Methods and systems that monitor for an impending myocardial infarction

1. For use with an implanted system, a method for monitoring for an impending myocardial infarction (MI), the method comprising:

(a) using an implanted photoplethysmography sensor remote from the patient's heart to produce a photoplethysmography signal that is indicative of changes in arterial volume;

(b) for each of a plurality of periods of time, determining a metric indicative of the area under the curve of the photoplethysmography signal for the period of time;

(c) monitoring for an impending MI based on changes in the metric indicative of the area under the curve of the photoplethysmography signal; and

(d) triggering an alert and/or therapy in response to an impending MI being detected at step (c);

wherein one or more of steps (b), (c) and (d) is/are performed using a processor.

2. The method of claim 1 , further comprising determining a baseline of the metric indicative of area under the curve;

wherein step (c) includes distinguishing between an impending MI and a transient myocardial ischemic event based on a length of time that the metric indicative of the area under the curve falls below the baseline by at least a specified threshold.

3. The method of claim 1 , further comprising determining a baseline of the metric indicative of area under the curve;

wherein step (c) comprises:

(c.1) comparing the determined metrics indicative of the area under the curve to the baseline; and

(c.2) predicting an impending MI if the determined metric indicative of the area under the curve falls below the baseline by at least a specified threshold for at least a specified length of time.

4. The method of claim 3 , wherein step (c.2) includes distinguishing between an impending MI and a transient myocardial ischemic event based on a length of time that the metric indicative of the area under the curve falls below the baseline by at least the specified threshold.

5. The method of claim 1 , wherein step (c) comprises predicting an impending MI if a decrease beyond a specified threshold is detected, in the metric indicative of the area under the curve of the photoplethysmography signal, from one of the periods of time to the immediately following one of the periods of time.

6. The method of claim 1 , wherein step (c) comprises predicting an impending MI if the metric indicative of the area under the curve of the photoplethysmography signal decreases by at least a specified amount for at least a specified period of time.

7. The method of claim 1 , wherein the metric indicative of area under the curve is selected from the group consisting of:

an integral of at least one cycle of the photoplethysmography signal;

a width from the start to the end of a cycle of the photoplethysmography signal; and

a full width at half maximum (FWHM) of a cycle of the photoplethysmography signal.

8. The method of claim 1 , wherein step (c) includes:

(c.1) detecting changes in the area under the curve of the photoplethysmography signal that are indicative of changes in vascular stiffness; and

(c.2) monitoring for an impending MI based on changes in the area under the curve of the photoplethysmography signal that are indicative of changes in vascular stiffness.

9. The method of claim 8 , wherein step (c.2) comprises predicting an impending MI if a change in the area under the curve of the photoplethysmography signal, which is indicative of an increase in vascular stiffness beyond a specified threshold, is detected.

10. The method of claim 8 , wherein step (c.2) comprises predicting an impending MI if a change in the area under the curve of the photoplethysmography signal, which is indicative of an increase in vascular stiffness beyond a specified threshold, is detected within a specified time period.

11. The method of claim 1 , wherein the metric indicative of area under the curve, which is determined at step (b) for each of a plurality of periods of time, is indicative of the area under the curve of at least one entire cycle of the photoplethysmography signal.

12. An implantable system for monitoring for an impending myocardial infarction (MI), comprising:

an implantable photoplethysmography sensor configured to be implanted remote from a patient's heart and to produce a photoplethysmography signal that is indicative of changes in arterial volume;

a monitor configured to:

determine a metric indicative of the area under the curve of the photoplethysmography signal for each of a plurality of periods of time,

monitor for an impending MI based on changes in the metric indicative of the area under the curve of the photoplethysmography signal, and

trigger an alert and/or therapy in response to an impending MI being detected.

13. The system of claim 12 , wherein the monitor is configured to:

determine a baseline of the metric indicative of area under the curve; and

monitor for an impending MI, based on changes in the metric indicative of the area under the curve of the photoplethysmography signal, by comparing the determined metrics indicative of the area under the curve to the baseline, and predicting an impending MI if the determined metric indicative of the area under the curve falls below the baseline by at least a specified threshold for at least a specified length of time.

14. The system of claim 12 , wherein the metric indicative of area under the curve is indicative of the area under the curve of at least one entire cycle of the photoplethysmography signal.

15. For use with a chronically implanted device, a method for monitoring for an impending myocardial infarction (MI), the method comprising:

(a) using an implanted photoplethysmography sensor remote from a patient's heart to produce a photoplethysmography signal that is indicative of changes in arterial volume;

(b) for each of a plurality of cycles of the photoplethysmography signal, determining a metric indicative of a number of inflections in the photoplethysmography signal for the cycle;

(c) monitoring for an impending MI based on changes in the metric indicative of the number of inflections in the photoplethysmography signal; and

(d) triggering an alert and/or therapy in response to an impending MI being detected at step (c);

wherein one or more of steps (b), (c) and (d) is/are performed using a processor.

16. The method of claim 15 , further comprising determining a baseline of the metric of the number of inflections;

wherein step (c) includes distinguishing between an impending MI and a transient myocardial ischemic event based on a length of time that the metric indicative of the number of inflections increases beyond the baseline by at least a specified threshold.

17. The method of claim 15 , further comprising determining a baseline of the metric indicative of the number of inflections in the photoplethysmography signal;

wherein step (c) comprises:

(c.1) comparing the determined metrics indicative of the number of inflections to the baseline; and

(c.2) predicting an impending MI if the determined metric indicative of the metric indicative of the number of inflections increases beyond the baseline by at least a specified threshold.

18. The method of claim 17 , wherein step (c.2) includes distinguishing between an impending MI and a transient myocardial ischemic event based on a length of time that the metric indicative of the number of inflections remains increased beyond the baseline by at least the specified threshold.

19. The method of claim 15 , wherein step (c) comprises predicting an impending MI if an increase beyond a specified threshold is detected, in the metric indicative of the number of inflections in the photoplethysmography signal, from one of the periods of time to the immediately following one of the periods of time.

20. The method of claim 15 , wherein step (c) comprises predicting an impending MI if the metric indicative of the number of inflections in the photoplethysmography signal increases by at least a specified amount for at least a specified period of time.

21. An implantable system for monitoring for an impending myocardial infarction (MI), comprising:

an implantable photoplethysmography sensor configured to be implanted remote from a patient's heart and to produce a photoplethysmography signal that is indicative of changes in arterial volume;

a monitor configured to

determine, for each of a plurality of cycles of the photoplethysmography signal, a metric indicative of a number of inflections in the photoplethysmography signal for the cycle,

monitor for an impending MI based on changes in the metric indicative of the number of inflections in the photoplethysmography signal, and

trigger an alert and/or therapy in response to an impending MI being detected.

22. The system of claim 21 , wherein the monitor is configured to monitor for an impending MI, based on changes in the metric indicative of the number of inflections in the photoplethysmography signal, by comparing the determined metrics indicative of the number of inflections to a baseline, and predicting an impending MI if the determined metric indicative of the number of inflections increases above the baseline by at least a specified threshold.