Propagation Pattern Quantification
Complex propagation patterns described above (LIA, LRA and FF) were identified using the AcQTrack (Acutus Medical) system during AF to ensure objective classification of activation patterns, as outlined in the supplementary methods. Representative examples of these patterns are seen in figure 1 and supplementary videos 1-3. Every wavefront is scrutinised at each vertex of the anatomy. Planar wavefronts are discarded, whilst if the parameters for LIA, LRA and FF are met within a discreet zone (300mm2 for LRA and 200mm2 for LIA) the vertices within this zone are highlighted and recorded by the system.
These data were exported and analysed using a custom designed programme to allow quantification. The process is outlined in figure 3 and supplementary figure S3. Initially, all AcQTrack data is exported to create a static map quantifying every pattern occurrence at each vertex of the chamber anatomy (approximately 3500 per chamber) for the entire recording duration (3A). Each single occurrence is signified by a disc that occurs in a specific region for the duration that pattern is present (3B). The number of these unique “discs” equates to the number of occurrences of the specified propagation pattern. When taken over the duration of the recording, the proportion of time in which these discs are detected on the chamber surface represents the time parameter. Similarly, the proportion of the chamber in which an occurrence is detected represents the surface area affected.
A cut off threshold is then applied to exclude outlying data and identify the localised region with the most repetitive pattern occurrences. The number of occurrences in each region and the proportion of time that they are present are known. These factors are used to determine the optimum threshold as outlined in figure 4. The initial static map displays all occurrences with no cut off applied (zero on the x axis i.e. every occurrence is counted). The percentage of the recording time with the relevant pattern is shown on the Y axis. As the cut off is increased along the X axis (i.e. only regions with increasing numbers of occurrences are included), the proportion of time these are present decreases. A threshold is applied relative to the total time pattern occurrences are present. In the example in figure 4, (for LIA) with no cut off, LIA was present for 85% of the mapping duration. Increases in the threshold resulted in a reduction in the percentage of time that LIA was present. A 10% threshold excludes LIA to the point at which only regions with LIA present for 75% of the recording duration are counted, which corresponds to more than 6 occurrences over the duration of the recording. Similarly, a threshold that corresponds to a 30% relative reduction from the initial maximum duration identifies the region with only the highest number of occurrences. Where discs representing a detection are overlapping at any time point (potentially representing a meandering central pivot or rotation point) these are counted as a single pattern detection. Once a cut off is applied, only occurrences with the geometric centre of the “disc” within the specified zone are included for quantification and any occurrence detected within 5ms of a preceding occurrence in the same location is excluded to avoid double counting.