Closed loop impedance-based cardiac resynchronization therapy systems, devices, and methods

• US 20060271119A1
• Filed: 11/02/2005
• Published: 11/30/2006
• Est. Priority Date: 05/25/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Spinelli, Julio C., Stahmann, Jeffrey E., Yu, Yinghong, Ding, Jiang, Ni, Quan, Daum, Douglas R.
• Granted Patent: US 7,440,803 B2
• Time in Patent Office: Days
• US Class Current: 607/9
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3682 with a variable atrioventricular delay
• CPC Class Codes: A61N 1/36842 Multi-site stimulation in the same chamber
• CPC Class Codes: A61N 1/36843 Bi-ventricular stimulation

Abstract

This document discusses, among other things, systems, devices, and methods measure an impedance and, in response, adjust an atrioventricular (AV) delay or other cardiac resynchronization therapy (CRT) parameter that synchronizes left and right ventricular contractions. A first example uses parameterizes a first ventricular volume against a second ventricular volume during a cardiac cycle, using a loop area to create a synchronization fraction (SF). The CRT parameter is adjusted in closed-loop fashion to increase the SF. A second example measures a septal-freewall phase difference (PD), and adjusts a CRT parameter to decrease the PD. A third example measures a peak-to-peak volume or maximum rate of change in ventricular volume, and adjusts a CRT parameter to increase the peak-to-peak volume or maximum rate of change in the ventricular volume.

Claims

1. A machine-assisted method comprising:

measuring a first impedance signal, the first impedance signal being substantially indicative of a volume of a first ventricle of a heart as the first ventricle expands and contracts during a cardiac cycle of the heart;

measuring a second impedance signal, the second impedance signal being substantially indicative of a volume of a second ventricle, different from the first ventricle, as the second ventricle expands and contracts during the same cardiac cycle;

forming a function that parameterizes the first impedance signal as the function of the second impedance signal during the same cardiac cycle; and

computing an indication of a degree of synchrony or asynchrony between the right and left ventricles using the function.

2. The method of claim 1, in which:

the measuring the first impedance signal includes using a first electrode in a right atrium and a second electrode in a right ventricle; and

the measuring the second impedance signal includes using the first electrode and a third electrode introduced into a coronary sinus vein such that the third electrode is in association with a left ventricular freewall.

3. The method of claim 1, in which:

the measuring the first impedance signal includes using a first electrode in a right atrium and a second electrode in a right ventricle; and

the measuring the second impedance signal includes using a third electrode introduced into a coronary sinus vein such that the third electrode is in association with a left atrium, and a fourth electrode located in a coronary sinus vein such that the fourth electrode is in association with a left ventricular freewall.

4. The method of claim 1, in which the measuring the first impedance includes using a right ventricular electrode and a reference electrode located on a hermetically sealed housing of an implantable device or located on an insulating header extending from the housing of the implantable device, and in which the measuring the second impedance includes using a left ventricular electrode and a reference electrode located on a hermetically sealed housing of an implantable device or located on an insulating header extending from the housing of the implantable device.

5. The method of claim 1, in which:

the forming the first function includes forming a Lissajous function that parameterizes the first impedance signal as the function of the second impedance signal during the same cardiac cycle, the Lissajous function enclosing a loop area during the cardiac cycle; and

the computing the degree of synchrony or asynchrony includes using the loop area.

6. The method of claim 5, in which the computing the degree of synchrony or asynchrony includes:

computing a rectangular area defined by maximum and minimum impedances of each of the first and second ventricles during the cardiac cycle; and

computing a synchronization fraction by forming a difference of the rectangular area less the loop area, and dividing the difference by the rectangular area.

7. The method of claim 6, further comprising:

automatically adjusting a cardiac resynchronization therapy parameter that synchronizes left and right ventricular heart contractions, using the synchronization fraction, in a way such that the synchronization tends to increase the degree of synchrony or decrease the degree of asynchrony given by the indication.

8. The method of claim 1, further comprising:

automatically adjusting a cardiac resynchronization therapy parameter, using the indication, in a way that tends to increase the degree of synchrony or decrease the degree of asynchrony given by the indication.

9. The method of claim 8, in which the adjusting the cardiac resynchronization therapy parameter includes adjusting an atrioventricular (AV) delay.

10. The method of claim 8, in which the adjusting the cardiac resynchronization therapy parameter includes adjusting an interventricular delay.

11. The method of claim 8, in which the adjusting the cardiac resynchronization therapy parameter includes adjusting an intraventricular delay.

12. The method of claim 1, further comprising communicating information about the indication of the degree of synchrony or asynchrony from an implantable cardiac rhythm management device.

13. A machine-assisted method comprising:

measuring a first impedance signal of a first ventricle as the first ventricle expands and contracts during a cardiac cycle, the first impedance signal measured by delivering a current to the first ventricle and measuring a resulting voltage across a first electrode and a second electrode, the first and second electrodes located near opposing sides of the first ventricle;

measuring a second impedance signal of a second ventricle, different from the first ventricle, as the second ventricle expands and contracts during the same cardiac cycle, the second impedance signal measured by delivering a current to the second ventricle and measuring a resulting voltage across a third electrode and a fourth electrode, the third and fourth electrodes located near opposing sides of the second ventricle;

forming a Lissajous function that parameterizes the first impedance signal as the function of the second impedance signal during the same cardiac cycle, the Lissajous function enclosing a loop area during the cardiac cycle; and

automatically adjusting a cardiac resynchronization therapy parameter that synchronizes left and right ventricular heart contractions, the automatically adjusting performed in a way that tends to decrease the loop area for at least one subsequent cardiac cycle.

14. The method of claim 13, in which the automatically adjusting the cardiac resynchronization therapy parameter to decrease the loop area includes decreasing the loop area relative to a rectangle defined by maximum and minimum impedances of each of the first and second ventricles during the cardiac cycle.

15. A system comprising:

a device comprising;

an impedance measurement circuit, including terminals configured to be coupled to electrodes in association with a first ventricle of a heart to measure a first impedance signal that is substantially indicative of a volume of the first ventricle of the heart as the first ventricle expands and contracts during a cardiac cycle of the heart, and in association with a second ventricle of the heart to measure a second impedance signal that is substantially indicative of a volume of the second ventricle of the heart as the second ventricle expands and contracts during the same cardiac cycle of the heart;

and

a processor circuit, coupled to the impedance measurement circuit to receive information about the first and second impedance signals over the cardiac cycle, the processor performing instructions to form a function that parameterizes the first impedance signal as the function of the second impedance signal during the same cardiac cycle, and to compute an indication of a degree of synchrony or asynchrony between the right and left ventricles using the function.

16. The system of claim 15, in which the device includes an implantable medical device that further comprises a telemetry circuit, coupled to the processor circuit to receive information about the indication of the degree of synchrony or asynchrony, the telemetry circuit configured to communicate data about the indication of degree of synchrony or asynchrony from the implantable medical device.

17. The system of claim 15, in which the device includes an implantable medical device that further comprises a therapy circuit configured to provide cardiac resynchronization therapy to the heart, the processor adjusting delivery of the cardiac resynchronization therapy in a closed-loop fashion in a way that tends to increase, for at least one subsequent cardiac cycle, the indication of the degree of synchrony computed by the processor circuit or to decrease the indication of the degree of asynchrony computed by the processor circuit.

18. The system of claim 15, in which the processor circuit performs instructions to form a Lissajous function that parameterizes the first impedance signal as the function of the second impedance signal over the same cardiac cycle, the Lissajous function enclosing a loop area during the cardiac cycle, and in which the computing the degree of synchrony or asynchrony includes using the loop area.

19. The system of claim 15, in which the processor includes instructions performable to compute the degree of synchrony or asynchrony by:

computing a rectangular area defined by maximum and minimum impedances of the first and second ventricles during the cardiac cycle; and

computing a synchronization fraction by forming a difference of the rectangular area less the loop area, and dividing the difference by the rectangular area.

20. A machine-assisted method comprising:

measuring a first impedance, during at least a portion of a cardiac cycle, between a first electrode associated with a first ventricle of a heart and a reference electrode;

measuring a second impedance, during at least the portion of the cardiac cycle, between a second electrode associated with a second ventricle of the heart, in which the second ventricle is different from the first ventricle, and the same or a different reference electrode;

measuring a phase difference between the first and second impedances; and

automatically adjusting in a closed loop manner, using the measured phase difference as an error signal, a cardiac resynchronization therapy parameter that synchronizes left and right ventricular heart contractions, the automatically adjusting tending to reduce the phase difference during a subsequent cardiac cycle.

21. The method of claim 20, further comprising:

if the measured phase difference shows the second impedance leading the first impedance in phase by more than a first threshold value, then lengthening an atrioventricular (AV) delay; and

if the measured phase difference shows the first impedance leading the second impedance in phase by more than a second threshold value, then shortening the AV delay.

22. The method of claim 20, in which the first ventricle is a left ventricle, and further comprising:

if the measured phase difference shows the second impedance leading the first impedance in phase by more than a first threshold value, then making a left ventricular (LV) offset more negative, wherein the LV offset defines a time duration by which an LV pace is scheduled to lead a right ventricular pace; and

if the measured phase difference shows the first impedance leading the second impedance in phase by more than a second threshold value, then making the LV offset more positive.

23. The method of claim 20, in which the measuring the first and second impedances includes using as the reference electrode an electrode located on a hermetically sealed housing of an implantable device or located on an insulating header extending from the housing of the implantable device.

24. The method of claim 20, in which the measuring the first and second impedances includes using as the reference electrode a supraventricular electrode of an intravascular lead.

25. The method of claim 20, in which the measuring the phase difference includes measuring a time difference between like fiducial artifacts of the first and second impedances.

26. The method of claim 20, further comprising communicating data indicative of the phase difference from an implantable medical device.

27. The method of claim 26, further comprising displaying an indication of the phase difference using an external display monitor.

28. The method of claim 20, in which the measuring the phase difference includes constraining the measuring the phase difference to occur during a time window that is measured from a cardiac depolarization.

29. A system comprising:

an implantable medical device comprising;

an impedance measurement circuit, including terminals configured to be coupled to electrodes for association with a first ventricle of a heart and a second ventricle of the heart, respectively, and configured to be coupled to a reference electrode location separate from each of the first and second ventricles, the impedance measurement circuit configured to measure a first impedance between the first ventricle and the reference electrode location, and to measure a second impedance between the second ventricle and the reference electrode location; and

a processor circuit, coupled to the impedance measurement circuit to receive signals indicative of the first and second impedances during the cardiac cycle, the processor configured to perform instructions to measure a phase difference between the first and second impedances to provide an indication of a degree of synchrony or asynchrony between the first and second ventricles, the processor further configured to perform instructions to automatically adjust in a closed-loop manner, using the measured phase difference as an error signal, a cardiac resynchronization therapy parameter that synchronizes left and right ventricular heart contractions in a way that tends to reduce the phase difference during a subsequent cardiac cycle.

30. The system of claim 29, in which the processor is further configured to perform instructions such that:

if the measured phase difference shows the second impedance leading the first impedance in phase by more than a first threshold value, then lengthening an atrioventricular (AV) delay; and

if the measured phase difference shows the first impedance leading the second impedance in phase by more than a second threshold value, then shortening the AV delay.

31. The system of claim 29, in which the processor further performs instructions such that:

if the measured phase difference shows the second impedance leading the first impedance in phase by more than a first threshold value, then making an interventricular offset more negative, wherein the interventricular offset defines a time duration by which an second ventricular pace is scheduled to lead a first ventricular pace; and

if the measured phase difference shows the first impedance leading the second impedance in phase by more than a second threshold value, then making the interventricular offset more positive.

32. The system of claim 29, in which the implantable device includes the reference electrode, and wherein the reference electrode is located on a hermetically sealed housing of an implantable device or located on an insulating header extending from the housing of the implantable device.

33. The system of claim 29, further comprising an intravascular lead including a supraventricular electrode serving as the reference electrode.

34. The system of claim 29, further comprising a telemetry circuit, coupled to the processor, the telemetry circuit configured for transmitting from the implantable device data indicative of the phase difference.

35. The system of claim 34, further comprising an external user interface device that is configured to receive the data indicative of the phase difference from the implantable device, the external user interface device including a display monitor configured to display information about the phase difference.