Background

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.

Method

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)
• _HRSD4
• Value(HRSD4_cyc0)  >= 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

• _HRSD4_series
• 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