IBI Filtering

IBI Filtering

IBI filtering is used to mark IBI “outliers”. If an outlier is detected based on the user selected criteria, the beat that initiated the IBI and the IBI itself is marked as an outlier on the plots. Outliers are marked by a filled red circle. Although the term filter is used in this section, no change to the original IBI occurs during ectopic interval detection.

Filter Types

1. percentage filter – marks intervals that change by more than a user defined percentage (often 20%) from the previous interval [55].This method locates any sudden or abrupt IBI changes.

2. standard deviation filter – marks outliers as being intervals that lie beyond the mean IBI by a user defined value of standard deviations (often 3 SD) [55].

3. median filter – acts as an impulse rejection filter with threshold to delineate ectopic intervals [50]. The median filter of a random variable x of length N using a threshold of τ is given by

   

4. above threshold filter – marks any interval lying above the user defined threshold limit as outliers

5. below threshold filter – marks any interval lying below the user defined threshold limit as outliers

6. custom filter – this was a personal filter used to ignore IBI near large spikes in the ECG signal. The first box defines the amplitude limit, and the second box defines the window width. Any IBI within the window width around ECG that has an amplitude above the limit is ignored.