R-wave detection method

1. A method for detecting an R-wave from an ECG signal derived from a living body, the method comprising the steps of:

acquiring the ECG signal from the living body;

digitizing the ECG signal into a digital ECG signal;

filtering the digital ECG signal with a bandpass filter and applying an absolute value filter thereto to create a filtered ECG signal;

for each sequential value of the filtered ECG signal, comparing the filtered ECG signal to an ECG tracking threshold (TT);

if the filtered ECG signal is no greater than TT, incrementing a counter, but if greater than TT, setting the counter to zero; and

comparing the counter to a predetermined refractory count RC and, if the count is equal to RC, outputting an R-wave trigger indicating that an R-wave has been detected.

2. The method of claim 1 wherein TT is determined by applying the following computation:

TT=TT p +c 2 ( ST−TT p ),

where TT p is the previous value of TT, c 2 is a constant, and ST is a fraction (c 1 ) of the maximum value of the filtered ECG signal during a previous predetermined time period (t m ).

3. The method of claim 2 wherein, if no R-wave trigger has occurred for a predetermined dropout period (t D ), TT is set to ST.

4. The method of claim 3 wherein c 1 is 0.5, c 2 is 0.25, t m is 2 seconds, RC corresponds to a time period of 90 milliseconds, and t D is 5 seconds.

5. The method of claim 3 wherein t D is within the range of 2 to 10 seconds.

6. The method of claim 5 wherein c 1 is within the range of 0.4 to 0.7.

7. The method of claim 5 wherein c 2 is within the range of 0.15 to 0.8.

8. The method of claim 3 wherein t m is at least 1.5 seconds.

9. The method of claim 3 wherein the refractory count RC corresponds to a period within the range of 30 to 250 milliseconds.