Atrial Fibrillation (AFib) is characterized by disorganized atrial electrical activity and contraction.
During AFib, the heart rate is irregular, and there are no P-waves.
The method described below only relies on changes in heart rate to identify potential regions of AFib. P waves were not used since they are often not reliably identified. If clearly defined P waves are available, the absence of P-waves can be incorporated into these searches.
Ensure the ECG signal is well marked
- Use the following Data Insights (DI) searches to identify and correct marking errors:
- dv_HR Change
- dv_HR Limits
- dv_HR Missed Beats
- Missed beats and triggering on noise can introduce variability in the heart rate that is misinterpreted by the search
- In the case of missed beats an option would be to discard results where the HR or beat to beat HR change fell outside of a defined range but cleaning up the data is the preferred method.
Create new Custom Derived Parameters to detect high heart rate variability
- Changes in heart rate are evaluated over a range of beats to account for the inherent variability during an AFib event and to group adjacent AFib events that may be separated by a few sinus beats
- The selected Standard Deviation (SD) range is used to construct Custom Derived Parameters (CDP) that are used in AFib DI searches
- The attached file (HRSD.XML) can be imported through the CDP dialog to add 6 CDPs with standard deviations over 2 through 9 cycles (HRSD2, HRSD3, HRSD4, HRSD5, HRSD7, HRSD9)
- HRSDx, x represents the number of cycles over which the SD is calculated. Additional CDPs can be constructed if needed.
Create Data Insights Searches
- The CDP HRSD4 has been used in the searches in this example – and will close a gap of up to 3 beats will low HR change. A different CDP may be used based on the SD range selected.
- Two searches are used, _HRSD4 and _HRSD4_series. The two searches can be imported using the attached file (HRSD4_Searches.XML)
- Value(HRSD4cyc0) >= 25
- This identifies beats where the CDP HRSD4 exceeds a threshold (25 bpm)
- The threshold of 25 bpm was selected based on the two datasets provided and was set slightly above the SD of non AFib mice
- Series(_HRSD4, 1) >= 9
- This identifies cycles where 9 or more cycles satisfy the _HRSD4 search
- The number 9 can be increased to only identify longer AFib runs, alternatively the search results can be sorted by the number of cycles in the Series
- Smaller runs of AFib can be identified by decreasing 9 or by creating another Series based search that looks for a specific number of consecutive cycles that match _HRSD4