZ/dT indicative of a rate of change in the RVZ,

and wherein detecting the predetermined-type tachyarrhythmia comprises detecting ventricular fibrillation (VF) using the LV dZ/dT and the RV dZ/dT.

33. The method of claim 32, wherein detecting VF comprises:

detecting LV impedance events by comparing the LV local impedance derivative signal (LV dZ/dT) to an LV event threshold, the LV impedance events each representative of an LV local wall motion during a systolic phase of a cardiac cycle; and

detecting RV impedance events by comparing the RV local impedance derivative signal (RV dZ/dT) to an RV event threshold, the RV impedance events each representative of an RV local wall motion during the systolic phase of the cardiac cycle.

34. The method of claim 33, wherein detecting VF further comprises determining whether a pattern of the LV impedance events and the RV impedance events indicates a degree of dyssynchrony between the LV and RV local wall motions that exceeds a predetermined threshold degree.