System and method for electrocardiographic data signal gain determination with the aid of a digital computer
In one embodiment, ECG data collected during the long-term monitoring are compressed through a two-step compression algorithm executed by an electrocardiography monitor. Minimum amplitude signals may become indistinguishable from noise if overly inclusive encoding is employed in which voltage ranges are set too wide. The resulting ECG signal will appear “choppy” and uneven with an abrupt slope. The encoding used in the first stage of compression can be dynamically rescaled on-the-fly when the granularity of the encoding is too coarse. In a further embodiment, offloaded ECG signals are automatically gained as appropriate on a recording-by-recording basis to preserve the amplitude relationship between the signals. Raw decompressed ECG signals are filtered for noise content and any gaps in the signals are bridged. An appropriate signal gain is determined based on a statistical evaluation of peak-to-peak voltage (or other indicator) to land as many ECG waveforms within a desired range of display.
1. A method for electrocardiographic data signal gain determination with the aid of a digital computer, comprising the steps of:
receiving, by a download station from an ambulatory monitor recorder interfaced to the download station, compression codes representing cutaneous action potentials recorded by the monitor recorder;
decompressing by the download station the compression codes into a time series that comprises a digital representation of a raw electrocardiography (“ECG”) signal;
identifying by the download station cardiac waveforms within the time series falling within one or more temporal windows and measuring peak-to-peak voltages in the identified cardiac waveforms; and
statistically representing a correlation between the peak-to-peak voltages on the download station and determining based on the statistical representation a signal gain that places the correlation between the peak-to-peak voltages within a range preferred for visualizing the cardiac waveforms.
2. A method in accordance with claim 1 , further comprising the step of:
defining the temporal windows to be of a sufficient length to capture at least one of the cardiac waveforms.
3. A method in accordance with claim 1 , further comprising the steps of:
defining one or more parameters for one or more noise filters;
applying the one or more filters to the digital representation of the raw electrocardiography signal to identify noise in the signal; and
ignoring those portions of the raw electrocardiography signal that have been marked as noise when measuring the peak-to-peak voltages in the cardiac waveforms.
4. A method in accordance with claim 3 , further comprising the step of:
creating a continuous ECG signal for display by bridging segments of the raw electrocardiography signal that have not been marked as noise,
wherein the cardiac waveforms are identified among the bridged segments.
5. A method in accordance with claim 3 , wherein the one or more filters comprise one or more of a high pass filter, a low pass filter, an amplitude change filter, and a zero-crossings filter.
6. A method in accordance with claim 1 , wherein the preferred range is substantially between 2 mV and 10 mV.
7. A non-transitory computer readable storage medium storing code for executing on a computer system to perform the method according to claim 1 .
8. A system for providing dynamic gain over electrocardiographic data with the aid of a digital computer, comprising:
a download station configured to interface to an ambulatory monitor recorder and configured to execute code comprising:
a receipt module configured to receive from the monitor recorder when the recorder is interfaced to the download station compression codes representing cutaneous action potentials recorded by the monitor recorder;
a decompression module configured to decompress the compression codes into a time series of a plurality of values that comprises a digital representation of a raw electrocardiography (“ECG”) signal;
an identification module configured to identify cardiac waveforms within the time series falling within one or more temporal windows and to measure peak-to-peak voltages in the identified cardiac waveforms; and
a correlation module configured to statistically representing a correlation between the peak-to-peak voltages on the download station and to determine based on the statistical representation a signal gain that places the correlation between the peak-to-peak voltages within a range preferred for visualizing the cardiac waveforms.
9. A system in accordance with claim 8 , further comprising:
a window module configured to define the temporal windows to be of a sufficient length to capture at least one of the cardiac waveforms.
10. A system in accordance with claim 8 , further comprising:
a parameter module configured to define one or more parameters for one or more noise filters;
an application module configured to apply the one or more filters to the digital representation of the raw electrocardiography signal to identify noise in the signal; and
a noise module configured to ignore those portions of the raw electrocardiography signal that have been marked as noise when measuring the peak-to-peak voltages in the cardiac waveforms.
11. A system in accordance with claim 10 , further comprising:
a signal module configured to create a continuous ECG signal for display by bridging segments of the raw electrocardiography signal that have not been marked as noise,
wherein the cardiac waveforms are identified among the bridged segments.
12. A system in accordance with claim 10 , wherein the one or more filters comprise one or more of a high pass filter, a low pass filter, an amplitude change filter, and a zero-crossings filter.
13. A system in accordance with claim 8 , wherein the preferred range is substantially between 2 mV and 10 mV.
14. A system in accordance with claim 8 , further comprising:
a range module configured to set the preferred range.
15. A method for providing resealable encoding during an ambulatory monitor recorder monitoring, comprising the steps of:
sensing a series of electrocardiography values with a monitor recorder;
maintaining a plurality of codes, each associated with a range of electrocardiographic values;
processing the series of the electrocardiography values in successively-occurring temporal windows, for each temporal window comprising the steps of:
calculating a peak-to-peak voltage of the electrocardiography values in the temporal window;
comparing the peak-to-peak voltage to a threshold and adjusting the range associated with each of the codes when the peak-to-peak value is less than the threshold;
encoding each of the electrocardiography values from the series with the code associated with the range into which the electrocardiography value falls; and
writing each of the codes into a sequence in a non-volatile memory of the monitor recorder.
16. A method in accordance with claim 15 , further comprising the step of:
adjusting a highest electrocardiography value and a lowest electrocardiography value of each of the ranges when the peak-to-peak voltage is smaller than the threshold.
17. A method in accordance with claim 16 , wherein the thresholds are adjusted by a factor of substantially 0.5.
18. A method in accordance with claim 15 , further comprising the steps of:
calculating a difference between the threshold and the peak-to-peak voltage;
comparing the difference to a highest electrocardiography value in the range associated with the code into which at least one of the electrocardiographic value in that temporal window falls; and
adjusting the highest value when the highest values is less than the difference.
19. A method in accordance with claim 18 , wherein an encoding table lists the codes and the associated ranges, further comprising the step of:
associating the message regarding the highest value adjustment with the table.
20. A non-transitory computer readable storage medium storing code for executing on the monitor recorder to perform the method according to claim 15 .