Myocardial contractile reserve measured during activities of daily living

1. A system comprising:

a physical activity sensor, configured to detect a physical activity signal from a subject;

a cardiac contractility sensor, configured to detect an indication of cardiac contractility from the subject;

a processor, coupled to the cardiac contractility sensor and the physical activity sensor, the processor configured to determine a contractile reserve indicator using a characteristic of a function of the indication of cardiac contractility across various different activity levels, wherein the contractile reserve indicator corresponds to a predicted value of a maximum change in contractility that can be achieved by the subject; and

a memory, coupled to the processor and configured to receive and store the contractile reserve indicator to be provided to a process or a user.

2. The system of claim 1 , wherein the processor is configured to use the physical activity signal to define time periods corresponding to different steady-state activity levels, and wherein the processor is configured to determine the contractile reserve indicator using a characteristic of a function of the indication of cardiac contractility across the different steady-state activity levels.

3. The system of claim 1 , wherein the cardiac contractility sensor is configured to detect the indication of cardiac contractility using at least one of: a pulse pressure, a rate of change of blood pressure during a cardiac ejection period, a rate of change of intraventricular blood pressure during a cardiac ejection period, a S1 heart sound magnitude, a pre-ejection period, or a change in cardiac stroke.

4. The system of claim 1 , wherein the processor is configured to classify the subject as one of (1) a therapy responder or (2) a therapy non-responder using the contractile reserve indicator.

5. The system of claim 1 , comprising:

a dyssynchrony sensor configured to detect an indication of cardiac dyssynchrony from the subject, the dyssynchrony sensor coupled to the processor;

wherein the processor is configured to:

determine a dyssynchrony indicator using the indication of cardiac dyssynchrony; and

determine a diagnostic indicator using both the dyssynchrony indicator and the contractile reserve indicator; and

wherein the memory is coupled to receive and store the diagnostic indicator to be provided to a user or process.

6. The system of claim 5 , wherein the dyssynchrony sensor is configured to detect an indication of cardiac dyssynchrony using at least one of an electrocardiogram, an intracardiac impedance, an indication of heart wall motion, or a magnitude of a heart sound.

7. The system of claim 1 , comprising a therapy circuit, coupled to the processor, the therapy circuit configured to provide a therapy to the subject;

and wherein the processor is configured to control the therapy provided by the therapy circuit using information about the contractile reserve indicator.

8. The system of claim 7 , wherein the therapy circuit includes at least one of a cardiac resynchronization therapy circuit, a neuromodulation therapy circuit, or a drug therapy control circuit.

9. The system of claim 7 , wherein the processor is configured to trigger the therapy circuit to provide therapy when the contractile reserve indicator indicates that the subject exhibits a contractile reserve that is above a specified threshold.

10. The system of claim 7 , wherein the processor is configured to trigger the therapy circuit to withhold therapy when the contractile reserve indicator indicates that the subject exhibits a contractile reserve that is below a specified threshold.

11. A method comprising:

detecting a physical activity signal from a subject; and

detecting an indication of cardiac contractility from the subject;

determining a contractile reserve indicator using a characteristic of a function of the indication of cardiac contractility across various different activity levels, wherein the contractile reserve indicator corresponds to a predicted value of a maximum change in contractility that can be achieved by the subject; and

providing the contractile reserve indicator to a user or process.

12. The method of claim 11 comprising:

using the physical activity signal to define time periods corresponding to different steady-state activity levels; and

wherein determining a contractile reserve indicator includes using a characteristic of a function of the indication of cardiac contractility across the different steady-state activity levels.

13. The method of claim 11 , wherein detecting an indication of cardiac contractility includes using at least one of: a pulse pressure, a rate of change of blood pressure during a cardiac ejection period, a rate of change of intraventricular blood pressure during a cardiac ejection period, a S1 heart sound magnitude, a pre-ejection period, or a change in cardiac stroke.

14. The method of claim 11 comprising classifying the subject as one of (1) a therapy responder or (2) a therapy non-responder using the contractile reserve indicator.

15. The method of claim 11 , comprising:

detecting an indication of cardiac dyssynchrony from the subject;

determining a dyssynchrony indicator using the indication of cardiac dyssynchrony;

determining a diagnostic indicator using both the dyssynchrony indicator and the contractile reserve indicator; and

providing the diagnostic indicator to a user or process.

16. The method of claim 15 , wherein detecting an indication of dyssynchrony includes using at least one of an electrocardiogram, an intracardiac impedance, an indication of heart wall motion, or a magnitude of a heart sound.

17. The method of claim 11 , comprising:

providing a therapy to the subject; and

controlling the therapy using information about the contractile reserve indicator.

18. The method of claim 17 , wherein providing the therapy includes providing at least one of cardiac resynchronization therapy, neuromodulation therapy, or drug therapy.

19. The method of claim 17 , comprising providing the therapy to the subject when the contractile reserve indicator indicates that the subject exhibits a contractile reserve that is above a specified threshold.

20. The method of claim 17 , comprising withholding the therapy from the subject when the contractile reserve indicator indicates that the subject exhibits a contractile reserve that is below a specified threshold.