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.