Method and system for determining QRS onset in cardiac signals

1. A method for determining a QRS onset point for a heartbeat comprising:

acquiring, N ECG signals, each comprising a plurality of QRS complexes;

selecting one QRS complex to form the basis of a search for the QRS onset point;

defining a starting location within the ECG signal that has the selected QRS complex for the search;

determining a derivative signal of the ECG signal that has the selected QRS complex, wherein the derivative signal is a combination of a first derivative and a second derivative of the selected QRS complex with respect to time;

searching backwards in time from said starting location for a first nadir in the derivative signal of the ECG signal that has the selected QRS complex; and

setting the time of the first nadir as the time for the QRS onset point.

2. The method of claim 1 , wherein the first nadir is the first nadir below a threshold.

3. The method of claim 2 , further comprising defining the threshold as a fraction of a peak value associated with the selected QRS complex.

4. The method of claim 3 , wherein said peak value comprises a peak in the derivative signal based on the selected QRS complex.

5. The method of claim 4 , wherein the threshold is set at 0.15 times the peak value.

6. The method of claim 1 , wherein the starting location is selected as the time of a peak in the first derivative with respect to time for the selected QRS complex.

7. The method of claim 1 , wherein selecting the QRS complex comprises:

calculating the first derivative with respect to time for all ECG signals; and

selecting that QRS complex wherein an absolute value of said first derivative is at a maximum.

8. The method of claim 1 , further comprises defining a window within which to constrain the backwards search.

9. The method of claim 8 , wherein said window is set to 300 ms.

10. A system for determining a QRS onset point for a heartbeat comprises:

electrical system for recording signal data from a probe when the probe is positioned in a heart of a living subject;

a processor;

a memory coupled to the processor, wherein the memory is configured to store a set of instructions to be executed by the processor, wherein the processor is configured to:

acquire, N ECG signals, each comprising a plurality of QRS complexes;

select one QRS complex to form the basis of a search for the QRS onset point;

define a starting location within the ECG signal that has the selected QRS complex for the search;

determine a derivative signal of the ECG signal that has the selected QRS complex, wherein the derivative signal is a combination of a first derivative and a second derivative of the selected QRS complex with respect to time;

search backwards in time from said starting location for a first nadir in the derivative signal of the ECG signal that has the selected QRS complex; and

set the time of the first nadir as the time for the QRS onset point.

11. The system of claim 10 , wherein the first nadir is the first nadir below a threshold.

12. The system of claim 11 , further comprising defining the threshold as a fraction of a peak value associated with the selected QRS complex.

13. The system of claim 12 , wherein said peak value comprises a peak in the derivative signal based on the selected QRS complex.

14. The system of claim 13 , wherein the threshold is set at 0.15 times the peak value.

15. The system of claim 10 , wherein the starting location is selected as the time of a peak in the first derivative with respect to time for the selected QRS complex.

16. The system of claim 10 , wherein selecting the QRS complex comprises:

calculating the first derivative with respect to time for all ECG signals; and

selecting that QRS complex wherein an absolute value of said first derivative is at a maximum.

17. The system of claim 10 , further comprises defining a window within which to constrain the backwards search.

18. The system of claim 17 , wherein said window is set to 300 ms.