QRS offset and onset determination

1. A system comprising:

electrode apparatus comprising a plurality of electrodes to monitor electrical activity from tissue of a patient; and

computing apparatus comprising processing circuitry and coupled to the electrode apparatus, the computing apparatus configured to:

monitor electrical activity using the plurality of electrodes to generate a plurality of cardiac signals over time,

generate a dispersion signal from the plurality of cardiac signals, wherein the dispersion signal is representative of the dispersion of the plurality of cardiac signals over time, and

determine a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal.

2. The system of claim 1 , wherein the computing apparatus is further configured to determine an activation time for each of the at least one QRS complex within each of the plurality of cardiac signals within the QRS duration between the QRS onset and offset time values corresponding to the at least one QRS complex.

3. The system of claim 2 , wherein the computing apparatus is further configured to determine at least one metric of electrical heterogeneity based on the activation time for each of the at least one QRS complex within each of the plurality of cardiac signals.

4. The system of claim 1 , wherein the plurality of electrodes comprises a plurality of external electrodes to be located proximate the patient's skin.

5. The system of claim 1 , wherein the plurality of electrodes comprises a plurality of internal electrodes to be located within the patient.

6. The system of claim 1 , wherein generating a dispersion signal from the plurality of cardiac signals comprises determining a standard deviation of the plurality of cardiac signals over time.

7. The system of claim 1 , wherein the computing apparatus is further configured to select a portion of the dispersion signal over a selected time period, and

wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal comprises determining the QRS onset time value and the QRS offset time value for each of the at least one QRS complex within the monitored electrical activity of the selected time period based on the selected portion of the dispersion signal.

8. The system of claim 1 , wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal further comprises:

determining a maximum dispersion value of the dispersion signal; and

determining the QRS onset time value and the QRS offset time value using the maximum dispersion value.

9. The system of claim 1 , wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal further comprises:

determining a minimum dispersion value of the dispersion signal within a first time period before a maximum dispersion value of the dispersion signal to determine the QRS onset time value, and

determining a minimum dispersion value of the dispersion signal within a second time period after the maximum dispersion value of the dispersion signal to determine the QRS offset time value.

10. The system of claim 1 , wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal further comprises:

determining a latest dispersion value of the dispersion signal within a first time period before a maximum dispersion value of the dispersion signal that is less than or equal to a selected percentage of a minimum dispersion value of the dispersion signal within the first time period to determine the QRS onset time value, and

determining an earliest dispersion value of the dispersion signal within a second time period after the maximum dispersion value of the dispersion signal that is less than or equal to a selected percentage of a minimum dispersion value of the dispersion signal within the second time period to determine the QRS onset time value.

11. The system of claim 1 , wherein the computing apparatus is further configured to:

determine an absolute amplitude between the QRS onset time value and the QRS offset time value for each of the at least QRS complex for each of the plurality of cardiac signals;

select one or more cardiac signals of the plurality of cardiac signals based on the absolute amplitude; and

determine an activation time for each of the at least one QRS complex within each of the selected one or more cardiac signals within the QRS duration between the QRS onset and offset time values corresponding to the at least one QRS complex.

12. The system of claim 1 , wherein the computing apparatus is further configured to remove one or more noisy cardiac signals from the plurality of cardiac signals prior to determining the dispersion signal, wherein the one or more noisy cardiac signals are identified by identifying cardiac signals comprising absolute areas-under-the-curve greater than or equal to a threshold value.

13. The system of claim 1 , wherein the computing apparatus is further configured to display on a graphical user interface one or more metrics derived using the determined QRS onset and offset time values, wherein the one or more metrics comprise activation time of each of the plurality of cardiac signals.

14. A method comprising:

monitoring electrical activity from tissue of a patient using a plurality of electrodes to generate a plurality of cardiac signals over time;

generating a dispersion signal from the plurality of cardiac signals, wherein the dispersion signal is representative of the dispersion of the plurality of cardiac signals over time; and

determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal.

15. The method of claim 14 further comprising determining an activation time for each of the at least one QRS complex within each of the plurality of cardiac signals within the QRS duration between the QRS onset and offset time values corresponding to the at least one QRS complex.

16. The method of claim 15 further comprising determining at least one metric of electrical heterogeneity based on the activation time for each of the at least one QRS complex within each of the plurality of cardiac signals.

17. The method of claim 14 , wherein generating a dispersion signal from the plurality of cardiac signals comprises determining a standard deviation of the plurality of cardiac signals over time.

18. The method of claim 14 further comprising selecting a portion of the dispersion signal over a selected time period, and

wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal comprises determining the QRS onset time value and the QRS offset time value for each of the at least one QRS complex within the monitored electrical activity of the selected time period based on the selected portion of the dispersion signal.

19. The method of claim 14 , wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal further comprises:

determining a maximum dispersion value of the dispersion signal; and

determining the QRS onset time value and the QRS offset time value using the maximum dispersion value.

20. The method of claim 19 , wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal further comprises:

filtering the dispersion signal to remove one or more values of the dispersion signal that are less than or equal to a selected percentage of the maximum dispersion value of the dispersion signal.

21. The method of claim 19 , wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal further comprises:

filtering the dispersion signal to remove one or more dispersion values of the dispersion signal corresponding to at least one of a T-wave and a P-wave in the plurality of cardiac signals.

22. The method of claim 14 , wherein determining a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the dispersion signal further comprises:

determining a latest dispersion value of the dispersion signal within a first time period before a maximum dispersion value of the dispersion signal that is less than or equal to a selected percentage of a minimum dispersion value of the dispersion signal within the first time period to determine the QRS onset time value, and

determining an earliest dispersion value of the dispersion signal within a second time period after the maximum dispersion value of the dispersion signal that is less than or equal to a selected percentage of a minimum dispersion value of the dispersion signal within the second time period to determine the QRS onset time value.

23. The method of claim 22 , wherein each of the first and second time periods are less than or equal to 200 milliseconds.

24. The method of claim 14 further comprising:

determining an absolute amplitude between the QRS onset time value and the QRS offset time value for each of the at least QRS complex for each of the plurality of cardiac signals;

selecting one or more cardiac signals of the plurality of cardiac signals based on the absolute amplitude; and

determining an activation time for each of the at least one QRS complex within each of the selected one or more cardiac signals within the QRS duration between the QRS onset and offset time values corresponding to the at least one QRS complex.

25. The method of claim 14 further comprising adjusting cardiac therapy in response to one or more metrics derived using the determined QRS onset and offset time values, wherein the one or more metrics comprise activation time of each of the plurality of cardiac signals.

26. A system comprising:

electrode apparatus comprising a plurality of electrodes to monitor electrical activity from tissue of a patient; and

computing apparatus comprising processing circuitry and coupled to the electrode apparatus, the computing apparatus configured to:

monitor electrical activity using the plurality of electrodes to generate a plurality of cardiac signals over time,

determine a standard deviation of the plurality of cardiac signals over time, and

determine a QRS onset time value and a QRS offset time value for each of at least one QRS complex within the monitored electrical activity based on the determined standard deviation.