Cardiac therapy based upon impedance signals

1. An implantable medical device for use in delivering therapy to a patient's heart comprising:

a sensing module configured to monitor an impedance between at least two electrodes proximate the patient's heart to provide an impedance signal;

a therapy delivery module configured to deliver cardiac therapy to the patient's heart; and

a control module coupled to the sensing module and the therapy delivery module and configured to:

determine an E-wave portion representative of an early diastolic filling phase during a cardiac cycle based on the impedance signal,

determine an A-wave portion representative of a late diastolic filling phase during the cardiac cycle based on the impedance signal,

deliver cardiac therapy to the patient based upon one or more characteristics associated with at least one of the E-wave portion and the A-wave portion, the one or more characteristics comprising an area of the E-wave portion,

determine a maximum peak impedance for the cardiac cycle, and

determine an earliest trough of the impedance signal following the maximum peak impedance as a start of the E-wave portion.

2. The device of claim 1 , wherein the control module is configured to:

determine the E-wave portion during the cardiac cycle using a derivative of the impedance signal, and

determine the A-wave portion during the cardiac cycle using the derivative of the impedance signal.

3. The device of claim 1 , wherein the control module is further configured to:

determine an E-A time interval from the E-wave portion to the A-wave portion, and

adjust the cardiac therapy delivered to the patient based upon the E-A time interval to optimize at least one of AV delay and VV delay.

4. The device of claim 1 , wherein the control module is further configured to:

determine a first derivative of the impedance signal to provide a derivative signal,

determine the E-wave portion using the derivative signal during the cardiac cycle,

determine the A-wave portion using the derivative signal during the cardiac cycle,

determine at least one of an E-wave maximum value of the E-wave portion and an A-wave maximum value of the A-wave portion, and

adjust the cardiac therapy delivered to the patient based upon at least one of the E-wave maximum value and the A-wave maximum value to optimize at least one of AV delay and VV delay.

5. The device of claim 1 , wherein the control module is further configured to:

determine a first derivative of the impedance signal to provide a derivative signal,

determine the E-wave portion using the derivative signal during the cardiac cycle,

determine the A-wave portion using the derivative signal during the cardiac cycle,

determine an E-A area under at least one of the E-wave portion and the A-wave portion, and

adjust the cardiac therapy delivered to the patient based upon the E-A area to optimize at least one of AV delay and VV delay.

6. The device of claim 1 , wherein the control module is further configured to:

determine a first derivative of the impedance signal to provide a derivative signal,

determine the E-wave portion using the derivative signal during the cardiac cycle,

determine the A-wave portion using the derivative signal during the cardiac cycle,

determine an E-A minimum trough value between a maximum value within the E-wave portion and a maximum value within the A-wave portion, and

adjust the cardiac therapy delivered to the patient based upon the E-A minimum trough value to optimize at least one of AV delay and VV delay.

7. The device of claim 1 , wherein the control module is further configured to execute at least one of the following:

adjust the cardiac therapy delivered to the patient by delaying atrial electrical stimulation by a first selected time period after a first selected fiducial point within the E-wave portion, and

adjust the cardiac therapy delivered to the patient by delaying ventricular electrical stimulation by a second selected time period after a second selected fiducial point within the A-wave portion.

8. A method for use in monitoring a patient comprising:

monitoring an impedance between at least two electrodes proximate the patient's heart to provide an impedance signal;

determining an E-wave portion representative of an early diastolic filling phase during a cardiac cycle based on the impedance signal;

determining an A-wave portion representative of a late diastolic filling phase during the cardiac cycle based on the impedance signal;

monitoring the E-wave portion and the A-wave portion to determine one or more characteristics of the patient, the one or more characteristics comprising an area of the E-wave portion;

determining a maximum peak impedance for the cardiac cycle and determining an earliest trough of the impedance signal following the maximum peak impedance as a start of the E-wave portion.

9. The method of claim 8 , further comprising delivering cardiac therapy to the patient based upon the one or more characteristics associated with at least one of the E-wave portion and the A-wave portion.

10. The method of claim 8 , further comprising:

determining the E-wave portion during the cardiac cycle using a derivative of the impedance signal, and

determining the A-wave portion during the cardiac cycle using the derivative of the impedance signal.

11. The method of claim 8 , further comprising:

determining an E-A time interval from the E-wave portion to the A-wave portion, and

adjusting the cardiac therapy delivered to the patient based upon the E-A time interval to optimize at least one of AV delay and VV delay.

12. The method of claim 8 , further comprising:

determining a first derivative of the impedance signal to provide a derivative signal,

determining the E-wave portion using the derivative signal during the cardiac cycle,

determining the A-wave portion using the derivative signal during the cardiac cycle,

determining at least one of an E-wave maximum value within the E-wave portion and an A-wave maximum value within the A-wave portion, and

adjusting the cardiac therapy delivered to the patient based upon at least one of the E-wave maximum value and the A-wave maximum value to optimize at least one of AV delay and VV delay.

13. The method of claim 8 , further comprising:

determining a first derivative of the impedance signal to provide a derivative signal,

determining the E-wave portion using the derivative signal during the cardiac cycle,

determining the A-wave portion using the derivative signal during the cardiac cycle,

determining an E-A area under at least one of the E-wave portion and the A-wave portion, and

adjusting the cardiac therapy delivered to the patient based upon the E-A area to optimize at least one of AV delay and VV delay.

14. The method of claim 8 , further comprising:

determining a first derivative of the impedance signal to provide a derivative signal,

determining the E-wave portion using the derivative signal during the cardiac cycle,

determining the A-wave portion using the derivative signal during the cardiac cycle,

determining an E-A minimum trough value between a maximum value within the E-wave portion and a maximum value within the A-wave portion, and

adjusting the cardiac therapy delivered to the patient based upon the E-A minimum trough value to optimize at least one of AV delay and VV delay.

15. The method of claim 8 , further comprising at least one of:

adjusting the cardiac therapy delivered to the patient by delaying atrial electrical stimulation by a first selected time period after a first selected fiducial point within the E-wave portion, and

adjusting the cardiac therapy delivered to the patient by delaying ventricular electrical stimulation by a second selected time period after a second selected fiducial point within the A-wave portion.